Novel protein kinases expressed in human breast cancer

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Abstract
The family of protein kinases includes many oncogenes and growth‐factor receptors, as well as genes that are involved in cell‐cycle regulation. We have identified protein kinases expressed in a human breast‐cancer cell line, 600PEI, and a primary human breast carcinoma, using PCR cloning techniques based on consensus sequences in the kinase domain. Twenty‐five different protein kinases were isolated, including 3 novel putative tyrosine kinases (designated TKI, TK2, and TK5), and 2 novel putative cell‐cycle‐associated serine/threonine kinases (designated STKI and STK2). TKI is a new member of the src family of kinases that is expressed predominantly in epithelial cells. TK2 is homologous to the receptor kinase, HEK, and TK5 appears to be another member of the J AK family of kinases. The novel serine/threonine kinases, designated STKI and STK2, were homologous to the human cdc2 and the Aspergillus nimA genes. We subsequently analyzed the levels of expression of all of these protein kinases in a panel of human breast carcinomas, using PCR‐based methods. This analysis revealed different expression profiles in different primary breast carcinomas and, therefore, may determine new molecular sub‐sets of human.