CONNECTIONS BETWEEN G-QUADRUPLEXES, THE WERNER AND BLOOM SYNDROMES, AND CELLULAR SENESCENCE

G-quadruplex DNA (G4-DNA) is a family of structures composed of stacked G-quartets, which themselves comprise four Hoogsteen-bonded guanines in a planar array. They have been shown to form in vivo at telomeres in at least one organism, S. lamnae. Several RecQ DNA helicases, including the human WRN and BLM proteins and S. cerevisiae Sgs1, are particularly active in unwinding G4-DNA in vitro. WRN and BLM are deficient in the Werner and Bloom syndromes, respectively, which are characterized by elevated rates of cancer and premature features of aging. The demonstrated roles for RecQ helicases in telomere maintenance has led to the hypothesis that these roles might be explained by the resolution of telomeric G4-DNA by the helicases. New experimental findings will be presented that support this idea directly. Outside of telomeres, sequences with intramolecular G-quadruplex forming potential (QFP) are concentrated in the promoter regions of organisms ranging from bacteria to humans, raising the possibility that they play roles in transcriptional regulation. Recently we reported highly significant correlations in S. cerevisiae between genes having QFP and those with altered expression in cells lacking Sgs1 or treated with a selective G4-DNA small molecule ligand N-methyl mesoporphyrin IX (NMM), thus supporting a direct role for G4-DNA in transcriptional regulation. We have now extended these findings to human cells, including analyses of altered gene expression in cells from individuals with Werner or Bloom syndrome, or in cells treated with NMM or another G4-DNA ligand, BRACO19. Similar to our findings in yeast, there are significant correlations between loci possessing QFP and those showing altered regulation under these conditions, each of which is predicted to alter G4-DNA levels or functions. We wondered if there might be connections between G4-DNA at telomeres and that involved in transcriptional regulation. Cellular senescence can be induced by telomere shortening and dysfunction in both S. cerevisiae mutants lacking telomerase and human cultured cells. We have found, in both yeast and human cells, that there are highly significant correlations between genes that are upregulated at senescence caused by telomere shortening and genes with QFP. These associations are apparently not explained by the binding of known transcription factors. We therefore propose that 1) there is competition between G4-DNA at telomeres and promoters for transcriptional regulators t