Human PXR Forms a Tryptophan Zipper-Mediated Homodimer †

The human nuclear receptor pregnane X receptor (PXR) responds to a wide variety of potentially harmful chemicals and coordinates the expression of genes central to xenobiotic and endobiotic metabolism. Structural studies reveal that the PXR ligand binding domain (LBD) uses a novel sequence insert to form a homodimer unique to the nuclear receptor superfamily. Terminal β-strands from each monomeric LBD interact in an ideal antiparallel fashion to bury potentially exposed surface β-strands, generating a ten-stranded intermolecular β-sheet. Conserved tryptophan and tyrosine residues lock across the dimer interface and provide the first tryptophan-zipper (Trp-Zip) interaction observed in a native protein. We show using analytical ultracentrifugation that the PXR LBD forms a homodimer in solution. We further find that removal of the interlocking aromatic residues eliminates dimer formation but does not affect PXR's ability to interact with DNA, RXRα, or ligands. Disruption of the homodimer significantly reduces receptor activity in transient transfection experiments, however, and effectively eliminates the receptor's recruitment of the transcriptional coactivator SRC-1 both in vitro and in vivo. Taken together, these results suggest that the unique Trp-Zip-mediated PXR homodimer plays a role in the function of this nuclear xenobiotic receptor

Uptake of bilateral-risk-reducing-mastectomy: prospective analysis of 7195 women at high-risk of breast cancer

BACKGROUND: Bilateral-Risk-Reducing-Mastectomy-(BRRM) is well described in BRCA1/2 pathogenic variant carriers. However, little is known about the relative uptake, time trends or factors influencing uptake in those at increased breast cancer risk not known to be carriers. The aim of this study is to assess these factors in both groups. METHODS: BRRM uptake was assessed from entry to the Manchester Family History Clinic or from date of personal BRCA1/2 test. Follow up was censored at BRRM, breast cancer diagnosis, death or January 01, 2020. Cumulative incidence and cause specific and competing risk regression analyses were used to assess the significance of factors associated with BRRM. RESULTS: Of 7195 women at ≥25% lifetime breast cancer risk followed for up to 32 years, 451 (6.2%) underwent pre-symptomatic BRRM. Of those eligible in different risk groups the 20-year uptake of BRRM was 47.7%-(95%CI = 42.4–53.2%) in 479 BRCA1/2 carriers; 9.0% (95%CI = 7.26–11.24%) in 1261 women at ≥40% lifetime risk (non-BRCA), 4.8%-(95%CI = 3.98–5.73%) in 3561 women at 30–39% risk and 2.9%-(95%CI = 2.09–4.09%) in 1783 women at 25–29% lifetime risk. In cause-specific Cox regression analysis death of a sister with breast cancer50; OR = 0.26,95%CI = 0.17–0.41). Uptake continued to rise to 20 years from initial risk assessment. CONCLUSION: We have identified several additional factors that correlate with BRRM uptake and demonstrate continued increases over time. These factors will help to tailor counselling and support for women

The Angelina Jolie effect: Contralateral risk-reducing mastectomy trends in patients at increased risk of breast cancer

Abstract Contralateral risk-reducing mastectomy (CRRM) rates have tripled over the last 2 decades. Reasons for this are multi-factorial, with those harbouring a pathogenic variant in the BRCA1/2 gene having the greatest survival benefit. On May 14th, 2013, Angelina Jolie shared the news of her bilateral risk-reducing mastectomy (BRRM), on the basis of her BRCA1 pathogenic variant status. We evaluated the impact of this news on rates of CRRM in women with increased risk for developing breast cancer after being diagnosed with unilateral breast cancer. The prospective cohort study included all women with at least a moderate lifetime risk of developing breast cancer who attended our family history clinic (1987–2019) and were subsequently diagnosed with unilateral breast cancer. Rates of CRRM were then compared between patients diagnosed with breast cancer before and after Angelina Jolie’s announcement (pre- vs. post-AJ). Of 386 breast cancer patients, with a mean age at diagnosis of 48 ± 8 years, 268 (69.4%) were diagnosed in the pre-AJ period, and 118 (30.6%) in the post-AJ period. Of these, 123 (31.9%) underwent CRRM, a median 42 (interquartile range: 11–54) days after the index cancer surgery. Rates of CRRM doubled following AJ’s news, from 23.9% pre-AJ to 50.0% post AJ (p < 0.001). Rates of CRRM were found to decrease with increasing age at breast cancer (p < 0.001) and tumour TNM stage (p = 0.040), and to increase with the estimated lifetime risk of breast cancer (p < 0.001) and tumour grade (p = 0.015) on univariable analysis. After adjusting for these factors, the step-change increase in CRRM rates post-AJ remained significant (odds ratio: 9.61, p < 0.001). The AJ effect appears to have been associated with higher rates of CRRM amongst breast cancer patients with increased cancer risk. CRRM rates were highest amongst younger women and those with the highest lifetime risk profile. Clinicians need to be aware of how media news can impact on the delivery of cancer related services. Communicating objective assessment of risk is important when counselling women on the merits of risk-reducing surgery