Figure 1. Regulation of lipolysis in adipocytes.

A, A current model for the hormonal regulation of lipolysis initiation is shown. Proteins depicted include perilipin 1A (Peri), Hormone Sensitive Lipase (HSL), Adipocyte Triglyceride Lipase (ATGL), CGI-58, and PKA. Lipid species depicted include triacylglycerol (TAG), diacylglycerol (DAG), monoacylglycerol (MAG), and fatty acid (FA). Under basal conditions, perilipin and HSL are unphosphorylated and HSL is found throughout the cytoplasm. Stimulation of lipolysis involves activation of PKA, phosphorylation of perilipin 1A and HSL, release of CGI-58 from perilipin, binding of CGI-58 to ATGL, and translocation of HSL to perilipin. TAG is sequentially processed to DAG by ATGL and to MAG by HSL with FA released at each step. B, Amino acid sequences are shown for perilipin 1A PKA site 5, and PKA site 6, and for HSL serine 563 and serine 660. The target serine in each sequence is underlined.