c-erbB3 gene encodes secreted as well as transmembrane receptor tyrosine kinase

c-erbB3 product is moderately expressed in gastric mucosa, especially in parietal cells. Northern blot analysis revealed that 6.2-kb c-erbB3 transcript was expressed in all gastric cancer cell lines examined, and that 1.4-kb c-erbB3 transcript was expressed as highly as 6.2-kb transcript in MKN45 cells. erbB3-S cDNA, corresponding to 1.4-kb c-erbB3 transcript, was cloned by rapid amplification of cDNA ends. Sequence analysis of erbB3-S cDNA showed that this 1.4-kb c-erbB3 mRNA encoded a secreted receptor. Analysis of partial genomic structure of c-erbB3 gene revealed that the exon specific to secreted receptor was identical with the 5' portion of the intron in c-erbB3 gene. c-erbB3 gene encodes secreted as well as transmembrane receptor tyrosine kinase due to alternative splicing.