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Nucleic Acids Res. 2014 Sep;42(15):9771-80. doi: 10.1093/nar/gku650. Epub 2014 Aug 6.

Double-strand break repair deficiency in NONO knockout murine embryonic fibroblasts and compensation by spontaneous upregulation of the PSPC1 paralog.

Author information

1
Department of Radiation Oncology, Emory University, Atlanta, GA 30322, USA Department of Biochemistry, Emory University, Atlanta, GA 30322, USA Institute of Molecular Medicine and Genetics, Georgia Regents University, Augusta, GA 30912, USA.
2
Department of Radiation Oncology, Emory University, Atlanta, GA 30322, USA.
3
Institute of Molecular Medicine and Genetics, Georgia Regents University, Augusta, GA 30912, USA State Key Laboratory of Virology/Institute of Medical Virology, Wuhan University, Wuhan 430071, China.
4
Institute of Molecular Medicine and Genetics, Georgia Regents University, Augusta, GA 30912, USA.
5
Department of Radiation Oncology, Emory University, Atlanta, GA 30322, USA Department of Biochemistry, Emory University, Atlanta, GA 30322, USA Institute of Molecular Medicine and Genetics, Georgia Regents University, Augusta, GA 30912, USA wsd.nar@gmail.com.

Abstract

NONO, SFPQ and PSPC1 make up a family of proteins with diverse roles in transcription, RNA processing and DNA double-strand break (DSB) repair. To understand long-term effects of loss of NONO, we characterized murine embryonic fibroblasts (MEFs) from knockout mice. In the absence of genotoxic stress, wild-type and mutant MEFs showed similar growth rates and cell cycle distributions, and the mutants were only mildly radiosensitive. Further investigation showed that NONO deficiency led to upregulation of PSPC1, which replaced NONO in a stable complex with SFPQ. Knockdown of PSPC1 in a NONO-deficient background led to severe radiosensitivity and delayed resolution of DSB repair foci. The DNA-dependent protein kinase (DNA-PK) inhibitor, NU7741, sensitized wild-type and singly deficient MEFs, but had no additional effect on doubly deficient cells, suggesting that NONO/PSPC1 and DNA-PK function in the same pathway. We tested whether NONO and PSPC1 might also affect repair indirectly by influencing mRNA levels for other DSB repair genes. Of 12 genes tested, none were downregulated, and several were upregulated. Thus, NONO or related proteins are critical for DSB repair, NONO and PSPC1 are functional homologs with partially interchangeable functions and a compensatory response involving PSPC1 blunts the effect of NONO deficiency.

PMID:
25100870
PMCID:
PMC4150768
DOI:
10.1093/nar/gku650
[Indexed for MEDLINE]
Free PMC Article

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