T-kininogen inhibits fibroblast proliferation in the G(1) phase of the cell cycle

By using synthetic protease inhibitors, several investigators have demonstr ated that cysteine proteinases are required for cell proliferation. Kininog ens are potent and specific physiological inhibitors of cysteine proteinase s. We have used several mouse fibroblast-derived cell lines that express bi ologically active T-kininogen under the control of the mouse metallothionei n promoter to test its effect on cell proliferation. Our results indicate t hat expression of T-kininogen results in diminished proliferative capacity, as measured by reduced cell numbers, both in logarithmically growing cultu res and in G(0) cells induced to proliferate in response to serum. Furtherm ore, both fluorescence-activated cell sorting (FACS) analysis and incorpora tion of radioactive precursors into DNA suggest that the cells are unable t o progress from G(0) through the S phase of the cell cycle in response to s erum stimulation. However, we find that T-kininogen-expressing cell lines a re still capable of responding to growth factors present in the serum, both by activating the ERK pathway and by expressing early genes, such as c-Fos and c-Jun. Thus, our results suggest that inhibition of cysteine proteinas es by T-kininogen leads to inhibition of cell proliferation between the G(1 ) and S phases of the cell cycle. (C) 2001 Academic Press.