AFF4 globally affects the release of paused RNA polymerase II in HEL cells [RNA-seq]

P-TEFb, a heterodimer of kinase, CDK9, and Cyclin T1, is a critical regulator of promoter-proximal pause release of Pol II in metazoans. It is capable of forming three larger multiprotein complexes, including the super elongation complex (SEC), the BRD4/P-TEFb complex and the 7SK snRNP. In the SEC or the BRD4/P-TEFb, P-TEFb is enzymatically active, while in the 7SK snRNP, its activity is inhibited. The SEC consists of AFF1 or 4, ENL or AF9, ELL1, 2 or 3 and EAF1 or 2 in addition to P-TEFb, the only subunit with catalytic activity, and the noncatalytic subunits have been found to be able to regulate pause release through P-TEFb. One recent study showed that in human DLD-1 cells, the SEC only regulates pause release of heat shock (HS) genes, whereas the BRD4/P-TEFb complex regulates pause release of the rest of the genes. In this study, we found that AFF4 knockdown in human HEL cells decreased not only cellular level but also global chromatin occupancy of CTD serine 2 phosphorylated Pol II, and notably, increased promoter-proximal pause of Pol II on several hundred HS and thousands of non-HS genes. Mechanistically, AFF4 facilitates pause release likely by facilitating the binding of P-TEFb to Pol II. These results suggest that the extent of impact of AFF4 on pause release is likely to be context-dependent or cell-type dependent.