Transient Expression of c-erbAβ1 Messenger Ribonucleic Acid andβ 1 Thyroid Hormone Receptor Early in Adipogenesis of Ob 17 Cells*

Abstract

In the murine Ob 17 preadipocyte cell line, the thyroid hormone T3 is an adipogenic factor necessary at an early stage for differentiation into adipocyte. We demonstrate here that this T3 dependence may involve a transient expression (at both the messenger RNA and the protein levels) of c-ErbA beta-type receptors (T3R), although a large body of T3R remained the product of the c-erbAalpha gene, as previously described. c-ErbAbeta1 (and not beta2) expression emerged significantly at growth arrest, peaked 2 days later, and almost disappeared in maturing adipocytes. This expression is related to the presence of T3, as total deprivation of culture medium from T3 prevented it, and the addition of 1.5 nM T3 to preconfluent cultures was able to restore it. When cells were cultured in the presence of T3 and thus were able to differentiate, the c-erbAbeta peak was accompanied by sequential rapid increases in CAAT/enhancer-binding protein-delta(C/EBPdelta), peroxisome proliferator-activated-gamma receptor (PPARgamma), and C/EBPalpha gene expressions. On the contrary, under thyroid hormone-deprived culture conditions that result in nondifferentiation of the preadipocytes, c-erbAbeta1, PPARgamma, and the large C/EBPalpha expressions were blunted, and a moderate early increase in c-erbAalpha1 transcripts was sustained for a longer period. Addition of T3 to T3-deprived preconfluent cells restored PPARgamma and C/EBPalpha expressions. Taken together, the results highlight the important role of T3 in the adipogenesis of Ob 17 cells through the involvement of both beta1 and alpha1 T3R subtypes.