The SEC family of RNA Polymerase II elongation factors: gene target specificity and transcriptional output
The elongation stage of transcription is a highly regulated in metazoan. We previously purified the AFF1/AFF4-containing Super Elongation Complex (SEC) as a major regulator of development and cancer pathogenesis. Here, we report the biochemical isolation of SEC-like 2 (SEC-L2) and SEC-like 3 (SEC-L3) containing AFF2 and AFF3 in association with P-TEFb, ENL, and AF9. The SEC family members demonstrate high levels of Pol II CTD kinase activity, however, only SEC is required for the proper induction of the HSP70 gene upon stress. Genome-wide mRNA-seq analyses demonstrate that SEC-L2-3 control the expression of different subsets of genes, while AFF4/SEC plays a more dominant role in rapid gene expression in cells. MYC is one of the direct targets of AFF4/SEC, and the SEC requirement to the MYC gene regulates its expression in different cancer cells bearing either acute myeloid or lymphoid leukemia. These findings suggest that AFF4/SEC could be a potential therapeutic target for the treatment of leukemia or other cancers associated with MYC overexpression. Overall design: RNA-seq in human embyonic kidney 293T cells of wild-type and after RNAi of AFF2, AFF3, AFF4. ChIP-seq of AFF4 and Pol2 in human 293T cells.