Distinct roles of estrogen receptors alpha and beta mediating acute vasodilation of epicardial coronary arteries.

This study investigated the contribution of estrogen receptors (ERs) alpha and beta for epicardial coronary artery function, vascular NO bioactivity, and superoxide (O(2)(-)) formation. Porcine coronary rings were suspended in organ chambers and precontracted with prostaglandin F(2alpha) to determine direct effects of the selective ER agonists 4,4',4''-(4-propyl-[(1)H]pyrazole-1,3,5-triyl)tris-phenol (PPT) or 2,3-bis(4-hydroxyphenyl)-propionitrile (DPN) or the nonselective ER agonist 17beta-estradiol. Indirect effects on contractility to U46619 and relaxation to bradykinin were assessed and effects on NO, nitrite, and O(2)(-) formation were measured in cultured cells. Within 5 minutes, selective ERalpha activation by PPT, but not 17beta-estradiol or the ERbeta agonist DPN, caused rapid, NO-dependent, and endothelium-dependent relaxation (49+/-5%; P<0.001 versus ethanol). PPT also caused sustained endothelium- and NO-independent vasodilation similar to 17beta-estradiol after 60 minutes (72+/-3%; P<0.001 versus ethanol). DPN induced endothelium-dependent NO-independent relaxation via endothelium-dependent hyperpolarization (40+/-4%; P<0.01 versus ethanol). 17beta-Estradiol and PPT, but not DPN, attenuated the responses to U46619 and bradykinin. All of the ER agonists increased NO and nitrite formation in vascular endothelial but not smooth muscle cells and attenuated vascular smooth muscle cell O(2)(-) formation (P<0.001). ERalpha activation had the most potent effects on both nitrite formation and inhibiting O(2)(-) (P<0.05). These data demonstrate novel and differential mechanisms by which ERalpha and ERbeta activation control coronary artery vasoreactivity in males and females and regulate vascular NO and O(2)(-) formation. The findings indicate that coronary vascular effects of sex hormones differ with regard to affinity to ERalpha and ERbeta, which will contribute to beneficial and adverse effects of hormone replacement therapy.

Posttranslational modifications of cardiac ryanodine receptors: Ca2+ signaling and EC-coupling

In cardiac muscle, a number of posttranslational protein modifications can alter the function of the Ca(2+) release channel of the sarcoplasmic reticulum (SR), also known as the ryanodine receptor (RyR). During every heartbeat RyRs are activated by the Ca(2+)-induced Ca(2+) release mechanism and contribute a large fraction of the Ca(2+) required for contraction. Some of the posttranslational modifications of the RyR are known to affect its gating and Ca(2+) sensitivity. Presently, research in a number of laboratories is focused on RyR phosphorylation, both by PKA and CaMKII, or on RyR modifications caused by reactive oxygen and nitrogen species (ROS/RNS). Both classes of posttranslational modifications are thought to play important roles in the physiological regulation of channel activity, but are also known to provoke abnormal alterations during various diseases. Only recently it was realized that several types of posttranslational modifications are tightly connected and form synergistic (or antagonistic) feed-back loops resulting in additive and potentially detrimental downstream effects. This review summarizes recent findings on such posttranslational modifications, attempts to bridge molecular with cellular findings, and opens a perspective for future work trying to understand the ramifications of crosstalk in these multiple signaling pathways. Clarifying these complex interactions will be important in the development of novel therapeutic approaches, since this may form the foundation for the implementation of multi-pronged treatment regimes in the future. This article is part of a Special Issue entitled: Cardiomyocyte Biology: Cardiac Pathways of Differentiation, Metabolism and Contraction.

Loss of TRAIL-receptors is a recurrent feature in pancreatic cancer and determines the prognosis of patients with no nodal metastasis after surgery

INTRODUCTION Agonistic antibodies targeting TRAIL-receptors 1 and 2 (TRAIL-R1 and TRAIL-R2) are being developed as a novel therapeutic approach in cancer therapy including pancreatic cancer. However, the cellular distribution of these receptors in primary pancreatic cancer samples has not been sufficiently investigated and no study has yet addressed the issue of their prognostic significance in this tumor entity. AIMS AND METHODS Applying tissue microarray (TMA) analysis, we performed an immunohistochemical assessment of TRAIL-receptors in surgical samples from 84 consecutive patients affected by pancreatic adenocarcinoma and in 26 additional selected specimens from patients with no lymph nodes metastasis at the time of surgery. The prognostic significance of membrane staining and staining intensity for TRAIL-receptors was evaluated. RESULTS The fraction of pancreatic cancer samples with positive membrane staining for TRAIL-R1 and TRAIL-R2 was lower than that of cells from surrounding non-tumor tissues (TRAIL-R1: p<0.001, TRAIL-R2: p = 0.006). In addition, subgroup analyses showed that loss of membrane staining for TRAIL-R2 was associated with poorer prognosis in patients without nodal metastases (multivariate Cox regression analysis, Hazard Ratio: 0.44 [95% confidence interval: 0.22-0.87]; p = 0.019). In contrast, analysis of decoy receptors TRAIL-R3 and -R4 in tumor samples showed an exclusively cytoplasmatic staining pattern and no prognostic relevance. CONCLUSION This is a first report on the prognostic significance of TRAIL-receptors expression in pancreatic cancer showing that TRAIL-R2 might represent a prognostic marker for patients with early stage disease. In addition, our data suggest that loss of membrane-bound TRAIL-receptors could represent a molecular mechanism for therapeutic failure upon administration of TRAIL-receptors-targeting antibodies in pancreatic cancer. This hypothesis should be evaluated in future clinical trials.

Early over-expression of GRP receptors in prostatic carcinogenesis

BACKGROUND The GRP receptor shows high over-expression in prostatic adenocarcinoma and high grade PIN, but low expression in normal prostate glands. This represents the molecular basis for GRP receptor imaging of prostate cancer with radioactive compounds. However, a focal, high density GRP receptor expression can be observed in hitherto uncharacterized prostate glands. METHODS GRP receptors were quantitatively measured with in vitro receptor autoradiography using ¹²⁵I-Tyr⁴ -bombesin in samples from 115 prostates. On successive tissue sections, ¹²⁵I-Tyr⁴ -bombesin autoradiography was compared with H&E staining and MIB-1 and 34βE12 immunohistochemistry. RESULTS On one hand, it was confirmed that GRP receptors were expressed in adenocarcinoma and high grade PIN in high density and high incidence (77% and 73%, respectively), but in normal prostate glands in low density and low frequency (18%). On the other hand, a novel and intriguing observation was the existence of focal non-invasive prostate glands with high GRP receptor density, characterized by low grade nuclear atypia and increased proliferation, compatible with lower grade PIN. There was a significant GRP receptor density gradient (P ≤ 0.005), increasing from normal prostate glands (mean relative optical density, ROD, of ¹²⁵I-Tyr⁴ -bombesin binding: 0.17) over atypical glands without increased MIB-1 labeling (0.28) and atypical glands with increased MIB-1 expression (0.44) to high grade PIN and adenocarcinoma (0.64 and 0.58, respectively). CONCLUSIONS GRP receptor over-expression may be a novel, specific marker of early prostatic neoplastic transformation, arising in low grade PIN, and progressively increasing during malignant progression. This should be considered when interpreting in vivo GRP receptor imaging in males.

Illuminating somatostatin analog action at neuroendocrine tumor receptors

Somatostatin analogs for the diagnosis and therapy of neuroendocrine tumors (NETs) have been used in clinical applications for more than two decades. Five somatostatin receptor subtypes have been identified and molecular mechanisms of somatostatin receptor signaling and regulation have been elucidated. These advances increased understanding of the biological role of each somatostatin receptor subtype, their distribution in NETs, as well as agonist-specific regulation of receptor signaling, internalization, and phosphorylation, particularly for the sst2 receptor subtype, which is the primary target of current somatostatin analog therapy for NETs. Various hypotheses exist to explain differences in patient responsiveness to somatostatin analog inhibition of tumor secretion and growth as well as differences in the development of tumor resistance to therapy. In addition, we now have a better understanding of the action of both first generation (octreotide, lanreotide, Octreoscan) and second generation (pasireotide) FDA-approved somatostatin analogs, including the biased agonistic character of some agonists. The increased understanding of somatostatin receptor pharmacology provides new opportunities to design more sophisticated assays to aid the future development of somatostatin analogs with increased efficacy.

P2X7 receptors mediate resistance to toxin-induced cell lysis

In the majority of cells, the integrity of the plasmalemma is recurrently compromised by mechanical or chemical stress. Serum complement or bacterial pore-forming toxins can perforate the plasma membrane provoking uncontrolled Ca(2+) influx, loss of cytoplasmic constituents and cell lysis. Plasmalemmal blebbing has previously been shown to protect cells against bacterial pore-forming toxins. The activation of the P2X7 receptor (P2X7R), an ATP-gated trimeric membrane cation channel, triggers Ca(2+) influx and induces blebbing. We have investigated the role of the P2X7R as a regulator of plasmalemmal protection after toxin-induced membrane perforation caused by bacterial streptolysin O (SLO). Our results show that the expression and activation of the P2X7R furnishes cells with an increased chance of surviving attacks by SLO. This protective effect can be demonstrated not only in human embryonic kidney 293 (HEK) cells transfected with the P2X7R, but also in human mast cells (HMC-1), which express the receptor endogenously. In addition, this effect is abolished by treatment with blebbistatin or A-438079, a selective P2X7R antagonist. Thus blebbing, which is elicited by the ATP-mediated, paracrine activation of the P2X7R, is part of a cellular non-immune defense mechanism. It pre-empts plasmalemmal damage and promotes cellular survival. This mechanism is of considerable importance for cells of the immune system which carry the P2X7R and which are specifically exposed to toxin attacks.