Perilipin A is essential for the translocation of hormone-sensitive lipase during lipolytic activation

Akey step in lipolytic activation of adipocytes is the translocation of hormone-sensitive lipase (HSL) from the cytosol to the surface of the lipid storage droplet. Adipocytes from perilipin-null animals have an elevated basal rate of lipolysis compared with adipocytes from wild-type mice, but fail to respond maximally to lipolytic stimuli. This defect is downstream of the β-adrenergic receptor–adenylyl cyclase complex. Now, we show that HSL is basally associated with lipid droplet surfaces at a low level in perilipin nulls, but that stimulated translocation from the cytosol to lipid droplets is absent in adipocytes derived from embryonic fibroblasts of perilipin-null mice. We have also reconstructed the HSL translocation reaction in the nonadipocyte Chinese hamster ovary cell line by introduction of GFP-tagged HSL with and without perilipin A. On activation of protein kinase A, HSL-GFP translocates to lipid droplets only in cells that express fully phosphorylatable perilipin A, confirming that perilipin is required to elicit the HSL translocation reaction. Moreover, in Chinese hamster ovary cells that express both HSL and perilipin A, these two proteins cooperate to produce a more rapidly accelerated lipolysis than do cells that express either of these proteins alone, indicating that lipolysis is a concerted reaction mediated by both protein kinase A–phosphorylated HSL and perilipin A

Dephosphorylation of perilipin by protein phosphatases present in rat adipocytes

AbstractBy incubating 32P-labelled adipocytes, and extracts from these cells, in the presence or absence of specific inhibitors, we evaluated the contribution of protein phosphatases PP1, PP2A and PP2C, to the dephosphorylation of perilipin, an acutely hormone-regulated adipocyte phosphoprotein. Under conditions to completely inhibit PP2A activity, perilipin phosphatase activity in extracts remain unaffected, but PP1 inhibition results in abolition of perilipin phosphatase activity. Inhibition of PP1 (and 2A) in intact adipocytes stimulated lipolysis and increased phosphorylation of perilipin. No involvement of PP2C was found. Hence, PP1 constitutes the predominant if not sole perilipin phosphatase in adipocytes

Decrease in intramuscular lipid droplets and translocation of HSL in response to muscle contraction and epinephrine.

A better understanding of skeletal muscle lipid metabolism is needed to identify the molecular mechanisms relating intramuscular triglyceride (IMTG) to muscle metabolism and insulin sensitivity. An increasing number of proteins have been reported to be associated with intracellular triglyceride (TG), among them the PAT family members: perilipin, ADRP ( for adipocyte differentiation-related protein), and TIP47 ( for tail-interacting protein of 47 kDa). Hormone-sensitive lipase (HSL) is thought to be the major enzyme responsible for IMTG hydrolysis in skeletal muscle. In adipocytes, regulation of HSL by intracellular redistribution has been demonstrated. The existence of such regulatory mechanisms in skeletal muscle has long been hypothesized but has never been demonstrated. The aim of this study was to characterize the PAT family proteins associated with IMTG and to investigate the effect of epinephrine stimulation or muscle contraction on skeletal muscle TG content and HSL intracellular distribution. Rat soleus muscles were either incubated with epinephrine or electrically stimulated for 15 min. Single muscle fibers were used for morphological analysis by confocal and transmission electron microscopy. We show a decrease in IMTG in response to both lipolytic stimuli. Furthermore, we identify two PAT family proteins, ADRP and TIP47, associated with IMTG. Finally, we demonstrate HSL translocation to IMTG and ADRP after stimulation with epinephrine or contraction