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Gene Review

PRG4  -  proteoglycan 4

Bos taurus

Synonyms: MSF, lubricin
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High impact information on PRG4

  • OBJECTIVE: To determine whether the synovial fluid (SF) constituents hyaluronan (HA), proteoglycan 4 (PRG4), and surface-active phospholipids (SAPL) contribute to boundary lubrication, either independently or additively, at an articular cartilage-cartilage interface [1].
  • CONCLUSION: Elevated coefficients of friction in arthritic joints occur concurrently with enhanced proteolytic degradation by up-regulated cathepsin B and other proteases, as well as decreased lubricin synthesis by synovial fibroblasts and superficial zone chondrocytes [2].
  • Chondrocytes expressing PRG4 were localized by immunohistochemistry, and depth-associated variations in chondrocyte PRG4 expression were quantified by image analysis [3].
  • OBJECTIVE: The boundary lubrication function of articular cartilage is mediated in part by proteoglycan 4 (PRG4) molecules at the articular surface and in synovial fluid [3].
  • In all of the culture systems, inclusion of ascorbic acid stimulated PRG4 secretion, and the source of PRG4 was immunolocalized to superficial cells [4].

Biological context of PRG4

  • In addition, analyses of human pathological tendon revealed that PRG4 may also be expressed as an alternatively spliced form lacking exons which encode part of the N-terminal matrix-binding and cell-proliferative domain; however, it remains to be determined whether such splice variants are a feature of human tendon, regardless of disease state [5].
  • Cartilage superficial zone protein/proteoglycan (SZP) or proteoglycan 4 (PRG4), has been demonstrated to have the potential for several distinct biological functions including cytoprotection, lubrication and matrix binding [5].
  • The marked up-regulation of PRG4 synthesis by ascorbic acid may have implications for cartilage homeostasis and prevention of osteoarthritic disease [4].
  • CONCLUSION: The results described here indicate that the phenotype of PRG4 secretion by chondrocytes in culture is generally maintained, in that PRG4 is expressed to a much greater degree by chondrocytes from the superficial zone than by those from the middle and deep zones [4].
  • Retention of cell fluorescence after PKH26 labeling and lack of adverse effects on cell proliferation and synthesis of PRG4 suggest that PKH26 can be useful in determining the fate and function of implanted chondrocytes in vivo, as well as monitoring proliferation in vitro [6].

Anatomical context of PRG4

  • In the present study, we have examined both the immunolocalisation and the mRNA expression pattern of PRG4 in tissue harvested from the compressed and tensional regions of young and mature bovine tendons [5].
  • OBJECTIVE: To quantify the levels of proteoglycan 4 (PRG4) expression by subpopulations of chondrocytes from superficial, middle, and deep layers of normal bovine calf cartilage in various culture systems [4].
  • PRG4 was immunolocalized at the articular cartilage surface, but not in deeper, cut surfaces (without treatment) [7].
  • PRG4 expression was quantified by enzyme-linked immunosorbent assay of spent medium and localized by immunohistochemistry at the articular surface and within chondrocytes in explants and cultured cells [4].
  • There was 0.20 +/- 0.01 and 0.25 +/- 0.04 microg PRG4/cm(2) area of lateral and medial meniscus surface, respectively [8].

Associations of PRG4 with chemical compounds


Analytical, diagnostic and therapeutic context of PRG4


  1. Boundary lubrication of articular cartilage: role of synovial fluid constituents. Schmidt, T.A., Gastelum, N.S., Nguyen, Q.T., Schumacher, B.L., Sah, R.L. Arthritis Rheum. (2007) [Pubmed]
  2. Reduced expression and proteolytic susceptibility of lubricin/superficial zone protein may explain early elevation in the coefficient of friction in the joints of rats with antigen-induced arthritis. Elsaid, K.A., Jay, G.D., Chichester, C.O. Arthritis Rheum. (2007) [Pubmed]
  3. Dynamic shear stimulation of bovine cartilage biosynthesis of proteoglycan 4. Nugent, G.E., Aneloski, N.M., Schmidt, T.A., Schumacher, B.L., Voegtline, M.S., Sah, R.L. Arthritis Rheum. (2006) [Pubmed]
  4. Synthesis of proteoglycan 4 by chondrocyte subpopulations in cartilage explants, monolayer cultures, and resurfaced cartilage cultures. Schmidt, T.A., Schumacher, B.L., Klein, T.J., Voegtline, M.S., Sah, R.L. Arthritis Rheum. (2004) [Pubmed]
  5. Immunolocalisation and expression of proteoglycan 4 (cartilage superficial zone proteoglycan) in tendon. Rees, S.G., Davies, J.R., Tudor, D., Flannery, C.R., Hughes, C.E., Dent, C.M., Caterson, B. Matrix Biol. (2002) [Pubmed]
  6. Tracking chondrocytes and assessing their proliferation with PKH26: effects on secretion of proteoglycan 4 (PRG4). Chawla, K., Klein, T.J., Schumacher, B.L., Schmidt, T.A., Voegtline, M.S., Thonar, E.J., Masuda, K., Sah, R.L. J. Orthop. Res. (2006) [Pubmed]
  7. Inhibition of integrative cartilage repair by proteoglycan 4 in synovial fluid. Englert, C., McGowan, K.B., Klein, T.J., Giurea, A., Schumacher, B.L., Sah, R.L. Arthritis Rheum. (2005) [Pubmed]
  8. Proteoglycan 4 (PRG4) synthesis and immunolocalization in bovine meniscus. Schumacher, B.L., Schmidt, T.A., Voegtline, M.S., Chen, A.C., Sah, R.L. J. Orthop. Res. (2005) [Pubmed]
  9. The molecular structure of lubricating glycoprotein-I, the boundary lubricant for articular cartilage. Swann, D.A., Slayter, H.S., Silver, F.H. J. Biol. Chem. (1981) [Pubmed]
  10. Lubricin reduces cartilage--cartilage integration. Schaefer, D.B., Wendt, D., Moretti, M., Jakob, M., Jay, G.D., Heberer, M., Martin, I. Biorheology. (2004) [Pubmed]
  11. The molecular structure and lubricating activity of lubricin isolated from bovine and human synovial fluids. Swann, D.A., Silver, F.H., Slayter, H.S., Stafford, W., Shore, E. Biochem. J. (1985) [Pubmed]
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