title: The regulatory and basal phosphorylation sites of hormone-sensitive lipase are dephosphorylated by protein phosphatase-1, 2A and 2C but not by protein phosphatase-2B.
abstract: The activity of hormone-sensitive lipase, the rate-limiting enzyme in adipose tissue lipolysis, is controlled by cAMP-mediated phosphorylation at a specific regulatory phosphorylation site. The lipase is also phosphorylated at a site, termed basal, without any effects on its activity [Strålfors et al. (1984) Proc. Natl Acad. Sci. USA 81, 3317-3321]. The capacity of protein phosphatase-1, 2A, 2B and 2C to dephosphorylate the lipase, selectively phosphorylated by glycogen synthase kinase-4 and cAMP-dependent protein kinase at the basal and regulatory phosphorylation sites, was compared with that towards glycogen phosphorylase and phosphorylase kinase (alpha subunit). Protein phosphatase-1, 2A and 2C were found to dephosphorylate both phosphorylation sites of hormone-sensitive lipase, while protein phosphatase-2B had no measureable activity towards any of the sites. When the activities of protein phosphatase-1, 2A and 2C were normalized with respect to the reference substrates, they were found to dephosphorylate the lipase regulatory site in the approximate relations of 1:4:3 and the basal site in the approximate relations of 1:6:4. Protein phosphatase-1 showed 20% higher and protein phosphatase-2A and 2C 80% higher activity towards the basal site compared to the regulatory site. The two phosphorylation sites of the lipase were comparable to good substrates for protein phosphatase-2A and 2C, but relatively poor substrates for protein phosphatase-1. Protein phosphatase-2C activity towards the lipase was completely dependent on Mg2+ with a half-maximal effect at 3 mM. Protamine increased the lipase dephosphorylation by protein phosphatase-1 3-5-fold with half-maximal effect at 0.6 microgram/ml, and by protein phosphatase-2A about 2-fold with half-maximal effect at 3-5 micrograms/ml, thus illustrating the potential for control of these lipase phosphatase activities.
authors.affiliation: Department of Medical and Physiological Chemistry, University of Lund, Sweden.
authors.forename: H
authors.initials: H
authors.lastname: Olsson
authors.forename: P
authors.initials: P
authors.lastname: Belfrage
mesh_terms: D000273:Adipose Tissue / Q000201:enzymology; D000818:Animals; D001665:Binding Sites; D000242:Cyclic AMP / Q000494:pharmacology; D008066:Lipolysis / Q000187:drug effects; D008274:Magnesium / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D010766:Phosphorylation; D011479:Protamines / Q000494:pharmacology; D011494:Protein Kinases / Q000378:metabolism; D054645:Protein Phosphatase 1; D054648:Protein Phosphatase 2; D051381:Rats; D002787:Sterol Esterase / Q000378:metabolism*
chemical_list: D011479:Protamines; D000242:Cyclic AMP; D011494:Protein Kinases; D002787:Sterol Esterase; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D054648:Protein Phosphatase 2; D008274:Magnesium