Isolation and characterization of four alternate c-erbB3 transcripts expressed in ovarian carcinoma-derived cell lines and normal human tissues.
ErbB-3 is a member of the epidermal growth factor receptor (EGFR/ErbB) family. In addition to the previously reported 6.2 kb full-length and 1.4 kb truncated c-erbB3 transcripts, we have observed a 1.7 kb c-erbB3 human transcript in Northern blots that specifically hybridizes to a probe of the extracellular domain of the receptor. Using 3'-RACE we have isolated four novel c-erbB3 cDNA clones of 1.6, 1.7, 2.1 and 2.3 kb from a human ovarian carcinoma-derived cell line. All four alternate transcripts are synthesized by readthrough of an intron and use of an alternative polyadenylation signal within this intron. Identical c-erbB3 transcripts are expressed in normal human placental tissues. Expression of these alternate transcripts is tissue-specific as indicated by Northern blot and RNase protection analyses. Fibroblasts transfected with expression vectors carrying these alternate c-erbB3 cDNA clones stably express truncated ErbB-3 products. Three of these four cDNA clones express a receptor product that is secreted. Immunoprecipitation analysis of primary cultures of human ovarian carcinomas also demonstrate the expression of a 90 kDa ErbB-3 related protein that is secreted. Furthermore, we demonstrate conservation of the exon-intron junctions between members of the erbB gene family in those regions of the gene encoding the extracellular domain. This gene structure is also conserved in the c-erbB1 homologues of Drosophila and C. elegans. Growth regulatory roles for related truncated ErbB products recently have been reported. It is, therefore, possible that the products of these four alternate c-erbB3 transcripts may also play important growth regulatory roles in normal and transformed cells.
Lee
H
H
Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, Minnesota 55905, USA.
Maihle
N J
NJ
D017398:Alternative Splicing; D000595:Amino Acid Sequence; D001483:Base Sequence; D002460:Cell Line; D017077:Culture Media, Conditioned / Q000737:chemistry; D018076:DNA, Complementary / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification; D066246:ErbB Receptors / Q000032:analysis / Q000235:genetics* / Q000302:isolation & purification*; D005057:Eukaryotic Cells / Q000737:chemistry / Q000166:cytology / Q000378:metabolism; D005091:Exons / Q000235:genetics; D005260:Female; D015870:Gene Expression / Q000235:genetics; D015723:Gene Library; D006801:Humans; D008969:Molecular Sequence Data; D010051:Ovarian Neoplasms / Q000737:chemistry / Q000235:genetics*; D010053:Ovary / Q000166:cytology* / Q000378:metabolism / Q000473:pathology; D010920:Placenta / Q000737:chemistry / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000032:analysis / Q000235:genetics* / Q000302:isolation & purification*; D020893:Receptor, ErbB-3; D012260:Ribonucleases / Q000378:metabolism; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D014158:Transcription, Genetic / Q000235:genetics; D014407:Tumor Cells, Cultured
D017077:Culture Media, Conditioned; D018076:DNA, Complementary; D011518:Proto-Oncogene Proteins; D066246:ErbB Receptors; D020893:Receptor, ErbB-3; D012260:Ribonucleases