Abstract
Chronic myeloid leukemia (CML) is a myeloproliferative neoplasm characterized by the t(9;22) translocation. As in most cancers, short telomeres are one of the features of CML cells, and telomere shortening accentuates as the disease progresses from the chronic phase to the blastic phase. Although most individual telomeres are short, some of them are lengthened, and long individual telomeres occur non-randomly and might be associated with clonal selection. Telomerase is the main mechanism used to maintain telomere lengths, and its activity increases when CML evolves toward advanced stages. ALT might be another mechanism employed by CML cells to sustain the homeostasis of their telomere lengths and this mechanism seems predominant at the early stage of leukemogenesis. Also, telomerase and ALT might jointly act to maintain telomere lengths at the chronic phase, and as CML progresses, telomerase becomes the major mechanism. Finally, CML cells display an altered nuclear organization of their telomeres which is characterized by the presence of high number of telomeric aggregates, a feature of genomic instability, and differential positioning of telomeres. CML represents a good model to study mechanisms responsible for dynamic changes of individual telomere lengths and the remodeling of telomeric nuclear organization throughout cancer progression.
Highlights
Chronic myeloid leukemia (CML) is a myeloproliferative neoplasm characterized by the t(9;22) translocation
A recent study showed that telomeres of myeloid cells (Ph negative) from CML patients in remission, after successful treatment, were shorter than those of age-matched healthy controls whereas telomere lengths of lymphoid cells did not present any statistical difference between the patients and the controls [54]
The concept of telomere shortening, being a feature of CML cells, when average length is only considered has been challenged by the lengthening of some individual telomeres which could possibly be associated with clonal selection
Summary
The ends of human chromosomes, called telomeres, are constituted of a tandem of repeats TTAGGG and nucleoprotein complexes, and they play a crucial role in cellular homeostasis by maintaining genome stability and integrity. Average length of telomeres (telomeres from groups of cells, tissues, or organs) and length of individual telomere (telomeres on each chromosome arm) can be assessed by using genomic DNA or cytological preparations [2] Both in vitro and in vivo studies have shown negative correlation between telomere length and cellular aging [3,4,5]. Mechanisms, and telomeric nuclear organization in CML This pathology offers a unique model to study different facets of telomere biology in cancer because of its well characterized natural history, the easy access of tumor cells, the availability of control tissue (same cellular origin), the good quality of karyotype (necessary for the measurement of individual telomere lengths), and the availability of good therapeutic which can enable to study the impact of successful treatment on telomere biology
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