Molecular Defects Underlying the Kell Null Phenotype

Lee, Soohee; Russo, David; Reiner, Alexander P.; Lee, Jeffrey H.; Sy, Michael; Telen, Marilyn J.; Judd, W. John; Simon, Philippe; Rodrigues, Maria J; Chabert, T; Poole, Joyce; Jovanovic-Srzentic, Snezana; Levene, C.; Yahalom, Vered; Redman, Colvin M.

doi:10.1074/jbc.m103433200

Cited by 78 publications

(125 citation statements)

References 43 publications

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“…They are a precedent for interactions between putative anion transporters and members of the M13 family of endopeptidases to which PHEX belongs. For example, XK associates with the Kell endopeptidase in red blood cell membranes (36), and mutations of XK are responsible for a hereditary l chorea-acanthocytosis disorder called the McLeod neuroacanthocytosis (36,37). It is possible that a similar interaction might exist between PHEX and factors regulating the mineralization process in osteoblasts.…”

Section: Tio An Acquired Disorder Resembling Adhr and Xlh Identifiementioning

confidence: 99%

FGF23, PHEX, and MEPE regulation of phosphate homeostasis and skeletal mineralization

Quarles

2003

American Journal of Physiology-Endocrinology and Metabolism

297

193

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Quarles, L. Darryl. FGF23, PHEX, and MEPE regulation of phosphate homeostasis and skeletal mineralization. Am J Physiol Endocrinol Metab 285: E1-E9, 2003;10.1152/ajpendo.00016.2003.-There is evidence for a hormone/enzyme/extracellular matrix protein cascade involving fibroblastic growth factor 23 (FGF23), a phosphate-regulating gene with homologies to endopeptidases on the X chromosome (PHEX), and a matrix extracellular phosphoglycoprotein (MEPE) that regulates systemic phosphate homeostasis and mineralization. Genetic studies of autosomal dominant hypophosphatemic rickets (ADHR) and X-linked hypophosphatemia (XLH) identified the phosphaturic hormone FGF23 and the membrane metalloprotease PHEX, and investigations of tumorinduced osteomalacia (TIO) discovered the extracellular matrix protein MEPE. Similarities between ADHR, XLH, and TIO suggest a model to explain the common pathogenesis of renal phosphate wasting and defective mineralization in these disorders. In this model, increments in FGF23 and MEPE, respectively, cause renal phosphate wasting and intrinsic mineralization abnormalities. FGF23 elevations in ADHR are due to mutations of FGF23 that block its degradation, in XLH from indirect actions of inactivating mutations of PHEX to modify the expression and/or degradation of FGF23 and MEPE, and in TIO because of increased production of FGF23 and MEPE. Although this model is attractive, several aspects need to be validated. First, the enzymes responsible for metabolizing FGF23 and MEPE need to be established. Second, the physiologically relevant PHEX substrates and the mechanisms whereby PHEX controls FGF23 and MEPE metabolism need to be elucidated. Finally, additional studies are required to establish the molecular mechanisms of FGF23 and MEPE actions on kidney and bone, as well as to confirm the role of these and other potential "phosphatonins," such as frizzled related protein-4, in the pathogenesis of the renal and skeletal phenotypes in XLH and TIO. Unraveling the components of this hormone/enzyme/extracellular matrix pathway will not only lead to a better understanding of phosphate homeostasis and mineralization but may also improve the diagnosis and treatment of hypo-and hyperphosphatemic disorders. phosphatonin; Hyp; X-linked hypophosphatemia; rickets; osteomalacia; hypophosphatemia OUR UNDERSTANDING OF HORMONAL REGULATION of phosphate homeostasis is rapidly expanding. The classical parathyroid hormone (PTH)/vitamin D axis is not sufficient to account for the physiological complexity of renal phosphate handling and bone mineralization (58). Rather, there is emerging evidence for other phosphaturic hormones, collectively called phosphatonins (35), as well as other local factors regulating the mineralization process in hypophosphatemic disorders, referred to as minhibins (57,78). Studies of two inherited hypophosphatemic disorders, autosomal dominant hypophosphatemic rickets (ADHR) (2), and X-linked hypophosphatemia (XLH) (70), and the sporadic tumorinduced osteomalacia (TIO, also called oncogenic oste...

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Section: Tio An Acquired Disorder Resembling Adhr and Xlh Identifiementioning

confidence: 99%

FGF23, PHEX, and MEPE regulation of phosphate homeostasis and skeletal mineralization

Quarles

2003

American Journal of Physiology-Endocrinology and Metabolism

297

193

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“…XLH is caused by inactivating mutations of PHEX (2-5), a member of the M13 family of type II cell surface zinc-dependent proteases that include neprilysin, endothelin-converting enzymes 1 and 2 (6, 7), KELL (8), and DINE/X-converting enzyme (9,10). The mouse Phex cDNA sequence is highly homologous to that of humans (11,12), and inactivating mutations of Phex are identified in several mouse homologues of XLH, including Hyp, Gy, and Ska1 mice (10,13,14).…”

Section: X-linked Hypophosphatemia (Xlh)mentioning

confidence: 99%

Regulation of Fibroblastic Growth Factor 23 Expression but Not Degradation by PHEX

Liu

Guo

Simpson

et al. 2003

Journal of Biological Chemistry

467

375

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Inactivating mutations of Phex cause X-linked hypophosphatemia (XLH) by increasing levels of a circulating phosphaturic factor. FGF23 is a candidate for this phosphaturic factor. Elevated serum FGF23 levels correlate with the degree of hypophosphatemia in XLH, suggesting that loss of Phex function in this disorder results in either diminished degradation and/or increased biosynthesis of FGF23. To establish the mechanisms whereby Phex regulates FGF23, we assessed Phex-dependent hydrolysis of recombinant FGF23 in vitro and measured fgf23 message levels in the Hyp mouse homologue of XLH. In COS-7 cells, overexpression of FGF23 resulted in its degradation into N-and C-terminal fragments by an endogenous decanoyl-Arg-Val-Lys-Arg-chloromethyl ketone-sensitive furin-type convertase. Phex-dependent hydrolysis of full-length FGF23 or its N-and C-terminal fragments could not be demonstrated in the presence or absence of decanoyl-Arg-Val-Lys-Arg-chloromethyl ketone in COS-7 cells expressing Phex and FGF23. In a reticulolysate system, apparent cleavage of FGF23 occurred with wild-type Phex, the inactive Phex-3M mutant, and vector controls, indicating nonspecific metabolism of FGF23 by contaminating enzymes. These findings suggest that FGF23 is not a direct Phex substrate. In contrast, by real-time reverse transcriptase PCR, the levels of fgf23 transcripts were highest in bone, the predominant site of Phex expression. In addition, Hyp mice displayed a bonerestricted increase in fgf23 transcripts in association with inactivating Phex mutations. Increased expression of fgf23 was also observed in Hyp-derived osteoblasts in culture. These findings suggest that Phex, possibly through the actions of unidentified Phex substrates or other downstream effectors, regulates fgf23 expression as part of a potential hormonal axis between bone and kidney that controls systemic phosphate homeostasis and mineralization. X-linked hypophosphatemia (XLH)1 is a disorder characterized by defective calcification of cartilage and bone, growth retardation, impaired renal tubular reabsorption of phosphate, aberrant regulation of 1,25(OH) 2 D 3 production, and resistance to phosphorus and vitamin D therapy (1). XLH is caused by inactivating mutations of PHEX (2-5), a member of the M13 family of type II cell surface zinc-dependent proteases that include neprilysin, endothelin-converting enzymes 1 and 2 (6, 7), KELL (8), and DINE/X-converting enzyme (9, 10). The mouse Phex cDNA sequence is highly homologous to that of humans (11,12), and inactivating mutations of Phex are identified in several mouse homologues of XLH, including Hyp, Gy, and Ska1 mice (10,13,14).Current data indicate that Phex regulates the production and/or degradation of a systemic phosphaturic hormone, referred to as phosphatonin (15). The presence of phosphatonin in XLH/Hyp was detected by parabiosis experiments in which Hyp mice transferred the phosphaturic phenotype to normal mice (16). Studies in parathyroidectomized Hyp mice eliminated parathyroid hormone as the responsible phosph...

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“…In some cases in which the mutation was too far from the restriction sites, 2 overlapping PCR products were produced, followed by another PCR step to link the 2 products. 11,32 The primer sets used, with the mutated base underlined, and the restriction enzyme sites used are listed in Table 1. The primers used to link the overlapping PCR products are marked with asterisks.…”

Section: Construction Of Mutant Kell Cdnasmentioning

confidence: 99%

Active amino acids of the Kell blood group protein and model of the ectodomain based on the structure of neutral endopeptidase 24.11

Lee

Debnath

Redman

2003

Blood

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In addition to its importance in transfusion, Kell protein is a member of the M13 family of zinc endopeptidases and functions as an endothelin-3-converting enzyme. To obtain information on the structure of Kell protein we built a model based on the crystal structure of the ectodomain of neutral endopeptidase 24.11 (NEP). Similar to NEP, the Kell protein has 2 globular domains consisting mostly of ␣-helical segments. The domain situated closest to the membrane contains both the N-and C-terminal sequences and the enzyme-active site. The outer domain contains all of the amino acids whose substitutions lead to different Kell blood group phenotypes. In the model, the zinc peptidase inhibitor, phosphoramidon, was docked in the active site. Site-directed mutagenesis of amino acids in the active site was performed and the enzymatic activities of expressed mutant Kell proteins analyzed and compared with NEP. IntroductionThe Kell blood group protein is a type II membrane glycoprotein that is important in transfusion medicine due to the immunogenicity of its many polymorphic forms. The primary structure of Kell protein and its enzyme function as an endothelin-converting enzyme, classifies it as a member of the neprilysin (M13) subfamily of zinc endopeptidases. Kell differs from other M13 members in that it is linked by a single disulfide bond to another protein, XK, which traverses the membrane 10 times (for reviews, see Lee et al 1,2 ). XK has the structural characteristics of a membrane transporter, but its function has not yet been determined. 3 As a group the mammalian M13 peptidases are involved in the activation of bioactive peptides by specific cleavages of larger inactive peptides and in the proteolysis of bioactive peptides. [4][5][6] The substrate specificities of the M13 family members vary with neutral endopeptidase (NEP; EC 3.4.24.11) 7 and secreted endopeptidase (SEP) 8 having a wide range of substrates and endothelinconverting enzyme 1 (ECE-1; EC 3.4.24.71), endothelin-converting enzyme 2 (ECE-2), 9,10 Kell, 11 and phosphate-regulating protein (PHEX) 12,13 with a restricted number of substrates. ECE-1 and ECE-2 preferentially cleave big endothelin-1-releasing endothelin-1 (ET-1) but can also cleave big endothelin-2 and big endothelin-3. 14 ECE-1 also hydrolyzes other bioactive peptides such as bradykinin, neurotensin, and substance P. 9 Kell, like ECE-1 and ECE-2, is also an endothelin-converting enzyme but, in contrast to ECE-1 and ECE-2, Kell preferentially cleaves big endothelin-3, releasing the active peptide endothelin-3 (ET-3) although it also, to a lesser degree, activates ET-1 and endothelin-2 (ET-2). 11 Thus far the parathyroid hormone-related fragment 107-139 and fibroblast growth factor 23 (FGF-23), which is involved in phosphate transport in the kidney, are the only known substrates for PHEX. 12,13 Substrates for XCE, which is mostly expressed in the central nervous system, have not yet been identified. 15,16 Site-directed mutagenesis of conserved amino acid residues in NEP have yielded valuab...

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Molecular Defects Underlying the Kell Null Phenotype

Cited by 78 publications

References 43 publications

FGF23, PHEX, and MEPE regulation of phosphate homeostasis and skeletal mineralization

FGF23, PHEX, and MEPE regulation of phosphate homeostasis and skeletal mineralization

Regulation of Fibroblastic Growth Factor 23 Expression but Not Degradation by PHEX

Active amino acids of the Kell blood group protein and model of the ectodomain based on the structure of neutral endopeptidase 24.11

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