Coupled alteration of transcription and splicing by a single oncogene: Boosting the effect on cyclin D1 activity

In cancer cells, gene expression is altered at the levels of transcription and mRNA maturation, with many splice variants being associated with cancer. Splicing is tightly connected to transcription and can be affected by transcription elongation dynamics. Moreover, various transcriptional coregulators that are altered in cancer, such as the proto-oncogene EWS, are thought to play a role in splicing. A recent study shows that an alteration of EWS in Ewing sarcoma alters the dynamics of RNA polymerase II over the CCND1 proto-oncogene encoding cyclin D1, leading to an increase in its transcription and to an alteration of splicing that results in high levels of the oncogenic cyclin D1b splice isoform. The cyclin D1b isoform is highly expressed in Ewing sarcoma cells and tumors and stimulates Ewing sarcoma cell growth. Thus, alterations of transcriptional regulators in disease may lead to splicing alterations. We review these data and discuss how this concept may apply to various factors that are altered in cancer.