Identification and modulation of a caveolae-dependent signal pathway that regulates plasminogen activator inhibitor-1 in insulin-resistant adipocytes

doi:10.1073/pnas.0405278101

Identification and modulation of a caveolae-dependent signal pathway that regulates plasminogen activator inhibitor-1 in insulin-resistant adipocytes

Friedrich Miescher Institute for Biomedical Research, Novartis Research Foundation, Maulbeerstrasse 66, 4058 Basel, Switzerland

Edited by Anthony Cerami, The Kenneth S. Warren Institute, Kitchawan, NY, and approved October 15, 2004 (received for review July 21, 2004)

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 Bα-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.

diabetes

Footnotes

↵ ‡ To whom correspondence should be addressed. E-mail: nagamine{at}fmi.ch.
↵ * J.V. and K.H. contributed equally to this work.
↵ † Present address: First Department of Physiology, School of Medicine, University of the Ryukyus, Okinawa 903-0215, Japan.
This paper was submitted directly (Track II) to the PNAS office.
Abbreviations: PAI-1, plasminogen activator inhibitor-1; PI3K, phosphatidylinositol 3-kinase; PKB, protein kinase B; S6K1, p70 ribosomal S6 kinase 1; pRB, retinoblastoma protein; E2F, E2 (adenoviral protein) factor; MBCD, methyl-β-cyclodextrin; IR, insulin receptor; IRS, IR substrate; Erk, extracellular regulated kinase; T2DM, type 2 diabetes mellitus; siRNA, small interfering RNA; NIH-IR, NIH 3T3 cells overexpressing the human IR.
↵ § Maianu, L., Chen, Y., Simmons, A., Wallace, P., Hutto, A., Shaughnessy, S., Fernandes, J. & Garvey, W. (2003) Diabetes 52, A330 (abstr).