Modulation of expression of RA-regulated genes by the oncoprotein v-erbA

Retinoic acid (RA) modulates the expression of genes involved in embryogenesis, development and differentiation processes in vertebrates. The v-erbA oncogene is known to exert a dominant-negative effect on the expression of RA-responsive genes. v-erbA belongs to a superfamily of transcription factors called nuclear receptors, which includes the retinoic acid receptors (RARs) responsible for mediating the effects of retinoic acid. While RA inhibits cell proliferation and promotes cell differentiation and apoptosis in a variety of tissues, v-erbA seems to play a role in oncogenesis, namely in the development of hepatocellular carcinoma (HCC) in a transgenic mouse model. In order to study the effect of v-erbA on RA-responsive genes, we used microarray analysis to identify genes differentially expressed in murine hepatocytes in culture (AML12 cells) stably transfected with v-erbA and exposed to RA for 3 h or 24 h. We have identified RA-responsive genes that are affected by v-erbA, as well as genes that are regulated by v-erbA alone. We have found that v-erbA can affect gene expression in the presence of RA and at the level of basal transcription. We have also identified a number of v-erbA-responsive genes that are known to be involved in carcinogenesis and which may play a role in the development of HCC.