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2020
Ibrahim, S. A., A. Kulshrestha, G. K. Katara, V. Riehl, M. Sahoo, and K. D. Beaman, "Cancer-associated V-ATPase induces delayed apoptosis of protumorigenic neutrophils.", Molecular oncology, vol. 14, issue 3, pp. 590-610, 2020 Mar. Abstract

Tumors and neutrophils undergo an unexpected interaction, in which products released by tumor cells interact to support neutrophils that in turn support cancer growth, angiogenesis, and metastasis. A key protein that is highly expressed by cancer cells in tumors is the a2 isoform V-ATPase (a2V). A peptide from a2V (a2NTD) is secreted specifically by cancer cells, but not normal cells, into the tumor microenvironment. This peptide reprograms neutrophils to promote angiogenesis, cancer cell invasiveness, and neutrophil recruitment. Here, we provide evidence that cancer-associated a2V regulates the life span of protumorigenic neutrophils by influencing the intrinsic pathway of apoptosis. Immunohistochemical analysis of human cancer tissue sections collected from four different organs shows that levels of a2NTD and neutrophil counts are increased in cancer compared with normal tissues. Significant increases in neutrophil counts were present in both poorly and moderately differentiated tumors. In addition, there is a positive correlation between the number of neutrophils and a2NTD expression. Human neutrophils treated with recombinant a2NTD show significantly delayed apoptosis, and such prolonged survival was dependent on NF-κB activation and ROS generation. Induction of antiapoptotic protein expression (Bcl-xL and Bcl-2A1) and decreased expression of proapoptotic proteins (Bax, Apaf-1, caspase-3, caspase-6, and caspase-7) were a hallmark of these treated neutrophils. Autocrine secretion of prosurvival cytokines of TNF-α and IL-8 by treated neutrophils prolongs their survival. Our findings highlight the important role of cancer-associated a2V in regulating protumorigenic innate immunity, identifying a2V as a potential important target for cancer therapy.

Katara, G. K., A. Kulshrestha, S. Schneiderman, V. Riehl, S. Ibrahim, and K. D. Beaman, "Interleukin-22 promotes development of malignant lesions in a mouse model of spontaneous breast cancer.", Molecular oncology, vol. 14, issue 1, pp. 211-224, 2020 Jan. Abstract

Interleukin (IL)-22 is recognized as a tumor-supporting cytokine and is implicated in the proliferation of multiple epithelial cancers. In breast cancer, the current knowledge of IL-22 function is based on cell line models and little is known about how IL-22 affects the tumor initiation, proliferation, invasion, and metastasis in the in vivo system. Here, we investigated the tumor stage-specific function of IL-22 in disease development by evaluating the stage-by-stage progression of breast cancer in an IL-22 knockout spontaneous breast cancer mouse model. We found that among all the stages, IL-22 is specifically upregulated in tumor microenvironment (TME) during the malignant transformation stage of breast tumor progression. The deletion of IL-22 gene leads to the arrest of malignant transition stage, and reduced invasion and tumor burden. Administration of recombinant IL-22 in the TME does not influence in vivo tumor initiation and proliferation but only promotes malignant transformation of cancer cells. Mechanistically, deletion of IL-22 gene causes downregulation of epithelial-to-mesenchymal transition (EMT)-associated transcription factors in breast tumors, suggesting EMT as the mechanism of regulation of malignancy by IL-22. Clinically, in human breast tumor tissues, increased number of IL-22 cells in the TME is associated with an aggressive phenotype of breast cancer. For the first time, this study provides an insight into the tumor stage-specific function of IL-22 in breast tumorigenesis.

Ibrahim, S. A., A. Kulshrestha, G. K. Katara, V. Riehl, M. Sahoo, and K. D. Beaman, "Cancer-associated V-ATPase induces delayed apoptosis of protumorigenic neutrophils.", Molecular oncology, vol. 14, issue 3, pp. 590-610, 2020. Abstract

Tumors and neutrophils undergo an unexpected interaction, in which products released by tumor cells interact to support neutrophils that in turn support cancer growth, angiogenesis, and metastasis. A key protein that is highly expressed by cancer cells in tumors is the a2 isoform V-ATPase (a2V). A peptide from a2V (a2NTD) is secreted specifically by cancer cells, but not normal cells, into the tumor microenvironment. This peptide reprograms neutrophils to promote angiogenesis, cancer cell invasiveness, and neutrophil recruitment. Here, we provide evidence that cancer-associated a2V regulates the life span of protumorigenic neutrophils by influencing the intrinsic pathway of apoptosis. Immunohistochemical analysis of human cancer tissue sections collected from four different organs shows that levels of a2NTD and neutrophil counts are increased in cancer compared with normal tissues. Significant increases in neutrophil counts were present in both poorly and moderately differentiated tumors. In addition, there is a positive correlation between the number of neutrophils and a2NTD expression. Human neutrophils treated with recombinant a2NTD show significantly delayed apoptosis, and such prolonged survival was dependent on NF-κB activation and ROS generation. Induction of antiapoptotic protein expression (Bcl-xL and Bcl-2A1) and decreased expression of proapoptotic proteins (Bax, Apaf-1, caspase-3, caspase-6, and caspase-7) were a hallmark of these treated neutrophils. Autocrine secretion of prosurvival cytokines of TNF-α and IL-8 by treated neutrophils prolongs their survival. Our findings highlight the important role of cancer-associated a2V in regulating protumorigenic innate immunity, identifying a2V as a potential important target for cancer therapy.

Kulshrestha, A., G. K. Katara, S. A. Ibrahim, V. E. Riehl, S. Schneiderman, M. Bilal, A. N. Young, S. Levine, S. Fleetwood, J. Dolan, et al., "In vivo anti-V-ATPase antibody treatment delays ovarian tumor growth by increasing antitumor immune responses.", Molecular oncology, vol. 14, issue 10, pp. 2436-2454, 2020. Abstract

Tumor acidity is the key metabolic feature promoting cancer progression and is modulated by pH regulators on a cancer cell's surface that pump out excess protons/lactic acid for cancer cell survival. Neutralizing tumor acidity improves the therapeutic efficacy of current treatments including immunotherapies. Vacuolar-ATPase (V-ATPase) proton pumps encompass unique plasma membrane-associated subunit isoforms, making this molecule an important target for anticancer therapy. Here, we examined the in vivo therapeutic efficacy of an antibody (a2v-mAB) targeting specific V-ATPase-'V0a2' surface isoform in controlling ovarian tumor growth. In vitro a2v-mAb treatment inhibited the proton pump activity in ovarian cancer (OVCA) cells. In vivo intraperitoneal a2v-mAb treatment drastically delayed ovarian tumor growth with no measurable in vivo toxicity in a transplant tumor model. To explore the possible mechanism causing delayed tumor growth, histochemical analysis of the a2v-mAb-treated tumor tissues displayed high immune cell infiltration (M1-macrophages, neutrophils, CD103 cells, and NK cells) and an enhanced antitumor response (iNOS, IFN-y, IL-1α) compared to control. There was marked decrease in CA-125-positive cancer cells and an enhanced active caspase-3 expression in a2v-mAb-treated tumors. RNA-seq analysis of a2v-mAb tumor tissues further revealed upregulation of apoptosis-related and toll-like receptor pathway-related genes. Indirect coculture of a2v-mAb-treated OVCA cells with human PBMCs in an unbuffered medium led to an enhanced gene expression of antitumor molecules IFN-y, IL-17, and IL-12-A in PBMCs, further validating the in vivo antitumor responses. In conclusion, V-ATPase inhibition using a monoclonal antibody directed against the V0a2 isoform increases antitumor immune responses and could therefore constitute an effective treatment strategy in OVCA.

Katara, G. K., A. Kulshrestha, S. Schneiderman, V. Riehl, S. Ibrahim, and K. D. Beaman, "Interleukin-22 promotes development of malignant lesions in a mouse model of spontaneous breast cancer.", Molecular oncology, vol. 14, issue 1, pp. 211-224, 2020. Abstract

Interleukin (IL)-22 is recognized as a tumor-supporting cytokine and is implicated in the proliferation of multiple epithelial cancers. In breast cancer, the current knowledge of IL-22 function is based on cell line models and little is known about how IL-22 affects the tumor initiation, proliferation, invasion, and metastasis in the in vivo system. Here, we investigated the tumor stage-specific function of IL-22 in disease development by evaluating the stage-by-stage progression of breast cancer in an IL-22 knockout spontaneous breast cancer mouse model. We found that among all the stages, IL-22 is specifically upregulated in tumor microenvironment (TME) during the malignant transformation stage of breast tumor progression. The deletion of IL-22 gene leads to the arrest of malignant transition stage, and reduced invasion and tumor burden. Administration of recombinant IL-22 in the TME does not influence in vivo tumor initiation and proliferation but only promotes malignant transformation of cancer cells. Mechanistically, deletion of IL-22 gene causes downregulation of epithelial-to-mesenchymal transition (EMT)-associated transcription factors in breast tumors, suggesting EMT as the mechanism of regulation of malignancy by IL-22. Clinically, in human breast tumor tissues, increased number of IL-22 cells in the TME is associated with an aggressive phenotype of breast cancer. For the first time, this study provides an insight into the tumor stage-specific function of IL-22 in breast tumorigenesis.

2019
Kulshrestha, A., G. K. Katara, S. A. Ibrahim, V. Riehl, M. Sahoo, J. Dolan, K. W. Meinke, M. R. Pins, and K. D. Beaman, "Targeting V-ATPase Isoform Restores Cisplatin Activity in Resistant Ovarian Cancer: Inhibition of Autophagy, Endosome Function, and ERK/MEK Pathway.", Journal of oncology, vol. 2019, pp. 2343876, 2019. Abstract

Ovarian cancer (OVCA) patients often develop tolerance to standard platinum therapy that accounts for extensive treatment failures. Cisplatin resistant OVCA cells (cis-R) display enhanced survival mechanisms to cope with therapeutic stress. In these cells, increased autophagy process assists in chemoresistance by boosting the nutrient pool under stress. To improve the treatment response, both protective autophagy inhibition and its overactivation are showing efficacy in chemosensitization. Autophagy requires a tightly regulated intracellular pH. Vacuolar ATPases (V-ATPases) are proton extruding nanomotors present on cellular/vesicular membranes where they act as primary pH regulators. V-ATPase 'a2' isoform (V0a2), the major pH sensing unit, is markedly overexpressed on the plasma membrane and the early endosomes of OVCA cells. Previously, V0a2 inhibition sensitized cis-R cells to platinum drugs by acidifying cytosolic pH that elevated DNA damage. Here, we examined how V0a2 inhibition affected endosomal function and the autophagy process as a possible factor for cisplatin sensitization. Clinically, V0a2 expression was significantly higher in tissues from drug nonresponder OVCA patients compared to treatment responders. In vitro V0a2 knockdown in cis-R cells (sh-V0a2-cisR) significantly reduced the tumor sphere-forming ability and caused complete disintegration of the spheres upon cisplatin treatment. The apoptotic capacity of sh-V0a2-cisR improved substantially with potentiation of both intrinsic and extrinsic apoptotic pathway when treated with cisplatin. Unlike the chemical V-ATPase inhibitors that acutely induce autophagy, here, the stable V0a2 inhibition dampened the protective autophagy process in sh-V0a2-cisR cells with downregulated expression of proteins beclin-1, ATG-7, and LC3B and low autophagosome numbers compared to control cis-R cells. These cells showed downregulated ERK/MEK pathway that is known to repress autophagy. Interestingly, upon cisplatin treatment of sh-V0a2-cisR, the autophagy initiation proteins (LC3B, ATG7, and Beclin 1) were found upregulated as a stress response compared to the untreated cells. However, there was a concomitant downstream autophagosome accumulation and an enhanced P62 protein levels indicating the overall block in autophagy flux. Mechanistically, V0a2 knockdown caused defects in early endosome function as the transferrin internalization was impaired. Taken together, this study provides a novel insight into the mechanism by which V-ATPase-isoform regulates autophagy that assists in chemoresistance in ovarian cancer. We conclude that V-ATPase-V0a2 is a potent target for developing an effective treatment to enhance patient survival rates in ovarian cancer.

2018
Sahoo, M., G. K. Katara, M. Y. Bilal, S. A. Ibrahim, A. Kulshrestha, S. Fleetwood, K. Suzue, and K. D. Beaman, "Hematopoietic stem cell specific V-ATPase controls breast cancer progression and metastasis via cytotoxic T cells.", Oncotarget, vol. 9, issue 69, pp. 33215-33231, 2018 Sep 04. Abstract

The interaction of recruited immune effector cells and cancer cells within tumor microenvironment (TME) shapes the fate of cancer progression and metastasis. Many cancers including breast cancer, express a specific vacuolar ATPase (a2V) on their cell surface which acidifies the extracellular milieu helping cancer cell proliferation and metastasis. To understand the role of immune cell-associated-a2V during breast tumor pathogenesis, we knocked-out a2V (KO) from the hematopoietic stem cells (HSC) and generated breast tumors in mice. The a2V-KO mice developed faster growing, larger, and metastatic breast tumors compared to control mice. Further investigation of the TME revealed a significant reduction in the presence of CD4 and CD8 T cells in the a2V-KO tumors. Targeted RNA-Seq of the cells of the TME demonstrated that pro-inflammatory cytokines, death receptors, death receptor ligands, and cytotoxic effectors were significantly down-regulated within the a2V-KO TME. Interestingly, analysis of immune cells in the blood, spleen, and thymus of the non-tumor bearing a2V-KO mice revealed a significant decrease in CD4 and CD8 T cell populations. For the first time, this study demonstrates that inhibition of V-ATPase expression in HSC leads to a decrease in CD4 and CD8 T cell populations and thus promotes breast tumor growth and metastasis.

Katara, G. K., A. Kulshrestha, L. Mao, X. Wang, M. Sahoo, S. Ibrahim, S. Pamarthy, K. Suzue, G. S. Shekhawat, A. Gilman-Sachs, et al., "Mammary epithelium-specific inactivation of V-ATPase reduces stiffness of extracellular matrix and enhances metastasis of breast cancer.", Molecular oncology, vol. 12, issue 2, pp. 208-223, 2018 02. Abstract

Extracellular matrix (ECM) critically impacts tumor progression and is influenced by both cancer and host tissue cells. While our understanding of cancer cell ECM remodeling is widespread, the importance of host tissue ECM, which provides initial congenial environment for primary tumor formation, is partly understood. Here, we report a novel role of epithelial cell-associated vacuolar ATPase 'a2' isoform (a2V) in regulating breast tissue ECM stiffness to control metastasis. Using a mammary gland-specific a2V-knockout model, we show that in the absence of a2V, breast tumors exhibit atypically soft tumor phenotype, less tumor rigidity, and necrotic tumor microenvironment. These tumors contain a decreased number of cancer cells at primary tumor site, but showed extensive metastases compared to control. Nanomechanical evaluation of normal breast tissues revealed a decrease in stiffness and collagen content in ECM of a2V-deleted breast tissues. Mechanistically, inhibition of a2V expression caused dispersed Golgi morphology with relocation of glycosyltransferase enzymes to early endosomes in mammary epithelial cells. This resulted in defective glycosylation of ECM proteins and production of compromised ECM that further influenced tumor metastasis. Clinically, in patients with cancer, low a2V expression levels in normal breast tissue correlated with lymph node metastasis. Thus, using a new knockout mouse model, we have identified a2V expression in epithelial cells as a key requirement for proper ECM formation in breast tissue and its expression levels can significantly modulate breast tumor dissemination. Evaluation of a2V expression in normal breast tissues can help in identifying patients with high risk of developing metastases.

2017
Kulshrestha, A., G. K. Katara, S. A. Ibrahim, R. Patil, S. A. Patil, and K. D. Beaman, "Microtubule inhibitor, SP-6-27 inhibits angiogenesis and induces apoptosis in ovarian cancer cells.", Oncotarget, vol. 8, issue 40, pp. 67017-67028, 2017 Sep 15. Abstract17549-256555-5-pb.pdf

In ovarian cancer (OVCA), treatment failure due to chemo-resistance is a serious challenge. It is therefore critical to identify new therapies that are effective against resistant tumors and have reduced side effects. We recently identified 4-H-chromenes as tubulin depolymerizing agents that bind to colchicine site of beta-tubulin. Here, we screened a chemical library of substituted 4-H-chromenes and identified SP-6-27 to exhibit most potent anti-proliferative activity towards a panel of human cisplatin sensitive and resistant OVCA cell lines with 50% inhibitory concentration (IC; mean ± SD) ranging from 0.10 ± 0.01 to 0.84 ± 0.20 μM. SP-6-27 exhibited minimum cytotoxicity to normal ovarian epithelia. A pronounced decrease in microtubule density as well as G2/M cell cycle arrest was observed in SP-6-27 treated cisplatin sensitive/resistant OVCA cells. The molecular mechanism of SP-6-27 induced cell death revealed modulation in cell-cycle regulation by upregulation of growth arrest and DNA damage inducible alpha transcripts (GADD45). An enhanced intrinsic apoptosis was observed in OVCA cells through upregulation of Bax, Apaf-1, caspase-6, -9, and caspase-3. wound healing assay revealed reduced OVCA cell migration upon SP-6-27 treatment. Additionally, SP-6-27 and cisplatin combinatorial treatment showed enhanced cytotoxicity in chemo-sensitive/resistant OVCA cells. Besides effect on cancer cells, SP-6-27 further restrained angiogenesis by inhibiting capillary tube formation by human umbilical vein endothelial cells (HUVEC). Together, these findings show that the chromene analog SP-6-27 is a novel chemotherapeutic agent that offers important advantages for the treatment of ovarian cancer.

2016
Ibrahim, S. A., A. Kulshrestha, G. K. Katara, M. A. Amin, and K. D. Beaman, "Cancer derived peptide of vacuolar ATPase 'a2' isoform promotes neutrophil migration by autocrine secretion of IL-8.", Scientific reports, vol. 6, pp. 36865, 2016 Nov 15. Abstractibrahim_2016.pdf

Neutrophils play significant regulatory roles within the tumor microenvironment by directly promoting tumor progression that leads to poor clinical outcomes. Identifying the tumor associated molecules that regulate neutrophil infiltration into tumors may provide new and specific therapeutic targets for cancer treatment. The a2-isoform of vacuolar ATPase (a2V) is uniquely and highly expressed on cancer cell plasma membrane. Cancer cells secrete a peptide from a2V (a2NTD) that promotes the pro-tumorigenic properties of neutrophils. This provides a2V the propensity to control neutrophil migration. Here, we report that the treatment of human neutrophils with recombinant a2NTD leads to neutrophil adherence and polarization. Moreover, a2NTD treatment activates surface adhesion receptors, as well as FAK and Src kinases that are essential regulators of the migration process in neutrophils. Functional analysis reveals that a2NTD can act as a chemo-attractant and promotes neutrophil migration. In addition, a2Neuɸ secrete high levels of IL-8 via NF-κB pathway activation. Confirmatory assays demonstrate that the promoted migration of a2Neuɸ was dependent on the autocrine secretion of IL-8 from a2Neuɸ. These findings demonstrate for the first time the direct regulatory role of cancer associated a2-isoform V-ATPase on neutrophil migration, suggesting a2V as a potential target for cancer therapy.

Kulshrestha, A., G. K. Katara, J. Ginter, S. Pamarthy, S. A. Ibrahim, M. K. Jaiswal, C. Sandulescu, R. Periakaruppan, J. Dolan, A. Gilman-Sachs, et al., "Selective inhibition of tumor cell associated Vacuolar-ATPase 'a2' isoform overcomes cisplatin resistance in ovarian cancer cells.", Molecular oncology, vol. 10, issue 6, pp. 789-805, 2016 Jun. Abstract

Development of resistance to platinum compounds significantly hinders successful ovarian cancer (OVCA) treatment. In tumor cells, dysregulated pH gradient across cell membranes is a key physiological mechanism of metastasis/chemo-resistance. These pH alterations are mediated by aberrant activation of key multi-subunit proton pumps, Vacuolar-ATPases (V-ATPases). In tumor cells, its 'a2' isoform (V-ATPase-V0a2) is a component of functional plasma-membrane complex and promotes tumor invasion through tumor-acidification and immuno-modulation. Its involvement in chemo-resistance has not been studied. Here, we show that V-ATPase-V0a2 is over-expressed in acquired-cisplatin resistant OVCA cells (cis-A2780/cis-TOV112D). Of all the 'a' subunit isoforms, V-ATPase-V0a2 exhibited an elevated expression on plasma membrane of cisplatin-resistant cells compared to sensitive counterparts. Immuno-histochemistry revealed V-ATPase-V0a2 expression in both low grade (highly drug-resistant) and high grade (highly recurrent) human OVCA tissues indicating its role in a centralized mechanism of tumor resistance. In cisplatin resistant cells, shRNA mediated inhibition of V-ATPase-V0a2 enhanced sensitivity towards both cisplatin and carboplatin. This improved cytotoxicity was mediated by enhanced cisplatin-DNA-adduct formation and suppressed DNA-repair pathway, leading to enhanced apoptosis. Suppression of V0a2 activity strongly reduced cytosolic pH in resistant tumor cells, which is known to enhance platinum-associated DNA-damage. As an indicator of reduced metastasis and chemo-resistance, in contrast to plasma membrane localization, a diffused cytoplasmic localization of acidic vacuoles was observed in V0a2-knockdown resistant cells. Interestingly, pre-treatment with monoclonal V0a2-inhibitory antibody enhanced cisplatin cytotoxicity in resistant cells. Taken together, our findings suggest that the isoform specific inhibition of V-ATPase-V0a2 could serve as a therapeutic strategy for chemo-resistant ovarian carcinoma and improve efficacy of platinum drugs.

Beaman, K. D., M. K. Jaiswal, G. K. Katara, A. Kulshreshta, S. Pamarthy, S. Ibrahim, J. Kwak-Kim, and A. Gilman-Sachs, "Pregnancy is a model for tumors, not transplantation.", American journal of reproductive immunology (New York, N.Y. : 1989), vol. 76, issue 1, pp. 3-7, 2016 Jul. Abstract

Nearly 65 years have passed since Peter Medawar posed the following question: "How does the pregnant mother contrive to nourish within itself, for many weeks or months, a fetus that is an antigenically foreign body." Now, understanding of reproductive immunology has demonstrated that the HLA antigens in the placenta are non-classical and do not induce rejection. In the placenta and in tumors, 50% or more of the cells are cells of the immune system and were once thought to be primed and ready for killing tumors or the "fetal transplant" but these cells are not potential killers but abet the growth of either the tumor or the placenta. We believe that these cells are there to create an environment, which enhances either placental or tumor growth. By examining the similarities of the placenta's and tumor's immune cells, novel mechanisms to cause tumors to be eliminated can be devised.

2015
Ibrahim, S. A., G. K. Katara, A. Kulshrestha, M. K. Jaiswal, M. A. Amin, and K. D. Beaman, "Breast cancer associated a2 isoform vacuolar ATPase immunomodulates neutrophils: potential role in tumor progression.", Oncotarget, vol. 6, issue 32, pp. 33033-45, 2015 Oct 20. Abstractoncotarget_2015_first_author.pdf

In invasive breast cancer, tumor associated neutrophils (TAN) represent a significant portion of the tumor mass and are associated with increased angiogenesis and metastasis. Identifying the regulatory factors that control TAN behavior will help in developing ideal immunotherapies. Vacuolar ATPases (V-ATPases), multi-subunit proton pumps, are highly expressed in metastatic breast cancer cells. A cleaved peptide from a2 isoform V-ATPase (a2NTD) has immunomodulatory role in tumor microenvironment. Here, we report for the first time the role of V-ATPase in neutrophils modulation. In invasive breast cancer cells, a2NTD was detected and a2V was highly expressed on the surface. Immunohistochemical analysis of invasive breast cancer tissues revealed that increased neutrophil recruitment and blood vessel density correlated with increased a2NTD levels. In order to determine the direct regulatory role of a2NTD on neutrophils, recombinant a2NTD was used for the treatment of neutrophils isolated from the peripheral blood of healthy volunteers. Neutrophils treated with a2NTD (a2Neuɸ) showed increased secretion of IL-1RA, IL-10, CCL-2 and IL-6 that are important mediators in cancer related inflammation. Moreover, a2Neuɸ exhibited an increased production of protumorigenic factors including IL-8, matrix metaloprotinase-9 and vascular endothelial growth factor. Further, functional characterization of a2Neuɸ revealed that a2Neuɸ derived products induce in vitro angiogenesis as well as increase the invasiveness of breast cancer cells. This study establishes the modulatory effect of breast cancer associated a2V on neutrophils, by the action of a2NTD, which has a positive impact on tumor progression, supporting that a2V can be a potential selective target for breast cancer therapy.

Kulshrestha, A., G. K. Katara, S. Ibrahim, S. Pamarthy, M. K. Jaiswal, A. Gilman Sachs, and K. D. Beaman, "Vacuolar ATPase 'a2' isoform exhibits distinct cell surface accumulation and modulates matrix metalloproteinase activity in ovarian cancer.", Oncotarget, vol. 6, issue 6, pp. 3797-810, 2015 Feb 28. Abstractoncotarget_2015_arpita.pdf

Tumor associated vacuolar H+-ATPases (V-ATPases) are multi-subunit proton pumps that acidify tumor microenvironment, thereby promoting tumor invasion. Subunit 'a' of its V0 domain is the major pH sensing unit that additionally controls sub-cellular targeting of V-ATPase and exists in four different isoforms. Our study reports an elevated expression of the V-ATPase-V0a2 isoform in ovarian cancer(OVCA) tissues and cell lines(A2780, SKOV-3 and TOV-112D). Among all V0'a' isoforms, V0a2 exhibited abundant expression on OVCA cell surface while normal ovarian epithelia did not. Sub-cellular distribution of V-ATPase-V0a2 confirmed its localization on plasma-membrane, where it was also co-associated with cortactin, an F-actin stabilizing protein at leading edges of cancer cells. Additionally, V0a2 was also localized in early and late endosomal compartments that are sites for modulations of several signaling pathways in cancer. Targeted inhibition of V-ATPase-V0a2 suppressed matrix metalloproteinase activity(MMP-9 & MMP-2) in OVCA cells. In conclusion, V-ATPase-V0a2 isoform is abundantly expressed on ovarian tumor cell surface in association with invasion assembly related proteins and plays critical role in tumor invasion by modulating the activity of matrix-degrading proteases. This study highlights for the first time, the importance of V-ATPase-V0a2 isoform as a distinct biomarker and possible therapeutic target for treatment of ovarian carcinoma.

2014
Salem, A. H., G. G. Zhanel, S. A. Ibrahim, and A. M. Noreddin, "Monte Carlo simulation analysis of ceftobiprole, dalbavancin, daptomycin, tigecycline, linezolid and vancomycin pharmacodynamics against intensive care unit-isolated methicillin-resistant Staphylococcus aureus", Clinical and Experimental Pharmacology and Physiology, vol. 41, no. 6: Wiley Online Library, pp. 437–443, 2014. Abstract
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Ibrahim, S. A., A. E. Ali, and A. K. Ahmady, "Phenotypic and genotypic identification of extended spectrum-lactamases (ESBLs) among clinical isolates of Escherichia coli", African Journal of Microbiology Research, vol. 8, no. 19: Academic Journals, pp. 1974–1981, 2014. Abstract
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