| abstract |
A DNA fragment distinct from the epidermal growth factor receptor (EGFR) and erbB-2 genes was detected by reduced stringency hybridization of v-erbB to normal genomic human DNA. Characterization of the cloned DNA fragment mapped the region of v-erbB homology to three exons with closest homology of 64% and 67% to a contiguous region within the tyrosine kinase domains of the EGFR and erbB-2 proteins, respectively. cDNA cloning revealed a predicted 148 kd transmembrane polypeptide with structural features identifying it as a member of the erbB family, prompting designation of the new gene as erbB-3. It was mapped to human chromosome 12 ql 11-13 and was shown to be expressed as a 6.2 kb transcript in a variety of normal tissues of epithelial origin. Markedly elevated erbB-3 mRNA levels were demonstrated in certain human mammary tumor cell lines. These findings indicate that increased erbB-3 expression, as in the case of EGFR and erbB-2, plays a role in some human malignancies. Using erbB-3 specific antibodies (polyclonal or monoclonal), the erbB-3 protein was identified as a 180 kDa glycoprotein, gp180EGFR/erbB-3. The intrinsic catalytic function of gp180erbB-3 was uncovered by its ability to autophosphorylate in vitro. Ligand-dependent signaling of its cytoplasmic domain was established employing transfectants which express a chimeric EGFR/erbB-3 protein, gp180EGFR/erbB-3. EGF induced tyrosine phosphorylation of the chimera and promoted soft agar colony formation of such transfectants. These findings, combined with the detection of constitutive tyrosine phosphorylation of gp180erbB-3 in 4 out of 12 human mammary tumor cell lines, implicate the activated erbB-3 product in the pathogenesis of some human malignancies. |