Functional analysis of cyclin D1 alternative transcript b

细胞周期蛋白D1/PRAD1癌基因是细胞周期G1期进程的关键调控因子，在伴有t(11；14)(q13；q32)易位的B细胞恶性肿瘤中被认为是长期寻找的bcl1癌基因。最近，我们发现了一种新的选择性剪接细胞周期蛋白D1转录本，称为转录本[b]。在几个人类非淋巴癌细胞系中，突变的转录本[b]的水平低于最初报道的Cyclin D1转录本，称为转录本[a]，但转录本[b]产物的内源性细胞表达尚未确定。Northern印迹分析和逆转录聚合酶链式反应(RT-PCR)分析表明，转录产物[b]mRNAs在t(11；14)(q13；q32)易位的B淋巴样细胞系中有较好的表达，而在其他细胞中表达水平较低或检测不到。用人类细胞周期蛋白D1特异性的单抗进行免疫印迹分析，可以识别和区分转录本[a]和[b]的产物，强烈表明转录本[b]蛋白确实在这些B细胞系中表达。本研究首次鉴定了Cyclin D1转录本[b]蛋白的内源性细胞表达，并强烈提示Cyclin D1的这种替代形式可能在t(11；14)(q13；q32)易位的B淋巴系恶性肿瘤的分子发病机制中发挥重要作用。转录本[b]的生物学功能及其在细胞周期调控中的作用有待进一步研究。

The cyclin D1/PRAD1 oncogene, a key regulator of the G1 phase progression of the cell cycle has been identified as the long-sought BCL-1 oncogene in B-cell malignancies with t(11;14)(q13;q32) translocation. Recently, a novel alternative spliced cyclin D1 transcript, called transcript [b], has been identified by ourselves. The level of the variant transcript [b] was lower than that of the originally reported cyclin D1 transcript, called transcript [a], in several human non-lymphoid cancer cell lines but the endogenous cellular expression of transcript [b] products has not yet been determined. Northern blot analysis and reverse transcription-polymerase chain reaction (RT-PCR) analysis revealed that the transcript [b] mRNAs are well expressed in B-lymphoid cell lines with t(11;14)(q13;q32) translocation and at much lower or undetectable levels in other cells. Western blot analysis using a human cyclin D1-specific monoclonal antibody, which can recognize and distinguish the products of transcripts [a] and [b], strongly suggested that the transcript [b] protein is indeed expressed in these B-cell lines. The present study provides the first identification of the endogenous cellular expression of the cyclin D1 transcript [b] protein and strongly suggests that this alternative form of cyclin D1 may play a significant role in the molecular pathogenesis of B-lymphoid malignancies with t(11;14)(q13;q32) translocation. Further studies are warranted to study the biological function of transcript [b] and its role in cell cycle control.