Pref-1 Interacts with Fibronectin To Inhibit Adipocyte Differentiation

Abstract

Pref-1/Dlk1 is made as an epidermal growth factor (EGF) repeat-containing transmembrane protein but is cleaved by tumor necrosis factor alpha converting enzyme (TACE) to generate a biologically active soluble form. Soluble Pref-1 inhibits adipocyte differentiation through the activation of extracellular signal-regulated kinase/mitogen-activated protein kinase (ERK/MAPK) and the subsequent upregulation of Sox9 expression. However, others have implicated Notch in Pref-1 signaling and function. Here, we show that Pref-1 does not interact with, or require, Notch for its function. Instead, we show a direct interaction of Pref-1 and fibronectin via the Pref-1 juxtamembrane domain and fibronectin C-terminal domain. We also show that fibronectin is required for the Pref-1-mediated inhibition of adipocyte differentiation, the activation of ERK/MAPK, and the upregulation of Sox9. Furthermore, disrupting fibronectin binding to integrin by the addition of RGD peptides or by the knockdown of α5 integrin prevents the Pref-1 inhibition of adipocyte differentiation. Pref-1 activates the integrin downstream signaling molecules, FAK and Rac, and ERK activation by Pref-1 is blunted by the knockdown of Rac or by the forced expression of dominant-negative Rac. We conclude that, by interacting with fibronectin, Pref-1 activates integrin downstream signaling to activate MEK/ERK and to inhibit adipocyte differentiation.

We thank Raphael Kopan and Gerry Weinmaster for providing expression vectors for Notch, Jagged1, and Dll 1. We thank Robin Duncan and Maryam Ahmadian for the careful reading of the manuscript.

The work was supported by NIH grant DK50808 to H.S.S.