Modulation of cell growth and mutation induction by introduction of the expression vector of human hsp70 gene

We constructed an expression vector of the human hsp70 gene in which the transcription was driven by a metallothionine IIA promoter. The expression vector was introduced into the SHOK cell line, derived from Syrian hamster embryo cells, and clones containing human hsp70 gene were isolated. Western blot analysis using monoclonal antibody against human HSP72 showed that the maximum induction level after the addition of 80 microM ZnSO4 was almost one-third of that by heat shock treatment at 43 degrees C for 2 h. The growth rate increased slightly when Zn2+ was present during cultivation. Zinc treatment enhanced the appearance of S-phase cells in exponentially growing cells, but not in confluent cells. Although overexpression of HSP72 had little or no effect on the recovery of S phase after uv irradiation, it decreased the killing effect slightly and increased the uv-induced mutation frequency significantly. These results suggest that overexpression of human HSP72 protein functions as a growth stimulating factor and that it affects genetic stability during the recovery process of S phase after uv irradiation.