Phosphorylation of the basal site of hormone-sensitive lipase by glycogen synthase kinase-4

In rat adipocytes hormone-sensitive lipase is phosphorylated at two sites termed ‘regulatory’ and ‘basal’, in the former case by cyclic AMP-dependent protein kinase causing an activation of the lipase [(1984) Proc. Natl. Acad. Sci. USA 81, 3317-3321]. Here, the basal phosphorylation site was found to be phosphorylated by glycogen synthase kinase-4 without any effects on lipase activity, or on the extent of its activation subsequent to phosphorylation of the regulatory site. Glycogen synthase kinase-3, casein kinase-I, and casein kinase-II did not phosphorylate the lipase. Phosphorylase kinase phosphorylated it to a very low extent at a third phosphorylation site not phosphorylated in the fat cell.