Liggett W H, Sewell D A, Rocco J, Ahrendt S A, Koch W, Sidransky D
Department of Otolaryngology-Head and Neck Surgery, Johns Hopkins Oncology Center, Johns Hopkins University, Baltimore, Maryland 21205, USA.
Cancer Res. 1996 Sep 15;56(18):4119-23.
p16 (CDKN2/MTS1/p16INK4a) is frequently deleted, methylated, or mutated in many malignancies including squamous cell carcinoma of the head and neck (HNSCC). p16 beta is an alternative transcript derived from a newly described exon (exon 1 beta) located more than 15 kb 5' to exon 1 of p16. Moreover, the p16 beta transcript theoretically encodes a protein distinct from p16 derived from a divergent reading frame putatively initiated in exon 1 beta. To test the contribution of both of these transcripts in carcinogenesis, full-length cDNA of p16 and p16 beta were cloned in separate vector constructs and then transfected into HNSCC cell lines characterized for p16 status (p16[+/+], p16[mut/-], and p16[methylated]). Transfection of either p16 or p16 beta resulted in marked growth inhibition in all three HNSCC lines tested, regardless of p16 status. However, p16 beta but not p16 inhibited the growth of HeLa cells, a cell line with inactive pRB due to expression of E7 papillomavirus protein. Moreover, transfection of all three HNSCC lines with either p16 or p16 beta resulted in a marked increase in cells in G0-G1 consistent with a cell cycle arrest in G1. These data are consistent with the hypothesis that p16 and p16 beta are growth-inhibitory genes active in HNSCC and that both act by blocking progression through the G1-S transition of the cell cycle. Furthermore, the suppressive effects of p16 beta on HeLa growth suggest that p16 beta mediates its effect independently from pRB.
p16（CDKN2/MTS1/p16INK4a）在包括头颈部鳞状细胞癌（HNSCC）在内的许多恶性肿瘤中经常发生缺失、甲基化或突变。p16β是一种源自新描述外显子（外显子1β）的可变转录本，该外显子位于p16外显子1的5'端超过15 kb处。此外，p16β转录本理论上编码一种与源自外显子1β中假定起始的不同阅读框的p16不同的蛋白质。为了测试这两种转录本在致癌作用中的贡献，将p16和p16β的全长cDNA克隆到单独的载体构建体中，然后转染到以p16状态（p16[+/+]、p16[mut/-]和p16[甲基化]）为特征的HNSCC细胞系中。无论p16状态如何，转染p16或p16β均导致在所有三种测试的HNSCC细胞系中显著的生长抑制。然而，p16β而非p16抑制了HeLa细胞的生长，HeLa细胞系由于乳头瘤病毒E7蛋白的表达而具有无活性的pRB。此外，用p16或p16β转染所有三种HNSCC细胞系导致G0-G1期细胞显著增加，这与G1期细胞周期停滞一致。这些数据与以下假设一致：p16和p16β是在HNSCC中具有活性的生长抑制基因，并通过阻断细胞周期的G1-S转换进程发挥作用。此外，p16β对HeLa生长的抑制作用表明p16β独立于pRB介导其作用。
