Characterization of 5’-Flanking Regions of Various Human Telomere Maintenance Factor-Encoding Genes

Abstract

Telomeres are the unique nucleoprotein complex structures located at the end of linear eukaryotic chromosomes (Blackburn, 2000; de Lange, 2006). They are composed of TTAGGG repeats that are typically 10 kb at birth and gradually shorten with cell divisions (de Lange, 2006). Telomerase is composed of the protein subunit TERT and the RNA subunit TERC (TR). It elongates the telomere by adding telomeric repeats (Greider & Blackburn, 1987). The 50 to 300 nucleotides from the terminal end of the telomeres are single stranded 3’-protluded Goverhang structures which make the t-loop configuration (de Lange, 2006; Griffith et al., 1999). Mammalian telomeres are included in heterochoromatin and attached to the nuclear matrix (Oberdoerffer & Sinclair, 2007; Gonzalez-Suarez & Gonzalo, 2008). Telomere shortening causes instability of the ends of chromosomes to lead to replicative senescence (O’Sullivan & Karlseder, 2010; Lundblad & Szostak, 1989). Therefore, the ends of telomeres should be protected from damaging or cellular activities. The t-loop structures are regulated by shelterin protein factors, TRF1, TRF2, Rap1, TIN2, TPP1, POT1 (Gilson & Geli, 2007; O’Sullivan & Karlseder, 2010), and Rec Q DNA helicases, WRN and BLM (Chu & Hickson, 2009). TRF1 and TRF2, which bind to duplex telomeric DNA and retain shelterin on the telomere repeats, were shown to interact with various functional proteins (Giannone et al., 2010). Molecular structural analysis of Rap1 revealed that its mechanism of action involves interaction with TRF2 and Taz1 proteins (Chen et al., 2011). A recent study showed that depletion of TPP1 and its partner TIN2 causes a loss of telomerase recruitment to telomeres (Abreu et al., 2010). POT1 is an important regulator of telomerase length, in stimulating the RecQ helicases WRN and BLM (Opresko et al., 2005). Tankyrase-1 (TANK1), which is classified as a poly(ADP-ribose) polymerase family protein, is also known to regulate telomere homeostasis by modifying TRF1 (Smith et al., 1998; Schreiber et al., 2006). Dyskerin, which is encoded by the DKC1 gene, is a key auxiliary protein that is contained in a Cajal body with TERT (Cohen et al., 2007). Defects in the shelterin components and telomerase are thought to down-regulate telomere structure