ADIPOSE DIFFERENTIATION-RELATED PROTEIN IS AN UBIQUITOUSLY EXPRESSED LIPID STORAGE DROPLET-ASSOCIATED PROTEIN

The adipose differentiation-related protein (ADRP) was first character ized as a mRNA induced early during adipocyte differentiation (Jiang, H. P., and G. Serrero. 1992. Proc. Natl. Acad. Sci. USA. 89:7856-7860) . The present study demonstrates that ADRP mRNA is expressed in a vari ety of tissues and cultured cell lines. Immunocytochemical examination revealed that ADRP localizes to neutral lipid storage droplets in cul tured murine 3T3-L1 adipocytes, murine MA-10 Leydig cells, Chinese ham ster ovary (CHO) fibroblasts, and human HepG2 hepatoma cells; the asso ciation of ADRP with lipid droplets was confirmed by subcellular fract ionation of MA-10 Leydig cells. In addition to ADRP, steroidogenic cel ls and adipocytes express the perilipins, a family of lipid droplet-as sociated proteins that share a highly related sequence domain with ADR P. ADRP and perilipins co-localize on lipid droplets in MA-10 Leydig c ells. While ADRP was found on small lipid droplets in 3T3-L1 preadipoc ytes and early differentiated adipocytes, it was absent in maturing ad ipocytes. In contrast, perilipins were absent early during differentia tion, but were found on small and large lipid droplets at latero stage s. The transition in surface protein composition of adipocyte lipid dr oplets from ADRP to perilipins occurred 3 days after the initiation of differentiation when cells displayed colocalization of both proteins on the same lipid droplets. The specific localization of adipose diffe rentiation-related protein to lipid droplets in a wide variety of cell s suggests that ADRP plays a role in management of neutral lipid store s.