Protein tyrosine (de-)phosphorylation in head and neck squamous cell carcinoma.

Protein phosphorylation plays an important role in signal transduction of both normal and neoplastic cells. Since increased protein tyrosine phosphorylation may be associated with malignant transformation, we studied the activities of protein tyrosine kinases (PTK) and protein tyrosine phosphatases (PTPase) in patients with various head and neck tumors. Furthermore, we determined the patterns of tyrosine phosphorylated protein (P-tyr) in tissues by western blotting. Enzyme activities were studied in tumor and histologically normal, non-tumorous tissues of 54 patients and in 11 controls. P-tyr patterns were determined in 3 patients and 2 controls. PTK and PTPase activities were greater in tumor tissues than in normal tissue of the cancer patients as well as controls. P-tyr levels in tumors were also higher than in normal tissues. Additionally, PTK activity in normal tissue of tumor patients was significantly higher than in normal tissue of the control group. The same trend was observed for the PTPase activity and P-tyr levels.