Isoforms A3 Research Articles

Isoform a4 of the vacuolar ATPase a subunit promotes 4T1-12B breast cancer cell–dependent tumor growth and metastasis in vivo

The vacuolar H+-ATPase (V-ATPase) is an ATP-dependent proton pump that governs the pH of various intracellular compartments and also functions at the plasma membrane in certain cell types, including cancer cells. Membrane targeting of the V-ATPase is controlled by isoforms of subunit a, and we have previously shown that isoforms a3 and a4 are important for the migration and invasion of several breast cancer cell lines in vitro. Using CRISPR-mediated genome editing to selectively disrupt each of the four a subunit isoforms, we also recently showed that a4 is critical to plasma membrane V-ATPase localization, as well as in vitro migration and invasion of 4T1-12B murine breast cancer cells. We now report that a4 is important for the growth of 4T1-12B tumors in vivo. We found that BALB/c mice bearing a4−/− 4T1-12B allografts had significantly smaller tumors than mice in the control group. In addition, we determined that a4−/− allografts showed dramatically reduced metastases to the lung and reduced luminescence intensity of metastases to bone relative to the control group. Taken together, these results suggest that the a4 isoform of the V-ATPase represents a novel potential therapeutic target to limit breast cancer growth and metastasis.

Aldehyde dehydrogenase 1a3 defines a subset of failing pancreatic β cells in diabetic mice.

Insulin-producing β cells become dedifferentiated during diabetes progression. An impaired ability to select substrates for oxidative phosphorylation, or metabolic inflexibility, initiates progression from β-cell dysfunction to β-cell dedifferentiation. The identification of pathways involved in dedifferentiation may provide clues to its reversal. Here we isolate and functionally characterize failing β cells from various experimental models of diabetes and report a striking enrichment in the expression of aldehyde dehydrogenase 1 isoform A3 (ALDH+) as β cells become dedifferentiated. Flow-sorted ALDH+ islet cells demonstrate impaired glucose-induced insulin secretion, are depleted of Foxo1 and MafA, and include a Neurogenin3-positive subset. RNA sequencing analysis demonstrates that ALDH+ cells are characterized by: (i) impaired oxidative phosphorylation and mitochondrial complex I, IV and V; (ii) activated RICTOR; and (iii) progenitor cell markers. We propose that impaired mitochondrial function marks the progression from metabolic inflexibility to dedifferentiation in the natural history of β-cell failure.

The a3 isoform of subunit a of the vacuolar ATPase localizes to the plasma membrane of invasive breast tumor cells and is overexpressed in human breast cancer.

The vacuolar (H+)-ATPases (V-ATPases) are a family of ATP-driven proton pumps that acidify intracellular compartments and transport protons across the plasma membrane. Previous work has demonstrated that plasma membrane V-ATPases are important for breast cancer invasion in vitro and that the V-ATPase subunit a isoform a3 is upregulated in and critical for MDA-MB231 and MCF10CA1a breast cancer cell invasion. It has been proposed that subunit a3 is present on the plasma membrane of invasive breast cancer cells and is overexpressed in human breast cancer. To test this, we used an a3-specific antibody to assess localization in breast cancer cells. Subunit a3 localizes to the leading edge of migrating breast cancer cells, but not the plasma membrane of normal breast epithelial cells. Furthermore, invasive breast cancer cells express a3 throughout all intracellular compartments tested, including endosomes, the Golgi, and lysosomes. Moreover, subunit a3 knockdown in MB231 breast cancer cells reduces in vitro migration. This reduction is not enhanced upon addition of a V-ATPase inhibitor, suggesting that a3-containing V-ATPases are critical for breast cancer migration. Finally, we have tested a3 expression in human breast cancer tissue and mRNA prepared from normal and cancerous breast tissue. a3 mRNA was upregulated 2.5-47 fold in all breast tumor cDNA samples tested relative to normal tissue, with expression generally correlated to cancer stage. Furthermore, a3 protein expression was increased in invasive breast cancer tissue relative to noninvasive cancer and normal breast tissue. These studies suggest that subunit a3 plays an important role in invasive human breast cancer.

Extracellular and Luminal pH Regulation by Vacuolar H+-ATPase Isoform Expression and Targeting to the Plasma Membrane and Endosomes

Plasma membrane vacuolar H+-ATPase (V-ATPase) activity of tumor cells is a major factor in control of cytoplasmic and extracellular pH and metastatic potential, but the isoforms involved and the factors governing plasma membrane recruitment remain uncertain. Here, we examined expression, distribution, and activity of V-ATPase isoforms in invasive prostate adenocarcinoma (PC-3) cells. Isoforms 1 and 3 were the most highly expressed forms of membrane subunit a, with a1 and a3 the dominant plasma membrane isoforms. Correlation between plasma membrane V-ATPase activity and invasiveness was limited, but RNAi knockdown of either a isoform did slow cell proliferation and inhibit invasion in vitro. Isoform a1 was recruited to the cell surface from the early endosome-recycling complex pathway, its knockdown arresting transferrin receptor recycling. Isoform a3 was associated with the late endosomal/lysosomal compartment. Both a isoforms associated with accessory protein Ac45, knockdown of which stalled transit of a1 and transferrin-transferrin receptor, decreased proton efflux, and reduced cell growth and invasiveness; this latter effect was at least partly due to decreased delivery of the membrane-bound matrix metalloproteinase MMP-14 to the plasma membrane. These data indicate that in prostatic carcinoma cells, a1 and a3 isoform populations predominate in different compartments where they maintain different luminal pH. Ac45 plays a central role in navigating the V-ATPase to the plasma membrane, and hence it is an important factor in expression of the invasive phenotype.

Green tea catechins can bind and modify ERp57/PDIA3 activity

BackgroundGreen tea is a rich source of polyphenols, mainly catechins (flavanols), which significantly contribute to the beneficial health effects of green tea in the prevention and treatment of various diseases. In this study the effects of four green tea catechins on protein ERp57, also known as protein disulfide isomerase isoform A3 (PDIA3), have been investigated in an in vitro model. MethodsThe interaction of catechins with ERp57 was explored by fluorescence quenching and surface plasmon resonance techniques and their effect on ERp57 activities was investigated. ResultsA higher affinity was observed for galloylated cathechins, which bind close to the thioredoxin-like redox-sensitive active sites of the protein, with a preference for the oxidized form. The effects of these catechins on ERp57 properties were also investigated and a moderate inhibition of the reductase activity of ERp57 was observed as well as a strong inhibition of ERp57 DNA binding activity. ConclusionsConsidering the high affinity of galloylated catechins for ERp57 and their capability to inhibit ERp57 binding to other macromolecular ligands, some effects of catechins interaction with this protein on eukaryotic cells may be expected. General significanceThis study provides information to better understand the molecular mechanisms underlying the biological activities of catechins and to design new polyphenol-based ERp57-specific inhibitors.

Effects of acute exercise and long-term exercise on total Na+,K+-ATPase content and Na+,K+-ATPase isoform expression profile in equine muscle

To investigate the effects of acute exercise and long-term training on Na(+),K(+)-ATPase content, mRNA isoforms, and protein concentration in equine muscle. 6 Standardbreds. Horses performed a bout of exercise on a treadmill before and after 18 weeks of combined interval and endurance training. Muscle biopsy specimens were obtained from vastus lateralis muscle (VLM) and pectoralis descendens muscle (PDM) before and after exercise. The Na(+),K(+)-ATPase content, mRNA isoforms, and protein concentrations were determined by use of [(3)H]ouabain binding, real-time PCR assay, and western blotting, respectively. 6 Na(+),K(+)-ATPase mRNA isoforms were present in equine muscle, but only A2 and B1 proteins were detected. Exercise before training resulted in increases of mRNA isoforms A1, A2, A3, and B2 in VLM and A1 and B3 in PDM. Training increased resting values for mRNA isoforms A3 and B1 in VLM and B3 in PDM. The Na(+),K(+)-ATPase, [(3)H]ouabain binding, and proteins of mRNA A2 and B1 increased in VLM, whereas in PDM, only A2 protein increased as a result of training. After training, effects of strenuous exercise on mRNA expression were no longer detectable. Equine muscle contained all Na(+),K(+)-ATPase mRNA isoforms, but only A2 and B1 proteins could be detected. Expression of these isoforms changed as a result of strenuous exercise and long-term training, representing an adaptive response. Determination of Na(+),K(+)-ATPase gene expression may be relevant for understanding alterations in excitability during neuromuscular diseases.

Evaluation of Archival Time on Shotgun Proteomics of Formalin-Fixed and Paraffin-Embedded Tissues

There is increasing acceptance of the critical importance of correlating the morphologic features of tissue with the data obtained from various molecular analytic techniques. Access to archived formalin-fixed and paraffin-embedded (FFPE) tissue specimens via shotgun-based proteomic analyses may, therefore, open new avenues for both prospective and retrospective translational research. However, one of the remaining issues in performing comparative proteomic measurements among FFPE tissues relates to potential variability in protein composition and retrieval based on length of storage periods. Optimized protein extraction and digestion procedures for handling FFPE tissues are coupled with the capillary isotachophoresis-based proteome technology to evaluate the effects of length of storage period on archival tissue proteome analysis across 10 archived uterine mesenchymal tumor tissue blocks, including 9 uterine leiomyomas dating from 1990 to 2002 and a single case of alveolar soft part sarcoma (ASPS) from 1980. Several statistical measures, including the Pearson correlation coefficient, coefficient of variance, k-means clustering, and ANOVA, are employed to evaluate the possibility of an archival effect on individual proteins or groups of proteins within nine leiomyomas. Low abundance proteins may be more susceptible to the long-term storage as these proteins are more difficult to be retrieved and extracted as the tissue block ages in paraffin. Despite using tissue blocks stored for as many as 28 years, high confidence and comparative proteome analysis between the leiomyomas and the sarcoma is achieved. Though sharing over 1800 common proteins in a core set, a total of 80 proteins unique to the sarcoma are identified distinguishing the ASPS from the leiomyomas. Vacuolar proton translocating ATPase 116 kDa subunit isoform a3, one of the unique proteins expressed in the ASPS, is further validated by immunohistochemistry (IHC). Although IHC is highly sensitive and provides the subcellular resolution, mass spectrometry-based proteome profiling enables global identification and quantification of thousands of proteins without a priori knowledge of individual proteins being analyzed or the need of validated antibodies.

Antifungal effects and mechanism of action of viscotoxin A3

Viscotoxins are cationic proteins, isolated from different mistletoe species, that belong to the group of thionins, a group of basic cysteine-rich peptides of approximately 5 kDa. They have been shown to be cytotoxic to different types of cell, including animal, bacterial and fungal. The aim of this study was to obtain information on the cell targets and the mechanism of action of viscotoxin isoform A3 (VtA3). We describe a detailed study of viscotoxin interaction with fungal-derived model membranes, its location inside spores of Fusarium solani, as well as their induced spore death. We show that VtA3 induces the appearance of ion-channel-like activity, the generation of H2O2, and an increase in cytoplasmic free Ca2+. Moreover, we show that Ca2+ is involved in VtA3-induced spore death and increased H2O2 concentration. The data presented here strongly support the notion that the antifungal activity of VtA3 is due to membrane binding and channel formation, leading to destabilization and disruption of the plasma membrane, thereby supporting a direct role for viscotoxins in the plant defence mechanism.

Genomic structure and sequence of a human homologue (NTHL1/NTH1) of Escherichia coli endonuclease III with those of the adjacent parts of TSC2 and SLC9A3R2 genes

Genomic cloning and sequencing of a human homologue (the gene name, endonuclease III-like 1; gene symbol, NTHL1 or NTH1) for Escherichia coli endonuclease III, that is involved in pyrimidine base excision repair, were performed. The sequence covered the entire NTHL1 gene consisting of six exons and five introns spanning 8kb with 5' flanking (8kb) and 3' flanking (3.8kb) regions. Southern blot analysis suggested that the NTHL1 gene exists as a single copy in a haploid genome. The sequenced 5' flanking region lacks typical TATA and CAAT boxes, but contains a CpG island having putative binding sites for several transcription factors such as Ets1 and Sp1. The NTHL1 gene lies immediately adjacent to the tuberous sclerosis 2 (TSC2) gene on chromosome 16p13.3 in a 5'-to-5' orientation. Transcription initiation sites of both NTHL1 and TSC2 genes were suggested to be multiple by 5' RACE experiments. The northern hybridization experiment suggested that both genes are expressed in all tissues, but at different levels. Downstream of the NTHL1 gene, the gene for the regulatory factor 2 (SLC9A3R2/E3KARP; also called OCTS2, TKA-1 and SIP-1) of the solute carrier family 9 (sodium/hydrogen exchanger), isoform A3, lies in a 3'-to-3' orientation. This paper demonstrates for the first time the spatial relationship of these three genes (TSC2, NTHL1 and SLC9A3R2) at the nucleotide level, and the presence of multiple transcription initiation sites of the NTHL1 and TSC2 genes.