Molecular stripping underpins derepression of a toxin-antitoxin system

Transcription factors control gene expression; among these, transcriptional repressors must liberate the promoter for derepression to occur. Toxin-antitoxin (TA) modules are bacterial elements that autoregulate their transcription by binding the promoter in a T:A ratio-dependent manner, known as conditional cooperativity. The molecular basis of how excess toxin triggers derepression has remained elusive, largely because monitoring the rearrangement of promoter-repressor complexes, which underpin derepression, is challenging. Here, we dissect the autoregulation of the Salmonella enterica tacAT3 module. Using a combination of assays targeting DNA binding and promoter activity, as well as structural characterization, we determine the essential TA and DNA elements required to control transcription, and we reconstitute a repression-to-derepression path. We demonstrate that excess toxin triggers molecular stripping of the repressor complex off the DNA through multiple allosteric changes causing DNA distortion and ultimately leading to derepression. Thus, our work provides important insight into the mechanisms underlying conditional cooperativity.

The vulnerable versatility of Salmonella antibiotic persisters during infection

Tolerance and persistence are superficially similar phenomena by which bacteria survive bactericidal antibiotics. It is assumed that the same physiology underlies survival of individual tolerant and persistent bacteria. However, by comparing tolerance and persistence during Salmonella Typhimurium infection, we reveal that these two phenomena are underpinned by different bacterial physiologies. Multidrug-tolerant mutant Salmonella enter a near-dormant state protected from immune-mediated genotoxic damages. However, the numerous tolerant cells, optimized for survival, lack the capabilities necessary to initiate infection relapse following antibiotic withdrawal. In contrast, persisters retain an active state. This leaves them vulnerable to accumulation of macrophage-induced dsDNA breaks but concurrently confers the versatility to initiate infection relapse if protected by RecA-mediated DNA repair. Accordingly, recurrent, invasive, non-typhoidal Salmonella clinical isolates display hallmarks of persistence rather than tolerance during antibiotic treatment. Our study highlights the complex trade-off that antibiotic-recalcitrant Salmonella balance to act as a reservoir for infection relapse.

Alternative splicing of the Wnt trafficking protein, Wntless and its effects on protein-protein interactions

Background

Wntless (Wls) is a protein that regulates secretion of Wnt signaling molecules from Wnt-producing cells. Wnt signaling is known to be critical for several developmental and homeostatic processes. However, Wnt-independent functions of Wls are now being elucidated. Primates express an alternative splice variant of Wls (here termed WlsX). WlsX contains an alternatively spliced COOH-terminus, and does not appear to be able to sustain significant levels of WNT secretion because of its inability to undergo retrograde trafficking to the endoplasmic reticulum. The functional significance for this alternatively spliced form of Wls has not yet been elucidated. We previously identified a cohort of Wls interacting proteins using a combination of yeast 2-hybrid and candidate gene approaches.

Results

In the present study, we analyzed the interaction of WlsX with previously identified Wls interactors, and additionally screened for novel protein interactors of WlsX utilizing a membrane yeast two hybrid screen. Three novel Wls interactors, Glycoprotein M6A (GPM6A), Alkylglycerol Monooxygenase (AGMO), and ORAI1 were identified. Each of these novel WlsX interactors, as well as all other Wls interacting proteins identified previously, with the exception of the mu-opioid receptor, were found to interact with both Wls and WlsX splice forms. We show that WlsX can form homodimers, but that WlsX may not interact with Wls.

Conclusions

WlsX has the ability to form homodimers and to interact with most known Wls interacting proteins. Taken together, our results suggest that Wls and WlsX may have overlapping, but distinct functions, including sensitivity to opioid drugs. While studies have focused on the ability of Wls interacting proteins to affect Wnt secretion, future efforts will explore the reciprocal regulation of these proteins by Wls, possibly via Wnt-independent mechanisms.

Contralateral prophylactic mastectomy in affected carriers of deleterious BRCA1 or BRCA2 mutations: Does timing of genetic testing matter?

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Introduction: Prophylactic mastectomy (PM) reduces breast cancer risk by >90% in women who are carriers of deleterious BRCA1 or BRCA2 mutations. Genetic testing prior to breast cancer surgery has been reported to affect PM decision in high-risk patients. The ideal timing of genetic testing as well as the clinical characteristics of affected mutation carriers electing PM remain unclear. This is a pilot study to identify significant clinical characteristics associated with affected carriers who had undergone PM. Methods: Retrospective chart review was performed on 103 breast cancer affected BRCA1 or BRCA2 mutation carriers that were seen at our high risk clinic who had undergone genetic testing between 1995 and 2005. Clinical characteristic, initial surgery treatment modalities, and dates of genetic testing and prophylactic mastectomy were collected and analyzed using the chi-square or Fisher exact tests. Results: Of the 103 affected mutation carriers, 30 (29%) underwent prophylactic mastectomy (PM) where as 73 (71%) did not (no PM). Ethnicity, age of diagnosis, tumor size, nodal status, family history and initial breast cancer surgery types (BCT vs. mastectomy) were not significantly different between the two groups. Of the 30 women who underwent PM, 19 (63%) vs. 9 (30%) underwent PM before and after their genetic testing respectively. Of the 19 women who had PM before their genetic testing, 4 (21%) had BCT as initial treatment whereas 15 (78.9%) had mastectomy as initial treatment and 9 of 15 (60%) had synchronous contralateral prophylactic mastectomy. For the 9 women who had PM after their genetic testing, 5 (56%) had BCT vs. 4 (44%) had mastectomy as their initial surgical treatment (p < 0.001). Conclusion: In this study, we found a significant correlation between the initial breast cancer surgical modality of mastectomy with women undergoing prophylactic mastectomy. The impact of family history of breast cancer does not appear to be significant. Physician recommendations or patient preference are unknown. Our data suggest that high risk women who elect mastectomy as their initial surgical management to treat their breast cancer are more likely to undergo prophylactic mastectomy regardless of knowledge of their mutation status.

No significant financial relationships to disclose.