E2F1 Regulates Adipocyte Differentiation and Adipogenesis by Activating ICAT.

Jingqing Chen,Fengchao Wang,Ying Yang,Zhenlong Wu,Shuai Li,Patrick Tso,Guoyao Wu,Yuchen Yang,Zhaolai Dai

doi:10.3390/cells9041024

Abstract

Wnt/β-catenin is a crucial repressor of adipogenesis. We have shown that E2 promoter binding factor 1 (E2F1) suppresses Wnt/β-catenin activity through transactivation of β-catenin interacting protein 1 (CTNNBIP1), also known as inhibitor of β-catenin and TCF4 (ICAT) in human colorectal cancers. However, it remains unknown whether ICAT is required for E2F1 to promote differentiation by inhibiting β-catenin activity in pre-adipocytes. In the present study, we found that 1-methyl-3-isobutylxanthine, dexamethasone, and insulin (MDI)-induced differentiation and lipid accumulation in 3T3-L1 pre-adipocytes was reversed by activation of β-catenin triggered by CHIR99021, a GSK3β inhibitor. Intriguingly, we observed a reduced protein level of E2F1 and ICAT at a later stage of pre-adipocytes differentiation. Importantly, overexpression of ICAT in 3T3-L1 pre-adipocytes markedly promote the adipogenesis and partially reversed the inhibitory effect of CHIR99021 on MDI-induced adipogenesis and lipid accumulation by regulating adipogenic regulators and Wnt/β-catenin targets. Moreover, pre-adipocytes differentiation induced by MDI were markedly inhibited in siE2F1 or siICAT transfected 3T3-L1 cells. Gene silencing of ICAT in the E2F1 overexpressed adipocytes also inhibited the adipogenesis. These data indicated that E2F1 is a metabolic regulator with an ability to promote pre-adipocyte differentiation by activating ICAT, therefore represses Wnt/β-catenin activity in 3T3-L1 cells. We also demonstrated that ICAT overexpression did not affect oleic acid-induced lipid accumulation at the surface of Hela and HepG2 cells. In conclusion, we show that E2F1 is a critical regulator with an ability to promote differentiation and adipogenesis by activating ICAT in pre-adipocytes.

Highlights

The alarming increase in the incidence of obesity among adults and children worldwide has prompted extensive researches on molecular mechanisms responsible for the synthesis and catabolism of triglycerides (TG) in white adipose tissues [1]
Protein levels of E2 promoter binding factor 1 (E2F1) and inhibitor of β-catenin and T-cell factor 4 (TCF4) (ICAT) were significantly increased (p < 0.05) at day 3 of differentiation and were reduced to an undetectable level at the later stages of adipocyte differentiation (Figure 1C). These results showed that MDI-induced differentiation in 3T3-L1 cells was associated with an increased protein level of E2F1/ICAT at day 3 of differentiation
We found a novel function of E2F1/ICAT on promoting pre-adipocytes differentiation and lipid accumulation in 3T3-L1 cells

Summary

Introduction

The alarming increase in the incidence of obesity among adults and children worldwide has prompted extensive researches on molecular mechanisms responsible for the synthesis and catabolism of triglycerides (TG) in white adipose tissues [1]. Pre-adipocyte differentiation has been one of the well-known models used to study adipogenesis [4], and underlying mechanisms, due to its implication in metabolic syndrome, such as insulin resistance, type 2 diabetes, hypertension, and atherosclerosis [5]. Protein level of E2F1 is increased in the visceral white adipose tissue of obese human subjects and is positively correlated with development of insulin resistance, circulating free fatty acids level, and incidence of non-alcoholic fatty liver disease [7,10,11,12,13]. Knockout of E2F1 in pre-adipocytes impairs its capacity to differentiate into adipocytes [14], indicating a critical role of E2F1 in differentiation These studies highlight an unexpected functional role of E2F1 on cellular metabolism in both humans and animals

Methods

Results

Conclusion