Involvement of DNA mismatch repair in folate deficiency-induced
apoptosis૾
Liya Gu, Jianxin Wu
†
, Lu Qiu, C. Darrell Jennings, Guo-Min Li*
Department of Pathology and Laboratory Medicine, Markey Cancer Center, University of Kentucky Medical Center,
University of Kentucky Medical Center, Lexington, Kentucky 40536 USA
Received 30 November 2001; received in revised form 16 January 2002; accepted 30 January 2002
Abstract
Folate is a critical factor for DNA metabolism and its deficiency is associated with a number of human diseases and cancers. Although
it has been shown that folate deficiency induces genomic instability and apoptotic cell death, the underlying mechanism is largely unknown.
Given the role of mismatch repair in maintaining genomic integrity, mismatch repair was tested for its involvement in folate deficiency-
induced genomic instability and cell death. Cells proficient in mismatch repair were highly sensitive to folate deficiency compared with cells
defective in either hMutS
␣
or hMutL
␣
. Since wild-type cells but not mutant cells underwent apoptosis upon extensive folate depletion, the
apoptotic response is dependent on a functional mismatch repair system. Our data also indicate that p53 is required for the folate
depletion-induced apoptosis. In vitro biochemical studies demonstrated that hMutS
␣
specifically recognized DNA damage induced by folate
deficiency, suggesting a direct participation of mismatch repair proteins in mediating the apoptotic response. We conclude that while the
mismatch repair-dependent apoptosis is necessary to protect damaged cells from tumorigenesis, it may damage a whole tissue or organ, as
seen in patients with megaloblastic anemia, during extensive folate deficiency. © 2002 Elsevier Science Inc. All rights reserved.
Keywords: Folate deficiency; DNA repair; Apoptosis
1. Introduction
Folate is an important cofactor in the transfer of one-
carbon moieties and plays a key role in DNA synthesis,
repair, and methylation. Classic folate deficiency causes a
macrocytic anemia and conspicuous megaloblastic changes
in the blood and bone marrow (for a review see [1]). Grow-
ing evidence indicates that folate deficiency is also associ-
ated with an increased risk of certain types of human cancer,
including colon [2], cervix [3], breast [4], pancreas [5], and
acute lymphocytic leukemia [6], as well as other diseases
such as neural tube defects and heart disease (reviewed in
[1,6]). Although the mechanism by which folate deficiency
contributes to these diseases is largely unknown, it has been
demonstrated that folate deficiency induces severe DNA
damage including massive uracil misincorporation and
chromosome breaks [7–10]. Since 5,10-methylenetetrahy-
drofolate (the folate cofactor for thymidylate synthase) is
the primary methyl donor for the de novo biosynthesis of
deoxythymine monophosphate (dTMP) from deoxyuridine
monophosphate (dUMP), folate deficiency results in an in-
creased cellular dUMP/dTMP ratio, thereby leading to
DNA polymerase-mediated dUTP incorporation into DNA.
In addition to genetic damage, folate deficiency results in
programmed cell death. However, the underlying mecha-
nism for this apoptotic cell death remains elusive.
Given the fact that folate depletion induces severe DNA
damage and increased mutagenesis, it has been postulated
that folate deficiency may be associated with defective
DNA repair [11]. It is intriguing that Choi et al. [12] have
recently reported the impairment of DNA excision repair in
rat colon cells by folate deficiency. Cravo et al. [13] dem-
onstrated that the status of folic acid can dominate the
microsatellite status in non-neoplastic mucosa in patients
with ulcerative colitis. Since microsatellite instability is a
hallmark of DNA mismatch repair (MMR) deficiency, these
૾This work is supported by grant CA72956 from the National Cancer
Institute and funds from Lucille P. Markey Trust (to G-M.L.).
†
Present address: The Capital Institute of Pediatrics, Beijing, China
* Corresponding author. Tel.: ϩ1-859-257-7053; fax: ϩ1-859-323-
2094.
E-mail address: gmli@pop.uky.edu (G-M. Li).
Journal of Nutritional Biochemistry 13 (2002) 355–363
0955-2863/02/$ – see front matter © 2002 Elsevier Science Inc. All rights reserved.
PII: S0955-2863(02)00178-X