Status and expression of the p16INK4 gene in human thyroid tumors and thyroid-tumor cell lines.

The p16INK4 tumor-suppressor gene (also known as CDKN2, CDK41 and MTS1) encodes a negative regulator of the cell cycle. This gene, located in 9p21, is mutated or homozygously deleted in a high percentage of tumor cell lines and specific types of primary tumors. We have examined the status of the p16INK4 gene in 31 thyroid tumors and 7 thyroid cell lines. No DNA abnormalities were found in primary tumors. Conversely, p16INK4 gene structural alterations, deletions and point mutations were found in 4 thyroid cell lines. The expression of the 2 different p16INK4 mRNAs, the p16alpha and p16beta transcripts, was determined by RNA-PCR experiments. All the primary thyroid tumors expressed the beta transcript, while the p16alpha was barely detectable. The thyroid cell lines always expressed the p16beta transcript, while the alpha transcript was absent or, whenever present, coded for a mutated form of the p16INK4 gene product. Taken together, our results suggest that loss of p16INK4 function is not directly involved in the process of thyroid-tumor development, but it probably gives cells in tissue culture a selective growth advantage.