Does presence of complex translocations involving BCR::ABL1 in chronic myeloid leukemia affect the response rate to tyrosine kinase inhibitors? A systematic review of the literature.

Philadelphia (Ph) chromosome (9;22)(q34;q11) comprises 90-95 % of chronic myeloid leukemia (CML), while 5-10 % of CML have translocations involving three or more chromosomes. The outcome of treating patients harbouring complex Ph-positive cytogenetics with tyrosine kinase inhibitors (TKI) is unclear. In the present systematic review, we aim to summarise the response of patients with complex Ph-positive cytogenetics to treatment with TKI therapy. We collated all available literature from databases such as PubMed, Google Scholar, Web of Science database, Cochrane library, Scopus and Embase (up until January 31st, 2024), which describe cases of patients with CML, harbouring complex Ph-positive variations (three and four-way translocations), and summarised their response to TKI therapy. The studies were screened for the following criteria: documented TKI intervention and outcome (whether CR was achieved). Studies that did not report the same, were excluded. Additionally, we report a case from our center of a 55-year-old patient with CML, positive for the Ph-chromosome, harbouring a three-way translocation involving chromosome 15 i.e. 46XX, t(9;15;22) (q34;p11;q11). Identification of BCR::ABL and involvement of chromosome 15 was carried out using conventional cytogenetics, fluorescence in situ hybridization (FISH), and quantitative PCR (qPCR). Based on the inclusion criteria, a total of 15 studies were included from which a total of 87 cases were covered. Overall, we identified 38 unique complex three- and four-way translocations across 87 Ph-positive cases and found that 85 patients with complex Ph-positive cytogenetics achieved complete remission upon treatment and did not appear to have a lesser response to TKI therapy.

Survivin inhibition ameliorates liver fibrosis by inducing hepatic stellate cell senescence and depleting hepatic macrophage population.

Persistent activation of hepatic stellate cells (HSCs) in the injured liver leads to the progression of liver injury from fibrosis to detrimental cirrhosis. In a previous study, we have shown that survivin protein is upregulated during the early activation of HSCs, which triggers the onset of liver fibrosis. However, the therapeutic potential of targeting survivin in a fully established fibrotic liver needs to be investigated. In this study, we chemically induced hepatic fibrosis in mice using carbon tetrachloride (CCl4) for 6 weeks, which was followed by treatment with a survivin suppressant (YM155). We also evaluated survivin expression in fibrotic human liver tissues, primary HSCs, and HSC cell line by histological analysis. αSMA+ HSCs in human and mice fibrotic liver tissues showed enhanced survivin expression, whereas the hepatocytes and quiescent (qHSCs) displayed minimal expression. Alternatively, activated M2 macrophage subtype induced survivin expression in HSCs through the TGF-ß-TGF-ß receptor-I/II signaling. Inhibition of survivin in HSCs promoted cell cycle arrest and senescence, which eventually suppressed their activation. In vivo, YM155 treatment increased the expression of cell senescence makers in HSCs around fibrotic septa such as p53, p21, and ß-galactosidase. YM155 treatment in vivo also reduced the hepatic macrophage population and inflammatory cytokine expression in the liver. In conclusion, downregulation of survivin in the fibrotic liver decreases HSC activation by inducing cellular senescence and modulating macrophage cytokine expression that collectively ameliorates liver fibrosis.

Transcriptome wide functional analysis of HBx expressing human hepatocytes stimulated with endothelial cell cross-talk.

Identification of genes dysregulated during the hepatitis B virus (HBV)-host cell interaction adds to the understanding of underlying molecular mechanisms and aids in discovering effective therapies to improve prognosis in hepatitis B virus (HBV)-infected individuals. Through bioinformatics analyses of transcriptomics data, this study aimed to identify potential genes involved in the cross-talk of human hepatocytes expressing the HBV viral protein HBx with endothelial cells. Transient transfection of HBV viral gene X (HBx) was performed in THLE2 cells using pcDNA3 constructs. Through mRNA Sequencing (RNA Seq) analysis, differentially expressed genes (DEGs) were identified. THLE2 cells transfected with HBx (THLE2x) were further treated with conditioned medium from cultured human umbilical vein derived endothelial cells (HUVEC-CM). Gene Ontology (GO) enrichment analysis revealed that interferon and cytokine signaling pathways were primarily enriched for the downregulated DEGs in THLE2x cells treated with HUVEC-CM. One significant module was selected following protein-protein interaction (PPI) network generation, and thirteen hub genes were identified from the module. The prognostic values of the hub genes were evaluated using Kaplan-Meier (KM) plotter, and three genes (IRF7, IFIT1, and IFITM1) correlated with poor disease specific survival (DSS) in HCC patients with chronic hepatitis. A comparison of the DEGs identified in HUVEC-stimulated THLE2x cells with four publicly available HBV-related HCC microarray datasets revealed that PLAC8 was consistently downregulated in all four HCC datasets as well as in HUVEC-CM treated THLE2x cells. KM plots revealed that PLAC8 correlated with worse relapse free survival and progression free survival in HCC patients with hepatitis B virus infection. This study provided molecular insights which may help develop a deeper understanding of HBV-host stromal cell interaction and open avenues for future research.

Divergent effect of Birinapant, and BV6 SMAC mimetic on TNFα induced NF-κB signaling and cell viability in activated hepatic stellate cells.

BACKGROUND: Tumor necrosis factor-α (TNFα) is a pleiotropic cytokine involved in nuclear factor kappa B (NF-κB) mediated cell survival as well as cell death. High serum TNFα levels correlate with liver fibrosis and enhance hepatic stellate cell (HSC) viability. However, the regulatory role of cellular inhibitor of apoptosis-1/2 (cIAP1/2) during TNFα induced NF-κB signaling in activated HSCs is largely unknown. METHOD AND RESULTS: Activated HSCs were treated with cIAP1/2 inhbitiors i.e., SMAC mimetic BV6, and Birinapant in the presence of TNFα and macrophage conditioned media. TNFα cytokine increased cIAP2 expression and enhanced cell viability through the canonical NF-κB signaling in activated HSCs. cIAP2 inhibition via BV6 decreased the TNFα induced canonical NF-κB signaling, and reduced cell viability in activated HSCs. SMAC mimetic, Birinapant alone did not affect the cell viability but treatment of TNFα sensitized HSCs with Birinapant induced cell death. While BV6 mediated cIAP2 ablation was able to decrease the TNFα induced canonical NF-κB signaling, this effect was not observed with Birinapant treatment. Secreted TNFα from M1 polarized macrophages sensitized activated HSCs to BV6 or Birinapant mediated cell death. However, M2 polarized macrophage conditioned medium rescued the activated HSCs from BV6 mediated cytotoxicity. CONCLUSION: In this study, we describe the regulatory role of cIAP2 in TNFα induced NF-κB signaling in activated HSCs. Targeting cIAP2 may be a promising approach for liver fibrosis treatment via modulating NF-κB signaling in activated HSCs.

Context dependent role of p53 during the interaction of hepatocellular carcinoma and endothelial cells.

BACKGROUND: During the progression of hepatocellular carcinoma (HCC), several angiogenic factors are overexpressed in the hepatic microenvironment, which play a critical role in governing the phenotype of the endothelial cells. Mutation in the p53 gene (TP53) is a common event in HCC that may dysregulate the angiogenic signals. However, their functional messages remain largely unexplored at the onset of metastasis. METHODS: Role of p53 was studied by siRNA mediated silencing of p53 in HepG2 cells (WTp53), collecting and analyzing their conditioned medium, followed by indirect co-culture with endothelial cells (HUVECs). Gene and protein expression in HCC cells and endothelial cells was studied by RT-qPCR and western blotting respectively. ß-catenin protein expression and localization were analyzed by immunocytochemistry. RESULTS: We have studied a cell-to-cell interaction model to investigate the crosstalk of endothelial and hepatoma cells by either knocking down p53 or by using p53 null low metastatic HCC cell line. In the absence of p53, the HCC cells influence the migration and vascular network formation of endothelial cells through paracrine signaling of VEGF. Secretory VEGF activated the VEGF receptor-2 along with the survival signaling in endothelial cells. However, the ß-catenin signal is upregulated in endothelial cells only during interaction with metastatic set up irrespective of absence and presence of p53, indicating context-dependent participation of p53 during communication between hepatoma cells and endothelial cells. CONCLUSION: This study highlights that the role of p53 on cellular responses during interaction of hepatocellular carcinoma and endothelial cells is distinct to cell types and context.

Application of elastin-like polypeptide (ELP) containing extra-cellular matrix (ECM) binding ligands in regenerative medicine.

Extracellular matrix (ECM) molecules play an important role in regulating molecular signaling associated with proliferation, migration, differentiation, and tissue repair. The identification of new kinds of ECM mimic biomaterials to recapitulate critical functions of biological systems are important for various applications in tissue engineering and regenerative medicine. The use of human elastin derived materials with controlled biological properties and other functionalities to improve their cell-response was proposed. Herein, we reported genetic encoded synthesis of ELP (elastin-like polypeptide) containing ECM domains like RGD (integrin binding ligand) and YIGSR (laminin-selective receptor binding ligand) to regulate cell behaviour in more complex ways, and also better model natural matrices. Thermal responsiveness of the ELPs and structural conformation were determined to confirm its phase transition behaviour. The fusion ELPs derivatives were analysed for mechanical involvement of growth mechanism, regenerative, and healing processes. The designed fusion ELPs promoted fast and strong attachment of fibroblast cells. The fusion ELP derivatives enhanced the migration of keratinocyte cells which of crucial for wound healing. Together it provides a profound matrix for endothelial cells and significantly enhanced tube formation of HUVEC cells. Thus, strategy of using cell adhesive ELP biopolymer emphasizing the role of bioactive ELPs as next generation skin substitutes for regenerative medicine.

Therapeutic strategies for miRNA delivery to reduce hepatocellular carcinoma.

Malignancies of hepatocellular carcinoma (HCC) are rapidly spreading and commonly fatal. Like most cancers, the gene expression patterns in HCC vary significantly from patient to patient. Moreover, the expression networks during HCC progression are largely controlled by microRNAs (miRNAs) regulating multiple oncogenes and tumor supressors. Therefore, miRNA-based therapeutic strategies altering these networks may significantly influence the cellular behavior enough for them to cure HCC. However, the most substantial challenges in developing such therapies are the stability of the oligos themselves and that of their delivery systems. Here we provide a comprehensive update describing various miRNA delivery systems, including virus-based delivery and non-viral delivery. The latter may be achieved using inorganic nanoparticles, polymer based nano-carriers, lipid-based vesicles, exosomes, and liposomes. Leaky vasculature in HCC-afflicted livers helps untargeted nanocarriers to accumulate in the tumor tissue but may result in side effects during higher dose of treatment. On the other hand, the strategies for actively targeting miRNA therepeutics to cancerous cells through nano-conjugates or vesicles by decorating their surface with antibodies against or ligands for HCC-specific antigens or receptors are more efficient in preventing damage to healthy tissue and cancer recurrence.

Cell-free EBV DNA as a biomarker during clinical management of nasopharyngeal carcinoma in a nonendemic region.

Nasopharyngeal carcinoma (NPC) is the most common malignant tumor of the nasopharynx. Although NPC is not endemic in India, higher incidences were observed in its North-Eastern regions particularly Sikkim, Nagaland, Manipur, and Mizoram. Early detection of NPC is difficult because the nasopharynx is not readily amenable to clinical examination and symptoms of NPC are nonspecific. The development of suitable biomarkers for early diagnosis of NPC as well as accurate monitoring of treatment response is needed urgently. In this exploratory pilot study, we have investigated the clinical significance of assessing plasma Epstein-Barr virus (EBV) DNA load at diagnosis and during treatment. We found that EBV DNA is detectable at diagnosis in the majority of patients with nonendemic NPC and the absolute copy number of circulating EBV DNA per milliliter increases progressively with the stage of the disease. The viral load declined significantly with induction chemotherapy and definitive chemoradiation but showed a sharp rise at relapse. Patients with EBV DNA levels ≥1500 copies/ml had a higher risk of disease progression or relapse when compared with patients who had EBV DNA <1500 copies/ml at baseline. Estimation of plasma EBV DNA may serve as an excellent noninvasive tool to monitor disease extent, response to therapy, and for better prediction of future relapse or progression-free survival in a nonendemic NPC patient population.

Survivin expression is essential for early activation of hepatic stellate cells and fibrosis progression in chronic liver injury.

AIM: Hepatic fibrosis in injured liver is characterized by the activation of hepatic stellate cells (HSCs) from their quiescent state. Survivin (BIRC5) is one of the key genes that are upregulated during activation of HSCs but their role in HSC activation and fibrosis progression is unknown. Here, we have investigated the role of survivin protein in early fibrogenic activation of HSCs and fibrosis progression in chronic liver injury. MATERIALS & METHODS: Primary quiescent HSCs were isolated from healthy mice liver through perfusion and cultured for fibrogenic activation. Survivin expression was suppressed by its pharmacological suppressant, YM155. We developed chronic liver injury induced fibrotic mice model through administrating repeated dose of CCl4 for 2 weeks and 4 weeks. Mice were pre-treated with YM155 a week before CCl4 administration till 2nd week of dosing and then discontinued. Hepatic parameters were characterized and underlying mechanisms were investigated. KEY FINDINGS: Survivin expression gradually increased along with the expression of αSMA, collagen I activation maker in HSCs during their activation from quiescent state. Survivin suppression through YM155 downregulated αSMA, collagen I. Pre-treatment of YM155 in mice ceased the early activation of HSCs and onset of fibrosis in injured liver. However, discontinuation of YM155 initiated the activation of HSCs and fibrosis progression that shows survivin expression in HSCs is essential for their early activation and onset of liver fibrosis. SIGNIFICANCE: Survivin expression induces with activation of HSCs and drives onset of liver fibrosis in injured liver. Targeting survivin protein in activated HSCs could be a potential anti-fibrotic therapeutic approach in chronic liver injury.

Cytoplasmic vacuolation with endoplasmic reticulum stress directs sorafenib induced non-apoptotic cell death in hepatic stellate cells.

The activated hepatic stellate cells (HSCs) are the major cells that secrete the ECM proteins and drive the pathogenesis of fibrosis in chronic liver disease. Targeting of HSCs by modulating their activation and proliferation has emerged as a promising approach in the development of anti-fibrotic therapy. Sorafenib, a multi-kinase inhibitor has shown anti-fibrotic properties by inhibiting the survival and proliferation of HSCs. In present study we investigated sorafenib induced cytoplasmic vacuolation mediated decreased cell viability of HSCs in dose and time dependent manner. In this circumstance, sorafenib induces ROS and ER stress in HSCs without involvement of autophagic signals. The protein synthesis inhibitor cycloheximide treatment significantly decreased the sorafenib-induced cytoplasmic vacuolation with increasing cell viability. Antioxidant human serum albumin influences the viability of HSCs by reducing sorafenib induced vacuolation and cell death. However, neither caspase inhibitor Z-VAD-FMK nor autophagy inhibitor chloroquine could rescue the HSCs from sorafenib-induced cytoplasmic vacuolation and cell death. Using TEM and ER organelle tracker, we conclude that the cytoplasmic vacuoles are due to ER dilation. Sorafenib treatment induces calreticulin and GPR78, and activates IRE1α-XBP1s axis of UPR pathway, which eventually trigger the non-apoptotic cell death in HSCs. This study provides a notable mechanistic insight into the ER stress directed non-apoptotic cell death with future directions for the development of efficient anti-fibrotic therapeutic strategies.

Dynamic Hyaluronan drives liver endothelial cells towards angiogenesis.

BACKGROUND: Angiogenesis, the formation of new blood vessels from pre-existing vasculature is essential in a number of physiological processes such as embryonic development, wound healing as well as pathological conditions like, tumor growth and metastasis. Hyaluronic acid (HA), a high molecular weight polysaccharide, major component of extracellular matrix is known to associate with malignant phenotypes in melanomas and various other carcinomas. Hyaluronic acid binding protein 1 (HABP1) has been previously reported to trigger enhanced cellular proliferation in human liver cancer cells upon its over-expression. In the present study, we have identified the HA mediated cellular behaviour of liver endothelial cells during angiogenesis. METHODS: Endothelial cells have been isolated from perfused liver of mice. Cell proliferation was studied using microwell plates with tetrazole dye. Cell migration was evaluated by measuring endothelial monolayer wound repair as well as through transwell migration assay. Alterations in proteins and mRNA expression were estimated by immunobloting and quantitative real time PCR using Applied Biosystems. The paraformaldehyde fixed endothelial cells were used for immuno- florescence staining and F-actin detection with conjugated antibodies. The images were captured by using Olympus florescence microscope (IX71). RESULTS: We observed that administration of HA enhanced cell proliferation, adhesion, tubular sprout formation as well as migration of liver endothelial cells (ECs). The effect of HA in the rearrangement of the actins confirmed HA -mediated cytoskeleton re-organization and cell migration. Further, we confirmed enhanced expression of angiogenic factors like VEGF-A and VEGFR1 in endothelial cells upon HA treatment. HA supplementation led to elevated expression of HABP1 in murine endothelial cells. It was interesting to note that, although protein levels of ß- catenin remained unaltered, but translocation of this protein from membrane to nucleus was observed upon HA treatment, suggesting its role not only in vessel formation but also its involvement in angiogenesis signalling. CONCLUSIONS: The elucidation of molecular mechanism (s) responsible for HA mediated regulation of endothelial cells and angiogenesis contributes not only to our understanding the mechanism of disease progression but also offer new avenues for therapeutic intervention.

Divergent impact of gender in advancement of liver injuries, diseases, and carcinogenesis.

Several investigations have revealed that liver diseases exhibit gender biases, but identifying the root causes of such biases has been challenging. Evidence of gender differences in liver function is present from the early stage of embryonic development. The differences in access to care and treatment as well as diagnostic deliberation may affect gender-specific differences in liver disease progression. Apart from the pathogenesis, xenobiotic metabolism, immune responses, gene expressions, mitochondrial function, lipid composition, and enzyme activities also differ in this sexually dimorphic organ. Differences in a social environment and lifestyle of men and women may also be involved in the basic mechanisms underlying the sex-associated differences and protective or aggravating effects of sex hormones during viral infections, alcoholic and non-alcoholic chronic and/or acute mode of liver injuries, carcinogenesis, autoimmune responses, and liver transplantation outcome. We summarized here the recent findings regarding the influence of sex hormones on immune responses underlying the pathology of the liver diseases in humans and animal models.

Role of PXR in Hepatic Cancer: Its Influences on Liver Detoxification Capacity and Cancer Progression.

The role of nuclear receptor PXR in detoxification and clearance of xenobiotics and endobiotics is well-established. However, its projected role in hepatic cancer is rather illusive where its expression is reported altered in different cancers depending on the tissue-type and microenvironment. The expression of PXR, its target genes and their biological or clinical significance have not been examined in hepatic cancer. In the present study, by generating DEN-induced hepatic cancer in mice, we report that the expression of PXR and its target genes CYP3A11 and GSTa2 are down-regulated implying impairment of hepatic detoxification capacity. A higher state of inflammation was observed in liver cancer tissues as evident from upregulation of inflammatory cytokines IL-6 and TNF-α along with NF-κB and STAT3. Our data in mouse model suggested a negative correlation between down-regulation of PXR and its target genes with that of higher expression of inflammatory proteins (like IL-6, TNF-α, NF-κB). In conjunction, our findings with relevant cell culture based assays showed that higher expression of PXR is involved in reduction of tumorigenic potential in hepatic cancer. Overall, the findings suggest that inflammation influences the expression of hepatic proteins important in drug metabolism while higher PXR level reduces tumorigenic potential in hepatic cancer.

Genotype-phenotype effects of Bmpr2 mutations on disease severity in mouse models of pulmonary hypertension.

More than 350 mutations in the type-2 BMP (bone morphogenetic protein) receptor, BMPR2, have been identified in patients with heritable pulmonary arterial hypertension (HPAH). However, only 30% of BMPR2 mutation carriers develop PAH, and we cannot predict which of these carriers will develop clinical disease. One possibility is that the nature of the BMPR2 mutation affects disease severity. This hypothesis has been difficult to test clinically, given the rarity of HPAH and the complexity of the confounding genetic and environmental risk factors. To test this hypothesis, therefore, we evaluated the susceptibility to experimental pulmonary hypertension (PH) of mice carrying different HPAH-associated Bmpr2 mutations on otherwise identical genetic backgrounds. Mice with Bmpr2ΔEx4-5 mutations (Bmpr2+/-), in which the mutant protein is not expressed, develop less severe PH in response to hypoxia or hypoxia with vascular endothelial growth factor receptor inhibition than mice with an extracellular-domain Bmpr2ΔEx2 mutation (Bmpr2ΔEx2/+), in which the mutant protein is expressed. This was associated with a marked decrease in stabilizing phosphorylation of threonine 495 endothelial nitric oxide synthase (pThr495 eNOS) in Bmpr2ΔEx2/+ compared to wild-type and Bmpr2+/- mouse lungs. These findings provide the first experimental evidence that BMPR2 mutation types influence the severity of HPAH and suggest that patients with BMPR2 mutations who express mutant BMPR2 proteins by escaping non-sense-mediated messenger RNA decay (NMD- mutations) will develop more severe disease than HPAH patients with NMD+ mutations who do not express BMPR2 mutant proteins. Since decreased levels of pThr495 eNOS are associated with increased eNOS uncoupling, our data also suggest that this effect may result from defects in eNOS function.

δ-Catenin activates Rho GTPase, promotes lymphangiogenesis and growth of tumor metastases.

δ-Catenin, an adherens junctions protein, is not only involved in early development, cell-cell adhesion and cell motility in neuronal cells, but it also plays an important role in vascular endothelial cell motility and pathological angiogenesis. In this study, we report a new function of δ-catenin in lymphangiogenesis. Consistent with expression of δ-catenin in vascular endothelial cells, we detected expression of the gene in lymphatic endothelial cells (LECs). Ectopic expression of δ-catenin in LECs increased cell motility and lymphatic vascular network formation in vitro and lymphangiogenesis in vivo in a Matrigel plug assay. Conversely, knockdown of δ-catenin in LECs impaired lymphangiogenesis in vitro and in vivo. Biochemical analysis shows that δ-catenin regulates activation of Rho family small GTPases, key mediators in cell motility. δ-catenin activates Rac1 and Cdc42 but inhibits RhoA in LECs. Notably, blocking of Rac1 activation impaired δ-catenin mediated lymphangiogenesis in a Matrigel assay. Consistently, loss of δ-catenin in mice inhibited the growth of tumor metastases. Taken together, these findings identify a new function of δ-catenin in lymphangiogenesis and tumor growth/metastasis, likely through modulation of small Rho GTPase activation. Targeting δ-catenin may offer a new way to control tumor metastasis.

Heterozygous null bone morphogenetic protein receptor type 2 mutations promote SRC kinase-dependent caveolar trafficking defects and endothelial dysfunction in pulmonary arterial hypertension.

Hereditary pulmonary arterial hypertension (HPAH) is a rare, fatal disease of the pulmonary vasculature. The majority of HPAH patients inherit mutations in the bone morphogenetic protein type 2 receptor gene (BMPR2), but how these promote pulmonary vascular disease is unclear. HPAH patients have features of pulmonary endothelial cell (PEC) dysfunction including increased vascular permeability and perivascular inflammation associated with decreased PEC barrier function. Recently, frameshift mutations in the caveolar structural protein gene Caveolin-1 (CAV-1) were identified in two patients with non-BMPR2-associated HPAH. Because caveolae regulate endothelial function and vascular permeability, we hypothesized that defects in caveolar function might be a common mechanism by which BMPR2 mutations promote pulmonary vascular disease. To explore this, we isolated PECs from mice carrying heterozygous null Bmpr2 mutations (Bmpr2(+/-)) similar to those found in the majority of HPAH patients. We show that Bmpr2(+/-) PECs have increased numbers and intracellular localization of caveolae and caveolar structural proteins CAV-1 and Cavin-1 and that these defects are reversed after blocking endocytosis with dynasore. SRC kinase is also constitutively activated in Bmpr2(+/-) PECs, and localization of CAV-1 to the plasma membrane is restored after treating Bmpr2(+/-) PECs with the SRC kinase inhibitor 3-(4-chlorophenyl)-1-(1,1-dimethylethyl)-1H-pyrazolo[3,4-d]pyrimidin-4-amine (PP2). Late outgrowth endothelial progenitor cells isolated from HPAH patients show similar increased activation of SRC kinase. Moreover, Bmpr2(+/-) PECs have impaired endothelial barrier function, and barrier function is restored after treatment with PP2. These data suggest that heterozygous null BMPR2 mutations promote SRC-dependent caveolar trafficking defects in PECs and that this may contribute to pulmonary endothelial barrier dysfunction in HPAH patients.

A novel tumor suppressor function of glycine N-methyltransferase is independent of its catalytic activity but requires nuclear localization.

Glycine N-methyltransferase (GNMT), an abundant cytosolic enzyme, catalyzes the transfer of a methyl group from S-adenosylmethionine (SAM) to glycine generating S-adenosylhomocysteine and sarcosine (N-methylglycine). This reaction is regulated by 5-methyltetrahydrofolate, which inhibits the enzyme catalysis. In the present study, we observed that GNMT is strongly down regulated in human cancers and is undetectable in cancer cell lines while the transient expression of the protein in cancer cells induces apoptosis and results in the activation of ERK1/2 as an early pro-survival response. The antiproliferative effect of GNMT can be partially reversed by treatment with the pan-caspase inhibitor zVAD-fmk but not by supplementation with high folate or SAM. GNMT exerts the suppressor effect primarily in cells originated from malignant tumors: transformed cell line of non-cancer origin, HEK293, was insensitive to GNMT. Of note, high levels of GNMT, detected in regenerating liver and in NIH3T3 mouse fibroblasts, do not produce cytotoxic effects. Importantly, GNMT, a predominantly cytoplasmic protein, was translocated into nuclei upon transfection of cancer cells. The presence of GNMT in the nuclei was also observed in normal human tissues by immunohistochemical staining. We further demonstrated that the induction of apoptosis is associated with the GNMT nuclear localization but is independent of its catalytic activity or folate binding. GNMT targeted to nuclei, through the fusion with nuclear localization signal, still exerts strong antiproliferative effects while its restriction to cytoplasm, through the fusion with nuclear export signal, prevents these effects (in each case the protein was excluded from cytosol or nuclei, respectively). Overall, our study indicates that GNMT has a secondary function, as a regulator of cellular proliferation, which is independent of its catalytic role.

10-formyltetrahydrofolate dehydrogenase-induced c-Jun-NH2-kinase pathways diverge at the c-Jun-NH2-kinase substrate level in cells with different p53 status.

10-Formyltetrahydrofolate dehydrogenase (FDH) suppresses cancer cell proliferation through p53-dependent apoptosis but also induces strong cytotoxicity in p53-deficient prostate cells. In the present study, we have shown that FDH induces apoptosis in PC-3 prostate cells through simultaneous activation of the c-Jun-NH(2)-kinase (JNK) and extracellular signal-regulated kinase (ERK) pathways with JNK phosphorylating c-Jun and ERK1/2 phosphorylating Elk-1. The JNK1/2 inhibitor SP600125 or ERK1/2 inhibitor PD98059 prevented phosphorylation of c-Jun and Elk-1, correspondingly and partially protected PC-3 cells from FDH-induced cytotoxicity. Combination of the two inhibitors produced an additive effect. The contribution from the JNK cascade to FDH-induced apoptosis was significantly stronger than from the ERK pathway. siRNA knockdown of JNK1/2 or "turning off" the downstream target c-Jun by either siRNA or expression of the dominant-negative c-Jun mutant, TAM67, rescued PC-3 cells from FDH-induced apoptosis. The pull-down assays on immobilized c-Jun showed that c-Jun is directly phosphorylated by JNK2 in FDH-expressing cells. Interestingly, the FDH-induced apoptosis in p53-proficient A549 cells also proceeds through activation of JNK1/2, but the down-stream target for JNK2 is p53 instead of c-Jun. Furthermore, in A549 cells, FDH activates caspase 9, whereas in PC-3 cells, it activates caspase 8. Our studies indicate that the JNK pathways are common downstream mechanisms of FDH-induced cytotoxicity in different cell types, whereas the end point target in the cascade is cell type specific. JNK activation in response to FDH was inhibited by high supplementation of reduced folate leucovorin, further indicating a functional connection between folate metabolism and mitogen-activated protein kinase pathways.