P53VAL135 TEMPERATURE-SENSITIVE MUTANT SUPPRESSES GROWTH OF HUMAN BREAST-CANCER CELLS

One common step in the malignant progression of a wide variety of huma n cancers seems to be inactivation of the p53 gene, via point mutation or deletion or both; or overexpression of mutated protein with domina nt transforming activity. This study shows a suppressive effect of wil d type p53 on the growth of human breast cancer cells. Introduction of wild type p53 versus mutant into five human breast cancer cell lines containing mutant p53 resulted in a marked reduction in colony formati on. Two of these were transfected with human wt p53 expression vectors and the other three were infected with retroviruses packaging human w t p53, both showing similar reduction in the number of surviving colon ies, suggesting a role for wt p53 in suppression of breast cancer cell growth. Direct evidence for growth suppression was obtained by introd uction of the temperature sensitive p53Val135 into Hs578T human breast cancer cells containing a mutant p53. This murine mutant allele p53Va 1135 functions as an oncogene at 37 degrees C and as a tumor suppresso r at 32 degrees C. The cell line generated was strongly growth inhibit ed at the restrictive temperature (31.5 degrees C), at which temperatu re the suppressor form is expressed. This inhibition of proliferation was reversible upon a temperature upshift. Analysis of the cell cycle distribution shows these growth suppressed cells to be inhibited in th e G1 phase of the cell cycle. Thus wt p53 may have an important role i n breast cancer tumorigenesis.