Deletion of the β2-adrenergic receptor prevents the development of cardiomyopathy in mice

Beta adrenergic receptor (β-AR) subtypes act through diverse signaling cascades to modulate cardiac function and remodeling. Previous in vitro studies suggest that β1-AR signaling is cardiotoxic whereas β2-AR signaling is cardioprotective, and may be the case during ischemia/reperfusion in vivo. The objective of this study was to assess whether β2-ARs also play a cardioprotective role in the pathogenesis of non-ischemic forms of cardiomyopathy. To dissect the role of β1 vs β2-ARs in modulating MLP (Muscle LIM Protein) cardiomyopathy, we crossbred MLP −/− with β1 −/− or β2 −/− mice. Deletion of the β2-AR improved survival, cardiac function, exercise capacity and myocyte shortening; by contrast haploinsufficency of the β1-AR reduced survival. Pathologic changes in Ca^2 + handling were reversed in the absence of β2-ARs: peak Ca^2 + and SR Ca^2 + were decreased in MLP −/− and β1 +/−/MLP −/− but restored in β2 −/− MLP −/−. These changes were associated with reversal of alterations in troponin I and phospholamban phosphorylation. Gi inhibition increased peak and baseline Ca^2 +, recapitulating changes observed in the β2 −/−/MLP −/−. The L-type Ca^2 + blocker verapamil significantly decreased cardiac function in β2 −/− MLP −/− vs WT. We next tested if the protective effects of β2-AR ablation were unique to the MLP model using TAC-induced heart failure. Similar to MLP, β2 −/− mice demonstrated delayed progression of heart failure with restoration of myocyte shortening and peak Ca^2 + and Ca^2 + release. Deletion of β2-ARs prevents the development of MLP −/− cardiomyopathy via positive modulation of Ca^2 + due to removal of inhibitory Gi signaling and increased phosphorylation of troponin I and phospholamban. Similar effects were seen after TAC. Unlike previous models where β2-ARs were found to be cardioprotective, in these two models, β2-AR signaling appears to be deleterious, potentially through negative regulation of Ca^2 + dynamics.     

Low-density lipoprotein receptor overexpression enhances the rate of brain-to-blood Aβ clearance in a mouse model of β-amyloidosis

The apolipoprotein E (APOE)-ε4 allele is the strongest genetic risk factor for late-onset, sporadic Alzheimer''s disease, likely increasing risk by altering amyloid-β (Aβ) accumulation. We recently demonstrated that the low-density lipoprotein receptor (LDLR) is a major apoE receptor in the brain that strongly regulates amyloid plaque deposition. In the current study, we sought to understand the mechanism by which LDLR regulates Aβ accumulation by altering Aβ clearance from brain interstitial fluid. We hypothesized that increasing LDLR levels enhances blood–brain barrier-mediated Aβ clearance, thus leading to reduced Aβ accumulation. Using the brain Aβ efflux index method, we found that blood–brain barrier-mediated clearance of exogenously administered Aβ is enhanced with LDLR overexpression. We next developed a method to directly assess the elimination of centrally derived, endogenous Aβ into the plasma of mice using an anti-Aβ antibody that prevents degradation of plasma Aβ, allowing its rate of appearance from the brain to be measured. Using this plasma Aβ accumulation technique, we found that LDLR overexpression enhances brain-to-blood Aβ transport. Together, our results suggest a unique mechanism by which LDLR regulates brain-to-blood Aβ clearance, which may serve as a useful therapeutic avenue in targeting Aβ clearance from the brain.     

Identification of βArrestin2 as a corepressor of androgen receptor signaling in prostate cancer

Androgen receptor (AR) signaling regulates the development and homeostasis of male reproductive organs, including the prostate. Deregulation of AR and AR coregulators, expression, or activity is involved in the initiation of prostate cancer and contributes to the transition of the disease to hormone-refractory stage. The ubiquitous βArrestin proteins are now recognized as bona fide adapters and signal transducers with target effectors found in both the cytosol and nucleus. Here, we provide evidence that βArrestin2 forms a complex with AR and acts as an AR corepressor in androgen-dependent prostate cancer cells. Accordingly, the forced overexpression of βArrestin2 diminishes, and knockdown of βArrestin2 expression with RNAi increases the androgen-induced prostate-specific antigen (PSA) gene expression. βArrestin2 serves as an adapter, bringing into close proximity the Mdm2 E3 ligase and AR, thereby promoting AR ubiquitylation and degradation. Human prostate tissues evidence an inverse relationship between the expression of βArrestin2 and AR activity: glands that express high levels of βArrestin2 exhibit low expression of PSA, and those glands that express low levels of βArrestin2 evidence elevated PSA levels. We conclude that βArrestin2 acts as a corepressor of AR by serving as a scaffold for Mdm2 leading to the AR ubiquitylation and degradation.     

Pin1 overexpression in colorectal cancer and its correlation with aberrant β-catenin expression

AIM: To investigate clinical significance of Pin1 and beta-catenin expression in colorectal cancers and to demonstrate the relationship of their expression. METHODS: The role of Pin1 and beta-catenin protein in colorectal tumorigenesis and their clinicopathologic significance were analyzed by immunohistochemistry, and the correlation between Pin1 and beta-catenin protein expressions was also studied in 124 patients with colorectal cancer who were surgically treated. RESULTS: Normal colonic epithelium either failed to express or showed focal and weak expression of Pin1 and beta-catenin. Overexpression of Pin1 and beta-catenin protein was found in 23 (18.54%) and 50 (40.3%) of 124 colorectal cancers, respectively. Overexpression of both proteins was not related to the lymph node metastasis, tumor stage and survival period after excision. Survival analysis results indicated that tumor stage was a valuable predictor of survival. Interestingly, a significant correlation was found between Pin1 and beta-catenin protein expression. CONCLUSION: Overexpression of Pin1 and beta-catenin may be closely related with the development and/or progression of colorectal carcinoma and further supports that Pin1 overexpression might contribute to the upregulation of beta-catenin.     

Pin1 overexpression in colorectal cancer and its correlation with aberrant β-catenin expression

AIM: To investigate clinical significance of Pin1 and β-catenin expression in colorectal cancers and to demonstrate the relationship of their expression. METHODS: The role of Pinl and β-catenin protein in colorectal tumorigenesis and their clinicopathologic significance were analyzed by immunohistochemistry, and the correlation between Pinl and β-catenin protein expressions was also studied in 124 patients with colorectal cancer who were surgically treated. RESULTS: Normal colonic epithelium either failed to express or showed focal and weak expression of Pinl and β-catenin. Overexpression of Pin1 and β-catenin protein was found in 23 (18.54%) and 50 (40.3%) of 124 colorectal cancers, respectively. Overexpression of both proteins was not related to the lymph node metastasis, tumor stage and survival period after excision. Survival analysis results indicated that tumor stage was a valuable predictor of survival. Interestingly, a significant correlation was found between Pin1 and β-catenin protein expression. CONCLUSION: Overexpression of Pin1 and β-catenin may be closely related with the development and/or progression of colorectal carcinoma and further supports that Pin1 overexpression might contribute to the upregulation of β-catenin.     

Age-associated alternations in cardiac β-adrenergic receptor signaling

During aging, cardiac contractile response to β-AR stimulation is decreased in humans and animal models. Recent studies demonstrate that the positive inotropic effects of both β1-AR and β2-AR stimulation are significantly decreased with aging.This is accompanied by decreases in both β-AR subtype densities and a reduction in membrane adenylyl cyclase activity. However,neither G protein-coupled receptor kinases (GRKs) nor inhibitory G proteins (Gi) appears to contribute to the age-associated reduction in the β-AR modulation of contraction. Thus, while both aging and chronic heart failure exhibit a diminution in cardiac β-AR responsiveness, only heart failure exhibits increased GRK-mediated desensitization ofβ-Ars and an upregulation of Gi proteins.     

Basic residues in the T-cell receptor ζ cytoplasmic domain mediate membrane association and modulate signaling

The T-cell receptor (TCR) consists of a TCRαβ heterodimer, a TCRζ homodimer, and CD3γε and CD3δε heterodimers. The precise mechanism of T-cell triggering following TCR ligand engagement remains elusive. Previous studies reported that the cytoplasmic tail of CD3ε binds to the plasma membrane through a basic residue-rich stretch (BRS) and proposed that dissociation from the membrane is required for phosphorylation thereof. In this report we show that BRS motifs within the cytoplasmic tail of TCRζ mediate association with the plasma membrane and that TCR engagement results in TCRζ dissociation from the membrane. This dissociation requires phosphorylation of the TCRζ immunoreceptor tyrosine-based activation motifs by lymphocyte cell-specificprotein tyrosine kinase (Lck) but not ζ-chain-associated protein kinase 70 binding. Mutations of the TCRζ BRS motifs that disrupt this membrane association attenuate proximal and distal responses induced by TCR engagement. These mutations appear to alter the localization of TCRζ with respect to Lck as well as the mobility of the TCR complex. This study reveals that tyrosine phosphorylation of the TCRζ cytoplasmic domain regulates its association with the plasma membrane and highlights the functional importance of TCRζ BRS motifs.     

Expression of β-catenin in hepatocellular carcinoma

AIM: The p-catenin has been recognized as a critical member of the Wnt signaling pathway and plays an important role in the generation/differentiation of many tissues. Inappropriate activation of this pathway has been implicated in carcinogenesis. The mechanism underlying the development as well as its prognosis of hepatocellular carcinoma (HCC) has remained unclear. The purpose of this study is to analyze the expression of p-catenin in HCC in relation to histological grades and viral hepatitis backgrounds. METHODS: Thirty-two sections were selected at random from autopsy and surgical cases of HCC. Immuohistologically, the location and positivity of p-catenin expression in HCC was examined. RESULTS: Normal hepatocytes did not express p-catenin. In 78% of HCC p-catenin was expressed at the membrane of the cells, with or without cytoplasmic and/or nuclear expression. The tumor cells with well- and moderately-differentiated grades expressed frequently at the membrane and cytoplasm compared with poorly-differentiated type. Nuclear expression of p-catenin was prone to occur in the tumor cells of poorly-differentiated grade. There were 15% of hepatitis C virus (HCV) backgrounds with nuclear expression. In contrast, there was 38% with nuclear expression in hepatitis B virus (HBV) backgrounds. In nonB-nonC hepatitis, no case expressed nuclear p-catenin. CONCLUSION: The β-catenin expression in HCC cells was heterogenous among types of hepatitis viral infection. Wnt signaling pathway might be deeply involved in less-differentiated HCC and HBV background.