Plasma membrane Ca2+-ATPase mRNA expression in murine hepatocarcinoma and regenerating liver cells

Pathophysiological role of ion channels and transporters in hepatocellular carcinoma

The incidence of hepatocellular carcinoma (HCC) has continued to increase annually worldwide, and HCC has become a common cause of cancer-related death. Despite great progress in understanding the molecular mechanisms underlying HCC development, the treatment of HCC remains a considerable challenge. Thus, the survival and prognosis of HCC patients remain extremely poor. In recent years, the role of ion channels in the pathogenesis of diseases has become a hot topic. In normal liver tissue, ion channels and transporters maintain water and electrolyte balance and acid‒base homeostasis. However, dysfunction of these ion channels and transporters can lead to the development and progression of HCC, and thus these ion channels and transporters are expected to become new therapeutic targets. In this review, ion channels and transporters associated with HCC are reviewed, and potential targets for new and effective therapies are proposed.

Ca2+ Transportome and the Interorganelle Communication in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is a type of liver cancer with a poor prognosis for survival given the complications it bears on the patient. Though damages to the liver are acknowledged prodromic factors, the precise molecular aetiology remains ill-defined. However, many genes coding for proteins involved in calcium (Ca²⁺) homeostasis emerge as either mutated or deregulated. Ca²⁺ is a versatile signalling messenger that regulates functions that prime and drive oncogenesis, favouring metabolic reprogramming and gene expression. Ca²⁺ is present in cell compartments, between which it is trafficked through a network of transporters and exchangers, known as the Ca²⁺ transportome. The latter regulates and controls Ca²⁺ dynamics and tonicity. In HCC, the deregulation of the Ca²⁺ transportome contributes to tumorigenesis, the formation of metastasizing cells, and evasion of cell death. In this review, we reflect on these aspects by summarizing the current knowledge of the Ca²⁺ transportome and overviewing its composition in the plasma membrane, endoplasmic reticulum, and the mitochondria.

Quantitative Expression of Key Cancer Markers in the AS-30D Hepatocarcinoma Model

Hepatocellular carcinoma is one of the cancers with the highest mortality rate worldwide. HCC is often diagnosed when the disease is already in an advanced stage, making the discovery and implementation of biomarkers for the disease a critical aim in cancer research. In this study, we aim to quantify the transcript levels of key signaling molecules relevant to different pathways known to participate in tumorigenesis, with special emphasis on those related to cancer hallmarks and epithelial-mesenchymal transition, using as a model the murine transplantable hepatocarcinoma AS-30D. Using qPCR to quantify the mRNA levels of genes involved in tumorigenesis, we found elevated levels for Tgfb1 and Spp1, two master regulators of EMT. A mesenchymal signature profile for AS-30D cells is also supported by the overexpression of genes encoding for molecules known to be associated to aggressiveness and metastatic phenotypes such as Foxm1, C-met, and Inppl1. This study supports the use of the AS-30D cells as an efficient and cost-effective model to study gene expression changes in HCC, especially those associated with the EMT process.

Establishment and characterization of the GC-030-35 cell line derived from gastric hepatoid adenocarcinoma

Purpose

Gastric hepatoid adenocarcinoma is a rare subtype of primary gastric cancer and is a high-grade form of malignancy. However, the pathogenesis and molecular biology of gastric hepatoid adenocarcinoma remain poorly understood. The aim of this study was to establish and characterize a new human gastric hepatoid adenocarcinoma cell line, GC-030-35.

Materials and methods

The GC-030-35 cell line was established from tumor cells from a 58-year-old Chinese man with gastric hepatoid adenocarcinoma. The cultured cells underwent immunocytochemistry and flow cytometry to confirm the tumor cell phenotype. RNA sequencing was performed to analyze the differences in gene expression between GC-030-35 cells compared with normal gastric epithelial cells. A zebrafish assay was performed. Gene enrichment analysis and interrogation of the bioinformatics databases, the Gene Ontology (GO) database and the Kyoto Encyclopedia of Genes and Genomes (KEGG) database, were used for pathway analysis.

Results

Flow cytometry analysis of the GC-030-35 cells showed a positive expression rate for CD44+ of 10.7%, high cell clonality, an average plating efficiency of 32%, cell-doubling time of 29.2 hours, and cell proliferation for >15 generations in serial culture. The zebrafish assay showed the ability of the GC-030-35 cells to proliferate, promote angiogenesis, and metastasize. RNA sequencing identified the functional clustering of 6,601 differentially expressed genes of GC-030-35, which were significantly different when compared with nonneoplastic gastric epithelial cells. Pathway enrichment analysis and interrogation of the GO and KEGG bioinformatics databases identified genes for microbial metabolism in diverse environments (63 genes), metabolism of xenobiotics by cytochrome P450 (CYP450; 25 genes), and the drug metabolism cytochrome P450 (28 genes).

Conclusion

A human gastric hepatoid adenocarcinoma cell line, GC-030-35, was developed and characterized by comparison with normal gastric epithelial cells. Bioinformatics and gene analysis data showed that the CYP450 gene was significantly differentially expressed by GC-030-35 cells.

The Plasma Membrane Calcium ATPases and Their Role as Major New Players in Human Disease

The Ca²⁺ extrusion function of the four mammalian isoforms of the plasma membrane calcium ATPases (PMCAs) is well established. There is also ever-increasing detail known of their roles in global and local Ca²⁺ homeostasis and intracellular Ca²⁺ signaling in a wide variety of cell types and tissues. It is becoming clear that the spatiotemporal patterns of expression of the PMCAs and the fact that their abundances and relative expression levels vary from cell type to cell type both reflect and impact on their specific functions in these cells. Over recent years it has become increasingly apparent that these genes have potentially significant roles in human health and disease, with PMCAs1-4 being associated with cardiovascular diseases, deafness, autism, ataxia, adenoma, and malarial resistance. This review will bring together evidence of the variety of tissue-specific functions of PMCAs and will highlight the roles these genes play in regulating normal physiological functions and the considerable impact the genes have on human disease.

Atherosclerosis and Cancer; A Resemblance with Far-reaching Implications

Atherosclerosis and cancer are chronic diseases considered two of the main causes of death all over the world. Taking into account that both diseases are multifactorial, they share not only several important molecular pathways but also many ethiological and mechanistical processes from the very early stages of development up to the advanced forms in both pathologies. Factors involved in their progression comprise genetic alterations, inflammatory processes, uncontrolled cell proliferation and oxidative stress, as the most important ones. The fact that external effectors such as an infective process or a chemical insult have been proposed to initiate the transformation of cells in the artery wall and the process of atherogenesis, emphasizes many similarities with the progression of the neoplastic process in cancer. Deregulation of cell proliferation and therefore cell cycle progression, changes in the synthesis of important transcription factors as well as adhesion molecules, an alteration in the control of angiogenesis and the molecular similarities that follow chronic inflammation, are just a few of the processes that become part of the phenomena that closely correlates atherosclerosis and cancer. The aim of the present study is therefore, to provide new evidence as well as to discuss new approaches that might promote the identification of closer molecular ties between these two pathologies that would permit the recognition of atherosclerosis as a pathological process with a very close resemblance to the way a neoplastic process develops, that might eventually lead to novel ways of treatment.

Relevance of the plasma membrane calcium-ATPase in the homeostasis of calcium in the fetal liver

During the early stages of development, the embryo depends on the placenta as provider of oxygen and calcium, among other essential compounds. Although fetal liver accomplishes a well-known haematopoietic function, its contribution to calcium homeostasis upon development is poorly understood. The homeostasis of cell calcium contributes to diverse signaling pathways across developmental stages of most tissues and the calcium-ATPase located at the plasma membrane (PMCA) helps pumping excess calcium into the extracellular space. To date, the understanding of the equilibrium shift between PMCA isoforms during liver development is still missing. This review focuses on the characterization of the hepatic PMCA along the early stages of development, followed by a description of modern approaches to study calcium homeostasis involving several types of pluripotent cells. The application of interdisciplinary techniques to improve our understanding of liver development and the role calcium homeostasis plays in the definition of pathogenesis is also discussed.

Plasma membrane calcium ATPase isoform 3 expression in single cells isolated from rat liver

The plasma membrane Ca(2+)-ATPase (PMCA) located in the hepatocyte is a controversial molecule in itself since it displays different features to those regarded as canonical for P-type Ca(2+)-ATPases, and from which transcript expression as well as catalytic activity continues to be under active investigation. Our aim in this study was to explore at a first glance, pmca isoform distribution using isolated parenchymal and non-parenchymal cells from rat liver tissue. Expression of pmca transcripts was analyzed in fresh or cell-enriched culture preparations, confirming pmca1 and pmca4 as the housekeeping isoforms in all cell types studied (hepatocytes, Kupffer cells, and stellate cells). However, for the first time we show expression of pmca3 transcripts edited at two different sites in both hepatocytes and non-parenchymal cells. Interestingly, employing non-parenchymal cells we demonstrate the specific expression of pmca3e transcripts previously considered nearly exclusive of excitable tissues. Real-time PCR quantification shows a significant decrease of pmca3 transcripts in cultured Kupffer and hepatic stellate cells in comparison with fresh cells. The presence of pmca2 along with pmca3 in all liver cell types studied suggests that high affinity isoforms are relevant to the adequate management of calcium in liver tissue, particularly when hepatic cells become activated by diverse stimuli.

Ca(2+) -permeable channels in the hepatocyte plasma membrane and their roles in hepatocyte physiology

Hepatocytes are highly differentiated and spatially polarised cells which conduct a wide range of functions, including intermediary metabolism, protein synthesis and secretion, and the synthesis, transport and secretion of bile acids. Changes in the concentrations of Ca(2+) in the cytoplasmic space, endoplasmic reticulum (ER), mitochondria, and other intracellular organelles make an essential contribution to the regulation of these hepatocyte functions. While not yet fully understood, the spatial and temporal parameters of the cytoplasmic Ca(2+) signals and the entry of Ca(2+) through Ca(2+)-permeable channels in the plasma membrane are critical to the regulation by Ca(2+) of hepatocyte function. Ca(2+) entry across the hepatocyte plasma membrane has been studied in hepatocytes in situ, in isolated hepatocytes and in liver cell lines. The types of Ca(2+)-permeable channels identified are store-operated, ligand-gated, receptor-activated and stretch-activated channels, and these may vary depending on the animal species studied. Rat liver cell store-operated Ca(2+) channels (SOCs) have a high selectivity for Ca(2+) and characteristics similar to those of the Ca(2+) release activated Ca(2+) channels in lymphocytes and mast cells. Liver cell SOCs are activated by a decrease in Ca(2+) in a sub-region of the ER enriched in type1 IP(3) receptors. Activation requires stromal interaction molecule type 1 (STIM1), and G(i2alpha,) F-actin and PLCgamma1 as facilitatory proteins. P(2x) purinergic channels are the only ligand-gated Ca(2+)-permeable channels in the liver cell membrane identified so far. Several types of receptor-activated Ca(2+) channels have been identified, and some partially characterised. It is likely that TRP (transient receptor potential) polypeptides, which can form Ca(2+)- and Na(+)-permeable channels, comprise many hepatocyte receptor-activated Ca(2+)-permeable channels. A number of TRP proteins have been detected in hepatocytes and in liver cell lines. Further experiments are required to characterise the receptor-activated Ca(2+) permeable channels more fully, and to determine the molecular nature, mechanisms of activation, and precise physiological functions of each of the different hepatocyte plasma membrane Ca(2+) permeable channels.

Protein stability and the evolution of the cell membrane

Cholesterol has been shown to regulate the activity of several membrane proteins. Although this phenomenon represents an important factor in the regulation of ion homeostasis, insights are needed to fully understand the role of this lipid in cell function in order to better comprehend the effect of bilayer components upon membrane function. Since evolution has shaped the composition of the membrane bilayer, it becomes of interest to study these changes in parallel with the many functions of membranes such as ion transport. The present study employing a plasma membrane preparation obtained from calf ventricular muscle demonstrates that cholesterol partially inhibits the Ca(2+),Mg(2+)-ATPase as the catalytic function of the calcium pump, when incubation reaction temperatures are below 42 degrees C. In contrast, when incubation reaction temperatures are above 42 degrees C, cholesterol apparently promotes enzyme stabilization reflected in higher activity. Although the activation energy values for the enzyme are almost the same at ranges between 15 and 40 degrees C, the use of elevated temperatures promote higher enzyme inactivation rates in control than in cholesterol enriched membranes. Cholesterol apparently is promoting stabilization that in turn protects the enzyme against thermal inactivation. This protective effect is reflected in a decrease of inactivation rate values and energy released during enzyme catalysis. The modification of many membrane properties throughout million of years made it possible for new evolutionary driving forces to show themselves as new characteristics in eukaryotes such as the one discussed in this study, dealing with the presence of cholesterol in the cell membrane directly associated to the promotion of protein thermostability.

Calcium signalling and cancer cell growth

Cancer is caused by defects in the mechanisms underlying cell proliferation and cell death. Calcium ions are central to both phenomena, serving as major signalling agents with spatial localization, magnitude and temporal characteristics of calcium signals ultimately determining cell's fate. There are four primary compartments: extracellular space, cytoplasm, endoplasmic reticulum and mitochondria that participate in the cellular Ca2+ circulation. They are separated by own membranes incorporating divers Ca2(+)-handling proteins whose concerted action provides for Ca2+ signals with the spatial and temporal characteristics necessary to account for specific cellular response. The transformation of a normal cell into a cancer cell is associated with a major re-arrangement of Ca2+ pumps, Na/Ca exchangers and Ca2+ channels, which leads to the enhanced proliferation and impaired ability to die. In the present chapter we examine what changes in Ca+ signalling and the mechanisms that support it underlie the passage from normal to pathological cell growth and death control. Understanding this changes and identifying molecular players involved provides new prospects for cancers treatment.

Is there a specific role for the plasma membrane Ca2+ -ATPase in the hepatocyte?

The plasma membrane Ca2+ -ATPase (PMCA) is responsible for the fine, long-term regulation of the cytoplasmic calcium concentration by extrusion of this cation from the cell. Although the general kinetic mechanisms for the action of both, well coordinated hydrolytic activity and calcium transport are reasonably understood in the majority of cell types, due to the complex physiologic and biochemical characteristics shown by the hepatocyte, the study of this enzyme in this cell type has become a real challenge. Here, we review the various molecular aspects known to date to be associated with liver PMCA activity, and outline the strategies to follow for establishing the role of this enzyme in the overall physiology of the hepatocyte. In this way, we first concentrate on the basic biochemical aspects of liver cell PMCA, and place an important emphasis on expression of its molecular forms to finally focus on the critical hormonal regulation of the enzyme. Although these complex aspects have been studied mainly under normal conditions, the significance of PMCA in the calcium homeostasis of an abnormal liver cell is also reviewed.