Inherent or acquired drug resistance is one of the major problems in chemotherapy. The mechanisms by which cancer cells survive and escape the cytotoxic e ects of chemotherapeutic agents are essentially unknown. In the present study, we demonstrate that in the MDA-MB-231 and MDA-MB-435 breast cancer cells, ligation of b1 integrins by their extracellular matrix ligands inhibits signi®cantly apoptosis induced by paclitaxel and vincristine, two microtubule-directed chemotherapeutic agents that are widely used in the therapy of breast cancer. We show that b1 integrin signaling inhibits drug-induced apoptosis by inhibiting the release of cytochrome c from the mitochondria in response to drug treatment. Further, integrin-mediated protection from drug-induced apoptosis and inhibition of cytochrome c release are dependent on the activation of the PI 3-kinase/Akt pathway. Our results identify b1 integrin signaling as an important survival pathway in drug-induced apoptosis in breast cancer cells and suggest that activation of this pathway may contribute to the generation of drug resistance. Oncogene (2001) 20, 4995 ± 5004.

Survival of endothelial cells is critical for cellular processes such as angiogenesis. Cell attachment to extracellular matrix inhibits apoptosis in endothelial cells both in vitro and in vivo, but the molecular mechanisms underlying matrix-induced survival signals or detachment-induced apoptotic signals are unknown. We demonstrate here that matrix attachment is an efficient regulator of Fas-mediated apoptosis in endothelial cells. Thus, matrix attachment protects cells from Fas-induced apoptosis, whereas matrix detachment results in susceptibility to Fas-mediated cell death. Matrix attachment modulates Fas-mediated apoptosis at two different levels: by regulating the expression level of Fas, and by regulating the expression level of c-Flip, an endogenous antagonist of caspase-8. The extracellular signal–regulated kinase (Erk) cascade functions as a survival pathway in adherent cells by regulating c-Flip expression. We further show that detachment-induced cell death, or anoikis, itself results from activation of the Fas pathway by its ligand, Fas-L. Fas-L/Fas interaction, Fas–FADD complex formation, and caspase-8 activation precede the bulk of anoikis in endothelial cells, and inhibition of any of these events blocks anoikis. These studies identify matrix attachment as a survival factor against death receptor–mediated apoptosis and provide a molecular mechanism for anoikis and previously observed Fas resistance in endothelial cells.

Resistance to apoptosis and chemotherapy is a hallmark of cancer cells, and it is a critical factor in cancer recurrence and patient relapse. Extracellular matrix (ECM)viaits receptors, the integrins, has emerged as a major pathway contributing to cancer cell survival and resistance to chemotherapy. Several studies over the last decade have demonstrated that ECM/integrin signaling provides a survival advantage to various cancer cell types against numerous chemotherapeutic drugs and against antibody therapy. In this paper, we will discuss the major findings on how ECM/integrin signaling protects tumor cells from drug-induced apoptosis. We will also discuss the potential role of ECM in malignant T-cell survival and in cancer stem cell resistance. Understanding how integrins and their signaling partners promote tumor cell survival and chemoresistance will likely lead to the development of new therapeutic strategies and agents for cancer treatment.

Melanoma is the most aggressive skin cancer in humans that often expresses MHC class II (MHC II) molecules, which could make these tumors eliminable by the immune system. However, this MHC II expression has been associated with poor prognosis, and there is a lack of immune-mediated eradication. The lymphocyte activation gene-3 (LAG-3) is a natural ligand for MHC II that is substantially expressed on melanoma-infiltrating T cells including those endowed with potent immune-suppressive activity. Based on our previous data showing the signaling capacity of MHC II in melanoma cells, we hypothesized that LAG-3 could contribute to melanoma survival through its MHC II signaling capacity in melanoma cells. In this study, we demonstrate that both soluble LAG-3 and LAG-3–transfected cells can protect MHC II-positive melanoma cells, but not MHC II-negative cells, from FAS-mediated and drug-induced apoptosis. Interaction of LAG-3 with MHC II expressed on melanoma cells upregulates both MAPK/Erk and PI3K/Akt pathways, albeit with different kinetics. Inhibition studies using specific inhibitors of both pathways provided evidence of their involvement in the LAG-3–induced protection from apoptosis. Altogether, our data suggest that the LAG-3–MHC II interaction could be viewed as a bidirectional immune escape pathway in melanoma, with direct consequences shared by both melanoma and immune cells. In the future, compounds that efficiently hinder LAG-3–MHC II interaction might be used as an adjuvant to current therapy for MHC II-positive melanoma.

The regulation of matrix metalloproteinase-9 (MMP-9) expression in glioma cells is one of the key processes in tumor invasion through the brain extracellular matrix. Although some studies have demonstrated the implication of classic protein kinase C (PKC) isoforms in the regulation of MMP-9 production by phorbol esters or lipopolysaccharide, the involvement of specific PKC isoforms in the signaling pathways leading to MMP-9 expression by inflammatory cytokines remains unclear. Here we report that the atypical PKC-isoform participates in the induction of MMP-9 expression by interleukin-1 (IL-1) and tumor necrosis factor-␣ (TNF-␣) in rat C6 glioma cells. Indeed, zymography and semi-quantitative reverse transcriptase-PCR analysis showed that pretreatment of C6 cells with PKC-pseudosubstrate abolished MMP-9 activity and gene expression induced by IL-1 or TNF-␣. Accordingly, IL-1 and TNF-␣ were able to induce PKC-activity, as demonstrated by in vitro kinase assay using immunoprecipitated PKC-. Furthermore, stable C6 clones overexpressing PKC-, but not PKC-⑀, displayed an up-regulation of MMP-9 constitutive expression as well as an increase of mmp-9 promoter activity. These processes were inhibited by an NF-B-blocking peptide and completely prevented by NF-B-binding site mutation in the mmp-9 promoter. Taken together, these results indicate that PKC-plays a key role in the regulation of MMP-9 expression in C6 glioma cells through NF-B.Glioma cells have the ability to invade brain tissues by secreting matrix metalloproteinases (MMPs), 1 a family of proteases able to degrade different components of the extracellular matrix including collagen, fibronectin, and proteoglycans. One of these MMPs, MMP-9, has received much attention as its expression correlates with the progression of glioma (1). Furthermore, MMP-9 seems to be essential for the invasiveness of glioma cells, as it was recently reported that the inhibition of MMP-9 expression by antisense gene transfer strongly reduced the invasion of glioblastoma cells in vitro and in vivo (2). Therefore, understanding the role of the molecules implicated in the signaling pathways leading to mmp-9 gene expression in glioma cells is important in order to identify new therapeutic targets. Several studies (3-5) have focused on the implication of protein kinase C (PKCs) in the regulation of mmp-9 gene expression, most notably by testing the effect of phorbol 12-myristate 13-acetate (PMA) on different types of cells, including human glioma cells. Members of the PKC family are divided into the following three groups of isoenzymes: the conventional PKC isoforms, which are activated by calcium and diacylglycerol (␣, ␤I, ␤II, and ␥); the novel PKCs, which are activated by diacylglycerol but are calcium-insensitive (␦, ⑀, , and ); and the atypical PKCs, which are calcium-and diacylglycerol-insensitive ( and /). Despite the fact that a large number of studies (5-7) have established a link between PKCs and MMP-9 expression using PKC inhibitors, very few studies have addressed the implicat...

SummaryInterleukin-7 (IL-7) is a crucial cytokine involved in T-cell survival and development but its signalling in human T cells, particularly in effector/ memory T cells, is poorly documented. In this study, we found that IL-7 protects human CD4 + effector/memory T cells from apoptosis induced upon the absence of stimulation and cytokines. We show that IL-7 upregulates not only Bcl-2 but also Bcl-xL and Mcl-1 as well. Interleukin-7-induced activation of the janus kinase/signal transducer and activator of transcription (JAK/STAT) signalling pathway is sufficient for cell survival and up-regulation of Bcl-2 proteins. In contrast to previous studies with naive T cells, we found that IL-7 is a weak activator of the phosphatidylinositol 3 kinase (PI3K)/AKT (also referred as protein kinase B) pathway and IL-7-mediated cell survival occurs independently from the PI3K/AKT pathway as well as from activation of the mitogen-activated protein kinase/extracellular signal-regulated kinase pathway. Considering the contribution of both IL-7 and CD4 + effector/memory T cells to the pathogenesis of autoimmune diseases such as rheumatoid arthritis and colitis, our study suggests that IL-7 can contribute to these diseases by promoting cell survival. A further understanding of the mechanisms of IL-7 signalling in effector/memory T cells associated with autoimmune inflammatory diseases may lead to potential new therapeutic avenues.

The mechanisms by which T lymphocytes escape apoptosis during their activation are still poorly defined. In this study, we elucidated the intracellular signaling pathways through which ␤ 1 integrins modulate Fas-mediated apoptosis in T lymphocytes. In experiments done in Jurkat T cells and activated peripheral blood T lymphocytes, engagement of ␣ 2 ␤ 1 integrin with collagen type I (Coll I) was found to significantly reduce Fasinduced apoptosis and caspase-8 activation; Annexin V binding and DNA fragmentation were reduced by ϳ42 and 38%, respectively. We demonstrated that the protective action of Coll I does not require new protein synthesis but was dependent on the activation of the MAPK/ Erk pathway. Furthermore, we found that activation of protein phosphatase 2A (PP2A) by Coll I was required for both Coll I-mediated activation of Erk, and inhibition of Fas-induced caspase-8 activation and apoptosis. Other ligands of ␤ 1 integrins, fibronectin (Fbn), and laminin (Lam), did not sustain significant Erk activation and had no effect on Fas-induced apoptosis. Taken together, these results provide the first evidence of a PP2A-dependent activation of the MAPK/Erk pathway downstream of ␣ 2 ␤ 1 integrin, which has a functional role in regulating Fas-mediated apoptosis in T lymphocytes. As such, this study emphasizes the potential importance that Coll I interactions may have on the control of T lymphocyte homeostasis and their persistence in chronic inflammatory diseases.

No abstract