Expression of p16(INK4a) suppresses the unbounded and anchorage-independent growth of a glioblastoma cell line that lacks p16(INK4a)

p16(INK4a) is a inhibitory protein of Cyclin-dependent kinase 4 (Cdk4). p16 negatively regulates the cell cycle progression from G1 to S phase. Functional pie is absent from many human cancers, as well as from many established lines of tumor cells. However, it is not clear whether expression of p16 in p16-deficient tumor cells can suppress their anchorage-independent growth. Therefore, we introduced a cDNA for p16(INK4a) into the human glioblastoma cell line T98G, which lacks a gene for p16(INK4a). We isolated several clones that stably expressed various amounts of pie protein. The doubling time of the various clones was generally prolonged. Clones with high-level expression of p16 protein had characteristics of restricted growth, such as contact inhibition, while the parental T98G cells had no such characteristics. Furthermore, the efficiency of colony formation in soft agar was dramatically decreased in the case of cells that expressed exogenous pie. Our observations suggest that the expression of pie protein restricts the unbounded growth and the anchorage-independent growth of tumor cells. (C) 1997 Academic Press.