tretinoin and mannose-6-phosphate

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.

Topics: Apoptosis; Cell Division; Cell Line; Cycloheximide; Humans; Insulin; Insulin-Like Growth Factor I; Insulin-Like Growth Factor II; Keratinocytes; Mannosephosphates; Receptor, IGF Type 1; Receptor, IGF Type 2; Recombinant Proteins; Tretinoin

Retinoic acid (RA) exerts diverse biological effects in the control of cell growth in embryogenesis and oncogenesis. These effects of RA are thought to be mediated by the nuclear retinoid receptors. Mannose-6-phosphate (M6P)/insulin-like growth factor-II (IGF-II) receptor is a multifunctional membrane glycoprotein that is known to bind both M6P and IGF-II and function primarily in the binding and trafficking of lysosomal enzymes, the activation of transforming growth factor-beta, and the degradation of IGF-II. M6P/IGF-II receptor has recently been implicated in fetal development and carcinogenesis. Despite the functional similarities between RA and the M6P/IGF-II receptor, no direct biochemical link has been established. Here, we show that the M6P/IGF-II receptor also binds RA with high affinity at a site that is distinct from those for M6P and IGF-II, as identified by a photoaffinity labeling technique. We also show that the binding of RA to the M6P/IGF-II receptor enhances the primary functions of this receptor. The biological consequence of the interaction appears to be the suppression of cell proliferation and/or induction of apoptosis. These findings suggest that the M6P/IGF-II receptor mediates a RA response pathway that is important in cell growth regulation. This discovery of the interaction of RA with the M6P/IGF-II receptor may have important implications for our understanding of the roles of RA and the M6P/IGF-II receptor in development, carcinogenesis, and lysosomal enzyme-related diseases.

Topics: Animals; Binding Sites; Blood Proteins; Cells, Cultured; Insulin-Like Growth Factor II; Kinetics; Mannosephosphates; Membrane Proteins; Myocardium; Photoaffinity Labels; Rats; Receptor, IGF Type 2; Receptors, Retinoic Acid; Tretinoin

13-cis-Retinoic acid, a drug used at high doses in the treatment of recalcitrant acne, increased the permeability of rat-liver microsomal membranes to mannose 6-phosphate in vitro, as indicated by an increase in mannose-6-phosphatase activity. At the same concentrations, four other amphiphiles, including all-trans-retinoic acid, were much less effective. 13-cis-Retinoic acid also inhibited retinol esterification and benzo[a]pyrene hydroxylation in microsome preparations in vitro. Although the molecular mechanism and the reversibility of these effects have not yet been studied, the interaction of 13-cis-retinoic acid with cell membranes may well be involved in both its therapeutic and toxic manifestations.

Topics: Animals; Benzo(a)pyrene; Female; Hexosephosphates; Hydrolysis; Hydroxylation; Isomerism; Isotretinoin; Kinetics; Mannosephosphates; Microsomes, Liver; Rats; Rats, Inbred F344; Tretinoin; Vitamin A