TLR9 stimulation of B-cells induces transcription of p53 and prevents spontaneous and irradiation-induced cell death independent of DNA damage responses. Implications for Common variable immunodeficiency

PLoS One. 2017 Oct 3;12(10):e0185708. doi: 10.1371/journal.pone.0185708. eCollection 2017.

Abstract

In the present study, we address the important issue of whether B-cells protected from irradiation-induced cell death, may survive with elevated levels of DNA damage. If so, such cells would be at higher risk of gaining mutations and undergoing malignant transformation. We show that stimulation of B-cells with the TLR9 ligands CpG-oligodeoxynucleotides (CpG-ODN) prevents spontaneous and irradiation-induced death of normal peripheral blood B-cells, and of B-cells from patients diagnosed with Common variable immunodeficiency (CVID). The TLR9-mediated survival is enhanced by the vitamin A metabolite retinoic acid (RA). Importantly, neither stimulation of B-cells via TLR9 alone or with RA increases irradiation-induced DNA strand breaks and DNA damage responses such as activation of ATM and DNA-PKcs. We prove that elevated levels of γH2AX imposed by irradiation of stimulated B-cells is not due to induction of DNA double strand breaks, but merely reflects increased levels of total H2AX upon stimulation. Interestingly however, we unexpectedly find that TLR9 stimulation of B-cells induces low amounts of inactive p53, explained by transcriptional induction of TP53. Taken together, we show that enhanced survival of irradiated B-cells is not accompanied by elevated levels of DNA damage. Our results imply that TLR9-mediated activation of B-cells not only promotes cell survival, but may via p53 provide cells with a barrier against harmful consequences of enhanced activation and proliferation. As CVID-derived B-cells are more radiosensitive and prone to undergo apoptosis than normal B-cells, our data support treatment of CVID patients with CpG-ODN and RA.

MeSH terms

  • B-Lymphocytes / physiology*
  • Case-Control Studies
  • Common Variable Immunodeficiency / genetics*
  • DNA Damage*
  • Humans
  • Infrared Rays*
  • Toll-Like Receptor 9 / physiology*
  • Transcription, Genetic / physiology*
  • Tumor Suppressor Protein p53 / genetics*

Substances

  • TLR9 protein, human
  • Toll-Like Receptor 9
  • Tumor Suppressor Protein p53

Grants and funding

This work has been supported by the University of Oslo (www.uio.no), the Norwegian Cancer Society (grant number 420156, kreftforeningen.no), the Anders Jahre Foundation (www.unifor.no/Fund.aspx?site=1&fund=290), the Blix Family Foundation, the Freia Foundation, the Nansen Foundation (www.nansenfondet.no) and the UNIFOR FRIMED Legacy (www.unifor.no/fund.aspx?fund=310). The funders had no role in the study design, data collection and analysis, decision to publish, or preparation of this work. Norgenotech & Comet Biotech financial involvement in the study: salary for SS and coverage of the reagents, materials, lab rent and technical assistance connected with carrying out the experiments (these actual costs of Norgenotech were covered by the University of Oslo with no commercial profit or overheads).