Isolation and characterization of an epithelial-specific receptor tyrosine kinase from an ovarian cancer cell line.

A protein receptor tyrosine kinase (RTK 6) has been isolated from a complementary DNA library of SKOV-3, an epithelial ovarian cancer cell line, using a polymerase chain reaction (PCR)-mediated approach. The primary structure of the predicted amino acid sequence of the protein shows a novel NH2-terminal region which has homology to a factor VIII-like domain. The juxtamembrane region is proline and glycine rich and is the longest for any known receptor kinase. The COOH-terminal catalytic domain has all of the canonical sequence motifs of a receptor tyrosine kinase with homology to the TRK-2H protein (49%). A single transcript of 4.5 kilobases is expressed at low levels in heart, placenta, lung, liver, muscle, kidney, and pancreas, with high levels of expression in the brain. Ribonuclease protection assay showed a varying level of expression of message in a panel of eight ovarian cancer cell lines compared to placenta. In situ hybridization analysis demonstrated localization of mRNA in the epithelial cells of the ovary, kidney, small bowel, lung, thymus, and brain. There was a lower level of message in normal, benign, and borderline tumors of the ovary compared to malignant tumors of the ovary. Polyclonal antisera raised against a COOH-terminal synthetic peptide recognize a M(r) 140,000 protein in ovarian cancer cells, which autophosphorylates in an in vitro kinase assay.