INHIBITION OF TUMOR PROMOTER ACTIVITY TOWARD MOUSE FIBROBLASTS AND THEIR IN-VITRO TRANSFORMATION BY TISSUE INHIBITOR OF METALLOPROTEINASES-1 (TIMP-1)

Tissue inhibitor of metalloproteinases-l (TIMP-1), a natural inhibitor of matrix metalloproteinases (MMPs), is known to inhibit invasion and metastasis of tumor cells, In the present study we examined anti-tumo r promoter activity of TIMP-1 and its effect on irt vitro cell transfo rmation using BALB/3T3 cells in low serum culture medium. In the dye t ransfer assay the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) continuously blocked gap-junctional intercellular communication (GJIC) of BALB/3T3 cells in confluent phase, TIMP-1 did not prevent tr ansient inhibition of GJIC induced by TPA, but it quickly restored the reduced GJIC level to the control level, The recovery of GJIC was dep endent on the concentration of TIMP-1 from 1 to 1000 ng/ml. In an irt vitro two-stage transformation assay in which BALB/3T3 cells were trea ted with 0.5 mu g/ml N-metyl-N'-nitro-N-nitrosogu-anidine as initiator and 100 ng/ml TPA as promoter, TIMP-1 at concentrations >10 ng/ml inh ibited the focus formation of transformed cells by similar to 60%, TIM P-2 and a synthetic MMP inhibitor showed a similar inhibitory activity on in vitro cell transformation, Furthermore, zymographyic analysis s howed that TPA treatment of BALB/3T3 cells induced secretion of gelati nase B and stromelysin-l into the culture medium, These results indica te that TIMP-1 and TIMP-2 have inhibitory activity on irt vitro transf ormation of cells. It seems likely that TPA-inducible MMPs are involve d in carcinogenesis and TIMPs have a protective role against carcinoge nesis in vivo.