Résumé
Retinoblastoma is the most common primary intra-ocular tumor in childhood. It has been established that recurrent cytogenetic abnormalities are the hallmark of mostly all malignant tumors. Recurrent atypical cytogenetic abnormalities of the short arm of chromosome 6 were reported in several cases of retinoblastoma, mainly in association with reciprocal translocations. In the present study, alterations of chromosome 6 associated with retinoblastoma were studies in the Y-79 and the WERI-Rb-1 cell lines established from highly malignant retinoblastomas. Fluorescence in situ hybridization (FISH) technique was used to identify the chromosomal breakpoint on 6p in this cell line. To perform this detection, yeast artificial chromosome (YAC) clones from p21 to p22 bands were used and the breakpoint was localized on 6p21.3. Previous studies had suggested that activation of some genes on 6p could be dependent on a translocation mechanism. Expression of a candidate gene localized near the chromosomal breakpoint was measured by immunocytochemistry and flow cytometry techniques. An enhancement of the tumor necrosis factor-alpha (TNF-α) protein expression in Y79 cells was detected by this approach. The relationship between TNF-α over-expression and the malignancy of retinoblastoma is discussed.