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Motlaghzadeh Y, Bilezikian JP, Sellmeyer DE. Rare Causes of Hypercalcemia: 2021 Update. J Clin Endocrinol Metab 2021; 106:3113-3128. [PMID: 34240162 DOI: 10.1210/clinem/dgab504] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/11/2021] [Indexed: 11/19/2022]
Abstract
CONTEXT Primary hyperparathyroidism and malignancy are the etiologies in 90% of cases of hypercalcemia. When these entities are not the etiology of hypercalcemia, uncommon conditions need to be considered. In 2005, Jacobs and Bilezikian published a clinical review of rare causes of hypercalcemia, focusing on mechanisms and pathophysiology. This review is an updated synopsis of rare causes of hypercalcemia, extending the observations of the original article. EVIDENCE ACQUISITION Articles reporting rare associations between hypercalcemia and unusual conditions were identified through a comprehensive extensive PubMed-based search using the search terms "hypercalcemia" and "etiology," as well as examining the references in the identified case reports. We categorized the reports by adults vs pediatric and further categorized the adult reports based on etiology. Some included reports lacked definitive assessment of etiology and are reported as unknown mechanism with discussion of likely etiology. EVIDENCE SYNTHESIS There is a growing understanding of the breadth of unusual causes of hypercalcemia. When the cause of hypercalcemia is elusive, a focus on mechanism and review of prior reported cases is key to successful determination of the etiology. CONCLUSIONS The ever-expanding reports of patients with rare and even unknown mechanisms of hypercalcemia illustrate the need for continued investigation into the complexities of human calcium metabolism.
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Affiliation(s)
- Yasaman Motlaghzadeh
- Stanford University School of Medicine, Division of Endocrinology, Gerontology and Metabolism, Palo Alto, CA 94305, USA
| | - John P Bilezikian
- Division of Endocrinology, Department of Medicine, Vagelos College of Physicians and Surgeons, Columbia University, New York, NY 10032, USA
| | - Deborah E Sellmeyer
- Stanford University School of Medicine, Division of Endocrinology, Gerontology and Metabolism, Palo Alto, CA 94305, USA
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Pitsava G, Stratakis CA, Faucz FR. PRKAR1A and Thyroid Tumors. Cancers (Basel) 2021; 13:cancers13153834. [PMID: 34359735 PMCID: PMC8345073 DOI: 10.3390/cancers13153834] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2021] [Revised: 07/24/2021] [Accepted: 07/27/2021] [Indexed: 12/12/2022] Open
Abstract
Simple Summary In 2021 it is estimated that there will be 44,280 new cases of thyroid cancer in the United States and the incidence rate is higher in women than in men by almost 3 times. Well-differentiated thyroid cancer is the most common subtype of thyroid cancer and includes follicular (FTC) and papillary (PTC) carcinomas. Over the last decade, researchers have been able to better understand the molecular mechanisms involved in thyroid carcinogenesis, identifying genes including but not limited to RAS, BRAF, PAX8/PPARγ chromosomal rearrangements and others, as well as several tumor genes involved in major signaling pathways regulating cell cycle, differentiation, growth, or proliferation. Patients with Carney complex (CNC) have increased incidence of thyroid tumors, including cancer, yet little is known about this association. CNC is a familial multiple neoplasia and lentiginosis syndrome cause by inactivating mutations in the PRKAR1A gene which encodes the regulatory subunit type 1α of protein kinase A. This work summarizes what we know today about PRKAR1A defects in humans and mice and their role in thyroid tumor development, as the first such review on this issue. Abstract Thyroid cancer is the most common type of endocrine malignancy and the incidence is rapidly increasing. Follicular (FTC) and papillary thyroid (PTC) carcinomas comprise the well-differentiated subtype and they are the two most common thyroid carcinomas. Multiple molecular genetic and epigenetic alterations have been identified in various types of thyroid tumors over the years. Point mutations in BRAF, RAS as well as RET/PTC and PAX8/PPARγ chromosomal rearrangements are common. Thyroid cancer, including both FTC and PTC, has been observed in patients with Carney Complex (CNC), a syndrome that is inherited in an autosomal dominant manner and predisposes to various tumors. CNC is caused by inactivating mutations in the tumor-suppressor gene encoding the cyclic AMP (cAMP)-dependent protein kinase A (PKA) type 1α regulatory subunit (PRKAR1A) mapped in chromosome 17 (17q22–24). Growth of the thyroid is driven by the TSH/cAMP/PKA signaling pathway and it has been shown in mouse models that PKA activation through genetic ablation of the regulatory subunit Prkar1a can cause FTC. In this review, we provide an overview of the molecular mechanisms contributing to thyroid tumorigenesis associated with inactivation of the RRKAR1A gene.
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Affiliation(s)
- Georgia Pitsava
- Division of Intramural Population Health Research, Eunice Kennedy Shriver National Institutes of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA;
- Section on Endocrinology and Genetics, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA;
| | - Constantine A. Stratakis
- Section on Endocrinology and Genetics, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA;
| | - Fabio R. Faucz
- Section on Endocrinology and Genetics, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA;
- Correspondence: ; Tel.: +1-301-451-7177
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Perez DR, Sklar LA, Chigaev A, Matlawska-Wasowska K. Drug repurposing for targeting cyclic nucleotide transporters in acute leukemias - A missed opportunity. Semin Cancer Biol 2020; 68:199-208. [PMID: 32044470 DOI: 10.1016/j.semcancer.2020.02.004] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2019] [Revised: 10/01/2019] [Accepted: 02/03/2020] [Indexed: 02/08/2023]
Abstract
While current treatment regimens for acute leukemia can dramatically improve patient survival, there remains room for improvement. Due to its roles in cell differentiation, cell survival, and apoptotic signaling, modulation of the cyclic AMP (cAMP) pathway has provided a meaningful target in hematological malignancies. Several studies have demonstrated that gene expression profiles associated with increased pro-survival cAMP activity or downregulation of various pro-apoptotic factors associated with the cAMP pathway are apparent in acute leukemia patients. Previous work to increase leukemia cell intracellular cAMP focused on the use of cAMP analogs, stimulating cAMP production via transmembrane-associated adenylyl cyclases, or decreasing cAMP degradation by inhibiting phosphodiesterase activity. However, targeting cyclic nucleotide efflux by ATP-binding cassette (ABC) transporters represents an unexplored approach for modulation of intracellular cyclic nucleotide levels. Preliminary studies have shown that inhibition of cAMP efflux can stimulate leukemia cell differentiation, cell growth arrest, and apoptosis, indicating that targeting cAMP efflux may show promise for future therapeutic development. Furthermore, inhibition of cyclic nucleotide transporter activity may also contribute multiple anticancer benefits by reducing extracellular pro-survival signaling in malignant cells. Hence, several opportunities for drug repurposing may exist for targeting cyclic nucleotide transporters.
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Affiliation(s)
- Dominique R Perez
- Department of Pathology, Health Sciences Center, University of New Mexico, Albuquerque, NM, USA; Center for Molecular Discovery, Health Sciences Center, University of New Mexico, Albuquerque, NM, USA
| | - Larry A Sklar
- Department of Pathology, Health Sciences Center, University of New Mexico, Albuquerque, NM, USA; Center for Molecular Discovery, Health Sciences Center, University of New Mexico, Albuquerque, NM, USA; University of New Mexico Comprehensive Cancer Center, Albuquerque, NM, USA
| | - Alexandre Chigaev
- Department of Pathology, Health Sciences Center, University of New Mexico, Albuquerque, NM, USA; Center for Molecular Discovery, Health Sciences Center, University of New Mexico, Albuquerque, NM, USA; University of New Mexico Comprehensive Cancer Center, Albuquerque, NM, USA.
| | - Ksenia Matlawska-Wasowska
- University of New Mexico Comprehensive Cancer Center, Albuquerque, NM, USA; Department of Pediatrics, Division of Hematology-Oncology, Health Sciences Center, University of New Mexico, Albuquerque, NM, USA.
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Russart KLG, Huk D, Nelson RJ, Kirschner LS. Elevated aggressive behavior in male mice with thyroid-specific Prkar1a and global Epac1 gene deletion. Horm Behav 2018; 98:121-129. [PMID: 29289659 PMCID: PMC5828986 DOI: 10.1016/j.yhbeh.2017.12.012] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/18/2017] [Revised: 12/19/2017] [Accepted: 12/23/2017] [Indexed: 11/25/2022]
Abstract
Alterations in circulating thyroid hormone concentrations are associated with several psychological and behavioral disorders. In humans, behavioral disorders such as anxiety, depression, and attention-deficit hyperactivity disorder can be associated with thyroid disease. The Tpo-Cre;Prkar1aflox/flox;Epac1-/- (R1A-Epac1KO) mice, originally bred to investigate the role of exchange protein directly activated by cAMP (Epac1) in follicular thyroid cancer, displayed self-mutilating and aggressive behaviors during casual observation. To assess these atypical responses, behavioral testing was conducted with the R1A-Epac1KO mice, as well as their single knockout counterparts, the thyroid-specific Prkar1a-/- and global Epac1-/- mice. Mice of all three genotypes demonstrated increased aggressive behavior against an intruder mouse. In addition, Epac1-/- mice increased response to an auditory stimulus, and the Prkar1a-/- and R1A-Epac1KO mice increased swimming behavior in the Porsolt forced swim test. Both Prkar1a-/- mice and R1A-Epac1KO mice have increased circulating thyroxine and corticosterone concentrations. Although hyperthyroidism has not been previously associated with aggression, increased thyroid hormone signaling might contribute to the increased aggressive response to the intruder mouse, as well as the increased swimming response. Mice with a genetic background of Tpo-Cre;Prkar1aflox/flox;Epac1-/- are aggressive, and both the thyroid-specific knockout of Prkar1a and global knockout of Epac1 likely contribute to this aggressive behavior. This study supports the hypothesis that altered thyroid signaling and aggressive behavior are linked.
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Affiliation(s)
- Kathryn L G Russart
- Department of Neuroscience, The Ohio State University Wexner Medical Center, Columbus, OH 43210, USA.
| | - Danielle Huk
- Department of Cancer Biology and Genetics, Internal Medicine, The Ohio State University, Columbus, OH 43210, USA
| | - Randy J Nelson
- Department of Neuroscience, The Ohio State University Wexner Medical Center, Columbus, OH 43210, USA
| | - Lawrence S Kirschner
- Department of Cancer Biology and Genetics, Internal Medicine, The Ohio State University, Columbus, OH 43210, USA; Division of Endocrinology, Diabetes, and Metabolism, Department of Internal Medicine, The Ohio State University Wexner Medical Center, Columbus, OH 43210, USA
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Pattabiraman DR, Bierie B, Kober KI, Thiru P, Krall JA, Zill C, Reinhardt F, Tam WL, Weinberg RA. Activation of PKA leads to mesenchymal-to-epithelial transition and loss of tumor-initiating ability. Science 2016; 351:aad3680. [PMID: 26941323 DOI: 10.1126/science.aad3680] [Citation(s) in RCA: 242] [Impact Index Per Article: 30.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The epithelial-to-mesenchymal transition enables carcinoma cells to acquire malignancy-associated traits and the properties of tumor-initiating cells (TICs). TICs have emerged in recent years as important targets for cancer therapy, owing to their ability to drive clinical relapse and enable metastasis. Here, we propose a strategy to eliminate mesenchymal TICs by inducing their conversion to more epithelial counterparts that have lost tumor-initiating ability. We report that increases in intracellular levels of the second messenger, adenosine 3',5'-monophosphate, and the subsequent activation of protein kinase A (PKA) induce a mesenchymal-to-epithelial transition (MET) in mesenchymal human mammary epithelial cells. PKA activation triggers epigenetic reprogramming of TICs by the histone demethylase PHF2, which promotes their differentiation and loss of tumor-initiating ability. This study provides proof-of-principle for inducing an MET as differentiation therapy for TICs and uncovers a role for PKA in enforcing and maintaining the epithelial state.
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Affiliation(s)
| | - Brian Bierie
- Whitehead Institute for Biomedical Research, Cambridge, MA 02142, USA
| | | | - Prathapan Thiru
- Whitehead Institute for Biomedical Research, Cambridge, MA 02142, USA
| | - Jordan A Krall
- Whitehead Institute for Biomedical Research, Cambridge, MA 02142, USA
| | - Christina Zill
- Whitehead Institute for Biomedical Research, Cambridge, MA 02142, USA
| | - Ferenc Reinhardt
- Whitehead Institute for Biomedical Research, Cambridge, MA 02142, USA
| | - Wai Leong Tam
- Whitehead Institute for Biomedical Research, Cambridge, MA 02142, USA. Genome Institute of Singapore, 60 Biopolis Street, Singapore. Cancer Science Institute of Singapore, 14 Medical Drive, Singapore
| | - Robert A Weinberg
- Whitehead Institute for Biomedical Research, Cambridge, MA 02142, USA. Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA. Ludwig Center for Molecular Oncology at MIT, Cambridge, MA 02142, USA.
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Kallas M, Green F, Hewison M, White C, Kline G. Rare causes of calcitriol-mediated hypercalcemia: a case report and literature review. J Clin Endocrinol Metab 2010; 95:3111-7. [PMID: 20427501 DOI: 10.1210/jc.2009-2673] [Citation(s) in RCA: 81] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/12/2023]
Abstract
CONTEXT Calcitriol-mediated hypercalcemia resulting from elevated extrarenal 25-hydroxyvitamin D-1alpha-hydroxylase (1alpha-hydroxylase) activity has not previously been described in giant cell polymyositis. CASE We report an unusual case of hypercalcemia due to disseminated granulomatous disease in a 62-yr-old woman with profound proximal muscle weakness and weight loss. She was initially diagnosed with vitamin D deficiency myopathy with a low serum 25-hydroxyvitamin D; serum calcium at this time was low-normal. Vitamin D(3) 3000 IU daily was prescribed. One month later, blood work showed new hypercalcemia and hypercalciuria with normalized 25-hydroxyvitamin D. 1,25-dihydroxyvitamin D was high-normal, despite a suppressed PTH, undetectable PTHrP, and essentially normal renal function. Her hypercalcemia resolved, and her strength improved only after prednisone was added to bisphosphonate therapy. Two weeks later, she died from acute congestive heart failure. METHODS AND RESULTS Autopsy revealed a disseminated giant cell myositis affecting skeletal, cardiac, and gastrointestinal smooth muscle. Immunohistochemistry localized 1alpha-hydroxylase to the inflammatory infiltrates in skeletal and cardiac muscle. EVIDENCE A review of English publications in Medline and Embase, including a reference search of retrieved articles, revealed that calcitriol-mediated hypercalcemia has been described in over 30 conditions, most of which are granulomatous in nature, ranging from inflammatory conditions and foreign body exposures to infections and neoplasms. CONCLUSIONS Hypercalcemia resulting from autonomous 1alpha-hydroxylase activity may be unmasked by low-dose vitamin D supplementation and should not be excluded from the differential diagnosis of nonparathyroid causes if the serum calcitriol is inappropriately normal, rather than frankly elevated.
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Affiliation(s)
- Melissa Kallas
- Department of Medicine, University of Calgary, 1403 29 Street NW, Calgary, Alberta, Canada T2N 4J8
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Abstract
CONTEXT Although hypercalcemia is usually caused by primary hyperparathyroidism or malignancy, a number of other conditions can be important to consider. This review considers unusual causes of hypercalcemia that are generally not found in reviews on this subject. EVIDENCE ACQUISITION Articles describing rarely reported associations between hypercalcemia and unusual causes were identified through a computer search of the terms hypercalcemia/etiology and through the references listed in those articles. We grouped the 58 different reports into categories defined by a presumed etiology: increased levels of 1,25-dihydroxyvitamin D or PTHrP, occult milk-alkali syndrome, and undefined mechanisms. Reports in infants and children are listed separately, as are reports of pseudohypercalcemia, situations that are not truly hypercalcemic because the ionized calcium is normal. EVIDENCE SYNTHESIS In some situations, as this review points out, a number of unusual causes of hypercalcemia are important to consider. The search for an elusive cause of hypercalcemia is best accomplished by the most likely potential mechanism. An orderly search in this manner is likely to reveal the underlying cause. CONCLUSIONS That so many patients have been described with rare and usually poorly understood causes of hypercalcemia highlights our incomplete understanding of calcium metabolism in humans and suggests additional areas in which directed clinical investigation might improve our knowledge of the normal metabolism of calcium.
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Affiliation(s)
- Thomas P Jacobs
- Columbia University Medical Center, 161 Fort Washington Avenue, New York, New York 10032, USA.
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O'Byrne KJ, Steward WP. Tumour angiogenesis: a novel therapeutic target in patients with malignant disease. Expert Opin Emerg Drugs 2005; 6:155-74. [PMID: 15989502 DOI: 10.1517/14728214.6.1.155] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Angiogenesis refers to the formation of new blood vessels from an existing vasculature and is recognised as a necessary requirement for most tumours to grow beyond 1-2 mm in diameter. Factors established as playing a role in angiogenesis may be divided into two principal groups: (a) those that stimulate endothelial cell proliferation and/or elongation, migration and vascular morphogenesis including vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), platelet derived endothelial cell growth factor (PD-ECGF) and the tie and tek receptors, and (b) proteases and their receptors involved in the breakdown of basement membranes and the extracellular matrix (ECM) including the matrix metalloproteinases (MMPs), cathepsins and those involved in the plasmin cascade. Angiogenesis has been identified as a potential target for development of anticancer agents. The discovery of a range of naturally-occurring factors which negatively regulate angiogenesis, including the thrombospondins, angiostatin and endostatin, and the tissue inhibitors of MMPs (TIMPs), has given added impetus to this approach. Synthetic anti-angiogenic compounds have been developed, including TNP-470, carboxyamidotriazole, VEGF-tyrosine kinase inhibitors and MMP inhibitors (MMPI) which, like the naturally-occurring anti-angiogenic factors, inhibit angiogenesis in vitro and in vivo, and tumour development, growth and metastasis in vivo. Anti-angiogenic agents also enhance the antitumour activity of many conventional cytotoxic chemotherapeutic agents. Such combinations may have a particular role as adjuvant therapies following surgical resection of primary tumours. Unlike tumour cells, tumour associated endothelial cells do not develop resistance to anti-angiogenic agents. Furthermore, anti-angiogenic agents are generally cytostatic rather than cytotoxic. As such, these agents are, in general, likely to be administered over long periods of time. Therefore, as well as having proven antitumour efficacy, an anti-angiogenic compound will need to be well-tolerated if it is to become established in the clinical management of patients with malignant disease.
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Affiliation(s)
- K J O'Byrne
- University Department of Oncology, Osborne Building, Leicester Royal Infirmary, Infirmary Square, Leicester, LE1 5WW, UK.
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Roymans D, Willems R, Vissenberg K, De Jonghe C, Grobben B, Claes P, Lascu I, Van Bockstaele D, Verbelen JP, Van Broeckhoven C, Slegers H. Nucleoside diphosphate kinase beta (Nm23-R1/NDPKbeta) is associated with intermediate filaments and becomes upregulated upon cAMP-induced differentiation of rat C6 glioma. Exp Cell Res 2000; 261:127-38. [PMID: 11082283 DOI: 10.1006/excr.2000.5037] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Nucleoside diphosphate kinases (Nm23/NDPK) are enzymes functional in cell proliferation, differentiation, development, tumor progression, and metastasis. Nevertheless, no consensus exists about the molecular mechanism by which Nm23/NDPK isoforms exert their role in these processes. We investigated the expression of the rat Nm23-R1/NDPKbeta and Nm23-R2/NDPKalpha isoforms, homologues of the human Nm23-H1/NDPK A and Nm23-H2/NDPK B proteins, respectively, upon cAMP-induced differentiation of rat C6 glioma cells and demonstrated a differential interaction with intermediate filaments. Semiquantitative RT-PCR, immunoblotting, and flow cytometry showed a constitutive expression of both Nm23 isoforms. After induction of differentiation in C6 cells with cAMP analogs or isoproterenol, a dose-dependent 2- and 2.5-fold upregulation of the Nm23-R1 mRNA and protein, respectively, was observed. In contrast, the expression of Nm23-R2 remained unchanged. Localization of both isoforms with confocal laser scanning microscopy demonstrated a punctate reticular staining pattern for both Nm23 isoforms in the cytosol and processes of the cells which was particularly intense in the perinuclear region. In addition, while Nm23-R2 was colocalized and coimmunoprecipitated with vimentin in nondifferentiated cells, both isoforms were associated with GFAP in differentiated cells. The significance of these findings in relation to a possible function of Nm23 isoforms in cell proliferation, differentiation, and tumor-associated mechanisms is discussed.
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Affiliation(s)
- D Roymans
- Laboratory of Cellular Biochemistry, University of Antwerp, Wilrijk-Antwerpen, B-2610, Belgium
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Tortora G, Ciardiello F. Targeting of epidermal growth factor receptor and protein kinase A: molecular basis and therapeutic applications. Ann Oncol 2000; 11:777-83. [PMID: 10997803 DOI: 10.1023/a:1008390206250] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Affiliation(s)
- G Tortora
- Dipartimento di Endocrinologia e Oncologia Molecolare e Clinica, Università di Napoli Federico II, Italy.
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Budillon A, Di Gennaro E, Caraglia M, Barbarulo D, Abbruzzese A, Tagliaferri P. 8-Cl-cAMP antagonizes mitogen-activated protein kinase activation and cell growth stimulation induced by epidermal growth factor. Br J Cancer 1999; 81:1134-41. [PMID: 10584873 PMCID: PMC2374321 DOI: 10.1038/sj.bjc.6690820] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
The growth factor-activated mitogenic pathways are often disregulated in tumour cells and, therefore, they can provide specific molecular targets for novel anti-tumour approaches. 8-Chloro-cAMP (8-Cl-cAMP), a synthetic cAMP analogue, is a novel anti-tumour agent that has recently undergone clinical evaluation. We investigated the effects of 8-Cl-cAMP on the epidermal growth factor (EGF)/EGF receptor (EGF-R) signalling in human epidermoid cancer KB cells, which are responsive to the mitogenic stimulus of EGF. We found that the growth-promoting activity of EGF was completely abolished when EGF treatment was performed in combination with 8-Cl-cAMP. The inhibition of the EGF-induced proliferation by 8-Cl-cAMP was paralleled by the blockade of the EGF-stimulated activation of mitogen-activated protein kinases (MAPK), ERK-1 and ERK-2. Conversely, we found an increase of EGF-R expression and EGF-R tyrosine phosphorylation when KB cells were growth inhibited by 8-Cl-cAMP. Moreover, the activity of Raf-1 and MEK-1 protein kinases, the activators upstream MAPK in the phosphorylation cascade induced by EGF, was not modified in 8-Cl-cAMP-treated cells. We concluded that the impairment of KB cell response to EGF, induced by 8-Cl-cAMP, resides in the specific inhibition of MAPK/ERKs activity while the function of the upstream elements in the EGF-R signalling is preserved.
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Affiliation(s)
- A Budillon
- Istituto Nazionale dei Tumori, Fondazione G Pascale, Napoli, Italy
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