Adapter protein connections: The MRL and Grb7 protein families

Insulin-like growth factor-1 receptor (IGF-1R) has been shown to be important for melanoma cell growth and survival. In this study we first show, using immunohistochemistry, that progression from benign nevi to malignant melanoma is paralleled by an increased expression of IGF-1R and a down-regulation of the cyclin-dependent kinase inhibitor p27^Kip1. Even though the expression of p27^Kip1 was drastically reduced compared to benign tumors, detectable amounts of it could be assayed by Western blotting in cultured melanoma cells. To analyze whether there is a causative relationship between the IGF-1 pathway and p27^Kip1 expression, melanoma cells were treated with αIR-3, an antibody blocking the IGF-1 binding to IGF-1R, or Tunicamycin, which inhibits the translocation of IGF-1R to the cell surface. From these studies we could conclude that the overall expression of p27^Kip1 is independent of the IGF-1 pathway. In contrast, the association of p27^Kip1 with the different cyclins was drastically affected. Both TM and αIR-3 decreased the binding of p27^Kip1 to cyclin D1, whose expression was drastically reduced. On the other hand there was an increased binding of p27^Kip1 to cyclin E and cyclin A. This redistribution of p27^Kip1 may be a mechanism for growth arrest and induction of apoptosis following interruption of the IGF-1 pathway in melanoma cells.