SUPPRESSION OF GROWTH IN-VITRO AND TUMORIGENICITY IN-VIVO OF HUMAN CARCINOMA CELL-LINES BY TRANSFECTED P16(INK4)

The function of p16(INK4) as a putative tumor suppressor gene was exam ined by investigating its ability to inhibit the growth of cancer cell lines in vitro and tumor formation in vivo. A p16(INK4) cDNA expressi on vector was transfected into five human cancer cell lines that varie d in their p16(INK4) and retinoblastoma (Rb) status. Suppression of co lony-forming efficiency was seen in four cell lines. Of two cell lines wild type for p16(INK4) but null for Rb protein expression, one (Hep 3B) showed inhibition of colony formation, whereas the other (Saos-2) did not. This observation may demonstrate involvement of p16(INK4) ind ependent of Rb. The transfected p16(INK4) gene was frequently selected against and lost during continued growth in vitro. When compared to t he colon carcinoma cell line (DLD-1), p16(INK4)-transfected DLD-1 clon e 1 cells were less tumorigenic in athymic nude mice. Tumors arising f rom p16(INK4)-transfected DLD-1 clones, which were growth suppressed i n vitro, either lost the integrated exogenous p16(INK4) or expressed r educed amounts of p16(INK4) protein. Therefore, p16(INK4) was also sel ected against during tumor formation in vivo. These data are consisten t with the hypothesis that p16(INK4) isa tumor suppressor gene. (C) 19 96 Wiley-Liss, Inc.