abnormalities involving telomeric associations (TAs) often precede replicative senescence and irregular chromosome configurations. telomeric-repeat binding element (TRF) Intro Telomeres the short tandem DNA repeats of (T2AG3)n [1 2 localized to the distal ends of chromosomes play a R788 (Fostamatinib) crucial part in chromosomal safety and replication [3-6]. In most normal somatic cells telomeric DNA is definitely lost at a rate of 50 to 200 bp per doubling due to replication-associated erosion [7-10]. Eventually telomere erosion leads to cell cycle arrest and senescence [8 9 11 and it has been suggested that telomere erosion may consequently dictate R788 (Fostamatinib) cellular life-span. However tumor cells are capable of resynthesizing telomeric DNA through the activation/upregulation of an enzyme complex known as telomerase [5]. Some cells can exploit telomerase-dependent and telomerase-independent or alternate lengthening of telomeres (ALT) pathways to reverse telomeric DNA loss leading to immortalization associated with malignancy development [12-19]. Recent studies have shown that malignancy chemotherapeutic providers (cisplatin AZT) capable of binding to or becoming integrated into telomeric repeats cause telomere erosion in malignancy cells [20 21 Because these providers also induce apoptosis we pondered whether telomere cleavage was linked R788 (Fostamatinib) to programmed cell death. Here we demonstrate a rapid erosion of telomeres in different types of Rabbit Polyclonal to CRHR2. malignancy cells R788 (Fostamatinib) exposed to pro-apoptotic stimuli including staurosporine thapsigargin anti-Fas antibody and the malignancy chemotherapeutic agent 1-(TNF[36] have shown that the lack of TRF2 protein in telomeres may result in the loss of the G-strand overhangs from telomere termini and may be responsible for fusion of chromosome ends or TAs. The TRF1 and TRF2 proteins play essential tasks in the maintenance of telomere size [36-41]. TRF1 is a negative regulator of telomerase activity therefore the loss of TRF1 may enable telomerase to extend telomeric ends [41]. The main function of TRF2 is to bind and guard the 3′ telomeric end by folding back the single-stranded 5′-TTAGGG-3′ overhang into upstream telomeric duplex DNA forming a displacement loop (D-loop) with complimentary 3′-AATCCC-5′ sequences hence protecting telomere ends from degradation and chromosome endoreduplication [36 42 Furthermore the loss of TRF2 may generate G overhangs at the end of telomeres which may produce DNA damage signals hence revitalizing cell cycle arrest and/or apoptosis [36]. Endoreduplication of chromosomes has been a consistent characteristic feature of apoptotic cells [12 13 43 In the present studies our results display telomere loss cell cycle arrest in G2/M phase and considerable endoreduplication of chromosomes (a pro-apoptotic stage of cell death of K1735 clone X-21 cells after treatment with ara-C). If the level of TRF2 is associated with telomere loss endoreduplication and cell death then K1735 clone X-21 cells treated with ara-C could be expected to display decreased levels of TRF2. Therefore to establish a correlation R788 (Fostamatinib) between TRF2 levels the loss of telomere size and endoreduplication of chromosomes we treated K1735 clone X-21 cells with different concentrations of ara-C. For assessment we used two human being prostate malignancy cell lines Personal computer-3M and C4-2. The Personal computer-3M cells showed neither loss of telomere size nor endoreduplication of chromosomes and were resistant to apoptosis after treatment with ara-C. The C4-2 cells exhibited characteristics similar to K1735 clone X-21 cells (data not shown). The level of TRF1 in the K1735 clone X-21 cells was drastically reduced (Number 6); however the level of TRF1 in Personal computer-3M and C4-2 cells was unchanged after treatment with ara-C (Number 6). The ara-C-induced level of TRF2 in Personal computer-3M cells was unchanged but it was significantly decreased in the C4-2 and the X-21 cells (Number 6). The..