Interaction between HMGA1 and Retinoblastoma Protein Is Required for Adipocyte Differentiation

Giovanna Maria Pierantoni,Stefania Scala,Sabrina Battista,Alfredo Fusco,Paolo Chieffi,Rosa Marina Melillo,Francesco Esposito,Monica Fedele

doi:10.1074/jbc.m109.034280

Abstract

It is generally accepted that the regulation of adipogenesis prevents obesity. However, the mechanisms controlling adipogenesis have not been completely defined. We have previously demonstrated that HMGA1 proteins play a critical role in adipogenesis. In fact, suppression of HMGA1 protein synthesis by antisense technology dramatically increased growth rate and impaired adipocyte differentiation in 3T3-L1 cells. Furthermore, we showed that HMGA1 strongly potentiates the capacity of the CCAAT/enhancer-binding protein beta (C/EBPbeta) transcriptional factor to transactivate the leptin promoter, an adipocytic-specific promoter. In this study we demonstrate that HMGA1 physically interacts with retinoblastoma protein (RB), which is also required in adipocyte differentiation. Moreover, we show that RB, C/EBPbeta, and HMGA1 proteins all cooperate in controlling both Id1 and leptin gene transcriptions, which are down- and up-regulated during adipocyte differentiation, respectively. We also demonstrate that HMGA1/RB interaction regulates CDC25A and CDC6 promoter activities, which are induced by E2F-1 protein during early adipocyte differentiation, by displacing HDAC1 from the RB-E2F1 complex. Furthermore, by using Hmga1(-/-) embryonic stem cells, which failed to undergo adipocyte differentiation, we show the crucial role of HMGA1 proteins in adipocyte differentiation due to its pivotal involvement in the formation of the RB-C/EBPbeta complex. Altogether these data demonstrate a key role of the interaction between HMGA1 and RB in adipocyte differentiation.

Highlights

In this study we demonstrate that HMGA1 physically interacts with retinoblastoma protein (RB), which is required in adipocyte differentiation
We show that RB, CCAAT/enhancer-binding proteins (C/EBPs)␤, and HMGA1 proteins all cooperate in controlling both Id1 and leptin gene transcriptions, which are down- and up-regulated during adipocyte differentiation, respectively
We demonstrate that HMGA1/RB interaction regulates CDC25A and CDC6 promoter activities, which are induced by E2F-1 protein during early adipocyte differentiation, by displacing HDAC1 from the RB-E2F1 complex

Summary

Introduction

It has been shown that suppression of the protein synthesis in the preadipocytic 3T3-L1 cells stimulates cell proliferation [10], and that the impairment of even one allele of the Hmga gene by homologous recombination results in the accumulation of fat patches in the abdominal/pelvic region in mice [11] These effects are consistent with a critical role of HMGA1 and HMGA2 alterations in the generation of human lipomas [11]. Role of HMGA1 and RB Interaction in Adipogenesis interacts with RB and induces E2F1 activity in mouse pituitary adenomas by displacing HDAC1 from the RB-E2F1 complex [19] These data prompted us to investigate the hypothesis that HMGA1 proteins might bind the RB proteins giving rise to a multiprotein complex able to regulate adipocyte differentiation. This interaction is direct because in vitro translated RB binds GST-HMGA1

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Conclusion