PNRC is a unique nuclear receptor coactivator that stimulates RNA polymerase III-dependent transcription

BACKGROUND: PNRC transcriptionally regulates a wide range of RNA polymerase (pol) II-transcribed genes by functioning as a nuclear receptor coactivator. To search for additional PNRC-interacting proteins other than nuclear receptors, a PNRC fragment was used as bait in a yeast two-hybrid screening of a human mammary gland cDNA expression library. RESULTS: RNA pol III/RPC39 fragments were repeatedly identified as PNRC-interacting partners in two independent screenings. The interaction between these RPC39 fragments and PNRC was further confirmed in the independent yeast two-hybrid assays. The association of endogenous PNRC and RPC39 in MCF7 cells was demonstrated by co-immunoprecipitation. Furthermore, ChIP analysis detected co-recruitment of PNRC and RPC39 to tRNA and U6 RNA promoters. The biological consequence of the interaction between PNRC and RPC39 was further studied. Overexpression of PNRC, either by transient or stable transfection, increased RNA pol III-dependent transcription in MCF7 cells, while a decrease in transcription in MCF7 cells treated with PNRC/siRNA was observed. CONCLUSION: Here, we demonstrate that human PNRC stimulates RNA pol III transcription through its interaction with the subunit RPC39 of RNA pol III. PNRC is a unique coactivator that has profound effects on many aspects of cellular function by directly influencing both RNA pol II- and RNA pol III-dependent transcription.