Serum starvation induces BACE1 processing and secretion

Background: β-secretase (BACE1) is a type 1 transmembrane protein implicated in Alzheimer’s Disease (AD) pathogenesis. Cleavage of Amyloid Precursor Protein (APP), initiated by BACE1 and followed by γ-secretase, leads to the formation of toxic Aβ peptides. Increased levels of BACE1 have been detected in the CSF of AD patients compared to age-matched healthy controls indicating that neurodegenerative conditions induce shedding of BACE1. Method: Detection of BACE1 secretion in BACE1 overexpressing cells or ADAM10/ADAM17 knockout fibroblasts cultured under serum deprivation conditions, using western blot analysis. Results: We found that serum deprivation of U251 neuroblastoma or HEK293T cells overexpressing BACE1 stimulated secretion of BACE1. Using ADAM10/ADAM17 knockout fibroblasts and inhibitors of both ADAM10 and ADAM17, we obtained data indicating that these proteases are involved in serum-starvation induced shedding of BACE1. This is unexpected since BACE1 is localized mainly in lipid rafts while ADAM10 is localized mainly in nonlipid raft domains. We hypothesized that serum deprivation results in alterations in the lipid composition of the membrane which can alter the localization of ADAM10 and BACE1. In support, we obtained results indicating that extraction of membrane cholesterol following incubation with methyl β cyclodextrin potentiated the effect of serum deprivation. Secreted BACE1 was also found to be enzymatically active towards immunoprecipiated full length APP. Conclusion: Serum starvation induces ADAM10-mediated BACE1 secretion. © 2017 Bentham Science Publishers

An integrated bacterial system for the discovery of chemical rescuers of disease-associated protein misfolding

Protein misfolding and aggregation are common pathological features of several human diseases, including Alzheimer's disease and type 2 diabetes. Here, we report an integrated and generalizable bacterial system for the facile discovery of chemical rescuers of disease-associated protein misfolding. In this system, large combinatorial libraries of macrocyclic molecules are biosynthesized in Escherichia coli cells and simultaneously screened for their ability to rescue pathogenic protein misfolding and aggregation using a flow cytometric assay. We demonstrate the effectiveness of this approach by identifying drug-like, head-to-tail cyclic peptides that modulate the aggregation of the Alzheimer's disease-associated amyloid β peptide. Biochemical, biophysical and biological assays using isolated amyloid β peptide, primary neurons and various established Alzheimer's disease nematode models showed that the selected macrocycles potently inhibit the formation of neurotoxic amyloid β peptide aggregates. We also applied the system to the identification of misfolding rescuers of mutant Cu/Zn superoxide dismutase-an enzyme linked with inherited forms of amyotrophic lateral sclerosis. Overall, the system enables the identification of molecules with therapeutic potential for rescuing the misfolding of disease-associated polypeptides. © 2017 The Author(s)

Publisher Correction: An integrated bacterial system for the discovery of chemical rescuers of disease-associated protein misfolding

In the version of this Article originally published, in Fig. 1c–e, on the x axes, the lines labelled ‘Aβ42’ and ‘Aβ42(F19S;L34P)’ grouped the data incorrectly; the line labelled Aβ42 should have grouped the data for Random 1–2 and Clones 1–10, and the line labelled Aβ42(F19S;L34P) should have only grouped the data for Random 1–2 on the right end of the plots and blots. These figures have now been corrected in all versions of the Article. © 2017 The Author(s

Prevalence of BRCA1 mutations among 403 women with triple-negative breast cancer: Implications for genetic screening selection criteria: A Hellenic Cooperative Oncology Group Study

In spite the close association of the triple-negative breast cancer immunophenotype with hereditary breast cancers and the BRCA1 pathway, there is a lack of population studies that determine the frequency of BRCA1 mutations among triple-negative breast cancer patients. To address this, we have screened a large sample of 403 women diagnosed with triple-negative invasive breast cancer, independently of their age or family history, for germline BRCA1 mutations. Median age at diagnosis was 50 years (range 20-83). The overall prevalence of triple-negative cases among the initial patient group with invasive breast cancer was 8 %. BRCA1 was screened by direct DNA sequencing in all patients, including all exons where a mutation was previously found in the Greek population (exons 5, 11, 12, 16, 20, 21, 22, 23, 24-77 % of the BRCA1 coding region), including diagnostic PCRs to detect the three Greek founder large genomic rearrangements. Sixty-five deleterious BRCA1 mutations were identified among the 403 triple-negative breast cancer patients (16 %). Median age of onset for mutation carriers was 39 years. Among a total of 106 women with early-onset triple-negative breast cancer (<40 years), 38 (36 %) had a BRCA1 mutation, while 27 % of women with triple-negative breast cancer diagnosed before 50 years (56/208) had a BRCA1 mutation. A mutation was found in 48 % (50/105) of the triple-negative breast cancer patients with family history of breast or ovarian cancer. It is noteworthy, however, that of the 65 carriers, 15 (23 %) had no reported family history of related cancers. All but one of the carriers had grade III tumors (98 %). These results indicate that women with early-onset triple-negative breast cancer, and ideally all triple-negative breast cancer patients, are candidates for BRCA1 genetic testing even in the absence of a family history of breast or ovarian cancer. © 2012 Springer Science+Business Media, LLC

A Nonsynonymous Polymorphism in IRS1 Modifies Risk of Developing Breast and Ovarian Cancers in BRCA1 and Ovarian Cancer in BRCA2 Mutation Carriers

Background: We previously reported significant associations between genetic variants in insulin receptor substrate 1 (IRS1) and breast cancer risk in women carrying BRCA1 mutations. The objectives of this study were to investigate whether the IRS1 variants modified ovarian cancer risk and were associated with breast cancer risk in a larger cohort of BRCA1 and BRCA2 mutation carriers. Methods: IRS1 rs1801123, rs1330645, and rs1801278 were genotyped in samples from 36 centers in the Consortium of Investigators of Modifiers of BRCA1/2 (CIMBA). Data were analyzed by a retrospective cohort approach modeling the associations with breast and ovarian cancer risks simultaneously. Analyses were stratified by BRCA1 and BRCA2 status and mutation class in BRCA1 carriers. Results: Rs1801278 (Gly972Arg) was associated with ovarian cancer risk for both BRCA1 (HR, 1.43; 95% confidence interval (CI), 1.06–1.92; P = 0.019) and BRCA2 mutation carriers (HR, 2.21; 95% CI, 1.39–3.52, P = 0.0008). For BRCA1 mutation carriers, the breast cancer risk was higher in carriers with class II mutations than class I mutations (class II HR, 1.86; 95% CI, 1.28–2.70; class I HR, 0.86; 95%CI, 0.69–1.09; Pdifference, 0.0006). Rs13306465 was associated with ovarian cancer risk in BRCA1 class II mutation carriers (HR, 2.42; P = 0.03). Conclusion: The IRS1 Gly972Arg single-nucleotide polymorphism, which affects insulin-like growth factor and insulin signaling, modifies ovarian cancer risk in BRCA1 and BRCA2 mutation carriers and breast cancer risk in BRCA1 class II mutation carriers. Impact: These findings may prove useful for risk prediction for breast and ovarian cancers in BRCA1 and BRCA2 mutation carriers. Cancer Epidemiol Biomarkers Prev; 21(8); 1362–70. ©2012 AACR