Urokinase-type plasminogen activator expression and proliferation stimulation in head and neck squamous cell carcinoma in vitro and in situ

BACKGROUND: Stimulation of proliferative activity by urokinase-type plasminogen activator (uPA) has been demonstrated in vitro for cultured primary and carcinoma cells. OBJECTIVE: To examine the effect of uPA stimulation on cultured squamous cell carcinoma cell lines of the head and neck in vitro and to compare the results with the situation in tumor tissue specimens. DESIGN: The uPA-mediated growth stimulation of 2 head and neck squamous cell carcinoma cell lines after suppression of endogenous uPA production was monitored by measuring (3)H-thymidine uptake into cellular DNA. Alternatively, applications of antibodies against the uPA-binding domain of the urokinase receptor were used to suppress autostimulation. To analyze the situation in situ we performed Western blot and zymographic studies on tissue homogenates of 25 squamous cell carcinoma specimens. We tested the expression of proliferating cell nuclear antigen (PCNA), a marker for proliferative activity, and uPA in tissue lysates and correlated uPA and PCNA expression by regression analysis. RESULTS: High-molecular-weight urokinase had a proliferation stimulative effect on both cell lines in vitro. The uPA autostimulation was decreased by blocking the uPA-binding domain of urokinase receptor with antibodies. Regression analysis of zymographic and Western blot data of tumor tissue lysates revealed no significant coherency between PCNA and uPA expression. Immunohistochemical stainings frequently showed different sublocalization of uPA and PCNA within tumors. CONCLUSION: In vitro uPA-mediated growth stimulation is not necessarily transferable to the in situ situation.