Deregulation of the p14/MDM2/p53 Pathway Is a Prerequisite for Human Astrocytic Gliomas with G1-S Transition Control Gene Abnormalities

Deregulation of G1-S transition control in cell cycle is one of the important mechanisms in the development of human tumors including astrocytic gliomas. We have previously reported that approximately twothirds of glioblastomas (GBs) had abnormalities of G1-S transition control either by mutation/homozygous deletion of RB1 or CDKN2A (p16), or amplification of CDK4 (K. Ichimura et al., Oncogene, 13: 1065–1072, 1996). However, abnormalities of G1-S transition control genes may induce p53-dependent apoptosis in cells. Recent investigations suggest that p14 is induced in response to abnormal cell cycle entry and results in p53 accumulation by inhibiting MDM2-mediated transactivational silencing and degradation of p53. To investigate the roles of the G1-S transition control system and the p14/MDM2/p53 pathway in the development of astrocytic gliomas, we examined abnormalities of genes involved in these regulatory pathways in a total of 190 primary human astrocytic gliomas of different malignancy grades [136 GBs, 39 anaplastic astrocytomas (AAs) and 15 astrocytomas (As)]. Sixty-seven percent of GBs (91/136) and 21% of AAs (8/39) had abnormalities of the G1-S control system either by mutation/homozygous deletion of RB1, CDKN2A or CDKN2B, or amplification of CDK4. Seventy-six percent of GBs (103 of 136), 72% of AAs (28 of 39), and 67% of As (10 of 15) had deregulated p53 pathway either by mutation of TP53, amplification of MDM2, or homozygous deletion/mutation of p14. When all of the data were combined and compared, 96% of GBs (87 of 91) and 88% of AAs (7 of 8) with abnormal G1-S transition control also had deregulated p53 pathway. Thus, we demonstrate that deregulation of the G1-S transition control system was almost always accompanied by inactivation of the p53 pathway, clearly illustrating the cooperative roles of these two systems in the development/progression of primary human astrocytic gliomas.