β-Actin regulates interleukin 6-induced p21 transcription by interacting with the Rpb5 and Rpb7 subunits of RNA polymerase II

ABSTRACTIn pre-initiation complexes, RNA helicase A interacts with β-actin and acts as a bridging factor linking nuclear actin with RNA polymerase II (Pol II). In addition, β-actin participates in Pol II-dependent transcription elongation by interacting with the positive transcription elongation factor Cdk9. However, many relationships between β-actin and Pol II remain to be identified. In an interleukin 6 (IL-6)-induced p21 expression model, we demonstrated that β-actin knockdown reduced p21 expression. Immunofluorescence analysis showed that the colocalization of β-actin and Pol II increased significantly in cells treated with IL-6. It is known that the Rpb5, Rpb6 and Rpb7 subunits are located at the surface of the enzyme. We next constructed recombinant pcDNA-HA-Rpb5, pcDNA-HA-Rpb6 and pcDNA-HA-Rpb7 plasmids and expressed the three polymerase II subunits in HepG2 cells. We found that β-actin could be immunoprecipitated with HA-Rpb5 and HA-Rpb7. A Glutathione-S-transferase pull-down assay revealed that ...