Transcriptional induction of the urokinase receptor gene by a constitutively active Src - Requirement of an upstream motif (-152/-135) bound with Sp1

Since c-src overexpression increases colonic cell invasiveness and because both Src activity and urokinase receptor protein are elevated in invasive c olon cancers, the present study was undertaken: 1) to determine if a consti tutively active Src regulates urokinase receptor expression and 2) to ident ify required cis-elements and trans-acting factors. SW480 colon cancer cell s transfected with an expression plasmid (c-srcY527F) encoding a constituti vely active Src protein manifested increased urokinase receptor gene expres sion and Src activity. Treatment of the src transfectants with a Src-inhibi tor (PD173955) reduced urokinase receptor protein levels and laminin degrad ation. Inasmuch as we recently implicated an upstream region of the urokina se receptor promoter (-152/-135) in constitutive urokinase receptor express ion, we determined its role for the induction by src, Whereas the activity of a CAT reporter driven by this region was stimulated by c-srcY527F, the u -PAR promoter mutated at the Spl-binding motif in the -152/-135 region was not. Nuclear extracts from the src transfectants demonstrated increased Spl binding to region -152/-135 compared with those from SW480 cells. Finally, endogenous urokinase receptor protein amounts in 10 colon cancers and corr esponding normal colon correlated with Src specific activity. These data su ggest that urokinase receptor gene expression is regulated by Src partly vi a increased Spl binding.