Bisphenol A binds to Ras proteins and competes with guanine nucleotide exchange: implications for GTPase-selective antagonists.

We show for the first time that bisphenol A (10) has the capacity to interact directly with K-Ras and that Rheb weakly binds to bisphenol A (10) and 4,4'-biphenol derivatives. We have characterized these interactions at atomic resolution suggesting that these compounds sterically interfere with the Sos-mediated nucleotide exchange in H- and K-Ras. We show that 4,4'-biphenol (5) selectively inhibits Rheb signaling and induces cell death suggesting that this compound might be a novel candidate for treatment of tuberous sclerosis-mediated tumor growth. Our results propose a new mode of action for bisphenol A (10) that advocates a reduced exposure to this compound in our environment. Our data may lay the foundation for the future design of GTPase-selective antagonists with higher affinity to benefit of the treatment of cancer because K-Ras inhibition is regarded to be a promising strategy with a potential therapeutic window for targeting Sos in Ras-driven tumors.

MR-pro-atrial natriuretic peptide (MR-proANP) predicts short- and long-term outcomes in respiratory tract infections: a prospective validation study.

BACKGROUND: Previous research found precursor levels of the atrial natriuretic peptide (MR-proANP) to be promising prognostic markers. This study aims to validate these findings and describe patterns of MR-proANP in a large cohort of patients with lower respiratory tract infections. METHODS: We conducted a multicenter prospective cohort study, and measured MR-proANP in patients with lower respiratory tract infections on admission, and days 3, 5 and 7. The prognostic value of MR-proANP for predicting 30-day and 180-day mortalities was evaluated. We stratified MR-proANP levels a priori into quartiles, and compared it with severity of illness using the pneumonia severity index. RESULTS: A total of 1359 patients, including 925 with community-acquired pneumonia, were enrolled. The mortality risk at days 30 and 180 significantly increased with increasing MR-proANP quartiles (<84 pmol/L, 84-158 pmol/L, >158-311 pmol/L, and >311 pmol/L). This was true for low-risk, as well as high-risk subjects (pneumonia severity index classes I-III and IV-V). In Kaplan-Meier survival curves, MR-proANP quartiles significantly separated survivors from non-survivors in the overall cohort (p log-rank<0.001), and in low-risk (p log-rank<0.03) and high-risk (p log-rank=0.007) pneumonia severity index patients at day 30. In multivariate logistic regression analysis, MR-proANP was an independent risk factor for 30-day and 180-day mortalities (odds ratio per unit increase of log transformation MR-proANP level: 5.58, 95%CI 1.97-15.82 and 5.08, 95%CI 2.44-10.60). CONCLUSION: This study confirms the high prognostic performance of MR-proANP for short- and long-term mortality, particularly its high negative predictive value, in lower respiratory tract infections and community-acquired pneumonia, thereby complementing clinical risk assessment with the pneumonia severity index.

Ras homolog enriched in brain (Rheb) enhances apoptotic signaling.

Rheb is a homolog of Ras GTPase that regulates cell growth, proliferation, and regeneration via mammalian target of rapamycin (mTOR). Because of the well established potential of activated Ras to promote survival, we sought to investigate the ability of Rheb signaling to phenocopy Ras. We found that overexpression of lipid-anchored Rheb enhanced the apoptotic effects induced by UV light, TNFα, or tunicamycin in an mTOR complex 1 (mTORC1)-dependent manner. Knocking down endogenous Rheb or applying rapamycin led to partial protection, identifying Rheb as a mediator of cell death. Ras and c-Raf kinase opposed the apoptotic effects induced by UV light or TNFα but did not prevent Rheb-mediated apoptosis. To gain structural insight into the signaling mechanisms, we determined the structure of Rheb-GDP by NMR. The complex adopts the typical canonical fold of RasGTPases and displays the characteristic GDP-dependent picosecond to nanosecond backbone dynamics of the switch I and switch II regions. NMR revealed Ras effector-like binding of activated Rheb to the c-Raf-Ras-binding domain (RBD), but the affinity was 1000-fold lower than the Ras/RBD interaction, suggesting a lack of functional interaction. shRNA-mediated knockdown of apoptosis signal-regulating kinase 1 (ASK-1) strongly reduced UV or TNFα-induced apoptosis and suppressed enhancement by Rheb overexpression. In conclusion, Rheb-mTOR activation not only promotes normal cell growth but also enhances apoptosis in response to diverse toxic stimuli via an ASK-1-mediated mechanism. Pharmacological regulation of the Rheb/mTORC1 pathway using rapamycin should take the presence of cellular stress into consideration, as this may have clinical implications.