Journal Article

ATR/Chk1 pathway is essential for resumption of DNA synthesis and cell survival in UV-irradiated XP variant cells

Emmanuelle Despras, Fayza Daboussi, Olivier Hyrien, Kathrin Marheineke and Patricia L. Kannouche

in Human Molecular Genetics

Volume 19, issue 9, pages 1690-1701
Published in print May 2010 | ISSN: 0964-6906
Published online February 2010 | e-ISSN: 1460-2083 | DOI: http://dx.doi.org/10.1093/hmg/ddq046
ATR/Chk1 pathway is essential for resumption of DNA synthesis and cell survival in UV-irradiated XP variant cells

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DNA polymerase eta (polη) performs translesion synthesis past ultraviolet (UV) photoproducts and is deficient in cancer-prone xeroderma pigmentosum variant (XP-V) syndrome. The slight sensitivity of XP-V cells to UV is dramatically enhanced by low concentrations of caffeine. So far, the biological explanation for this feature remains elusive. Using DNA combing, we showed that translesion synthesis defect leads to a strong reduction in the number of active replication forks and a high proportion of stalled forks in human cells, which contrasts with budding yeast. Moreover, extensive regions of single-strand DNA are formed during replication in irradiated XP-V cells, leading to an over-activation of ATR/Chk1 pathway after low UVC doses. Addition of a low concentration of caffeine post-irradiation, although inefficient to restore S-phase progression, significantly decreases Chk1 activation and abrogates DNA synthesis in XP-V cells. While inhibition of Chk1 activity by UCN-01 prevents UVC-induced S-phase delay in wild-type cells, it aggravates replication defect in XP-V cells by increasing fork stalling. Consequently, UCN-01 sensitizes XP-V cells to UVC as caffeine does. Our findings indicate that polη acts at stalled forks to resume their progression, preventing the requirement for efficient replication checkpoint after low UVC doses. In the absence of polη, Chk1 kinase becomes essential for replication resumption by alternative pathways, via fork stabilization.

Journal Article.  7392 words.  Illustrated.

Subjects: Genetics and Genomics

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