Carcinogen-induced DNA structural distortion differences in the RAS gene isoforms; the importance of local sequence

BACKGROUND: Local sequence context is known to have an impact on the mutational pattern seen in cancer. The RAS genes and a smoking carcinogen, Benzo[a]pyrene diol epoxide (BPDE), have been utilised to explore these context effects. BPDE is known to form an adduct at the guanines in a number of RAS gene sites, KRAS codons 12, 13 and 14, NRAS codon 12, and HRAS codons 12 and 14. RESULTS: Molecular modelling techniques, along with multivariate analysis, have been utilised to determine the sequence influenced differences between BPDE-adducted RAS gene sequences as well as the local distortion caused by the adducts. CONCLUSIONS: We conclude that G:C > T:A mutations at KRAS codon 12 in the tumours of lung cancer patients (who smoke), proposed to be predominantly caused by BPDE, are due to the effect of the interaction methyl group at the C5 position of the thymine base in the KRAS sequence with the BPDE carcinogen investigated causing increased distortion. We further suggest methylated cytosine would have a similar effect, showing the importance of methylation in cancer development. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s13065-021-00777-8

Pirin Allosterically Modulates The Dynamics And Interactions Of The κB DNA In The NF-κB Supramolecular Complex

The NF-κB family of transcription factors controls a number of essential cellular functions. Pirin is a non-heme iron (Fe) redox specific co-regulator of NF-κB (p65) and has been shown to modulate the affinity between the homodimeric p65 and the DNA. The allosteric effect of the active Fe(III) form of Pirin on the DNA is not known and has not been investigated. We carry out multiple microsecond-long molecular dynamics simulations of the free DNA, p65-DNA complex, and the Pirin-p65-DNA supramolecular complexes in explicit water. We show that, unlike the Fe(II) form of Pirin, the Fe(III) form in the Pirin-p65-DNA supramolecular complex enhances the interactions and affinity between p65 and the DNA, in agreement with experiments. The results further provide atomistic details of the effect of the Fe(III) form of Pirin on the DNA upon binding to p65 to form the supramolecular complex