Regulation of miRNA expression by α4ß1 integrin-dependent multiple myeloma cell adhesion.

The α4ß1 integrin regulates the trafficking of multiple myeloma (MM) cells and contributes to MM disease progression. MicroRNAs (miRNAs) can have both tumor suppressor and oncogenic roles and thus are key controllers of tumor evolution, and have been associated with different phases of MM pathogenesis. Using small RNAseq analysis, we show here that α4ß1-dependent MM cell adhesion regulates the expression of forty different miRNAs, therefore expanding our current view of the α4ß1 involvement in MM cell biology. Specific upregulation of miR-324-5p and miR-331-3p in cells attached to α4ß1 ligands was confirmed upon silencing the α4 integrin subunit, and their increased levels found to be dependent on Erk1/2- and PI3K-Akt-, but not Src-dependent signaling. Enhanced miR-324-5p expression upon α4ß1-mediated MM cell adhesion aimed the hedgehog (Hh) component SMO, revealing that the miR-324-5p-SMO module represents a α4ß1-regulated pathway that could control Hh-dependent cellular responses in myeloma. Our results open new therapy research avenues around the α4ß1 contribution to MM progression that deserve to be investigated.

Upregulated expression and function of the α4ß1 integrin in multiple myeloma cells resistant to bortezomib.

The interaction of multiple myeloma (MM) cells with the bone marrow (BM) microenvironment promotes MM cell retention, survival, and resistance to different anti-MM agents, including proteasome inhibitors (PIs) such as bortezomib (BTZ). The α4ß1 integrin is a main adhesion receptor mediating MM cell-stroma interactions and MM cell survival, and its expression and function are downregulated by BTZ, leading to inhibition of cell adhesion-mediated drug resistance (CAM-DR) and MM cell apoptosis. Whether decreased α4ß1 expression and activity are maintained or recovered upon development of resistance to BTZ represents an important question, as a potential rescue of α4ß1 function could boost MM cell survival and disease progression. Using BTZ-resistant MM cells, we found that they not only rescue their α4ß1 expression, but its levels were higher than in parental cells. Increased α4ß1 expression in resistant cells correlated with enhanced α4ß1-mediated cell lodging in the BM, and with disease progression. BTZ-resistant MM cells displayed enhanced NF-κB pathway activation relative to parental counterparts, which contributed to upregulated α4 expression and to α4ß1-dependent MM cell adhesion. These data emphasize the upregulation of α4ß1 expression and function as a key event during resistance to BTZ in MM, which might indirectly contribute to stabilize this resistance, as stronger MM cell attachment to BM stroma will regain CAM-DR and MM cell growth and survival. Finally, we found a strong correlation between high ITGB1 (integrin ß1) expression in MM and poor progression-free survival (PFS) and overall survival (OS) during treatment of MM patients with BTZ and IMIDs, and combination of high ITGB1 levels and presence of the high-risk genetic factor amp1q causes low PFS and OS. These results unravel a novel prognostic value for ITGB1 in myeloma. © 2020 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

The good and bad faces of the CXCR4 chemokine receptor.

Chemokines are chemotactic cytokines that promote cell migration and activation under homeostatic and inflammatory conditions. Chemokines bind to seven transmembrane-spanning receptors that are coupled to heterotrimeric guanine nucleotide-binding (G) proteins, which are the responsible for intracellularly transmitting the activating signals for cell migration. Hematopoiesis, vascular development, lymphoid organ morphogenesis, cardiogenesis and neural differentiation are amongst the processes involving chemokine function. In addition, immune cell trafficking from bone marrow to blood circulation, and from blood and lymph to lymphoid and inflamed tissues, is tightly regulated by chemokines both under physiological conditions and also in autoimmune diseases. Furthermore, chemokine binding to their receptors stimulate trafficking to and positioning of cancer cells into target tissues and organs during tumour dissemination. The CXCL12 chemokine (also known as stromal-cell derived factor-1α, SDF-1α) plays key roles in hematopoiesis and lymphoid tissue architecture, in cardiogenesis, vascular formation and neurogenesis, as well as in the trafficking of solid and hematological cancer cell types. CXCL12 binds to the CXCR4 receptor, a multi-facetted molecule which tightly mirrors CXCL12 functions in homeostasis and disease. This review addresses the important roles of the CXCR4-CXCL12 axis in homeostasis, specially focusing in hematopoiesis, as well as it provides a picture of CXCR4 as mediator of cancer cell spreading, and a view of the available CXCR4 antagonists in different cancer types.

Evaluation of the potential therapeutic benefits of macrophage reprogramming in multiple myeloma.

Tumor-associated macrophages (TAM) are important components of the multiple myeloma (MM) microenvironment that support malignant plasma cell survival and resistance to therapy. It has been proposed that macrophages (MØ) retain the capacity to change in response to stimuli that can restore their antitumor functions. Here, we investigated several approaches to reprogram MØ as a novel therapeutic strategy in MM. First, we found tumor-limiting and tumor-supporting capabilities for monocyte-derived M1-like MØ and M2-like MØ, respectively, when mixed with MM cells, both in vitro and in vivo. Multicolor confocal microscopy revealed that MM-associated MØ displayed a predominant M2-like phenotype in the bone marrow of MM patient samples, and a high expression of the pro-M2 cytokine macrophage migration inhibitory factor (MIF). To reprogram the protumoral M2-like MØ present in MM toward antitumoral M1-like MØ, we tested the pro-M1 cytokine granulocyte-macrophage colony-stimulating factor (GM-CSF) plus blockade of the M2 cytokines macrophage colony-stimulating factor or MIF. The combination of GM-CSF plus the MIF inhibitor 4-iodo-6-phenyl-pyrimidine achieved the best reprogramming responses toward an M1 profile, at both gene and protein expression levels, as well as remarkable tumoricidal effects. Furthermore, this combined treatment elicited MØ-dependent therapeutic responses in MM xenograft mouse models, which were linked to upregulation of M1 and reciprocal downregulation of M2 MØ markers. Our results reveal the therapeutic potential of reprogramming MØ in the context of MM.

FoxO-dependent regulation of diacylglycerol kinase α gene expression.

Diacylglycerol kinase α (DGKα) regulates diacylglycerol levels, catalyzing its conversion into phosphatidic acid. The α isoform is central to immune response regulation; it downmodulates Ras-dependent pathways and is necessary for establishment of the unresponsive state termed anergy. DGKα functions are regulated in part at the transcriptional level although the mechanisms involved remain poorly understood. Here, we analyzed the 5' end structure of the mouse DGKα gene and detected three binding sites for forkhead box O (FoxO) transcription factors, whose function was confirmed using luciferase reporter constructs. FoxO1 and FoxO3 bound to the 5' regulatory region of DGKα in quiescent T cells, as well as after interleukin-2 (IL-2) withdrawal in activated T cells. FoxO binding to this region was lost after complete T cell activation or IL-2 addition, events that correlated with FoxO phosphorylation and a sustained decrease in DGKα gene expression. These data strongly support a role for FoxO proteins in promoting high DGKα levels and indicate a mechanism by which DGKα function is downregulated during productive T cell responses. Our study establishes a basis for a causal relationship between DGKα downregulation, IL-2, and anergy avoidance.

LC8 dynein light chain (DYNLL1) binds to the C-terminal domain of ATM-interacting protein (ATMIN/ASCIZ) and regulates its subcellular localization.

LC8 dynein light chain (now termed DYNLL1 and DYNLL2 in mammals), a dimeric 89 amino acid protein, is a component of the dynein multi-protein complex. However a substantial amount of DYNLL1 is not associated to microtubules and it can thus interact with dozens of cellular and viral proteins that display well-defined, short linear motifs. Using DYNLL1 as bait in a yeast two-hybrid screen of a human heart library we identified ATMIN, an ATM kinase-interacting protein, as a DYNLL1-binding partner. Interestingly, ATMIN displays at least 18 SQ/TQ motifs in its sequence and DYNLL1 is known to bind to proteins with KXTQT motifs. Using pepscan and yeast two-hybrid techniques we show that DYNLL1 binds to multiple SQ/TQ motifs present in the carboxy-terminal domain of ATMIN. Recombinant expression and purification of the DYNLL1-binding region of ATMIN allowed us to obtain a polypeptide with an apparent molecular mass in gel filtration close to 400 kDa that could bind to DYNLL1 in vitro. The NMR data-driven modelled complexes of DYNLL1 with two selected ATMIN peptides revealed a similar mode of binding to that observed between DYNLL1 and other peptide targets. Remarkably, co-expression of mCherry-DYNLL1 and GFP-ATMIN mutually affected intracellular protein localization. In GFP-ATMIN expressing-cells DNA damage induced efficiently nuclear foci formation, which was partly impeded by the presence of mCherry-DYNLL1. Thus, our results imply a potential cellular interference between DYNLL1 and ATMIN functions.

Structural basis for the interaction between dynein light chain 1 and the glutamate channel homolog GRINL1A.

Human dynein light chain 1 (DYNLL1) is a dimeric 89-residue protein that is known to be involved in cargo binding within the dynein multiprotein complex. Over 20 protein targets, of both cellular and viral origin, have been shown to interact with DYNLL1, and some of them are transported in a retrograde manner along microtubules. Using DYNLL1 as bait in a yeast two-hybrid screen with a human heart library, we identified GRINL1A (ionotropic glutamate receptor N-methyl-D-aspartate-like 1A), a homolog of the ionotropic glutamate receptor N-methyl D-aspartate, as a DYNLL1 binding partner. Binding of DYNLL1 to GRINL1A was also demonstrated using GST fusion proteins and pepscan membranes. Progressive deletions allowed us to narrow the DYNLL1 binding region of GRINL1A to the sequence REIGVGCDL. Combining these results with NMR data, we have modelled the structure of the GRINL1A-DYNLL1 complex. By analogy with known structures of DYNLL1 bound to BCL-2-interacting mediator (BIM) or neuronal nitric oxide synthase (nNOS), the GRINL1A peptide also adopts an extended beta-strand conformation that expands the central beta-sheet within DYNLL1. Structural comparison with the nNOS-DYNLL1 complex reveals that a glycine residue of GRINL1A occupies the conserved glutamine site within the DYNLL1 binding groove. Hence, our data identify a novel membrane-associated DYNLL1 binding partner and suggest that additional DYNLL1-binding partners are present near this glutamate channel homolog.

Binding of CAP70 to inducible nitric oxide synthase and implications for the vectorial release of nitric oxide in polarized cells.

In this article we analyze the mechanisms by which the C-terminal four amino acids of inducible nitric oxide synthase (NOS2) interact with proteins that contain PDZ (PSD-95/DLG/ZO-1) domains resulting in the translocation of NOS2 to the cellular apical domain. It has been reported that human hepatic NOS2 associates to EBP50, a protein with two PDZ domains present in epithelial cells. We describe herein that NOS2 binds through its four carboxy-terminal residues to CAP70, a protein that contains four PDZ modules that is targeted to apical membranes. Interestingly, this interaction augments both the cytochrome c reductase and .NO-synthase activities of NOS2. Binding of CAP70 to NOS2 also results in an increase in the population of active NOS2 dimers. In addition, CAP70 participates in the correct subcellular targeting of NOS2 in a process that is also dependent on the acylation state of the N-terminal end of NOS2. Hence, nonpalmitoylated NOS2 is unable to progress toward the apical side of the cell despite its interaction with either EBP50 or CAP70. Likewise, if we abrogate the interaction of NOS2 with either EBP50 or CAP70 by fusing the GFP reporter to the carboxy-terminal end of NOS2 palmitoylation is not sufficient to confer an apical targeting.

Nitric oxide down-regulates caveolin-3 levels through the interaction with myogenin, its transcription factor.

Certain patients suffering from chronic diseases such as AIDS or cancer experience a constant cellular secretion of tumor necrosis factor alpha and other pro-inflammatory cytokines that results in a continuous release of nitric oxide (*NO) to the bloodstream. One immediate consequence of the deleterious action of *NO is weight loss and the progressive destruction of muscular mass in a process known as cachexia. We have previously reported that caveolin-3, a specific marker of muscle cells, becomes down-regulated by the action of *NO on muscular myotubes. We describe herein that the changes observed in caveolin-3 levels are due to the alteration of the DNA binding activity of the muscular transcription factor myogenin. In the presence of *NO, the binding of transcription factors from cell nuclear extracts of muscular tissues to the E boxes present in the caveolin-3 promoter become substantially reduced. When we purified recombinant myogenin and treated it with *NO donors, we could detect its S-nitrosylation by three independent methods, suggesting that very likely one of the cysteine residues of the molecule is being modified. Given the role of myogenin as a regulatory protein that determines the level of multiple muscle genes expressed during late myogenesis, our results might represent a novel mode of regulation of muscle development under conditions of nitric oxide-mediated toxicity.

Direct interaction between the reductase domain of endothelial nitric oxide synthase and the ryanodine receptor.

We have performed the recombinant expression and purification of the reductase domain of endothelial nitric oxide synthase (eNOS) and used it as a bait in search for interacting proteins present in endothelial cells. Using mass spectrometry of the bound proteins run in a PAGE-SDS gel, we were able to identify the ryanodine receptor (RyR) as a novel eNOS-binding partner. This interaction was confirmed through immunoprecipitation of both RyR and eNOS from endothelial cells and cardiac myocytes. Immunofluorescence data indicated that a subpopulation of eNOS associates with RyR in perinuclear regions of the cell, where eNOS might be responsible for the known nitrosylation of RyR.

Matrix metalloproteinase 13 mediates nitric oxide activation of endothelial cell migration.

To explore the mechanisms by which NO elicits endothelial cell (EC) migration we used murine and bovine aortic ECs in an in vitro wound-healing model. We found that exogenous or endogenous NO stimulated EC migration. Moreover, migration was significantly delayed in ECs derived from endothelial NO synthase-deficient mice compared with WT murine aortic EC. To assess the contribution of matrix metalloproteinase (MMP)-13 to NO-mediated EC migration, we used RNA interference to silence MMP-13 expression in ECs. Migration was delayed in cells in which MMP-13 was silenced. In untreated cells MMP-13 was localized to caveolae, forming a complex with caveolin-1. Stimulation with NO disrupted this complex and significantly increased extracellular MMP-13 abundance, leading to collagen breakdown. Our findings show that MMP-13 is an important effector of NO-activated endothelial migration.

Proteomic identification of brain proteins that interact with dynein light chain LC8.

Cytoplasmic dynein is a large minus end-directed microtubule motor that translocates cargos towards the minus end of microtubules. Light chain 8 of the dynein machinery (LC8) has been reported to interact with a large variety of proteins that possess K/RSTQT or GIQVD motifs in their sequence, hence permitting their transport in a retrograde manner. Yeast two-hybrid analysis has revealed that in brain, LC8 associates directly with several proteins such as neuronal nitric oxide synthase, guanylate kinase domain-associated protein and gephyrin. In this work, we report the identification of over 40 polypeptides, by means of a proteomic approach, that interact with LC8 either directly or indirectly. Many of the neuronal proteins that we identified cluster at the post-synaptic terminal, and some of them such as phosphofructokinase, lactate dehydrogenase or aldolase are directly involved in glutamate metabolism. Other pool of proteins identified displayed the LC8 consensus binding motif. Finally, recombinant LC8 was produced and a library of overlapping dodecapeptides (pepscan) was employed to map the LC8 binding site of some of the proteins that were previously identified using the proteomic approach, hence confirming binding to the consensus binding sites.

Recognition of novel viral sequences that associate with the dynein light chain LC8 identified through a pepscan technique.

Recent data from multiple laboratories indicate that upon infection, many different families of viruses hijack the dynein motor machinery and become transported in a retrograde manner towards the cell nucleus. In certain cases, one of the dynein light chains, LC8, is involved in this interaction. Using a library of overlapping dodecapeptides synthesized on a cellulose membrane (pepscan technique) we have analyzed the interaction of the dynein light chain LC8 with 17 polypeptides of viral origin. We demonstrate the strong binding of two herpesvirus polypeptides, the human adenovirus protease, vaccinia virus polymerase, human papillomavirus E4 protein, yam mosaic virus polyprotein, human respiratory syncytial virus attachment glycoprotein, human coxsackievirus capsid protein and the product of the AMV179 gene of an insect poxvirus to LC8. Our data corroborate the manipulation of the dynein macromolecular complex of the cell during viral infection and point towards the light chain LC8 as one of the most frequently used targets of virus manipulation.