Protection from ultraviolet damage and photocarcinogenesis by vitamin d compounds

© Springer Nature Switzerland AG 2020. Exposure of skin cells to UV radiation results in DNA damage, which if inadequately repaired, may cause mutations. UV-induced DNA damage and reactive oxygen and nitrogen species also cause local and systemic suppression of the adaptive immune system. Together, these changes underpin the development of skin tumours. The hormone derived from vitamin D, calcitriol (1,25-dihydroxyvitamin D3) and other related compounds, working via the vitamin D receptor and at least in part through endoplasmic reticulum protein 57 (ERp57), reduce cyclobutane pyrimidine dimers and oxidative DNA damage in keratinocytes and other skin cell types after UV. Calcitriol and related compounds enhance DNA repair in keratinocytes, in part through decreased reactive oxygen species, increased p53 expression and/or activation, increased repair proteins and increased energy availability in the cell when calcitriol is present after UV exposure. There is mitochondrial damage in keratinocytes after UV. In the presence of calcitriol, but not vehicle, glycolysis is increased after UV, along with increased energy-conserving autophagy and changes consistent with enhanced mitophagy. Reduced DNA damage and reduced ROS/RNS should help reduce UV-induced immune suppression. Reduced UV immune suppression is observed after topical treatment with calcitriol and related compounds in hairless mice. These protective effects of calcitriol and related compounds presumably contribute to the observed reduction in skin tumour formation in mice after chronic exposure to UV followed by topical post-irradiation treatment with calcitriol and some, though not all, related compounds

Disease-specific ACMG/AMP guidelines improve sequence variant interpretation for hearing loss

The ClinGen Variant Curation Expert Panels (VCEPs) provide disease-specific rules for accurate variant interpretation. Using the hearing loss-specific American College of Medical Genetics and Genomics/Association for Molecular Pathology (ACMG/AMP) guidelines, the Hearing Loss VCEP (HL VCEP) illustrates the utility of expert specifications in variant interpretation. A total of 157 variants across nine HL genes, previously submitted to ClinVar, were curated by the HL VCEP. The curation process involved collecting published and unpublished data for each variant by biocurators, followed by bimonthly meetings of an expert curation subgroup that reviewed all evidence and applied the HL-specific ACMG/AMP guidelines to reach a final classification. Before expert curation, 75% (117/157) of variants had single or multiple variants of uncertain significance (VUS) submissions (17/157) or had conflicting interpretations in ClinVar (100/157). After applying the HL-specific ACMG/AMP guidelines, 24% (4/17) of VUS and 69% (69/100) of discordant variants were resolved into benign (B), likely benign (LB), likely pathogenic (LP), or pathogenic (P). Overall, 70% (109/157) variants had unambiguous classifications (B, LB, LP, P). We quantify the contribution of the HL-specified ACMG/AMP codes to variant classification. Expert specification and application of the HL-specific ACMG/AMP guidelines effectively resolved discordant interpretations in ClinVar. This study highlights the utility of ClinGen VCEPs in supporting more consistent clinical variant interpretation

Computational studies support the role of the C7-sibirosamine sugar of the pyrrolobenzodiazepine (PBD) sibiromycin in transcription factor inhibition

The pyrrolo[2,1-c][1,4]benzodiazepines (PBDs) are a group of sequence-selective, DNA minor-groove binding agents that covalently attach to guanine residues. Originally derived from Streptomyces species, a number of naturally occurring PBD monomers exist with varying A-Ring and C2-substituents. One such agent, sibiromycin, is unusual in having a glycosyl residue (sibirosamine) at its A-Ring C7-position. It is the most cytotoxic member of the naturally occurring PBD family and has the highest DNA-binding affinity. Recently, the analogue 9-deoxysibiromyin was produced biosynthetically by Yonemoto and co-workers.1 Differing only in the loss of the A-Ring C9-hydroxyl group, it was reported to have a significantly higher DNA-binding affinity than sibiromycin based on DNA thermal denaturation studies, although these data have since been retracted.2 As deletion of the C9-OH moiety, which points toward the DNA minor groove floor, might intuitively be expected to reduce DNA-binding affinity through the loss of hydrogen bonding, we carried out molecular dynamics simulations on the interaction of both molecules with DNA over a 10 ns time-course in explicit solvent. Our results suggest that the two molecules may differ in their sequence-selectivity and that 9-deoxysibiromycin should have a lower binding affinity for certain sequences of DNA compared to sibiromycin. Our molecular dynamics results indicate that the C7-sibirosamine sugar does not form hydrogen bonding interactions with groups in the DNA minor-groove wall as previously reported, but instead points orthogonally out from the minor groove where it may inhibit the approach of DNA control proteins such as transcription factors. This was confirmed through a docking study involving sibiromycin and the GAL4 transcription factor, and these results could explain the significantly enhanced cytotoxicity of sibiromycin compared to other PBD family members without bulky C7-substituents