ErbB380 kDa, a nuclear variant of the ErbB3 receptor, binds to the Cyclin D1 promoter to activate cell proliferation but is negatively controlled by p14ARF

Abstract EGFR family members are tyrosine kinase transmembrane receptors that, in response to specific extracellular ligands, activate cytoplasmic pathways involved in cell proliferation, migration and differentiation. More recently, a pivotal role for EGF receptors has emerged, through the description of their nuclear localization.We report here the characterization of a nuclear variant of the kinase-defective ErbB3 receptor, ErbB3 80 kDa , spanning the intracytoplasmic domain of the receptor. We assessed the putative transcriptional functions of ErbB3 80 KDa in cancer cells, through the regulation of the proliferative Cyclin D1 gene, an already known target of the ErbB3 cytoplasmic signaling. We demonstrate here that the binding of ErbB3 80 KDa on the promoter activates Cyclin D1 transcription and subsequent protein expression, leading to an increased cell proliferation. This mechanism can be balanced in response to the ectopic expression of the tumor suppressor p14 ARF that physically interacts with ErbB3 100 kDa and sequesters it into nucleoli. Our data also show that ErbB3 80 kDa increases the transcription of proliferative genes even though the cytoplasmic pathways are not activated. This nuclear ErbB3 pathway and the target genes concerned need to be further studied. Indeed, such mechanism could explain the tumor relapse observed in response to treatments aimed at blocking the receptor activation in response to ligand binding.