OVEREXPRESSION OF TRANSFECTED HUMAN RIBONUCLEOTIDE REDUCTASE M2 SUBUNIT IN HUMAN CANCER-CELLS ENHANCES THEIR INVASIVE POTENTIAL

The ribonucleotide reductase (RR) gene has been associated,vith malign ant transformation and metastatic potential. In this report, the signi ficance of the expression of RR mRNA and enzymatic activity to the inv asive potential was examined by Boyden chamber invasion assay. Our res ults suggest that overexpression of RR M2 mRNA and RR enzymatic activi ty correlates to an increase in cell invasive potential. The drug-indu ced HURs clone expressed a higher level RR M2 mRNA and enzyme activity which contributes significantly to the 3-fold increase in invasive po tential of the cells observed relative to the KB wild-type control. On the contrary, the HUr revertant clone decreased the RR M2 mRNA level and enzymatic activity, concomitantly decreasing their invasive potent ial. This phenomenon is most likely due to the return of RR to levels comparable to that of the KB wild-type cells. To confirm that this obs ervation was not of a drug-resistance phenotype associated with multip le gene alterations, the panel of RR transfectants (M1-D transfected M 1 subunit cDNA, M2-D transfected M2 subunit cDNA, X-D transfected M1/M 2 cDNA) characterized in a previous study were also tested in the inva sion assay. The M2-D clone expressed 6-fold higher RR M2 mRNA and RR a ctivity and also demonstrated 6-fold higher invasive potential in vitr o than either the parental or vector only transfected cell line (KB-V) . The X-D clone demonstrated 3-fold higher M2 mRNA expression and reve aled 4-fold higher invasive potential than control cells. The M1-D clo ne, in contrast, expressed a baseline level of RR M2 mRNA and higher M 1 mRNA. In contrast to the X-D and M2-D cells, the invasive potential of M1-D reached an even lower level in the invasive assay than the con trol. These results, therefore, suggest that RR M2 overexpression play s an important role in a tumor's invasiveness.