Quantitative analysis of the expression and regulation of an activation-regulated phosphoprotein (oncoprotein 18) in normal and neoplastic cells

Leukemia. 1993 Apr;7(4):569-79.


Activation of protein kinase C results in phosphorylation of a 19-kDa protein termed 19K. Isolation and sequence analysis of a cDNA encoding the 19K protein revealed that this protein has been studied in other systems under different names. The name oncoprotein 18 (Op18) has been proposed on the basis of a postulated up-regulation in neoplastic cells. In the present report we adopt the designation Op18 for the 19K protein, and quantify this phosphoprotein in a series of leukemia/lymphoma cell lines, a panel of non-transformed cells and some terminally differentiated cell types. For this purpose we have developed reagents allowing quantitative Western-blot analysis, and quantification of Op18 on the single cell level by flow cytometric analysis. The data demonstrates a pronounced up-regulation of the Op18 protein in most leukemia/lymphoma cell lines. The HPB-ALL cell line provided the most extreme case and expressed 7 x 10(6) Op18 molecules/cell, which compares with 0.65 x 10(6) Op18 molecules/cell in non-transformed lymphoblastoid cells. The expression of Op18 appears to be restricted to cell types with proliferative potential, but it is clear from our results that up-regulation of Op18 is uncoupled from cellular proliferation. Moreover, by employing an Epstein-Barr virus based shuttle vector, we expressed Op18 cDNA in lymphoblastoid cells. This resulted in a three to fourfold up-regulation of Op18 that did not have any detectable consequences for cell-surface phenotype or cell size. However, increased expression of Op18 resulted in a partial inhibition of cell proliferation. Taken altogether, the results suggest that up-regulation Op18 levels in leukemia/lymphoma cells are strongly associated with, but not a direct cause of tumour progression.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Blotting, Western
  • Cell Differentiation
  • Cell Division
  • Cell Line
  • Cell Transformation, Neoplastic
  • Enzyme Activation*
  • Flow Cytometry
  • Gene Expression Regulation, Neoplastic*
  • Humans
  • Leukemia / metabolism*
  • Lymphoma / metabolism*
  • Microtubule Proteins*
  • Phosphoproteins / analysis
  • Phosphoproteins / biosynthesis*
  • Phosphoproteins / genetics
  • Phosphorylation
  • Protein Kinase C / biosynthesis
  • Stathmin
  • Transfection
  • Tumor Cells, Cultured


  • Microtubule Proteins
  • Phosphoproteins
  • STMN1 protein, human
  • Stathmin
  • Protein Kinase C