Chapter Category: DNA

From the book DNA Repair and Human Disease

Orchestration of Telomeres and DNA Repair Factors in Mammalian Cells Implications for Cancer and Ageing

M. Prakash Hande

Loss of telomere homeostasis via chromosome-genomic instability might effectively pro mote tumour progression. Telomere function may have contrasting roles: inducing rep licative senescence and promoting tumourigenesis and these roles may vary between cell types depending on the expression of telomerase enzyme, the level of mutations induced, and deficiency of related DNA repair pathways. Earlier studies in yeast and their recent extension to mammalian systems have convincingly indicated a role for DNA repair proteins in telomere maintenance. An alternative telomere maintenance mechanism has been identified in mouse embryonic stem cells lacking the telomerase RNA unit (mTERC) in which nontelomeric sequences adjacent to existing short stretches of telomere repeats are amplified. Our quest for identifying telomerase-independent or alternative mechanisms for telomere maintenance in mammalian cells has identified the involvement of potential DNA repair factors in such pathways. Studies by us and others have shown the association between the DNA repair factors and telomere function in mammalian cells. Mice deficient in a DNA-break sensing molecule, PARP-1 (poly [ADP]-ribopolymerase), have increased levels of chromosomal instability associated with extensive telomere shortening. Ku80 null cells showed telomere shortening associated with extensive chromosome end fusions whereas Ku80+/– cells exhibited an intermediate level of telomere shortening. This overview will focus mainly on the role of DNA repair/recombination and DNA damage signalling molecules such as PARP-1, DNA-PKcs, Ku70/80, XRCC4 and ATM, which we have been studying for quite sometime. As the maintenance of telomere function is crucial for genomic stability, our results are likely to provide new insights into the telomere regulatory mechanisms and their impact on chromosome instability, ageing and tumour formation.

Taken from the book

DNA Repair and Human Disease

Edited by: Adayabalam Balajee

More chapters from the book:

RecQ family DNA helicases are defined by amino acid sequence similarities to Escheri chia coli RecQ which has been known to act in homologous recombination and to suppress illegitimate recombination, particularly during the repair of DNA double strand breaks. Five RecQ family genes have been...


Down’s syndrome (DS) is an autosomal recessive human disorder caused by an extra copy of chromosome 21. DS patients are characterized by dwarfism and mental re tardation accompanied by an increased incidence of cancer development in various tissues and organs. DS patients also show signs of...


Studies on cancer-prone and rare human genetic disorders often lead to significant advances in our understanding of the complex network of genome stability and DNA repair pathways that have evolved in the human genome to prevent the harmful effects of exposure to DNA damaging agents. One such...


Xeroderma pigmentosum (XP),1 Cockayne syndrome (CS)2,3 and xeroderma pigmentosum-Cockayne syndrome (XP-CS)4,5 are rare disorders with autosomal recessive inheritance, characterized by extreme sensitivity to sunlight. This sensitivity reflects the inadequate removal and/or repair of UV-induced...


Ataxia telangiectasia (AT) is an autosomal recessive multisystem human disorder and patients are characterized by cerebellar ataxia, oculocutaneous telangiectasia, immuno deficiency, chromosomal instability and radio sensitivity with an increased predisposition to lymphoid cancer in childhood....


Loss of telomere homeostasis via chromosome-genomic instability might effectively pro mote tumour progression. Telomere function may have contrasting roles: inducing rep licative senescence and promoting tumourigenesis and these roles may vary between cell types depending on the expression of...


Roles of the BRCA1 and BRCA2 Breast Cancer Susceptibility Proteins in DNA Repair
Katrin Gudmundsdottir, Emily Witt and Alan Ashworth

Since the cloning of the BRCA1 and BRCA2 genes less than 10 years ago, a great deal of effort has been expended in attempting to uncover the functions of the encoded proteins. BRCA1 and BRCA2 have now been linked to a wide variety of cellular functions through binding or colocalization with...


Werner’s syndrome (WS) and Cockayne syndrome (CS) are rare human autosomal recessive disorders classified as segmental progeroid disorders. WS is marked by premature onset of age-related phenotypic changes (such as cataract and greying of hair etc) and genome instability. Cells derived from...


Trichothiodystrophy (TTD) is a rare autosomal recessive multisystem disorder characterized by sulfur-deficient brittle hair, mental and physical retardation, ichthyosis, and, in many patients, cutaneous photosensitivity but no cancer incidence. All sun-sensitive TTD cases appear to be...


Mechanisms of DNA Damage and Repair in Alzheimer Disease
V. Prakash Reddy, George Perry, Marcus S. Cooke, Lawrence M. Sayre and Mark A. Smith

Reactive oxygen species (ROS) are produced during the respiratory cycle in mitochon- dria,1 as well as normal cellular and xenobiotic metabolism. Exposure to various noxious insults can also lead to ROS production. In addition, ROS are also generated through metal-catalyzed reactions. A...


Advertisements