Download Biochemical Analysis of the Human Mismatch Repair Proteins

Metastasis suppressor NM23-H1 promotes repair of UV-induced DNA damage and
suppresses UV-induced melanomagenesis
Stuart G. Jarrett, Marian Novak, Sandrine Dabernat, et al.
Cancer Res 2012;72:133-143.
Presenter: LI -YAN, HUANG
Commentator: Christina Ling Chang, Ph.D.
Date/ Time: 2012/12/27 17:10- 18:00
Location: Room 601, Med College Building
Background :
NM23-H1 is a metastatic suppressor gene, initially identified by reduced expression of its nm23-m1
homolog in murine metastatic melanoma. NM23-H1 possesses two major enzymatic activities. The first one
is the nucleoside diphosphate kinase (NDPK) activity, which catalyzes transfer of γ-phosphate between
nucleoside triphosphates and diphosphates. The second one is the 3'-5' exonuclease activity, which is
involved in repair of UV-induced DNA damage in yeasts. UV radiation is one of the most widespread
inducers of DNA damage in our environment. UV-induced DNA damage inhibits DNA replication as well
as transcription thus causing genomic instability. Two major types of UV lesions are cyclobutane pyrimidine
dimmers (CPDs) and pyrimidine (6-4) pyrimidone photoproducts (6-4PPs). The nucleotide excision repair
(NER) pathway is primarily involved in removing CPDs and 6-4PPs. If UV-induced DNA damage were not
repaired, it may result in melanomagenesis. Melanomagenesis starts from a radial growth phase, melanoma
cells then grow intraepidermally, followed by invasion of the dermis in the vertical growth phase, and
culminating with metastasis.
Objective:
To investigate whether NM23-H1 is involved in the repair of UV-induced DNA damage and
melanomagenesis.
Results:
The XL-PCR assay showed that forced expression of NM23-H1 in human melanoma WM793 cells
accelerated repair of UV-induced DNA damage. However, deletion of nm23-m1-/- mouse embryonic
fibroblasts (MEF) delayed such repair. Deletions of both nm23-m1 and nm23-m2 genes delayed the repair
even more in MEF. To understand which function is involved in UV-damage repair, different enzymatically
defective variants of NM23-H1 were analyzed by XL-PCR and immunoslot blot assays. The results showed
that kinase activity of NM23-H1, but not its 3’-5’exonuclease function, promoted NER-mediated removal of
6-4PPs in the cell nucleus. Immunolocolization studies showed that NM23-H1 was rapidly translocated to
site of 6-4PPs in the cell nucleus, suggesting its direct participation in the early DNA damage repair
response. The 6-thioguanine-resistance (6-TGr) colony formation assay showed that NM23-H1 deficiency
increased the mutagenic potential, and suggested that the 3’-5’exonuclease activity of NM23-H1 is the
predominant function for suppressing UV-induced mutations. Compared to the wild type, mice with
hemizygous-null for nm23-m1 and nm23-m2 exhibited UV-induced melanoma and follicular infundibular
cyst formation, whereas tumor-associated melanocytes exhibited invasion into adjacent dermis. This
suggests that NM23-H1 suppresses UV-induced melanomagenesis.
Conclusion:
Human NM23-H1 and mouse NM23-M1 promote the early repair response to UV-induced DNA damage,
and also suppress UV-induced skin tumorigenesis.
References:
1. Andrew W. Farrell, Gary M. Halliday and James Guy Lyons. Chromatin Structure Following UV-Induced
DNA Damage—Repair or Death? Int. J. Mol. Sci. 2011, 12, 8063-8085
2. Zhang Q, McCorkle JR, Novak M, Yang M, Kaetzel DM. Metastasis suppressor function of NM23-H1
requires its 3’-5’ exonuclease activity. Int J Cancer 2010;128:40 – 50.