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DNA Damage and p16-mediated Growth Arrest in HIV-1-specific CD8+ T Cells
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Reported by Jules Levin
CROI 2010 Feb 16-19 SF
Thai Cung*1, K Seiss1, J Beamon1, P Burke1, F Pereyra1, B Walker1, E Rosenberg2, X Yu1, and M Lichterfeld2
1Ragon Inst of Massachusetts Gen Hosp, Massachusetts Inst of Tech, and Harvard Univ, Boston, US and 2Massachusetts Gen Hosp, Boston, US
ABSTRACT
Background: Accelerated T cell turnover leads to premature immune senescence in HIV-1 infection, and this process appears to be particularly pronounced in HIV-1-specific CD8+ T cells. Protection against immune senescence is mediated by telomerase, an enzyme that can actively extend telomeric DNA, and the shelterin complex, a regulatory network of nucleoproteins localized at telomeric DNA sites. Dysfunction of this protein complex can result in DNA damage responses that lead to growth arrest and cellular dysfunction. Perturbations of shelterin homeostasis and their contribution to immune senescence in HIV-1 infection are unclear.
Methods: mRNA expression of shelterin and DNA damage response genes were assessed in tet+ HIV-1-specific CD8+ T cells and reference populations of autologous tet+ CMV/EBV-specific cytotoxic T cells or bulk CD8+ T cells. Recruitment of DNA damage response factors to telomeric DNA was assessed using imaging flow cytometry. Functional consequences of shelterin protein depletion were analyzed using proliferation assays after targeted small interrupting RNA (siRNA) mediated gene knock out.
Results: Significant up-regulation (P <0.01) of the protective shelterin proteins TRF2, POT, TIN2 was found in HIV-1-specific CD8+ T cells from controllers, compared to autologous T cell populations and HIV-1-specfic CD8+ T cells from progressors. In contrast, the inhibitory shelterin protein TRF1 was down-regulated in cells from controllers, but strongly up-regulated in progressors (P =0.0096). Shelterin depletion in progressors was associated with recruitment of DNA damage response factors to telomeric DNA as "telomere dysfunction induced foci" and led to the up-regulation of the growth inhibitor p16 in HIV-1-specfic CD8+ T cells, in comparison to autologous T cells and HIV-1- specific CD8+ T cells from controllers (P =0.02). Selective silencing of the protective shelterin genes in HIV-1-specific CD8+ T cells by siRNA resulted in proliferative arrest and cellular dysfunction.
Conclusions: Shelterin dysfunction in HIV-1-specific T cells from progressors results in a DNA damage response signal that leads to recruitment of p16 and other DNA damage response factors arresting the cell cycle. Proliferative defects of HIV-1-specific CD8+ T cells might thus represent a physiologic response to DNA damage that protects against expansion of genetically unstable HIV-1-specific CD8+ T cells.
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