TITLE:
The role of XPC protein deficiency in tobacco smoke-induced DNA hypermethylation of tumor suppressor genes
AUTHORS:
Gan Wang, Le Wang, Vanitha Bhoopalan, Yue Xi, Deepak K. Bhalla, David Wang, Xiaoxin S. Xu
KEYWORDS:
DNA Hypermethylation; Tumor Suppressors; XPC; Tobacco Smoke; DNA Damage; DNA Repair Deficiency; ATR; DNMT3A
JOURNAL NAME:
Open Journal of Genetics,
Vol.3 No.4,
December
13,
2013
ABSTRACT: DNA hypermethylation of tumor suppressor genes has
been frequently observed in cancer patients, and therefore, may provide a valuable
biomarker for cancer prevention and treatment. DNA hypermethylation may
also provide an important mechanism in cancer progression. Lung cancer is
strongly associated with exposure to environmental carcinogens, especially
tobacco smoke. DNA damage generated by tobacco smoke is believed to play an
important role in lung cancer development. XPC is a DNA damage recognition
protein required for DNA repair and other DNA damage responses and attenuated
XPC protein levels have been detected in many lung cancer patients. We
studied the role of XPC protein deficiency in tobacco smoke-caused DNA hypermethylation
of important tumor suppressor genes. Using both normal human fibroblasts (NF)
and XPC-deficient hu man fibroblasts (XPC), our DNA methylation studies
demonstrated that the XPC deficiency caused elevated levels of DNA
hypermethylation in both Brca1 and Mlh1 tumor suppressor genes following
exposure to tobacco smoke condensate (TSC). The results of our ChIP studies
revealed that the XPC deficiency led to an increased binding of DNA
methyltransferase 3A (DNMT3A) at the promoter region CpG island-containing
sequences of these genes under the TSC treatment; however, this increase was
partially diminished with prior treatment with caffeine. The results of our
immuno-precipitation (IP) studies demonstrated
a protein-protein interaction of the ATR with
DNMT3A. Our western blots revealed that the
XPC deficiency caused an increase in TSC-induced ATR
phosphorylation at serine 428, an indicator of ATR activation. All these
results suggest that XPC deficiency causes an accelerated DNA hypermethylation
in important tumor suppressor genes under tobacco smoke exposure and
activation of the ATR signaling pathway is involved in this DNA hypermethylation
process.