Novel Selective Galectin-3 Antagonists Are Cytotoxic to Acute Lymphoblastic Leukemia.

Galectin-3 is a ß-galactoside-specific, carbohydrate-recognizing protein (lectin) that is strongly implicated in cancer development, metastasis, and drug resistance. Galectin-3 promotes migration and ability to withstand drug treatment of B-cell precursor acute lymphoblastic leukemia (BCP-ALL) cells. Due to high amino acid conservation among galectins and the shallow nature of their glycan-binding site, the design of selective potent antagonists targeting galectin-3 is challenging. Herein, we report the design and synthesis of novel taloside-based antagonists of galectin-3 with enhanced affinity and selectivity. The molecules were optimized by in silico docking, selectivity was established against four galectins, and the binding modes were confirmed by elucidation of X-ray crystal structures. Critically, the specific inhibition of galectin-3-induced BCP-ALL cell agglutination was demonstrated. The compounds decreased the viability of ALL cells even when grown in the presence of protective stromal cells. We conclude that these compounds are promising leads for therapeutics, targeting the tumor-supportive activities of galectin-3 in cancer.

Pre-B acute lymphoblastic leukemia expresses cell surface nucleolin as a 9-O-acetylated sialoglycoprotein.

Precursor B acute lymphoblastic leukemias (pre-B ALLs) abnormally express a specific glycan structure, 9-O-acetylated sialic acid (9-O-Ac-Sia), on their cell surface, but glycoproteins that carry this modification have not been identified. Using three different lectins that specifically recognize this structure, we establish that nucleolin (NCL), a protein implicated in cancer, contains 9-O-Ac-Sia. Surprisingly, antibodies against the glycolipid 9-O-Ac-Sia GD3 also detected 9-O-Ac-Sia NCL. NCL is present on the surface of pre-B ALL cells as a sialoglycoprotein that is partly 9-O-acetylated and conversely, 9-O-Ac-Sia-containing structures other than NCL are present on these cells as well. Interestingly, NCL and the 9-O-Ac-Sia signal had less co-localization on normal pre-B cells. We also investigated regulation of NCL on the cell surface and found that sialidase treatment increased the percentage of cells positive for cell surface NCL, suggesting that sialylation of NCL promotes internalization. Treatment of pre-B ALL cells with the chemotherapy drug vincristine also increased the percentage of cells with surface NCL and correlated with increased 9-O-Ac-Sia expression. All tested leukemia cells including primary samples expressed NCL, suggesting it as a possible therapeutic target. We confirmed this by showing inhibition of cell proliferation in some pre-B ALLs by exposure to a NCL-specific aptamer AS1411.

Treatment of B-cell precursor acute lymphoblastic leukemia with the Galectin-1 inhibitor PTX008.

BACKGROUND: Drug resistance of B-cell precursor acute lymphoblastic leukemia (BP-ALL) cells is conferred by both intrinsic and extrinsic factors, which could be targeted to promote chemo-sensitization. Our previous studies showed that Galectin-3, a lectin that clusters galactose-modified glycoproteins and that has both an intracellular and extracellular location, protects different subtypes of BP-ALL cells against chemotherapy. Galectin-1 is related to Galectin-3 and its expression was previously reported to be restricted to the MLL subtype of BP-ALL. METHODS AND RESULTS: Here, we report that Galectin-1 is expressed at different levels in and on different subclasses of BP-ALLs. Bone marrow plasma also contains high levels of Galectin-1. PTX008 is an allosteric inhibitor which inhibits Galectin-1 but not Galectin-3-mediated agglutination. The compound reduces migration of BP-ALL cells to CXCL12 and OP9 stromal cells and inhibits fibronectin-mediated adhesion. It also affects cell cycle progression of BCP-ALL cells. PTX008 is cytostatic for BP-ALL cells even when these are co-cultured with protective stroma, and can sensitize ALL cells to vincristine chemotherapy in vitro and in mice. CONCLUSIONS: PTX008 inhibits multiple functions that contribute to BP-ALL survival. The effects of Galectin-1 inhibition on both BP-ALL cell proliferation and migration suggest both the leukemia cells as well as the microenvironment that protects these cells may be targeted.

B-cell precursor acute lymphoblastic leukemia and stromal cells communicate through Galectin-3.

The molecular interactions between B-cell precursor acute lymphoblastic leukemia (pre-B ALL) cells and stromal cells in the bone marrow that provide microenvironmentally-mediated protection against therapeutic drugs are not well-defined. Galectin-3 (Lgals3) is a multifunctional galactose-binding lectin with reported location in the nucleus, cytoplasm and extracellular space in different cell types. We previously reported that ALL cells co-cultured with stroma contain high levels of Galectin-3. We here establish that, in contrast to more mature B-lineage cancers, Galectin-3 detected in and on the ALL cells originates from stromal cells, which express it on their surface, secrete it as soluble protein and also in exosomes. Soluble and stromal-bound Galectin-3 is internalized by ALL cells, transported to the nucleus and stimulates transcription of endogenous LGALS3 mRNA. When human and mouse ALL cells develop tolerance to different drugs while in contact with protective stromal cells, Galectin-3 protein levels are consistently increased. This correlates with induction of Galectin-3 transcription in the ALL cells. Thus Galectin-3 sourced from stroma becomes supplemented by endogenous Galectin-3 production in the pre-B ALL cells that are under continuous stress from drug treatment. Our data suggest that stromal Galectin-3 may protect ALL cells through auto-induction of Galectin-3 mRNA and tonic NFκB pathway activation. Since endogenously synthesized Galectin-3 protects pre-B ALL cells against drug treatment, we identify Galectin-3 as one possible target to counteract the protective effects of stroma.

Effector-mediated eradication of precursor B acute lymphoblastic leukemia with a novel Fc-engineered monoclonal antibody targeting the BAFF-R.

B-cell activating factor receptor (BAFF-R) is expressed on precursor B acute lymphoblastic leukemia (pre-B ALL) cells, but not on their pre-B normal counterparts. Thus, selective killing of ALL cells is possible by targeting this receptor. Here, we have further examined therapeutic targeting of pre-B ALL based on the presence of the BAFF-R. Mouse pre-B ALL cells lacking BAFF-R function had comparable viability and proliferation to wild-type cells, but were more sensitive to drug treatment in vitro. Viability of human pre-B ALL cells was further reduced when antibodies to the BAFF-R were combined with other drugs, even in the presence of stromal protection. This indicates that inhibition of BAFF-R function reduces fitness of stressed pre-B ALL cells. We tested a novel humanized anti-BAFF-R monoclonal antibody optimalized for FcRγIII-mediated, antibody-dependent cell killing by effector cells. Antibody binding to human ALL cells was inhibitable, in a dose-dependent manner, by recombinant human BAFF. There was no evidence for internalization of the antibodies. The antibodies significantly stimulated natural killer cell-mediated killing of different human patient-derived ALL cells. Moreover, incubation of such ALL cells with these antibodies stimulated phagocytosis by macrophages. When this was tested in an immunodeficient transplant model, mice that were treated with the antibody had a significantly decreased leukemia burden in bone marrow and spleen. In view of the restricted expression of the BAFF-R on normal cells and the multiple anti-pre-B ALL activities stimulated by this antibody, a further examination of its use for treatment of pre-B ALL is warranted.

Abr, a negative regulator of Rac, attenuates cockroach allergen-induced asthma in a mouse model.

Abr deactivates Ras-related C3 botulinum toxin substrate (Rac), a master molecular switch that positively regulates many immune cell functions, by converting it to its GDP-bound conformation. In this article, we report that, in the absence of Abr function, cockroach allergen (CRA)-immunized mice experienced a fatal asthma attack when challenged with CRA. The asthma in abr(-/-) mice was characterized by increased pulmonary mucus production, elevated serum IgE, and leukocyte airway infiltration. Decreased pulmonary compliance was further documented by increased airway resistance upon methacholine challenge. Peribronchial and bronchoalveolar lavage eosinophils, key cells associated with allergic asthma, were increased in abr(-/-) mice, but adoptive transfer of this cell type from immunized mice to naive controls, followed by CRA challenge, showed that eosinophils are not primarily responsible for differences in airway resistance between controls and abr-null mutants. CD4(+) T cell numbers in the airways of CRA-challenged abr(-/-) mice also were significantly increased compared with controls, as were the Th2 T cell-secreted cytokines IL-4 and IL-5 in total lung. Interestingly, when control and abr(-/-) CD4(+) T cells from CRA-immunized mice were transferred to wild-type animals, airway resistance upon challenge with CRA was significantly higher in mice transplanted with T cells lacking Abr function. CD4(+) T cells from CRA-immunized and challenged abr(-/-) mice contained elevated levels of activated GTP-bound Rac compared with wild-type controls. Functionally, abr(-/-) CD4(+) T cells from CRA-exposed mice showed significantly enhanced chemotaxis toward CCL21. These results identify Abr-regulated CD4(+) T cell migration as an important component of severe CRA-evoked allergic asthma in mice.

O-acetylated N-acetylneuraminic acid as a novel target for therapy in human pre-B acute lymphoblastic leukemia.

The development of resistance to chemotherapy is a major cause of relapse in acute lymphoblastic leukemia (ALL). Though several mechanisms associated with drug resistance have been studied in detail, the role of carbohydrate modification remains unexplored. Here, we investigated the contribution of 9-O-acetylated N-acetylneuraminic acid (Neu5Ac) to survival and drug resistance development in ALL cells. A strong induction of 9-O-acetylated Neu5Ac including 9-O-acetyl GD3 was detected in ALL cells that developed resistance against vincristine or nilotinib, drugs with distinct cytotoxic mechanisms. Removal of 9-O-acetyl residues from Neu5Ac on the cell surface by an O-acetylesterase made ALL cells more vulnerable to such drugs. Moreover, removal of intracellular and cell surface-resident 9-O-acetyl Neu5Ac by lentiviral transduction of the esterase was lethal to ALL cells in vitro even in the presence of stromal protection. Interestingly, expression of the esterase in normal fibroblasts or endothelial cells had no effect on their survival. Transplanted mice induced for expression of the O-acetylesterase in the ALL cells exhibited a reduction of leukemia to minimal cell numbers and significantly increased survival. This demonstrates that Neu5Ac 9-O-acetylation is essential for survival of these cells and suggests that Neu5Ac de-O-acetylation could be used as therapy to eradicate drug-resistant ALL cells.

Lack of bcr and abr promotes hypoxia-induced pulmonary hypertension in mice.

BACKGROUND: Bcr and Abr are GTPase activating proteins that specifically downregulate activity of the small GTPase Rac in restricted cell types in vivo. Rac1 is expressed in smooth muscle cells, a critical cell type involved in the pathogenesis of pulmonary hypertension. The molecular mechanisms that underlie hypoxia-associated pulmonary hypertension are not well-defined. METHODOLOGY/PRINCIPAL FINDINGS: Bcr and abr null mutant mice were compared to wild type controls for the development of pulmonary hypertension after exposure to hypoxia. Also, pulmonary arterial smooth muscle cells from those mice were cultured in hypoxia and examined for proliferation, p38 activation and IL-6 production. Mice lacking Bcr or Abr exposed to hypoxia developed increased right ventricular pressure, hypertrophy and pulmonary vascular remodeling. Perivascular leukocyte infiltration in the lungs was increased, and under hypoxia bcr-/- and abr-/- macrophages generated more reactive oxygen species. Consistent with a contribution of inflammation and oxidative stress in pulmonary hypertension-associated vascular damage, Bcr and Abr-deficient animals showed elevated endothelial leakage after hypoxia exposure. Hypoxia-treated pulmonary arterial smooth muscle cells from Bcr- or Abr-deficient mice also proliferated faster than those of wild type mice. Moreover, activated Rac1, phosphorylated p38 and interleukin 6 were increased in these cells in the absence of Bcr or Abr. Inhibition of Rac1 activation with Z62954982, a novel Rac inhibitor, decreased proliferation, p38 phosphorylation and IL-6 levels in pulmonary arterial smooth muscle cells exposed to hypoxia. CONCLUSIONS: Bcr and Abr play a critical role in down-regulating hypoxia-induced pulmonary hypertension by deactivating Rac1 and, through this, reducing both oxidative stress generated by leukocytes as well as p38 phosphorylation, IL-6 production and proliferation of pulmonary arterial smooth muscle cells.

Expression of cassini, a murine gamma-satellite sequence conserved in evolution, is regulated in normal and malignant hematopoietic cells.

BACKGROUND: Acute lymphoblastic leukemia (ALL) cells treated with drugs can become drug-tolerant if co-cultured with protective stromal mouse embryonic fibroblasts (MEFs). RESULTS: We performed transcriptional profiling on these stromal fibroblasts to investigate if they were affected by the presence of drug-treated ALL cells. These mitotically inactivated MEFs showed few changes in gene expression, but a family of sequences of which transcription is significantly increased was identified. A sequence related to this family, which we named cassini, was selected for further characterization. We found that cassini was highly upregulated in drug-treated ALL cells. Analysis of RNAs from different normal mouse tissues showed that cassini expression is highest in spleen and thymus, and can be further enhanced in these organs by exposure of mice to bacterial endotoxin. Heat shock, but not other types of stress, significantly induced the transcription of this locus in ALL cells. Transient overexpression of cassini in human 293 embryonic kidney cells did not increase the cytotoxic or cytostatic effects of chemotherapeutic drugs but provided some protection. Database searches revealed that sequences highly homologous to cassini are present in rodents, apicomplexans, flatworms and primates, indicating that they are conserved in evolution. Moreover, CASSINI RNA was induced in human ALL cells treated with vincristine. Surprisingly, cassini belongs to the previously reported murine family of γ-satellite/major satellite DNA sequences, which were not known to be present in other species. CONCLUSIONS: Our results show that the transcription of at least one member of these sequences is regulated, suggesting that this has a function in normal and transformed immune cells. Expression of these sequences may protect cells when they are exposed to specific stress stimuli.

Environment-mediated drug resistance in Bcr/Abl-positive acute lymphoblastic leukemia.

Although cure rates for acute lymphoblastic leukemia (ALL) have increased, development of resistance to drugs and patient relapse are common. The environment in which the leukemia cells are present during the drug treatment is known to provide significant survival benefit. Here, we have modeled this process by culturing murine Bcr/Abl-positive acute lymphoblastic leukemia cells in the presence of stroma while treating them with a moderate dose of two unrelated drugs, the farnesyltransferase inhibitor lonafarnib and the tyrosine kinase inhibitor nilotinib. This results in an initial large reduction in cell viability of the culture and inhibition of cell proliferation. However, after a number of days, cell death ceases and the culture becomes drug-tolerant, enabling cell division to resume. Using gene expression profiling, we found that the development of drug resistance was accompanied by massive transcriptional upregulation of genes that are associated with general inflammatory responses such as the metalloproteinase MMP9. MMP9 protein levels and enzymatic activity were also increased in ALL cells that had become nilotinib-tolerant. Activation of p38, Akt and Erk correlated with the development of environment-mediated drug resistance (EMDR), and inhibitors of Akt and Erk in combination with nilotinib reduced the ability of the cells to develop resistance. However, inhibition of p38 promoted increased resistance to nilotinib. We conclude that development of EMDR by ALL cells involves changes in numerous intracellular pathways. Development of tolerance to drugs such as nilotinib may therefore be circumvented by simultaneous treatment with other drugs having divergent targets.

TGFß signaling plays a critical role in promoting alternative macrophage activation.

BACKGROUND: Upon stimulation with different cytokines, macrophages can undergo classical or alternative activation to become M1 or M2 macrophages. Alternatively activated (or M2) macrophages are defined by their expression of specific gene products and play an important role in containing inflammation, removing apoptotic cells and repairing tissue damage. Whereas it is well-established that IL-4 can drive alternative activation, if lack of TGFß signaling at physiological levels affects M2 polarization has not been addressed. RESULTS: Vav1-Cre x TßRIIfx/fx mice, lacking TßRII function in hematopoietic cells, exhibited uncontrolled pulmonary inflammation and developed a lethal autoimmune syndrome at young age. This was accompanied by significantly increased numbers of splenic neutrophils and T cells as well as elevated hepatic macrophage infiltration and bone marrow monocyte counts. TßRII-/- CD4+ and CD8+ T-cells in the lymph nodes and spleen expressed increased cell surface CD44, and CD69 was also higher on CD4+ lymph node T-cells. Loss of TßRII in bone marrow-derived macrophages (BMDMs) did not affect the ability of these cells to perform efferocytosis. However, these cells were defective in basal and IL-4-induced arg1 mRNA and Arginase-1 protein production. Moreover, the transcription of genes that are typically upregulated in M2-polarized macrophages, such as ym1, mcr2 and mgl2, was also decreased in peritoneal macrophages and IL-4-stimulated TßRII-/- BMDMs. We found that cell surface and mRNA expression of Galectin-3, which also regulates M2 macrophage polarization, was lower in TßRII-/- BMDMs. Very interestingly, the impaired ability of these null mutant BMDMs to differentiate into IL-4 polarized macrophages was Stat6- and Smad3-independent, but correlated with reduced levels of phospho-Akt and ß-catenin. CONCLUSIONS: Our results establish a novel biological role for TGFß signaling in controlling expression of genes characteristic for alternatively activated macrophages. We speculate that lack of TßRII signaling reduces the anti-inflammatory M2 phenotype of macrophages because of reduced expression of these products. This would cause defects in the ability of the M2 macrophages to negatively regulate other immune cells such as T-cells in the lung, possibly explaining the systemic inflammation observed in Vav1-Cre x TßRIIfx/fx mice.

Treatment of human pre-B acute lymphoblastic leukemia with the Aurora kinase inhibitor PHA-739358 (Danusertib).

BACKGROUND: Treatment of Philadelphia chromosome-positive acute lymphoblastic leukemias (Ph-positive ALL) with clinically approved inhibitors of the Bcr/Abl tyrosine kinase frequently results in the emergence of a leukemic clone carrying the T315I mutation in Bcr/Abl, which confers resistance to these drugs. PHA-739358, an Aurora kinase inhibitor, was reported to inhibit the Bcr/Abl T315I mutant in CML cells but no preclinical studies have examined this in detail in human ALL. RESULTS: We compared the sensitivity of human Bcr/Abl T315I, Bcr/Abl wild type and non-Bcr/Abl ALL cells to this drug. PHA-739358 inhibited proliferation and induced apoptosis independently of Bcr/Abl, the T315I mutation, or presence of the tumor suppressor p53, but the degree of effectiveness varied between different ALL samples. Since short-term treatment with a single dose of drug only transiently inhibited proliferation, we tested combination treatments of PHA-739358 with the farnesyltransferase inhibitor Lonafarnib, with vincristine and with dasatinib. All combinations reduced viability and cell numbers compared to treatment with a single drug. Clonogenic assays showed that 25 nM PHA-739358 significantly reduced the colony growth potential of Ph-positive ALL cells, and combined treatment with a second drug abrogated colony growth in this assay. PHA-739358 further effectively blocked Bcr/Abl tyrosine kinase activity and Aurora kinase B in vivo, and mice transplanted with human Bcr/Abl T315I ALL cells treated with a 3x 7-day cycle of PHA-739358 as mono-treatment had significantly longer survival. CONCLUSIONS: PHA-739358 represents an alternative drug for the treatment of both Ph-positive and negative ALL, although combined treatment with a second drug may be needed to eradicate the leukemic cells.

Bcr is a substrate for Transglutaminase 2 cross-linking activity.

BACKGROUND: Breakpoint cluster region (Bcr) is a multi-domain protein that contains a C-terminal GTPase activating protein (GAP) domain for Rac. Transglutaminase 2 (TG2) regulates Bcr by direct binding to its GAP domain. Since TG2 has transglutaminase activity that has been implicated in the response to extreme stress, we investigated if Bcr can also act as a substrate for TG2. RESULTS: We here report that activation of TG2 by calcium caused the formation of covalently cross-linked Bcr. Abr, a protein related to Bcr but lacking its N-terminal oligomerization domain, was not cross-linked by TG2 even though it forms a complex with it. A Bcr mutant missing the first 62 amino acid residues remained monomeric in the presence of activated TG2, showing that this specific domain is necessary for the cross-linking reaction. Calcium influx induced by a calcium ionophore in primary human endothelial cells caused cross-linking of endogenous Bcr, which was inhibited by the TG2 inhibitor cystamine. Treatment of cells with cobalt chloride, a hypoxia-mimetic that causes cellular stress, also generated high molecular weight Bcr complexes. Cross-linked Bcr protein appeared in the TritonX-100-insoluble cell fraction and further accumulated in cells treated with a proteasome inhibitor. CONCLUSIONS: Bcr thus represents both an interacting partner under non-stressed conditions and a target of transglutaminase activity for TG2 during extreme stress.

The Fer tyrosine kinase regulates interactions of Rho GDP-Dissociation Inhibitor α with the small GTPase Rac.

BACKGROUND: RhoGDI proteins are important regulators of the small GTPase Rac, because they shuttle Rac from the cytoplasm to membranes and also protect Rac from activation, deactivation and degradation. How the binding and release of Rac from RhoGDI is regulated is not precisely understood. RESULTS: We report that the non-receptor tyrosine kinase Fer is able to phosphorylate RhoGDIα and form a direct protein complex with it. This interaction is mediated by the C-terminal end of RhoGDIα. Activation of Fer by reactive oxygen species caused increased phosphorylation of RhoGDIα and pervanadate treatment further augmented this. Tyrosine phosphorylation of RhoGDIα by Fer prevented subsequent binding of Rac to RhoGDIα, but once a RhoGDIα-Rac complex was formed, the Fer kinase was not able to cause Rac release through tyrosine phosphorylation of preformed RhoGDIα-Rac complexes. CONCLUSIONS: These results identify tyrosine phosphorylation of RhoGDIα by Fer as a mechanism to regulate binding of RhoGDIα to Rac.

Regulation of synaptic Rac1 activity, long-term potentiation maintenance, and learning and memory by BCR and ABR Rac GTPase-activating proteins.

Rho family small GTPases are important regulators of neuronal development. Defective Rho regulation causes nervous system dysfunctions including mental retardation and Alzheimer's disease. Rac1, a member of the Rho family, regulates dendritic spines and excitatory synapses, but relatively little is known about how synaptic Rac1 is negatively regulated. Breakpoint cluster region (BCR) is a Rac GTPase-activating protein known to form a fusion protein with the c-Abl tyrosine kinase in Philadelphia chromosome-positive chronic myelogenous leukemia. Despite the fact that BCR mRNAs are abundantly expressed in the brain, the neural functions of BCR protein have remained obscure. We report here that BCR and its close relative active BCR-related (ABR) localize at excitatory synapses and directly interact with PSD-95, an abundant postsynaptic scaffolding protein. Mice deficient for BCR or ABR show enhanced basal Rac1 activity but only a small increase in spine density. Importantly, mice lacking BCR or ABR exhibit a marked decrease in the maintenance, but not induction, of long-term potentiation, and show impaired spatial and object recognition memory. These results suggest that BCR and ABR have novel roles in the regulation of synaptic Rac1 signaling, synaptic plasticity, and learning and memory, and that excessive Rac1 activity negatively affects synaptic and cognitive functions.

Diet-induced obesity accelerates acute lymphoblastic leukemia progression in two murine models.

Obesity is associated with an increased incidence of many cancers, including leukemia, although it is unknown whether leukemia incidence is increased directly by obesity or rather by associated genetic, lifestyle, health, or socioeconomic factors. We developed animal models of obesity and leukemia to test whether obesity could directly accelerate acute lymphoblastic leukemia (ALL) using BCR/ABL transgenic and AKR/J mice weaned onto a high-fat diet. Mice were observed until development of progressive ALL. Although obese and control BCR/ABL mice had similar median survival, older obese mice had accelerated ALL onset, implying a time-dependent effect of obesity on ALL. Obese AKR mice developed ALL significantly earlier than controls. The effect of obesity was not explained by WBC count, thymus/spleen weight, or ALL phenotype. However, obese AKR mice had higher leptin, insulin, and interleukin-6 levels than controls, and these obesity-related hormones all have potential roles in leukemia pathogenesis. In conclusion, obesity directly accelerates presentation of ALL, likely by increasing the risk of an early event in leukemogenesis. This is the first study to show that obesity can directly accelerate the progression of ALL. Thus, the observed associations between obesity and leukemia incidence are likely to be directly related to biological effects of obesity.

Cell type-specific expression of adenomatous polyposis coli in lung development, injury, and repair.

Adenomatous polyposis coli (Apc) is critical for Wnt signaling and cell migration. The current study examined Apc expression during lung development, injury, and repair. Apc was first detectable in smooth muscle layers in early lung morphogenesis, and was highly expressed in ciliated and neuroendocrine cells in the advanced stages. No Apc immunoreactivity was detected in Clara or basal cells, which function as stem/progenitor cell in adult lung. In ciliated cells, Apc is associated mainly with apical cytoplasmic domain. In response to naphthalene-induced injury, Apc(positive) cells underwent squamous metaplasia, accompanied by changes in Apc subcellular distribution. In conclusion, both spatial and temporal expression of Apc is dynamically regulated during lung development and injury repair. Differential expression of Apc in progenitor vs. nonprogenitor cells suggests a functional role in cell-type specification. Subcellular localization changes of Apc in response to naphthalene injury suggest a role in cell shape and cell migration.

A functional receptor for B-cell-activating factor is expressed on human acute lymphoblastic leukemias.

B-lineage acute lymphoblastic leukemia (ALL) arises by transformation of a progenitor (pre-B) cell. Cure rates in adults remain low and treatment is complicated by support provided by the microenvironment to the leukemic cells, indicating an urgent need to better understand the factors that promote their survival. B-cell-activating factor (BAFF) and its receptor BAFF-R are important for survival and growth of mature normal and malignant B cells but are not expressed on pre-B cells. Unexpectedly, all cells in the primary Philadelphia chromosome (Ph)-positive and Ph-negative ALL samples tested were positive for high BAFF-R cell surface expression. BAFF-R was fully competent to bind BAFF, and stimulation of the receptor activated both the classic and the noncanonical NF-kappaB pathways. Recombinant BAFF supported survival of the ALL cells in the absence of stroma, and it significantly attenuated the rate of apoptosis caused by exposure to nilotinib, a drug used therapeutically to treat Ph-positive ALLs. Surprisingly, BAFF mRNA and protein were also expressed in the same cells but BAFF was not shed into the medium. Our report is the first showing universal expression of BAFF-R by pre-B ALL cells and opens the possibility of blocking its function as an adjuvant therapeutic strategy.

Activity of the Aurora kinase inhibitor VX-680 against Bcr/Abl-positive acute lymphoblastic leukemias.

The emergence of resistance to tyrosine kinase inhibitors due to point mutations in Bcr/Abl is a challenging problem for Philadelphia chromosome-positive (Ph-positive) acute lymphoblastic leukemia (ALL) patients, especially for those with the T315I mutation, against which neither nilotinib or dasatinib shows significant activity. VX-680 is a pan-Aurora kinase inhibitor active against all Bcr/Abl proteins but has not been extensively examined in preclinical models of Ph-positive ALL. Here, we have tested VX-680 for the treatment of Bcr/Abl-positive ALL when leukemic cells are protected by the presence of stroma. Under these conditions, VX-680 showed significant effects on primary human Ph-positive ALL cells both with and without the T315I mutation, including ablation of tyrosine phosphorylation downstream of Bcr/Abl, decreased viability, and induction of apoptosis. However, drug treatment of human Ph-positive ALL cells for 3 days followed by drug removal allowed the outgrowth of abnormal cells 21 days later, and on culture of mouse Bcr/Abl ALL cells on stroma with lower concentrations of VX-680, drug-resistant cells emerged. Combined treatment of human ALL cells lacking the T315I mutation with both VX-680 and dasatinib caused significantly more cytotoxicity than each drug alone. We suggest that use of VX-680 together with a second effective drug as first-line treatment for Ph-positive ALL is likely to be safer and more useful than second-line treatment with VX-680 as monotherapy for drug-resistant T315I Ph-positive ALL.

Transglutaminase 2 regulates the GTPase-activating activity of Bcr.

Transglutaminase 2 (TG2) is a multifunctional protein that has been implicated in numerous pathologies including that of neurodegeneration and celiac disease, but the molecular interactions that mediate its diverse activities are largely unknown. Bcr and the closely related Abr negatively regulate the small G-protein Rac: loss of their combined function in vivo results in increased reactivity of innate immune cells. Bcr and Abr are GTPase-activating proteins that catalyze the hydrolysis of the GTP bound to Rac. However, how the Bcr and Abr GTPase-activating activity is regulated is not precisely understood. We here report a novel mechanism of regulation through direct protein-protein interaction with TG2. TG2 bound to the Rac-binding pocket in the GTPase-activating domains of Bcr and Abr, blocked Bcr activity and, through this mechanism, increased levels of active GTP-bound Rac and EGF-stimulated membrane ruffling. TG2 exists in at least two different conformations. Interestingly, experiments using TG2 mutants showed that Bcr exhibits preferential binding to the non-compacted conformation of TG2, in which its catalytic domain is exposed, but transamidation is not needed for the interaction. Thus, TG2 regulates levels of cellular GTP-bound Rac and actin cytoskeletal reorganization through a new mechanism involving direct inhibition of Bcr GTPase-activating activity.