Navegando por Palavras-chave "XLH"

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    Estudo da ação da osteopontina na inibição da expressão genica do cotransportador de sódio-fosfato NPT2A
    (Universidade Federal de São Paulo, 2014-03-26) Chiarantin, Gabrielly Maria Denadai [UNIFESP]; Barros, Nilana Meza Tenório de [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)
    The X-linked hypophosphatemia (XLH) is the most prevalent form of inherited rickets in humans, occurring as a consequence of inactivating mutations in the PHEX gene (phosphate-regulating gene with homologies to endopeptidases on the X chromosome). XLH is characterized by growth retardation, rickets and osteomalacia leading to hypomineralized bones that deform, and soft tooth dentin prone to infection and abscesses. Associated with XLH and causing hypophosphatemia are defects in renal phosphate reabsorption and vitamin D metabolism. In vivo mouse studies have shown that the absence of PHEX leads to the release of a circulating factor(s) that decreases mineralization by inhibiting the sodium/phosphate co-transporter NPT2A, which mediates reabsorption of phosphate in the kidneys. Recently we demonstrated that osteopontin (OPN) is a physiologically relevant substrate for PHEX, whose inactivation by PHEX normally promotes bone mineralization. However, in PHEX-deficient Hyp mouse bone, OPN and its fragments accumulate to inhibit mineralization locally in the extracellular matrix. In the present study, we have extended these observations to show that OPN and a derived OPN fragment (ASARM peptide; acidic serine- and aspartate-rich motif) affect NPT2A expression. Using the supernatant from cultures of a constructed PHEX-deficient human osteosarcoma cell line (MG-63 shRNA-PHEX) we show that, in the absence of PHEX, a secreted factor found in the MG-63 osteosarcoma supernatant decreased NPT2A mRNA and protein expression in human kidney (HK-2) proximal tubule epithelial cell cultures. Based on this observation and on the fact that OPN is completely degraded by PHEX, we investigated the effects of exogenous OPN and its ASARM peptide on HK-2 cell NPT2A expression. RT-PCR revealed that OPN and its ASARM peptide significantly decreased NPT2A expression. In conclusion, these results provide new insight into circulating humoral factors that might influence phosphate handling in the kidney whose alterations contribute to the XLH phenotype, and they suggest that OPN and its ASARM peptide may be involved in this process.
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    Expression and inactivation of osteopontin-degrading PHEX enzyme in squamous cell carcinoma
    (Pergamon-Elsevier Science Ltd, 2016) Neves, Raquel L. [UNIFESP]; Chiarantin, Gabrielly M. D. [UNIFESP]; Nascimento, Fabio D.; Pesquero, Joao B. [UNIFESP]; Nader, Helena B. [UNIFESP]; Tersariol, Ivarne L. S. [UNIFESP]; McKee, Marc D.; Carmona, Adriana K. [UNIFESP]; Barros, Nilana M. T. [UNIFESP]
    Proteolytic enzymes mediate the activation or inactivation of many physiologic and pathologic processes. The PHEX gene (Phosphate-regulating gene with homologies to endopeptidase on the X chromosome) encodes a metallopeptidase, which is mutated in patients with a prevalent form (1:20,000) of inherited rickets-X-linked hypophosphatemia (XLH). XLH shows growth retardation, hypophosphatemia, osteo-malacia, and defective renal phosphate reabsorption and metabolism of vitamin D. Most PHEX studies have focused on bone, and recently we identified osteopontin (OPN) as the first protein substrate for PHEX, demonstrating in the murine model of XLH (Hyp mice) an increase in OPN that contributes to the osteomalacia. Besides its role in bone mineralization, OPN is expressed in many tissues, and therein has different functions. In tumor biology, OPN is known to be associated with metastasis. Here, we extend our PHEX-OPN studies to investigate PHEX expression in a squamous cell carcinoma (SCC) cell line and its possible involvement in modulating OPN function. Real-time PCR showed PHEX-OPN co-expression in SCC cells, with sequencing of the 22 exons showing no mutation of the PHEX gene. Although recombinant PHEX hydrolyze SCC-OPN fragments, unlike in bone cells, SCC-PHEX protein was not predominantly at the plasma membrane. Enzymatic activity assays, FACs and immunoblotting analyses demonstrated that membrane PHEX is degraded by cysteine proteases and the decreased PHEX activity could contribute to inappropriate OPN regulation. These results highlight for the first time PHEX in tumor biology. (C) 2016 Elsevier Ltd. All rights reserved.