TRANSFECTION WITH HUMAN THIOREDOXIN INCREASES CELL-PROLIFERATION AND A DOMINANT-NEGATIVE MUTANT THIOREDOXIN REVERSES THE TRANSFORMED PHENOTYPE OF HUMAN BREAST-CANCER CELLS

Thioredoxin, a redox protein with growth factor activity that modulate s the activity of several proteins important for cell growth, has been reported to be overexpressed in a number of human primary cancers. In the present study, the effects of stably transfecting mouse MB 3T3 ce lls and MCF-7 human breast cancer cells,vith cDNA for wild-type human thioredoxin or a redox-inactive mutant thioredoxin, Cys(32)-->Ser(32)/ Cys(35)-->Se-35 (C32S/C35S), on cell proliferation and transformed ph enotype have been investigated. NIH 3T3 cells transfected with thiored oxin achieved increased saturation densities compared with vector alon e-transfected cells, but were not transformed as assessed by tumor for mation in immunodeficient mice. Thioredoxin-transfected MCF-7 cells sh owed unaltered monolayer growth on plastic surfaces compared with vect or alone-transfected cells, but exhibited severalfold increased colony formation in soft agarose, Stable transfection of NIH 3T3 and MCF-7 c ells with C32S/C35S resulted in inhibition of monolayer growth on plas tic surfaces, and up to 73% inhibition of colony formation by MCF-7 ce lls in soft agarose, When inoculated into immunodeficient mice, thiore doxin-transfected MCF-7 cells formed tumors, although with a 38-57% gr owth rate compared with vector alone-transfected cells, whereas tumor formation by C32S/C35S-transfected MCF-7 cells was almost completely i nhibited, The results of the study suggest that thioredoxin plays an i mportant role in the growth and transformed phenotype of some human ca ncers, The inhibition of tumor cell growth by the dominant-negative re dox-inactive mutant thioredoxin suggests that thioredoxin could be a n ovel target for the development of drugs to treat human cancer.