Role of the IGF-II receptor in mediating acute, non-genomic effects of retinoids and IGF-II on keratinocyte cell death.

In this study, we have examined the effects of retinoic acid (RA) on the human immortalized keratinocyte cell line (HaCaT). A significant twofold (P < 0.01) increase in apoptotic cell death compared with the control was found within 24 h of treatment with 10-5 M of RA. Apoptosis was confirmed by flow cytometry. Cycloheximide did not inhibit this acute RA-induced apoptosis. Interestingly, insulin-like growth factor-II (IGF-II, 50 ng/ml) was able to significantly (67.3%; P < 0.05) reduce RA effects, whereas IGF-I (50 ng/ml) and insulin (75 ng/ml) were without effect. Furthermore, analogues of IGF-II [leu27 IGF-II and Des(1-6) IGF-II], with altered affinities for the IGF-I receptor and IGF-binding proteins (IGFBPs), but retained affinities for the IGF-II receptor, also completely inhibited (100%; P < 0.01) RA-induced apoptosis, while an IGF-I receptor antagonist did not reduce the survival effects of IGF-II. Insulin pretreatment negates the survival effect of IGF-II. In contrast, mannose 6 phosphate (M6P) did not alter RA or IGF-II actions. These results indicate that rapid induction of cell death by RA is independent of production or secretion of new proteins. The inhibition of RA action by IGF-II was independent of its ability to signal through the IGF-I receptor or to interact with IGFBPs.