Effects of genomic disruption of a guanine quadruplex in the 5' UTR of the Bcl-2 mRNA in melanoma cells.

G-quadruplex structures in the 5' UTR of mRNAs have been shown to suppress translation. However, all experiments published so far made use of artificial reporter systems. Here, we investigate for the first time the biological effects of the genomic disruption of a G-quadruplex by CRISPR/Cas9. In melanoma cells lacking the G-quadruplex-forming sequence in the mRNA of the apoptosis inhibitor Bcl-2, the protein level of Bcl-2 remains virtually unchanged. Consequently, sensitivity to an inducer of apoptosis is not reduced. Thus, it is likely that the inhibitory effects of G-quadruplexes observed to date were more pronounced due to the use of the strong overexpression in transfection experiments, whereas G-quadruplexes in endogenous mRNAs, expressed at moderate levels, are widely resolved by cellular RNA helicases.