Analysis of c-erb A RNA expression in the triiodothyronine-sensitive Ob 17 preadipocyte cell line.

The protooncogenes erb A alpha and beta encode, in the rat, three functional thyroid hormone receptors (erb A alpha1, beta1 and beta2), and two isoforms (erb A alpha2, alpha3) that do not bind triiodothyronine (T3). We previously reported on a mouse preadipocyte cell line (Ob 17) which was found to be sensitive to thyroid hormones and retinoic acid. Using antibodies or cDNA probes, we reported that the c-erb A products are mainly of the alpha-type in these cells. We also showed that the thyroid hormone receptors / c-erb A products are down-regulated moderately by T3 and strongly by retinoic acid added to the culture medium. In this work, different c-erb A subtypes are identified in this mouse cell line. Using couples of oligonucleotides known to be specific of each rat c-erb A subtype, we could detect the presence of alpha1, alpha2 and beta1-type transcripts. We also detected Rev transcripts of a Reverse erb Aalpha gene present in the rat at the c-erb Aalpha locus and that contains a region complementary to the c-erb A alpha2-specific region. These transcripts were identified by PCR amplification from cell cDNAs and in Northern analyses using the corresponding PCR-designed c-erb A probes. All the detected transcripts were found to be down-regulated by retinoic acid.