Transient expression of c-erbAβ1 messenger ribonucleic acid and β1 thyroid hormone receptor early in adipogenesis of Ob 17 cells

In the murine Ob 17 preadipocyte cell line, the thyroid hormone T-a, is an adipogenic factor necessary at an early stage for differentiation into adipocyte. We demonstrate here that this T-3 dependence may involve a transient expression (at both the messenger RNA and the protein levels) of c-ErbA P-type receptors (T3R), although a large body of T3R remained the product of the c-erbA alpha gene, as previously described, c-ErbA beta 1 (and not beta 2) expression emerged significantly at growth arrest, peaked 2 days later, and almost disappeared in maturing adipocytes. This expression is related to the presence of T-3 as total deprivation of culture medium from T-3 prevented it, and the addition of 1.5 nM T-3 to preconfluent cultures was able to restore it. When cells were cultured in the presence of T-3 and thus were able to differentiate, the c-erbA beta peak was accompanied by sequential rapid increases in CAAT/enhancer-binding protein-delta (C/EBP delta), peroxisome proliferator-activated-gamma receptor (PPAR gamma), and C/EBP alpha gene expressions. On the contrary, under thyroid hormone-deprived culture conditions that result in nondifferentiation of the preadipocytes, c-erbA beta 1, PPAR gamma; and the large C/EBP alpha expressions were blunted, and a moderate early increase in c-erbA alpha 1 transcripts was sustained for a longer period. Addition of T-a to T-3-deprived preconfluent cells restored PPAR gamma and C/EBP alpha expressions. Taken together, the results highlight the important role of T-3 in the adipogenesis of Ob 17 cells through the involvement of both pi and alpha 1 T3R subtypes.