Phospholipase C-Related Catalytically Inactive Protein (PRIP) Regulates Lipolysis in Adipose Tissue by Modulating the Phosphorylation of Hormone-Sensitive Lipase

Toshiya Okumura,Kae Harada,Akiko Mizokami,Masahiro Irifune,Satoshi Asano,Masato Hirata,Jun Zhang,Nobuyuki Kamata,Hiroto Tanaka,Takashi Kanematsu,Kana Oue,Masaki Hayashiuchi,Monika Oberer

doi:10.1371/journal.pone.0100559

Abstract

Phosphorylation of hormone-sensitive lipase (HSL) and perilipin by protein kinase A (PKA) promotes the hydrolysis of lipids in adipocytes. Although activation of lipolysis by PKA has been well studied, inactivation via protein phosphatases is poorly understood. Here, we investigated whether phospholipase C-related catalytically inactive protein (PRIP), a binding partner for protein phosphatase 1 and protein phosphatase 2A (PP2A), is involved in lipolysis by regulating phosphatase activity. PRIP knockout (PRIP-KO) mice displayed reduced body-fat mass as compared with wild-type mice fed with standard chow ad libitum. Most other organs appeared normal, suggesting that mutant mice had aberrant fat metabolism in adipocytes. HSL in PRIP-KO adipose tissue was highly phosphorylated compared to that in wild-type mice. Starvation of wild-type mice or stimulation of adipose tissue explants with the catabolic hormone, adrenaline, translocated both PRIP and PP2A from the cytosol to lipid droplets, but the translocation of PP2A was significantly reduced in PRIP-KO adipocytes. Consistently, the phosphatase activity associated with lipid droplet fraction in PRIP-KO adipocytes was significantly reduced and was independent of adrenaline stimulation. Lipolysis activity, as assessed by measurement of non-esterified fatty acids and glycerol, was higher in PRIP-KO adipocytes. When wild-type adipocytes were treated with a phosphatase inhibitor, they showed a high lipolysis activity at the similar level to PRIP-KO adipocytes. Collectively, these results suggest that PRIP promotes the translocation of phosphatases to lipid droplets to trigger the dephosphorylation of HSL and perilipin A, thus reducing PKA-mediated lipolysis.

Highlights

Obesity is associated with the development of type 2 diabetes mellitus, coronary heart disease, an increased incidence of cancer, and respiratory complications [1]
Excess energy is stored as triacylglycerol (TAG) in lipid droplets, while lipolysis of stored TAG followed by the release of both non-esterified fatty acids (NEFA) and glycerol is stimulated by food deprivation or stress
The mean weight of musculus rectus femoris was reduced in phospholipase C-related catalytically inactive protein (PRIP)-DKO mice, but that of musculus gastrocnemius was similar in both genotypes

Summary

Introduction

Obesity is associated with the development of type 2 diabetes mellitus, coronary heart disease, an increased incidence of cancer, and respiratory complications (e.g., obstructive sleep apnea) [1]. Obesity is characterized by excessive body fat accumulation in adipose tissue. Excess energy is stored as triacylglycerol (TAG) in lipid droplets, while lipolysis of stored TAG followed by the release of both non-esterified fatty acids (NEFA) and glycerol is stimulated by food deprivation (fasting) or stress. NEFA and glycerol are released from the adipocytes and transported to other tissues by circulation [2,3]. Lipolysis is regulated by several molecules, including adenosine 39,59-cyclic monophosphate (cAMP)-dependent protein kinase A (PKA) [4,5], cAMP phoshodiesterase 3 or 4 [6] protein phosphatase 1 (PP1) [7], protein phosphatase 2A (PP2A) [8,9], and perilipin A, a lipid droplet-associated protein [10,11]

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Results

Conclusion