Cell Genetic and Molecular Analysis of the Rearranged c-myc in Mouse Plasmacytoms

我们报道了在小鼠浆细胞瘤细胞与成纤维细胞融合后，重排的c-myc的高表达被抑制。在本研究中，我们分析了这种抑制的分子机制。重排的c-myc表达在浆细胞瘤和t细胞淋巴瘤或畸胎癌之间的杂交中也被发现受到抑制。通过比较亲本细胞和杂交细胞的甲基化模式，没有发现重排c-myc的DNA甲基化参与抑制。经环己亚胺处理后，未重排的c-myc表达增强，而重排的c-myc表达仍未检测到。Run-on实验表明，重排c-myc表达的抑制作用在转录水平，这与基因对DNase I的敏感性平行；浆细胞瘤中重排的c-myc与成纤维细胞融合后，其高DNase I敏感性降低。我们尝试用红细胞鬼影法将成纤维细胞的核蛋白转移到浆细胞瘤细胞中，但这种方法未能抑制重排的c-myc。最近有报道称，在免疫球蛋白C基因的3'端存在一个含有八聚体基序的b细胞特异性增强子。b细胞特异性Oct-2基因的表达在浆细胞瘤和非b细胞杂交中抑制重排的c-myc。

We have reported that high expression of the rearranged c-myc in mouse plasmacytoma cells is suppressed after cell fusion with fibroblastic cells. In this study, we analyzed molecular mechanism of this suppression. The suppression of the rearranged c-myc expression was also found in hybrids between plasmacytoma and T-cell lymphoma or teratocarcinoma. No involvement of DNA methylation of the rearranged c-myc in the suppression was suggested by comparing the methylation patterns in the parental and hybrid cells. Expression of the non-rearranged c-myc was enhanced by treatment of the hybrid cells with cycloheximide, while that of the rearranged c-myc was still undetectable. Run-on assay demonstrated that suppression of the rearranged c-myc expression of the rearranged c-myc expression was at transcriptional level, which was parallel to DNase I sensitivity of the gene ; higher DNase I sensitivity of the rearranged c-myc in plasmacytoma was reduced after cell fusion with fibroblastic cells. We attempted to transfer nuclear proteins from fibroblasts into plasmacytoma cells by using the rbc-ghost method, but we failed to suppress the rearranged c-myc by this method. Recently it has been reported that there is a B-cell specific enhancer containing octamer motif in 3' end of the immunoglobulin C gene. Expression of B-cell-specific Oct-2 gene is responsible for suppression of the rearranged c-myc in hybrids between plasmacytoma and non-B cells.