title: Identification and modulation of a caveolae-dependent signal pathway that regulates plasminogen activator inhibitor-1 in insulin-resistant adipocytes.
abstract: Plasminogen activator inhibitor-1 (PAI-1) plays an important role in the pathogenesis of obesity-driven type 2 diabetes mellitus and associated cardiovascular complications. Here, we show that perturbation of caveolar microdomains leads to insulin resistance and concomitant up-regulation of PAI-1 in 3T3L1 adipocytes. We present several lines of evidence showing that the phosphatidylinositol 3-kinase (PI3K) pathway negatively regulates PAI-1 gene expression. Insulin-induced PAI-1 gene expression is up-regulated by a specific inhibitor of PI3K. In addition, serum PAI-1 level is elevated in protein kinase Balpha-deficient mice, whereas it is reduced in p70 ribosomal S6 kinase 1-deficient mice. The PI3K pathway phosphorylates retinoblastoma protein (pRB), known to release free E2 (adenoviral protein) factor (E2F), which we have previously demonstrated to be a transcriptional repressor of PAI-1 gene expression. Accordingly, cell-penetrating peptides that disrupt pRB-E2F interaction, and thereby release free E2F, are able to suppress PAI-1 levels that are elevated during insulin-resistant conditions. This study identifies a caveolar-dependent signal pathway that up-regulates PAI-1 in insulin-resistant adipocytes and proposes a previously undescribed pharmacological paradigm of disrupting pRB-E2F interaction to suppress PAI-1 levels.
authors.affiliation: Friedrich Miescher Institute for Biomedical Research, Novartis Research Foundation, Maulbeerstrasse 66, 4058 Basel, Switzerland.
authors.forename: Joshi
authors.initials: J
authors.lastname: Venugopal
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Hanashiro
authors.forename: Zhong-Zhou
authors.initials: ZZ
authors.lastname: Yang
authors.forename: Yoshikuni
authors.initials: Y
authors.lastname: Nagamine
mesh_terms: D041721:3T3-L1 Cells; D017667:Adipocytes / Q000473:pathology / Q000648:ultrastructure; D000818:Animals; D021941:Caveolae / Q000502:physiology*; D018797:Cell Cycle Proteins / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D050684:E2F Transcription Factors; D005786:Gene Expression Regulation / Q000187:drug effects; D007328:Insulin / Q000494:pharmacology; D007333:Insulin Resistance; D021962:Membrane Microdomains; D051379:Mice; D010455:Peptides / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases; D017395:Plasminogen Activator Inhibitor 1 / Q000097:blood / Q000235:genetics*; D011485:Protein Binding / Q000187:drug effects; D016160:Retinoblastoma Protein / Q000378:metabolism; D015398:Signal Transduction; D014157:Transcription Factors / Q000378:metabolism
chemical_list: D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D007328:Insulin; D010455:Peptides; D017395:Plasminogen Activator Inhibitor 1; D016160:Retinoblastoma Protein; D014157:Transcription Factors; D019869:Phosphatidylinositol 3-Kinases