title: Tyrosine phosphate in melanoma progression.
abstract: BACKGROUND
  Cellular tyrosine phosphorylation is regulated by two large families of enzymes. Protein tyrosine kinases (PTK) mediate addition, and protein tyrosine phosphatases (PTP), removal of phosphate from protein substrates. PTKs are oncogenes and PTPs have been hypothesized to function as tumour suppressor genes.
  
  
  OBJECTIVE
  To determine changes in tyrosine phosphate and PTP activity that occur during melanoma progression.
  
  
  METHODS
  Immunohistochemistry was used to study phosphotyrosine in melanocytic lesions. In addition, PTP activity of normal melanocytes and melanoma cell lines was measured using an enzyme-linked immunosorbent assay-based system.
  
  
  RESULTS
  Melanocytes in normal skin and most (67%) benign naevi were not immunostained. Neither were early malignant lesions (80% of malignant melanoma in situ and radial growth phase melanomas) stained. However, most advanced melanomas (100% of vertical growth phase, and 90% of metastatic melanomas) were immunoreactive. When total PTP enzyme activity was assayed in normal melanocytes and malignant melanoma cell lines, there was a significant increase in activity associated with melanoma progression.
  
  
  CONCLUSIONS
  Taken together, the data suggest increased phosphotyrosine signalling occurs during melanoma progression at the stage when cells first become competent for metastasis.
authors.affiliation: Department of Pathology, Conway Institute, University College Dublin, Dublin 4, Ireland.
authors.forename: L
authors.initials: L
authors.lastname: McArdle
authors.forename: O
authors.initials: O
authors.lastname: Bergin
authors.forename: M E
authors.initials: ME
authors.lastname: Fallowfield
authors.forename: P A
authors.initials: PA
authors.lastname: Dervan
authors.forename: D J
authors.initials: DJ
authors.lastname: Easty
mesh_terms: D018450:Disease Progression; D006801:Humans; D007124:Immunoenzyme Techniques; D008544:Melanocytes / Q000201:enzymology; D008545:Melanoma / Q000201:enzymology / Q000378:metabolism* / Q000556:secondary; D010766:Phosphorylation; D019000:Phosphotyrosine / Q000378:metabolism*; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism; D012878:Skin Neoplasms / Q000201:enzymology / Q000378:metabolism*; D014407:Tumor Cells, Cultured
chemical_list: D019000:Phosphotyrosine; D017027:Protein Tyrosine Phosphatases