Expression of the lck tyrosine kinase gene in human colon carcinoma and other non-lymphoid human tumor cell lines.

The tyrosine kinase p56lck is felt to be expressed solely in cells and tissues of lymphoid lineage. We have observed in the particulate fractions of colon carcinoma cells the presence of a 56 kilodalton (kD) alkali resistant phosphoprotein containing phosphotyrosine. Further analysis revealed that the partial proteolytic cleavage pattern of this protein is analogous to that of the lck gene product found in murine and human T-cells. We have confirmed by cDNA cloning that lck RNA is also expressed in these cells proportionally to the amount of p56lck found in membrane preparations. Additional analysis demonstrated that lck RNA is frequently expressed in certain non-lymphoid tumor cell lines such as cell lines derived from colon carcinomas and carcinomas of the lung. Interestingly, higher levels of lck expression were found in human tumor cell lines derived from metastatic tumor sites when compared to those derived from primary tumors. These observations raise the possibility that the lck gene product may be involved in progression of some non-lymphoid human tumors.