Targeted disruption of the K-Ras oncogene in an invasive colon cancer cellline down-regulates urokinase receptor expression and plasminogen-dependent proteolysis

The urokinase receptor, overexpressed in invasive colon cancer, promotes tu mour cell invasion. Since K-Ras is activated in many colon cancers, we dete rmined if urokinase receptor overexpression is a consequence of this activa ted oncogene. Accordingly, urokinase receptor expression was compared in HC T 116 colon cancer cells containing either a mutation-activated K-Ras or di srupted for this oncogene (by homologous recombination). HCT 116 cells cont aining the disrupted K-Ras oncogene expressed between 50 and 85% less uroki nase receptor protein compared with the parental HCT 116 cells. Reduced uro kinase receptor expression in cells containing the disrupted mutated K-Ras was not due to a physical impairment of the urokinase receptor gene since p horbol ester treatment was inductive for its expression. Constitutive uroki nase receptor expression in HCT 116 cells required an intact AP-I motif in the promoter (at -184) and electrophoretic mobility shifting assays indicat ed less c-Jun, JunD, c-Fas and Fra-1 hound to this motif in the K-Ras-disru pted cells. Since the urokinase receptor accelerates proteolysis, laminin d egradation was compared in cells containing the mutation-activated and disr upted K-Ras oncogene. The latter cells displaying fewer urokinase receptors , degraded 80% less laminin. This is the first study to demonstrate a role for K-Ras asa regulator of the constitutive expression of the urokinase rec eptor.