DNA Repair 9 (2010) 161–168
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DNA Repair
journal homepage: www.elsevier.com/locate/dnarepair
Defining the DNA mismatch repair-dependent apoptotic pathway in primary
cells: Evidence for p53-independence and involvement of centrosomal caspase 2
Kelly A.D. Narine
a
, Angela M. Keuling
a
, Randi Gombos
a
, Victor A. Tron
b
,
Susan E. Andrew
a,∗
, Leah C. Young
a,∗
a
Department of Medical Genetics, University of Alberta, Edmonton, Alberta, Canada
b
Department of Pathology and Molecular Medicine, Queen’s University, Kingston, Ontario, Canada
article info
Article history:
Received 13 July 2009
Received in revised form
18 November 2009
Accepted 20 November 2009
Keywords:
DNA mismatch repair
Msh6
UVB
Apoptosis
p53
Caspase 2
Centrosome
abstract
Many studies have shown that DNA mismatch repair (MMR) has a role beyond that of repair in response
to several types of DNA damage, including ultraviolet radiation (UV). We have demonstrated previously
that the MMR-dependent component of UVB-induced apoptosis is integral to the suppression of UVB-
induced tumorigenesis. Here we demonstrate that Msh6-dependent UVB-induced apoptotic pathway is
both activated via the mitochondria and p53-independent. In addition, we have shown for the first time
that caspase 2, an initiator caspase, localizes to the centrosomes in mitotic primary mouse embryonic
fibroblasts, irrespective of MMR status and UVB treatment.
© 2009 Elsevier B.V. All rights reserved.
1. Introduction
DNA mismatch repair (MMR) plays a critical role in the mainte-
nance of genomic stability through the repair of mis-paired bases
and insertion/deletion loops (IDLs) that occur during DNA replica-
tion [1]. The first step in MMR is the binding to the site of DNA error:
the MSH2/MSH6 heterodimer binds mismatches and small IDLs,
while the MSH2/MSH3 heterodimer binds larger IDLs. The impor-
tance of MMR to tumor avoidance is illustrated by Lynch syndrome
(formerly termed HNPCC); loss of a key MMR protein (e.g., MSH2,
MLH1 and MSH6) culminates in a distinct tumor spectrum includ-
ing colon and endometrial tumors. Notably, colon tumors are the
predominate tumor associated with loss of either MSH2 or MLH1,
while endometrial tumors are associated with a loss of MSH6.
In addition to its role in post-replicative DNA repair, MMR pro-
teins are integral to the cellular response to exogenous DNA dam-
age; responses include processing of DNA lesion, as well as apopto-
sis and cell cycle arrest [2]. Lesions can be divided into three groups:
∗
Corresponding authors at: Department of Medical Genetics, 8-33 Medical Sci-
ences Bldg. University of Alberta, Edmonton, Alberta, Canada T6G 2H7.
Tel.: +1 780 492 1128; fax: +1 780 492 1998.
E-mail addresses: susan.andrew@ualberta.ca (S.E. Andrew),
leah.young@ualberta.ca (L.C. Young).
(i) lesions both bound and repaired by MMR; (ii) lesions that are
bound, but not repaired by MMR; and (iii) lesions that are not bound
by MMR. DNA damage induced by SN1-type alkylating agents (e.g.,
MNNG) is a classic example of MMR-processed lesions. MMR-
deficiency confers resistance to MNNG, as manifested by decreased
induction of apoptosis, decreased induction of G
2
M checkpoint
arrest, and increased DNA mutation accumulation [3–7].
In contrast, MMR binds to UVB-induced mismatch/
photoproduct compound lesions [8,9] (caused by translesion
synthesis across the original lesion), but does not participate in the
removal of this adduct (reviewed in [10]). In recent years several
studies by our laboratory and those of others have demonstrated
a role for MMR in the cellular response to UV-induced DNA
damage [11–17]. Using both primary cultures of MEFs and in vivo
keratinocytes, we have demonstrated that the loss of either Msh2
or Msh6 results in a 2-fold reduction in UVB-induced apoptosis
[11–13]; also, the reduced numbers of in apoptotic keratinocytes
in vivo (sunburn cells) is associated with increased levels of
residual photoproducts (thymine-dimers) [13] and accelerated
presentation and increased severity of squamous cell carcinoma
tumorigenesis [13–15]. Other research groups have demonstrated
clearly that Msh2-dependent apoptosis can be uncoupled from
Msh2-dependent repair, and that mice deficient only in Msh2-
dependent apoptosis remain predisposed to tumorigenesis, albeit
at a reduced rate than Msh2-null mice (deficient in both functions)
1568-7864/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.dnarep.2009.11.010