Receptor for activated C kinase (RACK) and protein kinase C (PKC) in egg activation

RACK1 plays a critical role in mast cell secretion and Ca2+ mobilization by modulating F-actin dynamics

Although RACK1 is known to act as a signaling hub in immune cells, its presence and role in mast cells (MCs) is undetermined. MC activation via antigen stimulation results in mediator release and is preceded by cytoskeleton reorganization and Ca2+ mobilization. In this study, we found that RACK1 was distributed throughout the MC cytoplasm both in vivo and in vitro. After RACK1 knockdown (KD), MCs were rounded, and the cortical F-actin was fragmented. Following antigen stimulation, in RACK1 KD MCs, there was a reduction in cortical F-actin, an increase in monomeric G-actin and a failure to organize F-actin. RACK1 KD also increased and accelerated degranulation. CD63+ secretory granules were localized in F-actin-free cortical regions in non-stimulated RACK1 KD MCs. Additionally, RACK1 KD increased antigen-stimulated Ca2+ mobilization, but attenuated antigen-stimulated depletion of ER Ca2+ stores and thapsigargin-induced Ca2+ entry. Following MC activation there was also an increase in interaction of RACK1 with Orai1 Ca2+-channels, β-actin and the actin-binding proteins vinculin and MyoVa. These results show that RACK1 is a critical regulator of actin dynamics, affecting mediator secretion and Ca2+ signaling in MCs. This article has an associated First Person interview with the first author of the paper.

Evaluating the current status of protein kinase C (PKC)-protein kinase D (PKD) signalling axis as a novel therapeutic target in ovarian cancer

Ovarian cancer, especially high grade serous ovarian cancer is one of the most lethal gynaecological malignancies with high relapse rate and patient death. Notwithstanding development of several targeted treatment and immunotherapeutic approaches, researchers fail to turn ovarian cancer into a manageable disease. Protein kinase C (PKC) and protein kinase D (PKD) are families of evolutionarily conserved serine/threonine kinases that can be activated by a plethora of extracellular stimuli such as hormones, growth factors and G-protein coupled receptor agonists. Recent literature suggests that a signalling cascade initiated by these two protein kinases regulates a battery of cellular and physiological processes involved in tumorigenesis including cell proliferation, migration, invasion and angiogenesis. In an urgent need to discover novel therapeutic interventions against a deadly pathology like ovarian cancer, we have discussed the status quo of PKC/PKD signalling axis in context of this disease. Additionally, apart from discussing the structural properties and activation mechanisms of PKC/PKD, we have provided a comprehensive review of the recent reports on tumor promoting functions of PKC isoforms and discussed the potential of PKC/PKD signalling axis as a novel target in this lethal pathology. Furthermore, in this review, we have discussed the significance of several recent clinical trials and development of small molecule inhibitors that target PKC/PKD signalling axis in ovarian cancer.

The interaction between RACK1 and WEE1 regulates the growth of gastric cancer cell line HGC27

Receptor of activated C Kinase 1 (RACK1) is an essential scaffold and anchoring protein, which serves an important role in multiple tumorigenesis signaling pathways. The present study aimed to investigate the expression of RACK1 in gastric cancer (GC), and its association with the occurrence and development of GC. In addition, the effect and mechanism of RACK1 overexpression on the growth, and proliferation of GC cells was examined. Firstly, the protein expression of RACK1 was detected in 70 cases of GC tissues and 30 cases of noncancerous tissues using immunohistochemical staining, and the association between clinical and pathological features of GC was analyzed. Secondly, the mRNA and protein expression of RACK1 was determined in the poorly-differentiated human gastric cancer cell line HGC27 and gastric epithelial cell line GES-1. The growth of HGC27 cells following the upregulation of RACK1 was detected using MTT method. Subsequently, the interaction and co-location between RACK1, and WEE1 homolog (S. pombe) (WEE1) in HGC27 cells was confirmed using co-immunoprecipitation and indirect immunofluorescence. The expression level of RACK1 in GC was significantly lower compared with that in pericarcinous tissues (P<0.05). The protein level of RACK1 expression correlated with tumor node metastasis stage, tumor differentiation and lymph node metastasis. The mRNA and protein levels of RACK1 in HGC27 cells were significantly reduced, and overexpressed RACK1 downregulated WEE1 protein expression, thus inhibiting the growth of HGC27 cells. Co-immunoprecipitation and immunofluorescence confirmed that RACK1, and WEE1 interacted and co-located in the cytoplasm of HGC27 cells. Therefore, the abnormal expression of RACK1 in GC tissues was identified to be involved in the occurrence and development of GC. Overexpression of RACK1 was able to inhibit the growth of HGC27 cells. The current study suggests that low expression of RACK1 is an important indicator of poor prognosis of GC. RACK1 and WEE1 interact to regulate the growth of HGC27 cells.

[Molecular targets for searching of endothelial-protective substances]

Endothelial dysfunction underlies the development of many cardiovascular diseases. Thus endothelium becomes an independent therapeutic target, and the search of new substances with endothelial-protective action to date is one of the promising tasks for pharmacotherapy and medicinal chemistry. Molecular modeling is an effective tool for solving this problem. Computer chemistry methods use is only possible in combination with detailed information on three dimensional structure and functions of molecular targets: receptors and enzymes, involved in signal transduction inside and outside of endothelial cells. Information on structure and function of various macromolecules involved in vascular tone regulation is collected in the review. The structure of endothelial NO-synthase (EC 1.14.13.39) (eNOS)--enzyme, responsible for the nitric oxide synthesis and involved in vascular tone regulation process is reviewed. The importance of eNOS substrate--L-arginine is underlined in the review in terms of this enzyme activity, regulation, the information on structure and functions of L-arginine transport system is provided. Also different ways of eNOS activity regulation are reviewed, among which are enzyme activation and concurrent inhibition by substances interaction with active center of enzyme, inhibition by caveoline binding with oxigenase domain, and also regulation by phosphorylation of certain amino acids of eNOS by proteinkinase and dephoshphorylation of them by phosphatases. The importance of membrane receptors of endothelial cells as targets for endothelial-protective substances is underlined. Among them are receptors of endothelin, platelet activation factor, prostanoids, bradykinin, histamine, serotonin and protease activated receptors. The important role of potassium and calcium ion channels of vascular cells in endothelial-protective activity is underlined. Macromolecules presented in the review finally are considered as targets for searching for medicinal substances with endothelial-protective activity using proposed ways and methods of molecular modeling.

Effect of Linolenic acid during in vitro maturation of ovine oocytes: embryonic developmental potential and mRNA abundances of genes involved in apoptosis

PURPOSE

To study the effect of α-linolenic acid (ALA) on meiotic maturation, mRNA abundance of apoptosis-related (Bax and Bcl-2) molecules, and blastocyst formation in ovine oocytes.

METHODS

A preliminary experiment was conducted to analyze the concentration of ALA in "small" (≤2 mm) and "large" (≥6 mm) follicles using gas chromatography/mass spectrometry analysis. The concentration of ALA in small and large follicles was determined to be in a range of 75.4 to 125.7 μM, respectively. In vitro maturation (IVM) of oocyte was then performed in presence of 0 (control), 10 (ALA-10), 50 (ALA-50), 100 (ALA-100), and 200 (ALA-200) μM of ALA. Meiotic maturation and mRNA abundance of Bax, and Bcl-2 genes was evaluated after 24 h of IVM. The embryonic cleavage and blastocyst formation following parthenogenetic activation were also determined for each group.

RESULTS

The highest concentration of ALA (ALA-200) decreased the oocyte maturation rate compared with the control group. Analysis of apoptosis-related genes in oocytes after IVM revealed lesser transcript abundances for Bax gene, and higher transcript abundances for Bcl-2 gene in ALA-treated oocytes as compared with the control oocytes. In term of cleavage rate (considered as 2-cell progression), we did not observe any differences among the groups. However, ALA-100 group promoted more blastocyst formation as compared with the control group.

CONCLUSION

Our results suggested that ALA treatment during IVM had a beneficial effect on developmental competence of ovine oocytes by increasing the blastocyst formation and this might be due to the altered abundance of apoptosis-regulatory genes.

Receptor for activated C kinase ortholog of second-generation merozoite in Eimeria tenella: clone, characterization, and diclazuril-induced mRNA expression

The receptor for activated C kinase (RACK) cDNA of second-generation merozoites of Eimeria tenella was cloned using reverse transcriptase polymerase chain reaction and rapid amplification of cDNA ends, compared with other species, and then successfully expressed using the pET-28a vector in Escherichia coli BL21 (DE3) (EtRACK). Nucleotide sequence analysis revealed that the full length of the cloned cDNA (1,264 bp) encompassed a 957-bp open reading frame encoding a polypeptide of 318 residues with an estimated molecular mass of 34.94 kDa and a theoretical isoelectric point of 5.97. Molecular analysis of EtRACK reveals the presence of seven WD40 repeat motifs. EtRACK localizes to the cytoplasm and nucleus in second-generation merozoites of E. tenella. The cDNA sequence has been submitted to the GenBank Database with accession number JQ292804. EtRACK shared 98% homology with the published sequence of a RACK protein from Toxoplasma gondii at the amino acid level (GenBank XP_002370996.1). Recombinant protein expression was induced using 1 mM of isopropyl β-D-1-thiogalactopyranoside in vitro at 30 °C. Sodium dodecyl sulfate polyacrylamide gel electrophoresis analysis showed that the 39.79-kDa fusion protein existed in unsolvable form. Quantitative real-time PCR analysis showed that compared with the control group, the level of EtRACK mRNA expression in the treatment group was downregulated by 81.3% by diclazuril treatment. The high similarity of EtRACK to previously described RACKs of other organisms, as well as its downregulated expression in second-generation merozoites induced by diclazuril, suggests that it could play a key role in the signaling event that precedes protein secretion and parasite invasion. Moreover, the downregulation of EtRACK mRNA expression also enriches studies on the mechanism of action of diclazuril on E. tenella.

The biology and dynamics of mammalian cortical granules

Cortical granules are membrane bound organelles located in the cortex of unfertilized oocytes. Following fertilization, cortical granules undergo exocytosis to release their contents into the perivitelline space. This secretory process, which is calcium dependent and SNARE protein-mediated pathway, is known as the cortical reaction. After exocytosis, the released cortical granule proteins are responsible for blocking polyspermy by modifying the oocytes' extracellular matrices, such as the zona pellucida in mammals. Mammalian cortical granules range in size from 0.2 um to 0.6 um in diameter and different from most other regulatory secretory organelles in that they are not renewed once released. These granules are only synthesized in female germ cells and transform an egg upon sperm entry; therefore, this unique cellular structure has inherent interest for our understanding of the biology of fertilization. Cortical granules are long thought to be static and awaiting in the cortex of unfertilized oocytes to be stimulated undergoing exocytosis upon gamete fusion. Not till recently, the dynamic nature of cortical granules is appreciated and understood. The latest studies of mammalian cortical granules document that this organelle is not only biochemically heterogeneous, but also displays complex distribution during oocyte development. Interestingly, some cortical granules undergo exocytosis prior to fertilization; and a number of granule components function beyond the time of fertilization in regulating embryonic cleavage and preimplantation development, demonstrating their functional significance in fertilization as well as early embryonic development. The following review will present studies that investigate the biology of cortical granules and will also discuss new findings that uncover the dynamic aspect of this organelle in mammals.

RACK1, A multifaceted scaffolding protein: Structure and function

The Receptor for Activated C Kinase 1 (RACK1) is a member of the tryptophan-aspartate repeat (WD-repeat) family of proteins and shares significant homology to the β subunit of G-proteins (Gβ). RACK1 adopts a seven-bladed β-propeller structure which facilitates protein binding. RACK1 has a significant role to play in shuttling proteins around the cell, anchoring proteins at particular locations and in stabilising protein activity. It interacts with the ribosomal machinery, with several cell surface receptors and with proteins in the nucleus. As a result, RACK1 is a key mediator of various pathways and contributes to numerous aspects of cellular function. Here, we discuss RACK1 gene and structure and its role in specific signaling pathways, and address how posttranslational modifications facilitate subcellular location and translocation of RACK1. This review condenses several recent studies suggesting a role for RACK1 in physiological processes such as development, cell migration, central nervous system (CN) function and circadian rhythm as well as reviewing the role of RACK1 in disease.