Abstract

Integrin αvβ3 plays a role in insulin-like growth factor 1 (IGF1) signaling (integrin-IGF1 receptor (IGF1R) cross-talk) in non-transformed cells in anchorage-dependent conditions. We reported previously that IGF1 directly binds to αvβ3 and induces αvβ3-IGF1-IGF1R ternary complex formation in these conditions. The integrin-binding defective IGF1 mutant (R36E/R37E) is defective in inducing ternary complex formation and IGF signaling, whereas it still binds to IGF1R. We studied if IGF1 can induce signaling in anchorage-independent conditions in transformed Chinese hamster ovary cells that express αvβ3 (β3-CHO) cells. Here we describe that IGF1 signals were more clearly detectable in anchorage-independent conditions (polyHEMA-coated plates) than in anchorage-dependent conditions. This suggests that IGF signaling is masked by signals from cell-matrix interaction in anchorage-dependent conditions. IGF signaling required αvβ3 expression, and R36E/R37E was defective in inducing signals in polyHEMA-coated plates. These results suggest that αvβ3-IGF1 interaction, not αvβ3-extracellular matrix interaction, is essential for IGF signaling. Inhibitors of IGF1R, Src, AKT, and ERK1/2 did not suppress αvβ3-IGF-IGF1R ternary complex formation, suggesting that activation of these kinases are not required for ternary complex formation. Also, mutations of the β3 cytoplasmic tail (Y747F and Y759F) that block β3 tyrosine phosphorylation did not affect IGF1R phosphorylation or AKT activation. We propose a model in which IGF1 binding to IGF1R induces recruitment of integrin αvβ3 to the IGF-IGF1R complex and then β3 and IGF1R are phosphorylated. It is likely that αvβ3 should be together with the IGF1-IGF1R complex for triggering IGF signaling.

Highlights

  • Insulin-like growth factor 1 (IGF1)2 is a polypeptide hormone that has a high degree of structural similarity to proinsulin

  • IGF1 Induces Signals in Anchorage-independent Conditions in an ␣v␤3-dependent Manner—IGF1 directly binds to integrin ␣v␤3 and induces integrin-IGF1-IGF1R ternary complex formation in non-transformed cells in anchorage-dependent conditions [5]

  • The enhancement in IGF1-induced cell survival and proliferation in ␤3-Chinese hamster ovary (CHO) cells is small, we showed that anti-␤3 mAb (7E3) suppressed it (Fig. 1, d and e), suggesting that IGF1-induced cell survival and proliferation in anchoragedependent condition is ␣v␤3-dependent

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Summary

Introduction

Insulin-like growth factor 1 (IGF1)2 is a polypeptide hormone that has a high degree of structural similarity to proinsulin. We used anchorage-independent conditions for studying the role of ␣v␤3 in IGF signaling because ␣v␤3-ECM interaction itself may induce ␤3 phosphorylation. In anchorage-dependent conditions (regular tissue culture plates without an ECM coating), we found that IGF1 induced a slightly higher cell survival (Fig. 1a) and cell proliferation (b) in ␤3-CHO cells than that of control CHO cells that express human ␤1 (␤1-CHO cells), and there was only small enhancement in ERK1/2 and AKT activation between ␤3- and ␤1-CHO cells (c).

Results
Conclusion

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