Skogseth H, Larsson E, Halgunset J. Urokinase plasminogen activator receptor (uPAR) expression is reduced by tyrosine kinase inhibitors. APMIS 2006;114:307–13. Previously we reported that tyrosine kinase inhibitors (TKI) produced a reduction in uPA expression in prostatic cancer cells, and that TKI-treated cells were less invasive compared to untreated cells. Nevertheless, no change in cell migration was observed when TKI-treated cells were supplied with external uPA, thus indicating more complex mechanisms leading to decreased cell invasion. uPAR expression was measured with an enzyme- linked immunosorbent assay (ELISA) in PC-3 and DU-145 prostate carcinoma cells treated with the two TKI genistein and AG-1478. uPAR mRNA levels were measured with real-time reverse transcriptase-polymerase chain reaction (RT-PCR). uPAR immunocytochemistry was used to examine the receptor distribution in cells grown on a reconstituted basal lamina. Immunocytochemistry showed an intense uPAR immunostaining in invading cells, particularly in the leading edge membrane. Treatment with genistein and AG-1478 led to a decreased expression of uPAR in DU-145, but not in PC-3. Furthermore, a reduction of uPAR mRNA was found in TKI-treated DU-145 cells, while PC-3 was not affected. Our results indicate a possible role of TKI as cancer suppressors by acting as a regulator of uPAR expression.