Alkylglycerol Functions as an Isotype-Specific Regulator of Protein Kinase C and Cell Proliferation

Document Type

Article

Publication Date

12-1-1996

Description

Our studies have shown that monoalkylglycerol (AG) accumulates during density-dependent inhibition of cell growth in MDCK cells. Synthetic AG is a potent inhibitor of protein kinase C (PKC) in vitro and treatment of cells with AG reduces membrane-associated PKC activity. In light of the role of PKC in the regulation of cell proliferation, we sought to determine if AG regulates specific PKC isoforms and to explore the role of AG in the regulation of mitogenesis. Western blotting using PKC isotype-specific antibodies was used to identify the α,βI,βII,ε and ζ isoforms in MDCK cells. In proliferating cells, 33% of the total PKCα was found associated with cellular membranes. Treatment of intact MDCK cells with 30μM AG for one hour decreased the fraction of PKCα that was membrane-associated to only 3%. AG treatment also effectively reduced the translocation of PKCα to the membrane fraction in response to phorbol ester treatment. In contrast, AG was ineffective in blocking phorbol-ester stimulated PKCε translocation to the membrane. AG had no effect on the subcellular distribuion of PKC βI,βII or ζ. We examined the effects of AG on the ability of various mitogens to stimulate [3H]thymidine incorporation into DNA in confluent, quiescent cultures of 3T3 fibroblasts. AG significantly reduced phorbol-ester stimulated mitogenesis but enhanced mitogenesis in response to insulin. These results support a role for AG as a negative regulator of cell proliferation through its ability to specifically inhibit the association of PKCα with membranes. The results also support a role for PKCα in phorbol ester, but not insulin, induced mitogenesis.

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