Refined mapping of 1q32 amplicons in malignant gliomas confirms MDM4 as the main amplification target

We previously reported on the amplification and overexpression of the mouse double minute 4 homolog gene (MDM4) from 1q32 in a subset of malignant gliomas (Riemenschneider et al., Cancer Res 1999;59:6091-6). More recently, amplification and overexpression of the neighboring contactin 2 gene (CNTN2) was reported in individual malignant gliomas without MDM4 amplification (Rickman et al., Cancer Res 2001;61:2162-8). To address the question of whether 1q32 carries 2 independent amplification targets or a common target other than MDM4 and CNTN2, we analyzed primary malignant gliomas for amplification and overexpression of 17 different genes from this region. Our results indicate a single region of amplification that comprises the genes MDM4, GAC1, PIK3C2B and PEPP3, with only MDM4 amplification being invariably associated with overexpression. CNTN2 was found to be coamplified with MDM4 in 3 malignant gliomas but overexpressed in only 1 of these tumors. No CNTN2 amplification was detected in any of 102 malignant gliomas without MDM4 amplification. Our data therefore corroborate the notion that MDM4 is the main amplification target on 1q32 in malignant gliomas. However, coamplification and overexpression of adjacent genes may provide an additional growth advantage in some malignant gliomas with MDM4 amplification.