Perilipins Are Associated with Cholesteryl Ester Droplets in Steroidogenic Adrenal Cortical and Leydig Cells

Abstract

Steroidogenic cells store cholesteryl esters, precursors for steroid hormone synthesis, in intracellular lipid droplets. Cholesteryl ester hydrolysis is activated by protein kinase A and catalyzed by cholesteryl esterase. The esterase is similar, if not identical, to hormone-sensitive lipase in adipocytes where an analogous lipolytic mechanism occurs. Perilipins, proteins located exclusively at lipid droplet surfaces in adipocytes, are polyphosphorylated by protein kinase A in response to lipolytic stimuli, suggesting a role for these proteins in mediating lipid metabolism. The present study reveals that perilipins are associated with cholesteryl ester droplets in two steroidogenic cell lines: Y-1 adrenal cortical cells and MA-10 Leydig cells. The relative abundance of perilipin mRNAs and protein is much less in steroidogenic cells than in adipocytes. Like adipocytes, steroidogenic cells express perilipin A; additionally, the latter cells contain relatively abundant amounts of perilipin C, a protein that is not detectable in adipocytes by Western analysis. The data suggest a strong link between perilipins and lipid hydrolysis that is mediated by the hormone-sensitive lipase/cholesteryl esterase class of enzymes.