DNA hypermethylation/boundary control loss identified in retinoblastomas associated with genetic and epigenetic inactivation of the RB1 gene promoter

DNA hypermethylation events occur frequently in human cancers, but less is known of the mechanisms leading to their initiation. Retinoblastoma, an intraocular cancer affecting young children, involves bi-allelic inactivation of the RB1 gene (RB−/-). RB1 encodes a tumour suppressing, cell cycle regulating transcription factor (pRB) that binds and regulates the RB1 core and other E2F responsive promoters with epigenetic functions that include recruitment of histone deacetylases (HDACs). Evidence suggests that bi-allelic epigenetic inactivation/hypermethylation of the RB1 core promoter (PrE-/E-), is specific to sporadic retinoblastomas (frequency~10%), whereas heritable RB1 promoter variants (Pr−/+, frequency~1-2%) are not associated with known epigenetic phenomena. We report heritable Pr−/- retinoblastomas with the expected loss of pRB expression, in which hypermethylation consistent with distal boundary displacement (BD) relative to normal peripheral blood DNAs was detected in 4/4 cases. In contrast, proximal BD was identified in 16/16 RB−/- retinoblastomas while multiple boundaries distal of the core promoter was further identified in PrE-/E-and PrE-/E+ retinoblastomas. However, weak or no DNA hypermethylation/BD in peripheral blood DNA was detected in 8/9 Pr−/+ patients, with the exception, a carrier of a microdeletion encompassing several RB1 promoter elements. These findings suggest that loss of boundary control may be a critical step leading to epigenetic inactivation of the RB1 gene and that novel DNA methylation boundaries/profiles identified in the RB1 promoter of Pr−/- retinoblastomas, may be the result of epigenetic phenomena associated with epimutation in conjunction with loss of pRB expression/binding and/or RB1 promoter interactions with boundary control elements

HIV and dyadic intervention: an interdependence and communal coping analysis.

BACKGROUND: The most common form of HIV transmission in sub-Saharan Africa is heterosexual sex between two partners. While most HIV prevention interventions are aimed at the individual, there is mounting evidence of the feasibility, acceptability, and efficacy of dyadic interventions. However, the mechanisms through which dyadic-level interventions achieve success remain little explored. We address this gap by using Lewis et al's interdependence model of couple communal coping and behaviour change to analyse data from partners participating in an HIV prevention trial in Uganda and Zambia. METHODS AND FINDINGS: We conducted a comparative qualitative study using in-depth interviews. Thirty-three interviews were conducted in total; ten with couples and twenty-three with staff members at the two sites. The Ugandan site recruited a sero-discordant couple cohort and the Zambian site recruited women alone. Spouses' transformation of motivation is strong where couples are recruited and both partners stand to gain considerably by participating in the research; it is weaker where this is not the case. As such, coping mechanisms differ in the two sites; among sero-discordant couples in Uganda, communal coping is evidenced through joint consent to participate, regular couple counselling and workshops, sharing of HIV test results, and strong spousal support for adherence and retention. By contrast, coping at the Zambian site is predominantly left to the individual woman and occurs against a backdrop of mutual mistrust and male disenfranchisement. We discuss these findings in light of practical and ethical considerations of recruiting couples to HIV research. CONCLUSIONS: We argue for the need to consider the broader context within which behaviour change occurs and propose that future dyadic research be situated within the framework of the 'risk environment'