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Lv W, Zheng Y, Jiao J, Fu Y, Xu T, Zhang L, Zhang Z, Ma N. The Role of XBP1 in bone metabolism. Front Endocrinol (Lausanne) 2023; 14:1217579. [PMID: 37795354 PMCID: PMC10546391 DOI: 10.3389/fendo.2023.1217579] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/10/2023] [Accepted: 09/04/2023] [Indexed: 10/06/2023] Open
Abstract
Bone is a dynamic organ that, once formed, undergoes a constant remodeling process that includes bone resorption and synthesis. Osteoclasts and osteoblasts are primarily responsible for controlling this process. X-box binding protein 1 (XBP1), a transcription factor, affects the metabolism of bones in various ways. In recent years, numerous studies have revealed that XBP1 plays a vital role in bone metabolism, including osteoclast and osteoblast development, as well as in regulating immune cell differentiation that affects the immune microenvironment of bone remodeling. In this review, we highlight the regulatory mechanisms of XBP1 on osteoclasts and osteoblasts, how XBP1 affects the immune microenvironment of bone remodeling by influencing the differentiation of immune cells, and predict the possible future research directions of XBP1 to provide new insights for the treatment of bone-related metabolic diseases.
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Affiliation(s)
- Wenhao Lv
- Hospital of Stomatology, Jilin University, Changchun, China
| | - Youli Zheng
- The School and Hospital of Stomatology, Tianjin Medical University, Tianjin, China
| | - Junjun Jiao
- Hospital of Stomatology, Jilin University, Changchun, China
| | - Yu Fu
- Hospital of Stomatology, Jilin University, Changchun, China
| | - Tingrui Xu
- Hospital of Stomatology, Jilin University, Changchun, China
| | - Li Zhang
- Hospital of Stomatology, Jilin University, Changchun, China
| | - Zheng Zhang
- Tianjin Stomatological Hospital, School of Medicine, Nankai University, Tianjin, China
- Tianjin Key Laboratory of Oral and Maxillofacial Function Reconstruction, Tianjin, China
| | - Ning Ma
- Hospital of Stomatology, Jilin University, Changchun, China
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Korff C, Atkinson E, Adaway M, Klunk A, Wek RC, Vashishth D, Wallace JM, Anderson-Baucum EK, Evans-Molina C, Robling AG, Bidwell JP. NMP4, an Arbiter of Bone Cell Secretory Capacity and Regulator of Skeletal Response to PTH Therapy. Calcif Tissue Int 2023; 113:110-125. [PMID: 37147466 PMCID: PMC10330242 DOI: 10.1007/s00223-023-01088-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/31/2023] [Accepted: 04/21/2023] [Indexed: 05/07/2023]
Abstract
The skeleton is a secretory organ, and the goal of some osteoporosis therapies is to maximize bone matrix output. Nmp4 encodes a novel transcription factor that regulates bone cell secretion as part of its functional repertoire. Loss of Nmp4 enhances bone response to osteoanabolic therapy, in part, by increasing the production and delivery of bone matrix. Nmp4 shares traits with scaling factors, which are transcription factors that influence the expression of hundreds of genes to govern proteome allocation for establishing secretory cell infrastructure and capacity. Nmp4 is expressed in all tissues and while global loss of this gene leads to no overt baseline phenotype, deletion of Nmp4 has broad tissue effects in mice challenged with certain stressors. In addition to an enhanced response to osteoporosis therapies, Nmp4-deficient mice are less sensitive to high fat diet-induced weight gain and insulin resistance, exhibit a reduced disease severity in response to influenza A virus (IAV) infection, and resist the development of some forms of rheumatoid arthritis. In this review, we present the current understanding of the mechanisms underlying Nmp4 regulation of the skeletal response to osteoanabolics, and we discuss how this unique gene contributes to the diverse phenotypes among different tissues and stresses. An emerging theme is that Nmp4 is important for the infrastructure and capacity of secretory cells that are critical for health and disease.
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Affiliation(s)
- Crystal Korff
- Department of Medical and Molecular Genetics, Indiana University School of Medicine (IUSM), Indianapolis, IN, 46202, USA
| | - Emily Atkinson
- Department of Anatomy, Cell Biology & Physiology, IUSM, Indianapolis, IN, 46202, USA
| | - Michele Adaway
- Department of Anatomy, Cell Biology & Physiology, IUSM, Indianapolis, IN, 46202, USA
| | - Angela Klunk
- Department of Anatomy, Cell Biology & Physiology, IUSM, Indianapolis, IN, 46202, USA
| | - Ronald C Wek
- Department of Biochemistry and Molecular Biology, IUSM, Indianapolis, IN, USA
| | - Deepak Vashishth
- Center for Biotechnology & Interdisciplinary Studies and Department of Biomedical Engineering, Rensselaer Polytechnic Institute, Troy, NY, 12180, USA
| | - Joseph M Wallace
- Department of Biomedical Engineering, Indiana University-Purdue University at Indianapolis, Indianapolis, IN, 46202, USA
- Indiana Center for Musculoskeletal Health, IUSM, Indianapolis, IN, USA
| | - Emily K Anderson-Baucum
- Department of Pediatrics and the Herman B Wells Center for Pediatric Research, IUSM, Indianapolis, IN, USA
| | - Carmella Evans-Molina
- Department of Pediatrics and the Herman B Wells Center for Pediatric Research, IUSM, Indianapolis, IN, USA
- Center for Diabetes and Metabolic Disease and the Wells Center for Pediatric Research, IUSM, Indianapolis, IN, USA
- Richard L. Roudebush VA Medical Center, Indianapolis, IN, 46202, USA
- Department of Medicine, IUSM, Indianapolis, IN, USA
| | - Alexander G Robling
- Department of Anatomy, Cell Biology & Physiology, IUSM, Indianapolis, IN, 46202, USA
- Indiana Center for Musculoskeletal Health, IUSM, Indianapolis, IN, USA
- Richard L. Roudebush VA Medical Center, Indianapolis, IN, 46202, USA
| | - Joseph P Bidwell
- Department of Anatomy, Cell Biology & Physiology, IUSM, Indianapolis, IN, 46202, USA.
- Indiana Center for Musculoskeletal Health, IUSM, Indianapolis, IN, USA.
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Wen S, Li A, Cui L, Huang Q, Chen H, Guo X, Luo Y, Hao Q, Hou J, Ba Y. The relationship of PTH Bst BI polymorphism, calciotropic hormone levels, and dental fluorosis of children in China. Biol Trace Elem Res 2012; 147:84-90. [PMID: 22219025 DOI: 10.1007/s12011-011-9313-5] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/16/2011] [Accepted: 12/20/2011] [Indexed: 11/26/2022]
Abstract
The aim of this study was to explore the association of parathyroid hormone (PTH) gene Bst BI polymorphism, calciotropic hormone levels, and dental fluorosis of children. A case-control study was conducted in two counties (Kaifeng and Tongxu) in Henan Province, China in 2005-2006. Two hundred and twenty-five children were recruited and divided into three groups including dental fluorosis group (DFG), non-dental fluorosis group (NDFG) from high fluoride areas, and control group (CG). Urine fluoride content was determined using fluoride ion selective electrode; PTH Bst BI were genotyped using PCR-RFLP; osteocalcin (OC) and calcitonin (CT) levels in serum were detected using radioimmunoassay. Genotype distributions were BB 85.3% (58/68), Bb 14.7% (10/68) for DFG; BB 77.6% (52/67), Bb 22.4% (15/67) for NDFG; and BB 73.3% (66/90), Bb 27.7% (24/90) for CG. No significant difference of Bst BI genotypes was observed among three groups (P > 0.05). Serum OC and urine fluoride of children were both significantly higher in DFG and NDFG than in CG (P < 0.05, respectively), while a similar situation was not observed between DFG and NDFG in high fluoride areas (P > 0.05). Serum OC level of children with BB genotype was significantly higher compared to those with Bb genotype in high fluoride areas (P < 0.05). However, no significant difference of serum CT or calcium (Ca) was observed. In conclusion, there is no correlation between dental fluorosis and PTH Bst BI polymorphism. Serum OC might be a more sensitive biomarker for detecting early stages of dental fluorosis, and further studies are needed.
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Affiliation(s)
- Shibao Wen
- Department of Environmental Health, School of Public Health, Zhengzhou University, Zhengzhou, Henan, People's Republic of China
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Lo T, Tsai CF, Shih YRV, Wang YT, Lu SC, Sung TY, Hsu WL, Chen YJ, Lee OK. Phosphoproteomic Analysis of Human Mesenchymal Stromal Cells during Osteogenic Differentiation. J Proteome Res 2011; 11:586-98. [DOI: 10.1021/pr200868p] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Affiliation(s)
- Ting Lo
- Department of Medical Research and Education and ‡Department of Orthopaedics and Traumatology, Taipei Veterans General Hospital, Taipei, Taiwan
- Institute of Clinical Medicine and ∥Stem Cell Research Center, National Yang-Ming University, Taipei, Taiwan
- Institute of Chemistry and Genomics Research Center, ¶Chemical Biology and Molecular Biophysics Program, Taiwan International Graduate Program, Institute of Chemistry, and #Institute of Information Science, Academia Sinica, Taipei, Taiwan
- Department of Chemistry and ○Institute of Biochemical Sciences, National Taiwan University, Taipei, Taiwan
| | - Chia-Feng Tsai
- Department of Medical Research and Education and ‡Department of Orthopaedics and Traumatology, Taipei Veterans General Hospital, Taipei, Taiwan
- Institute of Clinical Medicine and ∥Stem Cell Research Center, National Yang-Ming University, Taipei, Taiwan
- Institute of Chemistry and Genomics Research Center, ¶Chemical Biology and Molecular Biophysics Program, Taiwan International Graduate Program, Institute of Chemistry, and #Institute of Information Science, Academia Sinica, Taipei, Taiwan
- Department of Chemistry and ○Institute of Biochemical Sciences, National Taiwan University, Taipei, Taiwan
| | - Yu-Ru V. Shih
- Department of Medical Research and Education and ‡Department of Orthopaedics and Traumatology, Taipei Veterans General Hospital, Taipei, Taiwan
- Institute of Clinical Medicine and ∥Stem Cell Research Center, National Yang-Ming University, Taipei, Taiwan
- Institute of Chemistry and Genomics Research Center, ¶Chemical Biology and Molecular Biophysics Program, Taiwan International Graduate Program, Institute of Chemistry, and #Institute of Information Science, Academia Sinica, Taipei, Taiwan
- Department of Chemistry and ○Institute of Biochemical Sciences, National Taiwan University, Taipei, Taiwan
| | - Yi-Ting Wang
- Department of Medical Research and Education and ‡Department of Orthopaedics and Traumatology, Taipei Veterans General Hospital, Taipei, Taiwan
- Institute of Clinical Medicine and ∥Stem Cell Research Center, National Yang-Ming University, Taipei, Taiwan
- Institute of Chemistry and Genomics Research Center, ¶Chemical Biology and Molecular Biophysics Program, Taiwan International Graduate Program, Institute of Chemistry, and #Institute of Information Science, Academia Sinica, Taipei, Taiwan
- Department of Chemistry and ○Institute of Biochemical Sciences, National Taiwan University, Taipei, Taiwan
| | - Sheng-Chieh Lu
- Department of Medical Research and Education and ‡Department of Orthopaedics and Traumatology, Taipei Veterans General Hospital, Taipei, Taiwan
- Institute of Clinical Medicine and ∥Stem Cell Research Center, National Yang-Ming University, Taipei, Taiwan
- Institute of Chemistry and Genomics Research Center, ¶Chemical Biology and Molecular Biophysics Program, Taiwan International Graduate Program, Institute of Chemistry, and #Institute of Information Science, Academia Sinica, Taipei, Taiwan
- Department of Chemistry and ○Institute of Biochemical Sciences, National Taiwan University, Taipei, Taiwan
| | - Ting-Yi Sung
- Department of Medical Research and Education and ‡Department of Orthopaedics and Traumatology, Taipei Veterans General Hospital, Taipei, Taiwan
- Institute of Clinical Medicine and ∥Stem Cell Research Center, National Yang-Ming University, Taipei, Taiwan
- Institute of Chemistry and Genomics Research Center, ¶Chemical Biology and Molecular Biophysics Program, Taiwan International Graduate Program, Institute of Chemistry, and #Institute of Information Science, Academia Sinica, Taipei, Taiwan
- Department of Chemistry and ○Institute of Biochemical Sciences, National Taiwan University, Taipei, Taiwan
| | - Wen-Lian Hsu
- Department of Medical Research and Education and ‡Department of Orthopaedics and Traumatology, Taipei Veterans General Hospital, Taipei, Taiwan
- Institute of Clinical Medicine and ∥Stem Cell Research Center, National Yang-Ming University, Taipei, Taiwan
- Institute of Chemistry and Genomics Research Center, ¶Chemical Biology and Molecular Biophysics Program, Taiwan International Graduate Program, Institute of Chemistry, and #Institute of Information Science, Academia Sinica, Taipei, Taiwan
- Department of Chemistry and ○Institute of Biochemical Sciences, National Taiwan University, Taipei, Taiwan
| | - Yu-Ju Chen
- Department of Medical Research and Education and ‡Department of Orthopaedics and Traumatology, Taipei Veterans General Hospital, Taipei, Taiwan
- Institute of Clinical Medicine and ∥Stem Cell Research Center, National Yang-Ming University, Taipei, Taiwan
- Institute of Chemistry and Genomics Research Center, ¶Chemical Biology and Molecular Biophysics Program, Taiwan International Graduate Program, Institute of Chemistry, and #Institute of Information Science, Academia Sinica, Taipei, Taiwan
- Department of Chemistry and ○Institute of Biochemical Sciences, National Taiwan University, Taipei, Taiwan
| | - Oscar K. Lee
- Department of Medical Research and Education and ‡Department of Orthopaedics and Traumatology, Taipei Veterans General Hospital, Taipei, Taiwan
- Institute of Clinical Medicine and ∥Stem Cell Research Center, National Yang-Ming University, Taipei, Taiwan
- Institute of Chemistry and Genomics Research Center, ¶Chemical Biology and Molecular Biophysics Program, Taiwan International Graduate Program, Institute of Chemistry, and #Institute of Information Science, Academia Sinica, Taipei, Taiwan
- Department of Chemistry and ○Institute of Biochemical Sciences, National Taiwan University, Taipei, Taiwan
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Charoenpanich A, Wall ME, Tucker CJ, Andrews DMK, Lalush DS, Loboa EG. Microarray analysis of human adipose-derived stem cells in three-dimensional collagen culture: osteogenesis inhibits bone morphogenic protein and Wnt signaling pathways, and cyclic tensile strain causes upregulation of proinflammatory cytokine regulators and angiogenic factors. Tissue Eng Part A 2011; 17:2615-27. [PMID: 21767168 DOI: 10.1089/ten.tea.2011.0107] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Human adipose-derived stem cells (hASC) have shown great potential for bone tissue engineering. However, the molecular mechanisms underlying this potential are not yet known, in particular the separate and combined effects of three-dimensional (3D) culture and mechanical loading on hASC osteogenesis. Mechanical stimuli play a pivotal role in bone formation, remodeling, and fracture repair. To further understand hASC osteogenic differentiation and response to mechanical stimuli, gene expression profiles of proliferating or osteogenically induced hASC in 3D collagen I culture in the presence and absence of 10% uniaxial cyclic tensile strain were examined using microarray analysis. About 847 genes and 95 canonical pathways were affected during osteogenesis of hASC in 3D culture. Pathway analysis indicated the potential roles of Wnt/β-catenin signaling, bone morphogenic protein (BMP) signaling, platelet-derived growth factor (PDGF) signaling, and insulin-like growth factor 1 (IGF-1) signaling in hASC during osteogenic differentiation. Application of 10% uniaxial cyclic tensile strain suggested synergistic effects of strain with osteogenic differentiation media on hASC osteogenesis as indicated by significantly increased calcium accretion of hASC. There was no significant further alteration in the four major pathways (Wnt/β-catenin, BMP, PDGF, and IGF-1). However, 184 transcripts were affected by 10% cyclic tensile strain. Function and network analysis of these transcripts suggested that 10% cyclic tensile strain may play a role during hASC osteogenic differentiation by upregulating two crucial factors in bone regeneration: (1) proinflammatory cytokine regulators interleukin 1 receptor antagonist and suppressor of cytokine signaling 3; (2) known angiogenic inductors fibroblast growth factor 2, matrix metalloproteinase 2, and vascular endothelial growth factor A. This is the first study to investigate the effects of both 3D culture and mechanical load on hASC osteogenic differentiation. A complete microarray analysis investigating both the separate effect of soluble osteogenic inductive factors and the combined effects of chemical and mechanical stimulation was performed on hASC undergoing osteogenic differentiation. We have identified specific genes and pathways associated with mechanical response and osteogenic potential of hASC, thus providing significant information toward improved understanding of our use of hASC for functional bone tissue engineering applications.
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Affiliation(s)
- Adisri Charoenpanich
- Joint Department of Biomedical Engineering, University of North Carolina at Chapel Hill and North Carolina State University, Raleigh, North Carolina 27695-7115, USA
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Abstract
X-box binding protein 1 (XBP1) is a unique basic region leucine zipper (bZIP) transcription factor whose active form is generated by a nonconventional splicing reaction upon disruption of homeostasis in the endoplasmic reticulum (ER) and activation of the unfolded protein response (UPR). XBP1, first identified as a key regulator of major histocompatibility complex (MHC) class II gene expression in B cells, represents the most conserved signaling component of UPR and is critical for cell fate determination in response to ER stress. Here we review recent advances in our understanding of this multifaceted transcription factor in health and diseases.
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Affiliation(s)
- Yin He
- *Graduate Program in Genetics and Development, Cornell University, Ithaca, NY, USA
| | - Shengyi Sun
- †Graduate Program in Biochemistry, Molecular and Cell Biology, Cornell University, Ithaca, NY, USA
| | - Haibo Sha
- ‡Division of Nutritional Sciences, Cornell University, Ithaca, NY, USA
| | - Ziying Liu
- †Graduate Program in Biochemistry, Molecular and Cell Biology, Cornell University, Ithaca, NY, USA
| | - Liu Yang
- †Graduate Program in Biochemistry, Molecular and Cell Biology, Cornell University, Ithaca, NY, USA
| | - Zhen Xue
- §Graduate Program in Nutrition, Cornell University, Ithaca, NY, USA
| | - Hui Chen
- ‡Division of Nutritional Sciences, Cornell University, Ithaca, NY, USA
| | - Ling Qi
- *Graduate Program in Genetics and Development, Cornell University, Ithaca, NY, USA
- †Graduate Program in Biochemistry, Molecular and Cell Biology, Cornell University, Ithaca, NY, USA
- ‡Division of Nutritional Sciences, Cornell University, Ithaca, NY, USA
- §Graduate Program in Nutrition, Cornell University, Ithaca, NY, USA
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Roberts GG, Di Loreto MJ, Marshall M, Wang J, DeGracia DJ. Hippocampal cellular stress responses after global brain ischemia and reperfusion. Antioxid Redox Signal 2007; 9:2265-75. [PMID: 17715997 DOI: 10.1089/ars.2007.1786] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Brain ischemia and reperfusion (I/R) induce neuronal intracellular stress responses, including the heat-shock response (HSR) and the unfolded protein response (UPR), but the roles of each in neuronal survival or death are not well understood. We assessed the relative expression of UPR (ATF4, CHOP, GRP78, XBP-1) and HSR-related (HSP70 and HSC70) mRNAs and proteins after brain I/R. We evaluated these in hippocampal CA1 and CA3 after normothermic, transient global forebrain ischemia and up to 42 h of reperfusion. In CA1, chop and xbp-1 mRNA showed maximal 14- and 12-fold increases, and the only protein increase observed was for 30-kDa XBP-1. CA3 showed induction of only xbp-1. GRP78 protein declined in CA1, but increased twofold and then declined in CA3. Transcription of hsp70 was an order of magnitude greater than that of any UPR-induced transcript in either CA1 or CA3. HSP70 translation in CA1 lagged CA3 by approximately 24 h. We conclude that (a) in terms of functional end products, the ER stress response after brain ischemia and reperfusion more closely resembles the integrated stress response than the UPR; and (b) the HSR leads to quantitatively greater mRNA production in postischemic neurons, suggesting that cytoplasmic stress predominates over ER stress in reperfused neurons.
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Affiliation(s)
- George G Roberts
- Department of Physiology, Wayne State University School of Medicine, Detroit, Michigan, USA
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Wagner U, Wahle M, Malysheva O, Wagner U, Häntzschel H, Baerwald C. Sequence variants of the CRH 5'-flanking region: effects on DNA-protein interactions studied by EMSA in PC12 cells. Ann N Y Acad Sci 2006; 1069:20-33. [PMID: 16855132 DOI: 10.1196/annals.1351.003] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Recently, studies in adult rheumatoid arthritis patients have shown an association with four single-nucleotide polymorphisms (SNPs) in the 3.7-kb regulatory region of human corticotropin-releasing hormone (hCRH) gene located at positions -3531, -3371, -2353, and -684 bp. Three of these novel polymorphisms are in absolute linkage disequilibrium, resulting in three combined alleles, named A1B1, A2B1, and A2B2. To study whether the described polymorphic nucleotide sequences in the 5' region of the hCRH gene interfere with binding of nuclear proteins, an electric mobility shift assay (EMSA) was performed. At position -2353 bp, a specific DNA protein complex was detected for the wild-type sequence only, possibly interfering with a binding site for the activating transcription factor 6 (ATF6). In contrast, no difference could be detected for the other SNPs. However, at position -684, a quantitative difference in protein binding due to cAMP incubation could be observed. To further investigate whether these SNPs in the CRH promoter are associated with an altered regulation of the CRH gene, we performed a luciferase reporter gene assay with transiently transfected rat pheochromocytoma cells PC12. Incubation with 8-Br-cAMP alone or in combination with cytokines enhanced significantly the promoter activity in PC12 cells. The promoter haplotypes studied exhibited a differential capacity to modulate CRH gene expression. In all our experiments, haplotype A1B1 showed the most pronounced influence on promoter activity. Taken together, our results demonstrate a differential binding capacity of nuclear proteins of the promoter polymorphisms resulting in a different gene regulation. Most probably the SNP at position -2,353 plays a major role in mediating these differences.
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Affiliation(s)
- Uta Wagner
- Department of Internal Medicine IV, Division of Rheumatology, Neuroendocrine-Immunology Laboratory, University Hospital Leipzig, Leipzig, Germany.
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Mukhopadhyay S, Sehgal PB. Discordant regulatory changes in monocrotaline-induced megalocytosis of lung arterial endothelial and alveolar epithelial cells. Am J Physiol Lung Cell Mol Physiol 2006; 290:L1216-26. [PMID: 16414977 DOI: 10.1152/ajplung.00535.2005] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Monocrotaline (MCT) causes pulmonary hypertension in the rat by a mechanism characterized by megalocytosis (enlarged cells with enlarged endoplasmic reticulum and Golgi and a cell cycle arrest) of pulmonary arterial endothelial (PAEC), arterial smooth muscle, and type II alveolar epithelial cells. In cell culture, although megalocytosis is associated with a block in entry into mitosis in both lung endothelial and epithelial cells, DNA synthesis is stimulated in endothelial but inhibited in epithelial cells. The molecular mechanism(s) for this dichotomy are unclear. While MCTP-treated PAEC and lung epithelial (A549) cells both showed an increase in the “promitogenic” transcription factor STAT3 levels and in the IL-6-induced nuclear pool of PY-STAT3, this was transcriptionally inactive in A549 but not in PAEC cells. This lack of transcriptional activity of STAT3 in A549 cells correlated with the cytoplasmic sequestration of the STAT3 coactivators CBP/p300 and SRC1/NcoA in A549 cells but not in PAEC. Both cell types displayed a Golgi trafficking block, loss of caveolin-1 rafts, and increased nuclear Ire1α, but an incomplete unfolded protein response (UPR) with little change in levels of UPR-induced chaperones including GRP78/BiP. There were discordant alterations in cell cycle regulatory proteins in the two cell types such as increase in levels of both cyclin D1 and p21 simultaneously, but with a decrease in cdc2/cdk1, a kinase required for entry into mitosis. While both cell types showed increased cytoplasmic geminin, the DNA synthesis-initiating protein Cdt1 was predominantly nuclear in PAEC but remained cytoplasmic in A549 cells, consistent with the stimulation of DNA synthesis in the former but an inhibition in the latter cell type. Thus differences in cell type-specific alterations in subcellular trafficking of critical regulatory molecules (such as CBP/p300, SRC1/NcoA, Cdt1) likely account for the dichotomy of the effects of MCTP on DNA synthesis in endothelial and epithelial cells.
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Affiliation(s)
- Somshuvra Mukhopadhyay
- Department of Cell Biology and Anatomy, New York Medical College, Valhalla, NY 10595, USA
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