Phosphorylation of adaptor protein containing pleckstrin homology domain, phosphotyrosine binding domain, and leucine zipper motif 1 (APPL1) at Ser430 mediates endoplasmic reticulum (ER) stress-induced insulin resistance in hepatocytes.
APPL1 is an adaptor protein that plays a critical role in regulating adiponectin and insulin signaling. However, how APPL1 is regulated under normal and pathological conditions remains largely unknown. In this study, we show that APPL1 undergoes phosphorylation at Ser(430) and that this phosphorylation is enhanced in the liver of obese mice displaying insulin resistance. In cultured mouse hepatocytes, APPL1 phosphorylation at Ser(430) is stimulated by phorbol 12-myristate 13-acetate, an activator of classic PKC isoforms, and by the endoplasmic reticulum (ER) stress inducer, thapsigargin. Overexpression of wild-type but not dominant negative PKCα increases APPL1 phosphorylation at Ser(430) in mouse hepatocytes. In addition, suppressing PKCα expression by shRNA in hepatocytes reduces ER stress-induced APPL1 phosphorylation at Ser(430) as well as the inhibitory effect of ER stress on insulin-stimulated Akt phosphorylation. Consistent with a negative regulatory role of APPL1 phosphorylation at Ser(430) in insulin signaling, overexpression of APPL1(S430D) but not APPL1(S430A) impairs the potentiating effect of APPL1 on insulin-stimulated Akt phosphorylation at Thr(308). Taken together, our results identify APPL1 as a novel target in ER stress-induced insulin resistance and PKCα as the kinase mediating ER stress-induced phosphorylation of APPL1 at Ser(430).
Department of Pharmacology, University of Texas Health Science Center at San Antonio (UTHSCSA), San Antonio, Texas 78229, USA. lium2@uthscsa.edu
Meilian
M
Liu
Lijun
L
Zhou
Li
L
Wei
Ricardo
R
Villarreal
Xin
X
Yang
Derong
D
Hu
Ramon A
RA
Riojas
Bekke M
BM
Holmes
Paul R
PR
Langlais
Hakjoo
H
Lee
Lily Q
LQ
Dong
D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D000818:Animals; D002460:Cell Line; D059865:Endoplasmic Reticulum Stress; D020536:Enzyme Activators / Q000494:pharmacology; D022781:Hepatocytes / Q000201:enzymology / Q000378:metabolism*; D006801:Humans; D007328:Insulin / Q000502:physiology; D007333:Insulin Resistance; D007527:Isoenzymes / Q000378:metabolism; D008099:Liver / Q000201:enzymology / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008820:Mice, Obese; D009765:Obesity / Q000378:metabolism; D010766:Phosphorylation; D051571:Protein Kinase C-alpha / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D012694:Serine / Q000378:metabolism; D015398:Signal Transduction; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
C464801:APPL1 protein, human; D048868:Adaptor Proteins, Signal Transducing; D020536:Enzyme Activators; D007328:Insulin; D007527:Isoenzymes; D012694:Serine; D051571:Protein Kinase C-alpha; D013755:Tetradecanoylphorbol Acetate