Effects of RACK1 on cell migration and IGF-I signalling in cardiomyoctes are not dependent on an association with the IGF-IR

RACK1 can act as a scaffolding protein to integrate IGF-IR and integrin signalling in transformed cells but its actions in regulating IGF-IR signalling in non-transformed cells are less well understood. Here, we investigated the function of RACK1 in the non-transformed cardiomyocyte cell line H9c2. Overexpression of RACK1 in H9c2 cells was sufficient to increase cell size, increase adhesion to collagen 1, enhance protection from hydrogen peroxide-induced cell death, and increase cell migration. However, cell proliferation was decreased in these cells. Small interfering RNA (siRNA)-mediated suppression of RACK1 in H9c2 cells resulted in decreased cell adhesion and migration, but had no effect on cell proliferation or size. Increased basal and IGF-I-mediated Erk phosphorylation was observed in RACK1-overexpressing H9c2 cells. Interestingly, contrary to observations in transformed cells, RACK1 was not observed to interact with the IGF-IR in H9c2 cells. Also in contrast to observations in transformed cells, IGF-I promoted recruitment of Src to RACK1 as well as recruitment of PKCα, and PKCe{open} to RACK1. Overall, the data indicate that in H9c2 cells RACK1 can influence cell size, cell survival, adhesion, migration, but its responses to IGF-I are independent of an association with the IGF-IR. Thus, the composition of the RACK1 scaffolding complex and its effects on IGF-I signalling may be different in transformed and non-transformed cells.