De novo expression of the α5β1-fibronectin receptor in HT29 colon-cancer cells reduces activity of c-src. Increase of c-src activity by attachment on febronectin
✍ Scribed by Roland Schmidt; Michael Streit; Rolf Kaiser; Frank Herzberg; Michael Schirner; Kira Schramm; Christine Kaufmann; Maren Henneken; Monika Schäfer-Korting; Eckhard Thiel; Ernst-Dietrich Kreuser
- Publisher
- John Wiley and Sons
- Year
- 1998
- Tongue
- French
- Weight
- 228 KB
- Volume
- 76
- Category
- Article
- ISSN
- 0020-7136
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✦ Synopsis
Changes in integrin expression during malignant transformation have been observed in many tumors. Colon-carcinoma cells show reduced expression or even loss of the ␣51 integrin compared to normal or adenoma cells. To determine the significance of absent ␣51 integrin signaling, we transfected the cDNA coding for the ␣5 integrin sub-unit into the human colon-carcinoma cell line HT29, which constitutively lacks this subunit but does express the 1 subunit. We show here that the newly expressed fibronectin receptor ␣51 generates multiple signals, causing marked changes in cytoskeletal arrangements within a few minutes of adhesion to fibronectin. Cells expressing the ␣51 integrin exhibit the formation of actin stress fibers and focal adhesions, as well as the induction of tyrosine phosphorylation of several proteins, within 10 min. We identified the focal adhesion kinase pp125 FAK and the cytoskeletal protein paxillin as major phosphorylation substrates in these cells. These proteins remained hypophosphorylated when ␣5-negative control cells were plated on fibronectin. The tyrosine kinase pp60 c-src , regarded as central in the regulation of cellular proliferation and constitutively over-expressed in HT29 and in coloncarcinoma cells, showed reduced intrinsic kinase activity in unstimulated HT29␣5 cells. In contrast, fibronectin-induced signaling through ␣51 increased pp60 c-src activity. Moreover, immunoprecipitation of pp60 c-src from extracts of HT29␣5 cells cultivated on fibronectin for 20 min revealed complex formation of pp60 c-src and tyrosine-phosphorylated pp125 FAK . Our data suggest that de novo expression of the ␣51 integrin in HT29 colon-cancer cells restores signaling via pp125 FAK and pp60 c-src . Thus, loss of this receptor during malignant transformation may contribute to tumor-cell autonomy, while reduced activity of pp60 c-src in HT29␣5-cells may participate directly in growth control. Int.