Cloning and transcriptional regulation of a novel adipocyte-specific gene, FSP27. CAAT-enhancer-binding protein (C/EBP) and C/EBP-like proteins interact with sequences required for differentiation-dependent expression

Abstract

We have reported previously the cloning of several cDNAs whose mRNAs are induced during differentiation of the adipogenic cell line TA1. Here we characterize an adipocyte-specific gene, which we refer to as FSP27 (formerly clone 47), that encodes a protein of 27 kDa, the sequence of which is unrelated to any in the current data banks. The FSP27 promoter confers adipocyte-specific expression to a heterologous reporter gene in transfected adipogenic cell lines, e.g. TA1 and 3T3-L1. Analysis of regulatory elements in the FSP27 promoter region indicates the presence of (a) a proximal palindromic sequence that is necessary for adipocyte-specific expression; and (b) a distal differentiation-independent enhancer-like element. The palindromic sequence TTCGAAA is protected from digestion by DNase I using nuclear extracts from TA1 preadipocytes and adipocytes. Heated rat liver nuclear extract, a very abundant source of the transcription factor CAAT-enhancer-binding protein (C/EBP) and related proteins, generates an equivalent footprint over the palindrome. However, C/EBP can account for only a portion of the protein-DNA complexes in TA1 cells because preadipocytes as well as adipocytes contain proteins distinct from C/EBP which interact with the same sequence. We suggest that C/EBP and other C/EBP-like proteins play a critical role in regulating the transcription of the fat-specific gene FSP27.