Structural analysis of cyclin D1 and p16INKa genes in human male germ cell tumors of seminoma type.

J Fombonne, M Benahmed MD, PhD, S Krantic PhD

INSERM U.407, Faculté de Médecine Lyon-Sûd, Oullins, France

AIM: Altered expression of cell cycle regulators (e.g. over-expression of cyclin D and decreased expression of INK4 family of CDK-inhibitors) have been recently reported in human male germ cell tumors of seminoma type. The aim of the present study was to assess whether such altered expression could be related to the structural alteration of the relevant genes. METHODS: Mutational analysis of cyclin D1 and INK4a genes in seminoma patients was performed on genomic DNA obtained from 29 patients and on RNA isolated from 19 patients in order to study the promoter and coding sequences respectively. Two complementary techniques were used in parallel: RT-PCR-SSCP (Polymerase Chain Reaction-Single Strand Conformation Polymorphism) and automated DNA-sequencing. RESULTS: Coding sequences of neither cyclin D1 nor INK4a showed any alteration in comparison to the normal reference sequences. Similarly, no mutation was found in cyclin D1 promoter. By contrast, in p16INK4a promoter, an insertion of "A" at position -1973 and conversion of "C" (-1485) to "T" were identified. CONCLUSIONS: Increased expression of cyclin D1 protein found in some male germ tumors is apparently not related to the mutation-induced deregulated gene expression. However, if identified INK4a promoter mutations turn to be correlated with an altered expression of the corresponding gene at the protein level, INK4a might become a seminoma biomarker.

KEY WORDS: biomarker, DNA sequencing.

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Paper presented at the International Symposium on Predictive Oncology and Intervention Strategies; Paris, France; February 9 - 12, 2002; in the section on Gene Expression, Part 2.