Expression and inactivation of osteopontin-degrading PHEX enzyme in squamous cell carcinoma.
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, osteomalacia, 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.
Departamento de Biofísica, Universidade Federal de São Paulo, São Paulo, São Paulo, Brazil; Departamento de Ciências Biológicas, Universidade Federal de São Paulo, Diadema, São Paulo, Brazil.
Raquel L
RL
Neves
Departamento de Biofísica, Universidade Federal de São Paulo, São Paulo, São Paulo, Brazil; Departamento de Ciências Biológicas, Universidade Federal de São Paulo, Diadema, São Paulo, Brazil.
Gabrielly M D
GMD
Chiarantin
Universidade Anhanguera de São Paulo, São Paulo, São Paulo, Brazil.
Fábio D
FD
Nascimento
Departamento de Biofísica, Universidade Federal de São Paulo, São Paulo, São Paulo, Brazil.
João B
JB
Pesquero
Departamento de Bioquímica, Universidade Federal de São Paulo, São Paulo, São Paulo, Brazil.
Helena B
HB
Nader
Departamento de Bioquímica, Universidade Federal de São Paulo, São Paulo, São Paulo, Brazil; Centro Interdisciplinar de Investigação Bioquímica, Universidade de Mogi das Cruzes, Mogi das Cruzes, São Paulo, Brazil.
Ivarne L S
ILS
Tersariol
Faculty of Dentistry, McGill University, Montreal, Quebec, Canada; Department of Anatomy and Cell Biology, Faculty of Medicine, McGill University, Montreal, Quebec, Canada.
Marc D
MD
McKee
Departamento de Biofísica, Universidade Federal de São Paulo, São Paulo, São Paulo, Brazil. Electronic address: ak.carmona@unifesp.br.
Adriana K
AK
Carmona
Departamento de Biofísica, Universidade Federal de São Paulo, São Paulo, São Paulo, Brazil; Departamento de Ciências Biológicas, Universidade Federal de São Paulo, Diadema, São Paulo, Brazil. Electronic address: nilana.barros@unifesp.br.
Nilana M T
NMT
Barros
D002294:Carcinoma, Squamous Cell / Q000473:pathology*; D002462:Cell Membrane / Q000378:metabolism; D057056:Cysteine Proteases / Q000378:metabolism; D004789:Enzyme Activation; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D053495:Osteopontin / Q000235:genetics / Q000378:metabolism*; D053402:PHEX Phosphate Regulating Neutral Endopeptidase / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport; D059748:Proteolysis; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism
D012333:RNA, Messenger; D053495:Osteopontin; D057056:Cysteine Proteases; D053402:PHEX Phosphate Regulating Neutral Endopeptidase; C506231:PHEX protein, human
Osteopontin; PHEX; Squamous cell carcinoma; Tumor; XLH