Quantitative analysis of the expression and regulation of an activation-regulated phosphoprotein (oncoprotein 18) in normal and neoplastic cells.
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.
Brattsand
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G
Unit for Cell and Molecular Biology, University of Umeå, Sweden.
Roos
G
G
Marklund
U
U
Ueda
H
H
Landberg
G
G
Nånberg
E
E
Sideras
P
P
Gullberg
M
M
D015153:Blotting, Western; D002454:Cell Differentiation; D002455:Cell Division; D002460:Cell Line; D002471:Cell Transformation, Neoplastic; D004789:Enzyme Activation; D005434:Flow Cytometry; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007938:Leukemia / Q000378:metabolism*; D008223:Lymphoma / Q000378:metabolism*; D008868:Microtubule Proteins; D010750:Phosphoproteins / Q000032:analysis / Q000096:biosynthesis* / Q000235:genetics; D010766:Phosphorylation; D011493:Protein Kinase C / Q000096:biosynthesis; D050777:Stathmin; D014162:Transfection; D014407:Tumor Cells, Cultured
D008868:Microtubule Proteins; D010750:Phosphoproteins; C493995:STMN1 protein, human; D050777:Stathmin; D011493:Protein Kinase C