Transglutaminase 2: A multi-tasking protein in the complex circuitry of inflammation and cancer

Metastasis of primary tumors to distant sites and their inherent or acquired resistance to currently available therapies pose major clinical challenge to the successful treatment of cancer. The identification of tumor-coded genes and how they contribute to the progression of cancer is required to improve patient outcomes. Recently, cells that have undergone the epithelial-mesenchymal transition (EMT), which share characteristics with cancer stem cells (CSC) have been implicated to play a role in drug resistance and metastasis of several types of cancer. In this review, we discuss the relationship among transglutaminase 2 (TG2), the EMT, and CSCs in inflammation and cancer. TG2 is a structurally and functionally complex protein implicated in such diverse processes as tissue fibrosis, wound healing, apoptosis, neurodegenerative disorders, celiac disease, atherosclerosis and cancer. Depending on the cellular context, TG2 can either promote or inhibit cell death. Increased expression of TG2 in several types of cancer cells has been associated with increased cell invasiveness, cell survival and decreased survival of patients with cancer. Down-regulation of TG2 by small interfering RNA (siRNA) or its inhibition by small molecule inhibitors has been shown to significantly enhances the therapeutic efficacy of anticancer drugs and inhibit metastatic spread. In addition, TG2-regulated pathways are involved in promoting or protecting normal and tumor cells from death-induced signaling. We discuss the contribution of TG2-regulated pathways to the development of drug resistance and progression to metastatic disease and the therapeutic potential of TG2 for treating advanced-stage cancer.     

P2X7 receptor in cardiovascular disease: The heart side

The P2X7 receptor is a ligand‐gated purinergic receptor activated by extracellular ATP. The receptor is highly expressed in immune cells and in the brain, and, upon activation, the P2X7 receptor allows a cation flux, leading to the distinct activation of intracellular signalling pathways as the secretion of pro‐inflammatory cytokines, and modulation of cell survival. Through these molecular mechanisms, P2X7 is known to play important roles in physiology and pathophysiology of a wide spectrum of diseases, including cancer, inflammatory diseases, neurological, respiratory and more recently cardiovascular diseases. Recent studies demonstrated that the P2X7 could modulate the assembly of the NLRP3 inflammasome, leading to the secretion of pro‐inflammatory factors and worsen the cardiac disease phenotypes. This review discusses the critical molecular function of P2X7 in the modulation of the onset, progression and resolution of cardiovascular diseases and analyses the putative future use of P2X7‐based therapies that modulate the IL‐1β secretion arm and direct P2X7 antagonists.     

The phosphatidylinositol 3-kinase/Akt pathway negatively regulates Nod2-mediated NF-kappaB pathway

Nucleotide-binding oligomerization domain containing proteins (Nods) are intracellular pattern recognition receptors (PRRs) that recognize conserved moieties of bacterial peptidoglycan and activate downstream signaling pathways, including NF-kappaB pathway. Here, we show that Nod2 agonist muramyldipeptide (MDP) induces Akt phosphorylation in time and dose-dependent manner. The pharmacological inhibitor of phosphatidylinositol 3-kinase (PI3K) (wortmannin) and dominant-negative forms of p85 (the regulatory subunit of PI3K) or Akt enhance, while constitutive active forms of p110 (the catalytic subunit of PI3K) or Akt inhibit, NF-kappaB activation and the target gene interleukin (IL)-8 induced by MDP. In addition, the pharmacological inhibitors of PI3K (wortmannin and LY294002) enhance phosphorylation of NF-kappaB p65 on Ser529 and Ser536 residues, which result in enhanced p65 transactivation activity. Furthermore, we show that the inhibition of PI3K by the pharmacological inhibitors prevent the inactivation of glycogen synthase kinase (GSK)-3beta, suggesting that the negative regulation of PI3K/Akt on MDP-induced NF-kappaB activation is at least in part mediated through inactivation of GSK-3beta. Taken together, our results demonstrate that PI3K/Akt pathway is activated by Nod2 agonist MDP and negatively regulates NF-kappaB pathway downstream of Nod2 activation. Our results suggest that PI3K/Akt pathway may involve in the resolution of inflammatory responses induced by Nod2 activation.     

Tau蛋白在Alzheimers病中的作用研究进展

Tau蛋白是一种在神经系统广泛表达的微管相关蛋白 ,起到促进微管形成和稳定微管结构的作用。Tau蛋白过度磷酸化导致Tau蛋白自我聚集成双螺旋纤维细丝 ,进而产生神经纤维缠结 ,该病理改变与阿尔采末病密切相关。围绕tau蛋白的结构、功能 ,在AD病中的病理学意义 ,其与 β 淀粉样肽之间可能存在的相互关系和tau蛋白在诊断和寻找新的AD治疗途径中的应用前景作一综述。     

The long-term efficacy and safety of immunosuppressive therapy on the progression of IgA nephropathy: a meta-analysis of controlled clinical trials with more than 5-year follow-up

Objective: To evaluate the long-term efficacy of immunosuppressive therapy on Immunoglobulin A nephropathy (IgAN).

Methods: Trials with at least 5-year follow-up investigating immunosuppressive therapy were selected.

Main outcome measures: Primary outcome was end-stage renal disease (ESRD). Secondary outcome was deterioration in renal function defined as doubled serum creatinine or 50% reduction of eGFR.

Results: Seven studies were enrolled. Immunosuppression lowered the risk for ESRD risk ratio (RR = 0.30, 95% CI 0.19 – 0.48, p < 0.00001) and deterioration in renal function (RR = 0.19, 95% CI 0.07 – 0.54, p = 0.002). As for pooled RRs of ESRD, there were four studies with < 7-year follow-up, three followed for > 7 years, four adopted corticosteroids, two used corticosteroids plus other immunosuppressive agents, four were from Asia, and three from Europe. Pooled RRs were 0.32 (95% CI, 0.18 – 0.58, p = 0.0001), 0.28 (95% CI, 0.13 – 0.59, p = 0.0009), 0.34 (95% CI, 0.17 – 0.67, p = 0.002), 0.29 (95% CI, 0.15 – 0.58, p = 0.0005), 0.37 (95% CI, 0.20 – 0.68, p = 0.001) and 0.23 (95% CI, 0.11 – 0.47, p < 0.0001), respectively. Immunosuppression was associated with an increased risk for adverse events (RR = 2.13, 95% CI 1.17 – 3.86, p = 0.01).

Conclusions: Immunosuppressive therapy for IgAN might reduce long-term risk of ESRD and deterioration in renal function but increase risk of adverse events, and the efficacy on patients from Europe and Asia might be similar. Addition of other immunosuppressive agents did not provide additional benefit.     

Interaction of the D2short dopamine receptor with G proteins: analysis of receptor/G protein selectivity

The human D(2short) (D(2S)) dopamine receptor has been expressed together with the G proteins Gi2 and Go in insect cells using the baculovirus system. Levels of receptor were determined using [3H]spiperone binding. Levels of G protein heterotrimer were determined using quantitative Western blot and using [35S]GTPgammaS saturation binding experiments. Levels of the receptor and G protein and the receptor/G protein ratio were similar in the two preparations. Stimulation of [35S]GTPgammaS binding by a range of agonists occurred with higher relative efficacy and in some cases higher potency in the preparation expressing Go, indicating that interaction of the D(2S) receptor is more efficient with this G protein. The effects of various G protein-selective agents on 10,11-dihydroxy-N-n-propylnorapomorphine ([3H]NPA) binding were used to examine the receptor/G protein complex in the two preparations. Suramin inhibited [3H]NPA binding with slightly higher potency in the Gi2 preparation, whereas GppNHp inhibited [3H]NPA binding with greater potency ( approximately 6-fold) in the Go preparation. This may imply that the G protein is more readily activated in the D(2S)/Go preparation. [3H]Spiperone binding occurred with an increased B(max) in the presence of suramin in the Go preparation but not in the Gi2 preparation, suggesting a higher affinity interaction between the free receptor and this G protein. It is concluded that the higher efficiency activation of Go by the D(2S) receptor may be a function of higher affinity receptor/G protein interaction as well as a greater ability to activate the G protein.     

The NADPH oxidase cytosolic component p67phox is constitutively phosphorylated in human neutrophils: Regulation by a protein tyrosine kinase, MEK1/2 and phosphatases 1/2A

Neutrophils play a key role in host defense and inflammation through the production of superoxide anion and other reactive oxygen species (ROS) by the enzyme complex NADPH oxidase. The cytosolic NADPH oxidase component, p67phox, has been shown to be phosphorylated in human neutrophils but the pathways involved in this process are largely unknown. In this study, we show that p67phox is constitutively phosphorylated in resting human neutrophils and that neutrophil stimulation with PMA further enhanced this phosphorylation. Inhibition of the constitutively active serine/threonine phosphatases type 1 and type 2A (PP1/2A) by calyculin A resulted in the enhancement of p67phox phosphorylation. Constitutive and calyculin A-induced phosphorylation of p67phox was completely inhibited by the protein tyrosine kinase inhibitor genistein and partially inhibited by the MEK1/2 inhibitor PD98059, but was unaffected by GF109203X, wortmannin and SB203580, inhibitors of PKC, PI3K and p38MAP kinase, respectively. Two-dimensional phosphopeptide mapping revealed that constitutive and calyculin A-induced p67phox phosphorylation occurred on the same major sites. Interestingly, calyculin A enhanced formyl-Met-Leu-Phe (fMLP)-induced superoxide production, while genistein inhibited this process. Taken together, these results suggest that (i) p67phox undergoes a continual cycle of phosphorylation/dephosphorylation in resting cells; (ii) p67phox phosphorylation is controlled by MEK1/2 and an upstream tyrosine kinase; (iii) PP1/2A directly or indirectly antagonize this process. Thus, these pathways could play a role in regulating ROS production by human neutrophils at inflammatory sites.     

The aging brain, a key target for the future: The protein kinase C involvement

The brain represents the primary centre for the regulation and control of all our body activities, receiving and interpreting sensory impulses and transmitting information to the periphery. Most importantly, it is also the seat of consciousness, thought, emotion and especially memory, being in fact able to encode, store and recall any information. Memory is really what makes possible so many of our complex cognitive functions, including communication and learning, and surely without memory, life would lose all of its glamour and purpose. Age-associated mental impairment can range in severity from forgetfulness at the border with pathology to dementia, such as in Alzheimer's disease. In recent years, one of the most relevant observations of research on brain aging relates to data indicating that age-related cognitive decline is not only due to neuronal loss, as previously thought; instead, scientists now believe that age-associated functional changes have more to do with the dysfunctions occurring over time. Within this context a prominent role is certainly played by signal transduction cascades which guarantee neuronal cell to elaborate coordinated responses to the multiple signals coming from the outside and to adapt itself to the environmental changes and requests. This review will focus the attention on protein kinase C pathway, with a particular interest on its activation process, and on the role of protein-lipid and protein-protein interactions to selectively localize the cellular responses. Furthermore, information is emerging and will be discussed on the possibility of mRNA stabilization through PKC activation. This review will also approach the issue on how alterations of these molecular cascades may have implications in physiological and pathological brain aging, such as Alzheimer's disease.     

The P2X7 receptor: a new therapeutic target in Alzheimer’s disease

Introduction: Alzheimer’s disease (AD) is a neurodegenerative illness with genetic risk as an etiological factor in a subset of cases. In AD with autosomal dominant inheritance, the extracellular β-amyloid (Aβ) aggregates and intracellular neurofibrillary tangles which consist of hyperphosphorylated tau, appear to be involved in the neuronal damage; however, other forms of AD may have a polygenetic causality. Microglial cells orchestrate pathophysiological events responsible for neuronal damage in AD. They surround Aβ aggregates and the stimulation of microglial P2X7 receptors (P2X7Rs) by high local concentrations of ATP which originates from damaged CNS cells, results in degeneration of nearby neurons.

Areas covered: We discuss the pathogenesis of Alzheimer’s disease, the role of P2X7 receptors and their potential as therapeutic targets. We also address the fundamental hurdles in the development of new therapeutic strategies for Alzheimer’s disease.

Expert opinion: There are many difficulties associated with the development of efficient pharmacological strategies for AD; the lack of good animal and cellular models for this illness is a key obstacle. None of the pharmacological strategies developed so far have led to an improvement of the treatment of AD. Hence, the consideration of blood-brain barrier-permeable P2X7R antagonists as possible therapeutic agents in AD is a must.