title: Osteopontin promotes integrin activation through outside-in and inside-out mechanisms: OPN-CD44V interaction enhances survival in gastrointestinal cancer cells.
abstract: Osteopontin (OPN) and splice variants of CD44 (CD44(V)) have independently been identified as markers for tumor progression. In this study, we show that both OPN and CD44(V) are frequently overexpressed in human gastric cancer and that OPN-engaged CD44(V) ligation confers cells an increased survival mediated through integrin activation. First, we show that OPN treatment confers cells an increased resistance to UV-induced apoptosis. The OPN-mediated antiapoptosis is dependent on the expression of the variant exon 6 (V6)- or V7-containing CD44 as shown by overexpression of individual CD44(V) in gastric AZ521 cells that express no or very low level of endogenous CD44 and by knockdown of the constitutively expressed V6-containing CD44 isoforms in colon HT29 cells. Although OPN also interacts with RGD integrins, OPN-RGD sequence is dispensable for OPN-mediated antiapoptosis. OPN-induced antiapoptosis is mainly attributed to the engagement of CD44(V) isoforms and the relay of an inside-out signaling via Src activity, leading to robust integrin activation. Furthermore, OPN-elicited antiapoptosis was observed when cells were plated on fibronectin but not on poly-D-lysin, and preincubation of cells with anti-integrin beta(1) antibody to block integrin-extracellular matrix (ECM) interaction or ectopic expression of the dominant-negative forms of focal adhesion kinase to block ECM-derived signal abolished OPN-induced survival, suggesting that OPN-elicited antiapoptotic function is propagated from matrix transduced by integrin. Taken together, we showed that OPN-CD44(V) interaction promotes ECM-derived survival signal mediated through integrin activation, which may play an important role in the pathogenic development and progression of gastric cancer.
authors.affiliation: Institute of Biomedical Sciences, Academia Sinica, 128 Section 2 Academia Road, Taipei 11529, Taiwan.
authors.forename: Jia-Lin
authors.initials: JL
authors.lastname: Lee
authors.forename: Mei-Jung
authors.initials: MJ
authors.lastname: Wang
authors.forename: Putty-Reddy
authors.initials: PR
authors.lastname: Sudhir
authors.forename: Gen-Der
authors.initials: GD
authors.lastname: Chen
authors.forename: Chin-Wen
authors.initials: CW
authors.lastname: Chi
authors.forename: Jeou-Yuan
authors.initials: JY
authors.lastname: Chen
mesh_terms: D000230:Adenocarcinoma / Q000378:metabolism / Q000473:pathology*; D017209:Apoptosis / Q000187:drug effects / Q000528:radiation effects; D002448:Cell Adhesion / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D005770:Gastrointestinal Neoplasms / Q000378:metabolism / Q000473:pathology*; D019073:HT29 Cells; D006801:Humans; D018960:Hyaluronan Receptors / Q000378:metabolism*; D016023:Integrins / Q000378:metabolism*; D053495:Osteopontin / Q000378:metabolism / Q000494:pharmacology / Q000502:physiology*; D020033:Protein Isoforms / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D014407:Tumor Cells, Cultured; D014466:Ultraviolet Rays / Q000009:adverse effects
chemical_list: D018960:Hyaluronan Receptors; D016023:Integrins; D020033:Protein Isoforms; D053495:Osteopontin