Expression of alternatively spliced mdm2 transcripts correlates with stabilized wild-type p53 protein in human glioblastoma cells

A puzzling finding in various human tumors, including glioblastoma multifor me (GBM), is the stabilization of wildtype (wt) p53 protein, The biological significance of this phenomenon and the mechanism by which it occurs are u nexplained. Recent reports have revealed that mdm2 exerts its negative regu lation on the p53 signal by directly binding p53 protein and thereby instig ating its proteasomal degradation. mdm2 has been shown to exist in alternat ively spliced forms in human ovarian and bladder carcinomas, and recently i n GBM, with loss or disruption of its p53 binding domain. Here we report th at alternatively spliced transcripts of mdm2 are present in 7 of 16 human G BM primary cell cultures and in the established GBM cell lines LN 229 and L N 18, Sequencing demonstrated loss of the amino terminal p53 binding domain in these alternatively spliced mdm2 transcripts, and an out-of-frame splic ing in the majority of cases. A significant correlation between the presenc e of mdm2 splice variants and increased expression of wt p53 protein was ob served, Furthermore, in the presence of an mdm2 splice variant, wt p53 stab ilization occurred despite coincident MDM2 amplification. Our findings sugg est that wt p53 protein stabilization may arise as a consequence of alterna tive splicing of mdm2, Such a mechanism might account for wt p53 protein ac cumulation in GBM cells, even in the presence of MDM2 gene amplification. I nt. J. Cancer 80:930-934, 1999, (C) 1999 Wiley-Liss, Inc.