ALL-TRANS BETA-CAROTENE ENHANCES MITOGENIC RESPONSES AND ORNITHINE DECARBOXYLASE ACTIVITY OF BALB C 3T3 FIBROBLAST CELLS INDUCED BY TUMOR PROMOTER AND FETAL BOVINE SERUM BUT SUPPRESSES MUTAGEN-DEPENDENT UMU-C GENE-EXPRESSION N SALMONELLA-TYPHIMURIUM (TA-1535/PSK-1002)/

Although previous epidemiological studies have indicated that beta-car otene is an important agent for the chemical prevention against carcin ogenesis, a recent prospective study has strikingly suggested that sup plementation with beta-carotene significantly increased the incidence of some types of cancer (The alpha-Tocopherol and beta-carotene cancer Prevention Study Group, New Engl. J. Med., 330 (1994) 1031-1035). To analyze the discrepancy of this problem, the authors analyze the effec ts of beta-carotene on biochemical and biological events associated wi th carcinogenesis by in vitro experiments. (1) All-trans beta-carotene enhanced the proliferation and DNA synthesis of BALB/c 3T3 cells indu ced by a tumor promoter, 12-O-tetradecanoyl-phorbol-13-acetate (TPA) a nd fetal bovine serum, although beta-carotene itself did not show mito genic activity. (2) All-trans beta-carotene caused a remarkable stimul ation for the early induction of ornithine decarboxylase (ODC) activit y after the stimulation of TPA and fetal bovine serum. (3) All-trans b eta-carotene exhibited significant antimutagenic activity which suppre sses umu C gene expression in Salmonella typhimurium (TA 1535/pSK 1002 ) induced by a typical mutagen, 2-aminoanthracene (2-AA). These experi mental results suggest that all-trans beta-carotene might cause benefi cial and harmful effects on different phases of carcinogenesis.