Phosphorylation of TG-interacting factor 1 at carboxyl-terminal sites in response to insulin regulates adipocyte differentiation

TG-interacting factor 1 (TGIF1) contributes to the differentiation of murine white preadipocyte and human adipose tissue-derived stem cells; however, its regulation is not well elucidated. Insulin is a component of the adipogenic cocktail that induces ERK signaling. TGIF1 phosphorylation and sustained stability in response to insulin were reduced through the use of specific MEK inhibitor U0126. Mutagenesis at T235 or T239 residue of TGIF1 in preadipocytes led to dephosphorylation of TGIF1. The reduced TGIF1 stability resulted in an increase in p27^kip1 expression, a decrease in phosphorylated Rb expression and cellular proliferation, and a reduced accumulation of lipids compared to the TGIF1-overexpressed cells. These findings highlight that insulin/ERK-driven phosphorylation of the T235 or T239 residue at TGIF1 is crucial for adipocyte differentiation.