Lipotoxicity, ER Stress, and Cardiovascular Disease: Current Understanding and Future Directions.

The endoplasmic reticulum (ER) is a sub-cellular organelle that is responsible for the correct folding of proteins, lipid biosynthesis, calcium storage, and various post-translational modifications. In the disturbance of ER functioning, unfolded or misfolded proteins accumulate inside the ER lumen and initiate downstream signaling called unfolded protein response (UPR). The UPR signaling pathway is involved in lipolysis, triacylglycerol synthesis, lipogenesis, the mevalonate pathway, and low-density lipoprotein receptor recycling. ER stress also affects lipid metabolism by changing the levels of enzymes that are involved in the synthesis or modifications of lipids and causing lipotoxicity. Lipid metabolism and cardiac diseases are in close association as the deregulation of lipid metabolism leads to the development of various cardiovascular diseases (CVDs). Several studies have suggested that lipotoxicity is one of the important factors for cardiovascular disorders. In this review, we will discuss how ER stress affects lipid metabolism and their interplay in the development of cardiovascular disorders. Further, the current therapeutics available to target ER stress and lipid metabolism in various CVDs will be summarized.

Unfolded Protein Response Signaling in Liver Disorders: A 2023 Updated Review.

Endoplasmic reticulum (ER) is the site for synthesis and folding of secreted and transmembrane proteins. Disturbance in the functioning of ER leads to the accumulation of unfolded and misfolded proteins, which finally activate the unfolded protein response (UPR) signaling. The three branches of UPR-IRE1 (Inositol requiring enzyme 1), PERK (Protein kinase RNA-activated (PKR)-like ER kinase), and ATF6 (Activating transcription factor 6)-modulate the gene expression pattern through increased expression of chaperones and restore ER homeostasis by enhancing ER protein folding capacity. The liver is a central organ which performs a variety of functions which help in maintaining the overall well-being of our body. The liver plays many roles in cellular physiology, blood homeostasis, and detoxification, and is the main site at which protein synthesis occurs. Disturbance in ER homeostasis is triggered by calcium level imbalance, change in redox status, viral infection, and so on. ER dysfunction and subsequent UPR signaling participate in various hepatic disorders like metabolic (dysfunction) associated fatty liver disease, liver cancer, viral hepatitis, and cholestasis. The exact role of ER stress and UPR signaling in various liver diseases is not fully understood and needs further investigation. Targeting UPR signaling with drugs is the subject of intensive research for therapeutic use in liver diseases. The present review summarizes the role of UPR signaling in liver disorders and describes why UPR regulators are promising therapeutic targets.

Neuroepigenetics of ageing and neurodegeneration-associated dementia: An updated review.

Gene expression is tremendously altered in the brain during memory acquisition, recall, and forgetfulness. However, non-genetic factors, including environmental elements, epigenetic changes, and lifestyle, have grabbed significant attention in recent years regarding the etiology of neurodegenerative diseases (NDD) and age-associated dementia. Epigenetic modifications are essential in regulating gene expression in all living organisms in a DNA sequence-independent manner. The genes implicated in ageing and NDD-related memory disorders are epigenetically regulated by processes such as DNA methylation, histone acetylation as well as messenger RNA editing machinery. The physiological and optimal state of the epigenome, especially within the CNS of humans, plays an intricate role in helping us adjust to the changing environment, and alterations in it cause many brain disorders, but the mechanisms behind it still need to be well understood. When fully understood, these epigenetic landscapes could act as vital targets for pharmacogenetic rescue strategies for treating several diseases, including neurodegeneration- and age-induced dementia. Keeping this objective in mind, this updated review summarises the epigenetic changes associated with age and neurodegeneration-associated dementia.

Role of gut microbiota in tumorigenesis and antitumoral therapies: an updated review.

Gut microbiota plays a prominent role in regulation of host nutrientmetabolism, drug and xenobiotics metabolism, immunomodulation and defense against pathogens. It synthesizes numerous metabolites thatmaintain the homeostasis of host. Any disbalance in the normalmicrobiota of gut can lead to pathological conditions includinginflammation and tumorigenesis. In the past few decades, theimportance of gut microbiota and its implication in various diseases, including cancer has been a prime focus in the field of research. Itplays a dual role in tumorigenesis, where it can accelerate as wellas inhibit the process. Various evidences validate the effects of gutmicrobiota in development and progression of malignancies, wheremanipulation of gut microbiota by probiotics, prebiotics, dietarymodifications and faecal microbiota transfer play a significant role.In this review, we focus on the current understanding of theinterrelationship between gut microbiota, immune system and cancer,the mechanisms by which they play dual role in promotion andinhibition of tumorigenesis. We have also discussed the role ofcertain bacteria with probiotic characteristics which can be used tomodulate the outcome of the various anti-cancer therapies under theinfluence of the alteration in the composition of gut microbiota.Future research primarily focusing on the microbiota as a communitywhich affect and modulate the treatment for cancer would benoteworthy in the field of oncology. This necessitates acomprehensive knowledge of the roles of individual as well asconsortium of microbiota in relation to physiology and response ofthe host.

Striatin family proteins: The neglected scaffolds.

The Striatin family of proteins constitutes Striatin, SG2NA, and Zinedin. Members of this family of proteins act as a signaling scaffold due to the presence of multiple protein-protein interaction domains. At least two members of this family, namely Zinedin and SG2NA, have a proven role in cancer cell proliferation. SG2NA, the second member of this family, undergoes alternative splicing and gives rise to several isoforms which are differentially regulated in a tissue-dependent manner. SG2NA evolved earlier than the other two members of the family, and SG2NA undergoes not only alternative splicing but also other posttranscriptional gene regulation. Striatin also undergoes alternative splicing, and as a result, it gives rise to multiple isoforms. It has been shown that this family of proteins plays a significant role in estrogen signaling, neuroprotection, cancer as well as in cell cycle regulation. Members of the striatin family form a complex network of signaling hubs with different kinases and phosphatases, and other signaling proteins named STRIPAK. Here, in the present manuscript, we thoroughly reviewed the findings on striatin family members to elaborate on the overall structural and functional idea of this family of proteins. We also commented on the involvement of these proteins in STRIPAK complexes and their functional relevance.

The profile of expression of the scaffold protein SG2NA(s) differs between cancer types and its interactome in normal vis-a-vis breast tumor tissues suggests its wide roles in regulating multiple cellular pathways.

Striatin and SG2NA are scaffold proteins that form signaling complexes called STRIPAK. It has been associated with developmental abnormalities, cancer, and several other diseases. Our earlier studies have shown that SG2NA forms a complex with the cancer-associated protein DJ-1 and the signaling kinase Akt, promoting cancer cell survival. In the present study, we used bioinformatics analyses to confirm the existence of two isoforms of human SG2NA, i.e., 78 and 87 kDas. In addition, several smaller isoforms like 35 kDa were also seen in western blot analyses of human cell lysates. The expression of these isoforms varies between different cancer cell lines of human origin. Also, the protein levels do not corroborate with its transcript levels, suggesting a complex regulation of its expression. In breast tumor tissues, the expression of the 35 and 78 kDa isoforms was higher as compared to the adjacent normal tissues, while the 87 kDa isoform was found in the breast tumor tissues only. With the progression of stages of breast cancer, while the expression of 78 kDa isoform decreased, 87 kDa became undetectable. In co-immunoprecipitation assays, the profile of the SG2NA interactome in breast tumors vis-à-vis adjacent normal breast tissues showed hundreds of common proteins. Also, some proteins were interacted with SG2NA in breast tumor tissues only. We conclude that SG2NA is involved in diverse cellular pathways and has roles in cellular reprogramming during tumorigenesis of the breast.

Ectopic expression of 35 kDa and knocking down of 78 kDa SG2NAs induce cytoskeletal reorganization, alter membrane sialylation, and modulate the markers of EMT.

SG2NA is a protein of the striatin family that organizes STRIPAK complexes. It has splice variants expressing differentially in tissues. Its 78 kDa isoform regulates cell cycle, maintains homeostasis in the endoplasmic reticulum, and prevents oxidative injuries. The 35 kDa variant is devoid of the signature WD-40 repeats in the carboxy terminal, and its function is unknown. We expressed it in NIH 3T3 cells that otherwise express 78 kDa variant only. These cells (35 EE) have altered morphology, faster rate of migration, and enhanced growth as measured by the MTT assay. Similar phenotypes were also seen in cells where the endogenous 78 kDa isoform was downregulated by siRNA (78 KD). Proteomic analyses showed that several cancer-associated proteins are modulated in both 35 EE and 78 KD cells. The 35 EE cells have diffused actin fibers, distinctive ultrastructure, reduced sialylation, and increased expression of MMP2 & 9. The 78 KD cells also had diffused actin fibers and an upregulated expression of MMP2. In both cells, markers epithelial to mesenchymal transition (EMT) viz, E- & N-cadherins, ß-catenin, slug, vimentin, and ZO-1 were modulated partially in tune with the EMT process. Since NIH 3T3 cells are mesenchymal, we also expressed 35 kDa SG2NA in MCF-7 cells of epithelial origin. In these cells (MCF-7-35), the actin fibers were also diffused and the modulation of the markers was more in tune with the EMT process. However, unlike in 35 EE cells, in MCF-7-35 cells, membrane sialylation rather increased. We infer that ectopic expression of 35 kDa and downregulation of 78 kDa SG2NAs partially induce transformed phenotypes.

Genome Wide Analysis of WD40 Proteins in Saccharomyces cerevisiae and Their Orthologs in Candida albicans.

The WD40 domain containing proteins are present in the lower organisms (Monera) to higher complex metazoans with involvement in diverse cellular processes. The WD40 repeats fold into ß propeller structure due to which the proteins harbouring WD40 domains function as scaffold by offering platform for interactions, bring together diverse cellular proteins to form a single complex for mediating downstream effects. Multiple functions of WD40 domain containing proteins in lower eukaryote as in Fungi have been reported with involvement in vegetative and reproductive growth, virulence etc. In this article insilico analysis of the WDR proteins in the budding yeast Saccharomyces cerevisiae was performed. By WDSP software 83 proteins in S. cerevisiae were identified with at least one WD40 motif. WD40 proteins with 6 or more WD40 motifs were considered for further studies. The WD40 proteins in yeast which are involved in various biological processes show distribution on all chromosomes (16 chromosomes in yeast) except chromosome 1. Besides the WD40 domain some of these proteins also contain other protein domains which might be responsible for the diversity in the functions of WD40 proteins in the budding yeast. These proteins in budding yeast were analysed by DAVID and Blast2Go software for functional and domains categorization. Candida albicans, an opportunistic fungal pathogen also have orthologs of these WD40 proteins with possible similar functions. This is the first time genome wide analysis of WD40 proteins in lower eukaryote i.e. budding yeast. This data may be useful in further study of the functional diversity of yeast proteomes.

Biophysical Characterization of SG2NA Variants and their Interaction with DJ-1 and Calmodulin in vitro.

SG2NA was first discovered as nuclear autoantigen in lung and bladder cancer patient. It was named SG2NA as its expression increases during S to G2 phase of cell cycle. SG2NA/Striatin3 was classified as a member of Striatin family along with Straitin and Zinedin due to its structural and functional relatedness. At the molecular level, SG2NA is characterized by the presence of multiple protein-protein interaction domains viz., a caveolin binding motif, a coiled coil structure, Ca2+-calmodulin binding domain and a large WD-40 repeat domain in the same order from amino to the carboxyl termini. Analysis of secondary structures of 87 and 78 kDa SG2NA isoforms showed characteristic combinations of α-helix, ß-structure, ß-turns and random coil; suggesting of effective refolding after denaturation. This study for the first time establishes the structural differences between the two prevalent isoforms of SG2NA. Recently we observed that DJ-1 interacts with variants of SG2NA both in vitro and in vivo. The SG2NA isoforms purified from inclusion bodies showed the different secondary structure conformations, stability and interaction pattern for their interacting partners (DJ-1 and calmodulin) which imparts functional diversity of SG2NA. The SG2NA isoforms showed significant differential binding affinity to DJ-1 and Calmodulin.

WD40 Repeat Proteins: Signalling Scaffold with Diverse Functions.

The WD40 domain is one of the most abundant and interacting domains in the eukaryotic genome. In proteins the WD domain folds into a ß-propeller structure, providing a platform for the interaction and assembly of several proteins into a signalosome. WD40 repeats containing proteins, in lower eukaryotes, are mainly involved in growth, cell cycle, development and virulence, while in higher organisms, they play an important role in diverse cellular functions like signal transduction, cell cycle control, intracellular transport, chromatin remodelling, cytoskeletal organization, apoptosis, development, transcriptional regulation, immune responses. To play the regulatory role in various processes, they act as a scaffold for protein-protein or protein-DNA interaction. So far, no WD40 domain has been identified with intrinsic enzymatic activity. Several WD40 domain-containing proteins have been recently characterized in prokaryotes as well. The review summarizes the vast array of functions performed by different WD40 domain containing proteins, their domain organization and functional conservation during the course of evolution.

An Overview of Unfolded Protein Response Signaling and Its Role in Cancer.

Secretory and transmembrane proteins undergo post-translational modifications and folding in the subcellular organelle, that is, endoplasmic reticulum (ER) to become functionally active. Various factors such as high oxidative stress, low glucose, calcium imbalance, and viral infections interfere with the ER protein folding functions, leading to accumulation of unfolded and misfolded proteins that activate downstream signal transduction pathways, termed as unfolded protein response (UPR). This UPR signaling is adaptive and restored the normal function of cells by decreasing protein synthesis, increasing the folding capacity of ER and degradation of misfolded proteins. If the stress condition is overwhelmed, then UPR signaling shifts to apoptotic pathways. However, cancer cells utilized these UPR signaling for their survival and progression as an adaptive mechanism. In this review, the authors discuss about the overview of ER stress and subsequent UPR signaling and various aspects of cancer as survival, proliferation, and angiogenesis in relation to UPR. Understanding the UPR signaling in relation to cancer will be further helpful in designing therapeutics against cancer.

SG2NA is a regulator of endoplasmic reticulum (ER) homeostasis as its depletion leads to ER stress.

SG2NA belongs to a three-member striatin subfamily of WD40 repeat superfamily of proteins. It has multiple protein-protein interaction domains involved in assembling supramolecular signaling complexes. Earlier, we had demonstrated that there are at least five variants of SG2NA generated by alternative splicing, intron retention, and RNA editing. Such versatile and dynamic mode of regulation implicates it in tissue development. In order to shed light on its role in cell physiology, total proteome analysis was performed in NIH3T3 cells depleted of 78 kDa SG2NA, the only isoform expressing therein. A number of ER stress markers were among those modulated after knockdown of SG2NA. In cells treated with the ER stressors thapsigargin and tunicamycin, expression of SG2NA was increased at both mRNA and protein levels. The increased level of SG2NA was primarily in the mitochondria and the microsomes. A mouse injected with thapsigargin also had an increase in SG2NA in the liver but not in the brain. Cell cycle analysis suggested that while loss of SG2NA reduces the level of cyclin D1 and retains a population of cells in the G1 phase, concurrent ER stress facilitates their exit from G1 and traverse through subsequent phases with concomitant cell death. Thus, SG2NA is a component of intrinsic regulatory pathways that maintains ER homeostasis.

Tissue specific expression of SG2NA is regulated by differential splicing, RNA editing and differential polyadenylation.

SG2NA belongs to a three member Striatin subfamily of WD-40 repeat superfamily. It has multiple protein-protein interaction domains that are involved in the assembly of supra-molecular signaling complexes. Earlier we had demonstrated that there are at least five variants of SG2NA, generated by alternative splicing. We now demonstrate that a 52kDa novel variant is generated by the editing of the transcript for the 82kDa isoform. The 52kDa protein is abundant in mouse tissues but it is barely present in immortalized cells, suggesting its role in cell differentiation. Besides splicing and editing, expression of SG2NAs in tissues is also regulated by differential polyadenylation and mRNA/protein stability. Further, the longer UTR is seen only in the brain mRNA from 1month old mouse and 8-10day old chick embryo. Like alternative splicing, differential polyadenylation of Sg2na transcripts is also conserved in evolution. Taken together, these results suggest a highly versatile and dynamic mode of regulation of SG2NA with potential implications in tissue development.