Chaperoning RNA and DNA G-quadruplexes: putative CNBP role in proto-oncogenes expression control.

HECKEL, S.B.; ARMAS, P.

Rosario

Congreso; L Annual Meeting of the Argentine Society for Biochemestry and Molecular Biology Research.; 2014

Argentine Society for Biochemestry and Molecular Biology Research.

Cellular nucleic acid binding protein (CNBP) is a conserved nucleic acid chaperone associated to cell proliferation processes that participates in the complex transcriptional control of c-MYC. Recently, we have shown that CNBP binds in vitro to G-rich sequences present in the promoters of several human proto-oncogenes, including c-MYC, unfolding their guanine quadruplex (G4) structures. G4s are stable secondary structures of G-rich single-stranded DNA or RNA formed by the stacking of planar layers of four guanines. G4s have been found overrepresented not only in DNA transcriptional control regions of human proto-oncogenes, but also in their RNA translational control regions. We evaluated the effect of CNBP on RNA-G4s present in the translational control regions of VEGF, NRAS and BCL2 proto-oncogenes by Circular Dichroism (CD). We observed a clear decrease of the characteristic CD signals for NRAS and BCL2 G4s, and a milder decrease for VEGF. These results may indicate that CNBP destabilizes structured RNA G4s. Moreover, Electrophoretic Mobility Shift Assys (EMSA) showed that CNBP preferentially binds to unfolded rather than folded RNA-G4 sequences. These results are in agreement with previous DNA-G4 results and with a model where CNBP chaperones G4 unfolding by stabilization of unpaired guanines and displacement of G4 equilibrium towards the unfolded state.