Parcs/Gpn3 is required for the nuclear accumulation of RNA polymerase II

Biochim Biophys Acta. 2011 Oct;1813(10):1708-16. doi: 10.1016/j.bbamcr.2011.07.005. Epub 2011 Jul 18.

Abstract

Parcs/Gpn3 is a putative GTPase that is conserved in eukaryotic cells from yeast to humans, suggesting that it plays a fundamental, but still unknown, cellular function. Suppression of Parcs/Gpn3 expression by RNAi completely blocked cell proliferation in MCF-12A cells and other mammary epithelial cell lines. Unexpectedly, Parcs/Gpn3 knockdown had a more modest effect in the proliferation of the tumorigenic MDA-MB-231 and SK-BR3 cells. RNA polymerase II (RNAP II) co-immunoprecipitated with Parcs/Gpn3. Parcs/Gpn3 depletion caused a reduction in overall RNA synthesis in MCF-12A cells but not in MDA-MB-231 cells, demonstrating a role for Parcs/Gpn3 in transcription, and pointing to a defect in RNA synthesis by RNAP II as the possible cause of halted proliferation. The absence of Parcs/Gpn3 in MCF-12A cells caused a dramatic change in the sub-cellular localization of Rpb1, the largest subunit of RNAP II. As expected, Rpb1 was present only in the nucleus of MCF-12A control cells, whereas in Parcs/Gpn3-depleted MCF-12A cells, Rpb1 was detected exclusively in the cytoplasm. This effect was specific, as histones remained nuclear independently of Parcs/Gpn3. Rpb1 protein levels were markedly increased in Parcs/Gpn3-depleted MCF-12A cells. Interestingly, Rpb1 distribution was only marginally affected after knocking-down Parcs/Gpn3 in MDA-MB-231 cells. In conclusion, we report here, for the first time, that Parcs/Gpn3 plays a critical role in the nuclear accumulation of RNAP II, and we propose that this function explains the relative importance of Parcs/Gpn3 in cell proliferation. Intriguingly, at least some tumorigenic mammary cells have evolved mechanisms that allow them to proliferate in a Parcs/Gpn3-independent manner.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Breast / metabolism
  • Cell Nucleus / genetics
  • Cell Nucleus / metabolism*
  • Cell Proliferation / drug effects
  • Cells, Cultured
  • Epithelial Cells / metabolism
  • Female
  • GTP Phosphohydrolases / antagonists & inhibitors
  • GTP Phosphohydrolases / genetics
  • GTP Phosphohydrolases / metabolism
  • GTP Phosphohydrolases / physiology*
  • Humans
  • Immunoprecipitation
  • Protein Binding
  • Protein Transport / genetics
  • RNA Interference / physiology
  • RNA Polymerase II / metabolism*
  • RNA, Small Interfering / pharmacology
  • Transcriptional Activation / drug effects
  • Transcriptional Activation / genetics

Substances

  • RNA, Small Interfering
  • RNA Polymerase II
  • GTP Phosphohydrolases
  • Gpn3 protein, human