CNBP unfolds guanine cuadruplex in proto-oncogenes promoters.

CHALLIER, E.; CALCATERRA, N.B.; ARMAS, P.

Mendoza

Congreso; XLVIII Annual Meeting of the Argentine Society for Biochemestry and Molecular Biology Research.; 2012

Argentine Society for Biochemestry and Molecular Biology Research.

Cellular nucleic acid binding protein (CNBP) is a conserved nucleicacid chaperone protein associated to cell proliferation and survivalprocesses. CNBP binds to a G-rich sequence present in the c-MYCpromoter up-regulating its expression. Recently,we have shown thatCNBP modulates in vitro the folding of guanine quadruplex (G4)structures present in the c-MYC promoter. G4s are nucleic acidsecondary structures formed by the stacking of two or more planarlayers of four guanines interacting by Hoogsteen hydrogen bondsand stabilized by monovalent cations. G4s have been found with ahigh frequency in the control regions of human proto-oncogenes.Here we evaluated the effect of CNBP on G4s present in thepromoter of several proto-oncogenes by Circular Dichroism (CD)and Polymerase Stop Assays (PSA). CD spectra of RET, HRAS andBCL2 G4s did not change in presence of CNBP; however, itdecreased the characteristic parallel G4 positive signal observed forc-MYC, VEGF, c-KIT, HIF-1a, KRAS and PDGF G4s. Inagreement, PSA data indicate that CNBP destabilizes structured G4in the latter proto-oncogenes. Data suggest a relationship betweenthe CNBP effect and the intrinsic stability of the G4s, which maydepend on the length of their central loop. Further characterizationof the role of CNBP on proto-oncogene expression is being carriedout using cell culture lines overexpressing CNBP.