Tumorigenicity and gene amplification potentials of cyclin D1-overexpressing NIH3T3 cells.

Cyclin D1 is a key regulator of the G1-S transition in cell cycle, and its gene is amplified and overexpressed in many cancers. To address the gene amplification potential of the cells in which the cyclin D1 gene expression is deregulated, we have established NIH3T3 clones with various levels of cyclin D1 transgene message. Those transfectants showed anchorage independent growth and tumorigenicity without in vitro morphological transformation. The degree of the transformed phenotype apparently correlated with the cyclin D1 expression level. Upon selection by N-(phosphonoacetyl)-L-aspartate (PALA), the cyclin D1-transfected NIH3T3 cells showed a higher ability to develop PALA-resistant colonies by amplifying the CAD gene, as compared to the parental NIH3T3 cells.