RETINYL ESTER HYDROLYSIS AND RETINOL EFFLUX FROM BFC-1-BETA ADIPOCYTES

Adipose tissue is an important storage depot for retinol, but there ar e no data regarding retinol mobilization from adipose stores. To addre ss this, dibutyryl cAMP was provided to murine BFC-1 beta adipocytes a nd its effects on retinol efflux assessed. High performance liquid chr omatography analysis of retinol and retinyl esters in adipocytes and m edia indicated that cAMP stimulated, in a time- and dose-dependent man ner, retinol accumulation in the culture media and decreased cellular retinyl ester concentrations. Study of adipocyte retinol-binding prote in synthesis and secretion indicated that cAMP-stimulated retinol effl ux into the media did not result from increased retinol-retinol-bindin g protein secretion but was dependent on the presence of fetal bovine serum in the culture media. Since our data suggested that retinyl este rs can be hydrolyzed by a cAMP-dependent enzyme like hormone-sensitive lipase (HSL), in separate studies, we purified a HSL-containing fract ion from BFC-1 beta adipocytes and demonstrated that it catalyzed reti nyl palmitate hydrolysis. Homogenates of Chinese hamster ovary cells o verexpressing HSL catalyzed retinyl palmitate hydrolysis in a time-, p rotein-, and substrate-dependent manner, with an apparent K-m for reti nyl palmitate of 161 mu M, whereas homogenates from control Chinese ha mster ovary cells did not.