COLON-CARCINOMA KINASE-4 DEFINES A NEW SUBCLASS OF THE RECEPTOR TYROSINE KINASE FAMILY

Complementary DNA (cDNA) encoding a novel member of the receptor tyros ine kinase (RTK) family has been isolated from colon carcinoma tissue. Colon carcinoma kinase 4 (CCK-4) mRNA is highly expressed in human lu ng tissue and at lower levels in the thyroid gland and ovary. While no mRNA was found in human adult colon tissues, expression varied remark ably in colon carcinoma-derived cell lines. CCK-4 cDNA encodes a chick en KLG-related, 1071 amino acid-long transmembrane glycoprotein contai ning several genetic alterations within the RTK consensus sequences. T hese define CCK-4 as a catalytically inactive member of the RTK family of proteins and, in analogy to HER3, suggest a potentially tumor-char acteristic role as a signal amplifier or modulator for an as yet unide ntified kinase-competent partner.