An RNA interference-based screen identifies MAP4K4/NIK as a negative regulator of PPARgamma, adipogenesis, and insulin-responsive hexose transport.
The insulin-regulated glucose transporter GLUT4 is a key modulator of whole body glucose homeostasis, and its selective loss in adipose tissue or skeletal muscle causes insulin resistance and diabetes. Here we report an RNA interference-based screen of protein kinases expressed in adipocytes and identify four negative regulators of insulin-responsive glucose transport: the protein kinases PCTAIRE-1 (PCTK1), PFTAIRE-1 (PFTK1), IkappaB kinase alpha, and MAP4K4/NIK. Integrin-linked protein kinase was identified as a positive regulator of this process. We characterized one of these hits, MAP4K4/NIK, and found that it is unique among mitogen-activated protein (MAP) kinases expressed in cultured adipocytes in attenuating hexose transport. Remarkably, MAP4K4/NIK suppresses expression of the adipogenic transcription factors C/EBPalpha, C/EBPbeta, and PPARgamma and of GLUT4 itself in these cells. RNA interference-mediated depletion of MAP4K4/NIK early in differentiation enhances adipogenesis and triglyceride deposition, and even in fully differentiated adipocytes its loss up-regulates GLUT4. Conversely, conditions that inhibit adipogenesis such as TNF-alpha treatment or depletion of PPARgamma markedly up-regulate MAP4K4/NIK expression in cultured adipocytes. Furthermore, TNF-alpha signaling to down-regulate GLUT4 is impaired in the absence of MAP4K4/NIK, indicating that MAP4K4 expression is required for optimal TNF-alpha action. These results reveal a MAP4K4/NIK-dependent signaling pathway that potently inhibits PPARgamma-responsive gene expression, adipogenesis, and insulin-stimulated glucose transport.
Tang
Xiaoqing
X
Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, MA 01605, USA.
Guilherme
Adilson
A
Chakladar
Abhijit
A
Powelka
Aimee M
AM
Konda
Silvana
S
Virbasius
Joseph V
JV
Nicoloro
Sarah M C
SM
Straubhaar
Juerg
J
Czech
Michael P
MP
D041721:3T3-L1 Cells; D017667:Adipocytes / Q000187:drug effects / Q000378:metabolism; D050156:Adipogenesis / Q000235:genetics*; D000818:Animals; D001692:Biological Transport; D022763:CCAAT-Enhancer-Binding Protein-alpha / Q000235:genetics; D022782:CCAAT-Enhancer-Binding Protein-beta / Q000235:genetics; D015536:Down-Regulation; D005786:Gene Expression Regulation; D005947:Glucose / Q000378:metabolism*; D051275:Glucose Transporter Type 4 / Q000235:genetics*; D007328:Insulin / Q000494:pharmacology; D047908:Intracellular Signaling Peptides and Proteins; D051379:Mice; D051058:Oncogene Protein v-akt / Q000235:genetics / Q000378:metabolism; D047495:PPAR gamma / Q000235:genetics*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D013489:Suppression, Genetic; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
D022763:CCAAT-Enhancer-Binding Protein-alpha; D022782:CCAAT-Enhancer-Binding Protein-beta; D051275:Glucose Transporter Type 4; D007328:Insulin; D047908:Intracellular Signaling Peptides and Proteins; D047495:PPAR gamma; C495693:Slc2a4 protein, mouse; D014409:Tumor Necrosis Factor-alpha; C117090:MAP4K4 protein, human; D051058:Oncogene Protein v-akt; D017346:Protein Serine-Threonine Kinases; D005947:Glucose