title: Protein kinase C theta (PKCtheta)-dependent phosphorylation of PDK1 at Ser504 and Ser532 contributes to palmitate-induced insulin resistance.
abstract: Clinical, epidemiological, and biochemical studies have highlighted the role of obesity-induced insulin resistance in various metabolic diseases. However, the underlying molecular mechanisms remain to be established. In the present study, we show that palmitate-induced serine phosphorylation of phosphoinositide-dependent protein kinase-1 (PDK1) negatively regulates insulin signaling. PDK1-mediated Akt phosphorylation at Thr308 in the activation loop is reduced in C2C12 myotubes treated with palmitate or overexpressing protein kinase C theta (PKCtheta), a kinase that has been implicated in hyperlipidemia-induced insulin resistance. Palmitate treatment also inhibited platelet-derived growth factor-stimulated Akt phosphorylation, suggesting that the inhibition could occur at a site independent of IRS1/2. The inhibitory effect of palmitate on PDK1 and Akt was diminished in PKCtheta-deficient mouse embryonic fibroblasts (MEFs) by treating C2C12 myotubes with PKCtheta pseudosubstrates. In vivo labeling studies revealed that PDK1 undergoes palmitate-induced phosphorylation at two novel sites, Ser504 and Ser532. Replacing Ser504/532 with alanine disrupted PKCtheta-catalyzed PDK1 phosphorylation in vitro and palmitate-induced PDK1 phosphorylation in cells. PDK1-deficient MEFs transiently expressing PDK1S504A/S532A but not PDK1S504E/S532D showed increased basal and insulin-stimulated Akt phosphorylation at Thr308 when compared with MEFs expressing wild-type PDK1. Taken together, our results identify PDK1 as a novel target in free fatty acid-induced insulin resistance and PKCtheta as the kinase mediating the negative regulation.
authors.affiliation: Department of Pharmacology, Barshop Center for Longevity and Aging Studies, University of Texas Health Science Center, San Antonio, TX 78229, USA.
authors.forename: Changhua
authors.initials: C
authors.lastname: Wang
authors.forename: Meilian
authors.initials: M
authors.lastname: Liu
authors.forename: Ramon A
authors.initials: RA
authors.lastname: Riojas
authors.forename: Xiaoban
authors.initials: X
authors.lastname: Xin
authors.forename: Zhanguo
authors.initials: Z
authors.lastname: Gao
authors.forename: Rong
authors.initials: R
authors.lastname: Zeng
authors.forename: Jiarui
authors.initials: J
authors.lastname: Wu
authors.forename: Lily Q
authors.initials: LQ
authors.lastname: Dong
authors.forename: Feng
authors.initials: F
authors.lastname: Liu
mesh_terms: D064413:3-Phosphoinositide-Dependent Protein Kinases; D000818:Animals; D002460:Cell Line; D006224:Cricetinae; D004789:Enzyme Activation / Q000187:drug effects; D055504:Insulin Receptor Substrate Proteins / Q000378:metabolism; D007333:Insulin Resistance; D007527:Isoenzymes / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D009154:Mutation / Q000235:genetics; D010168:Palmitates / Q000494:pharmacology*; D010768:Phosphoserine / Q000378:metabolism*; D011493:Protein Kinase C / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D000074121:Protein Kinase C-theta; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism
chemical_list: D055504:Insulin Receptor Substrate Proteins; D007527:Isoenzymes; D010168:Palmitates; D010768:Phosphoserine; D064413:3-Phosphoinositide-Dependent Protein Kinases; C578564:Pdpk1 protein, mouse; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; C489593:Prkcq protein, mouse; D011493:Protein Kinase C; D000074121:Protein Kinase C-theta