EXPRESSION OF NUCLEOLAR PROTEIN P120 IN HUMAN LUNG-CANCER - DIFFERENCE IN HISTOLOGICAL TYPES AS A MARKER FOR PROLIFERATION

The function of proliferation-associated nucleolar protein p120 is unc lear, A recent report that a yeast protein, NOP2, 67% homologous to hu man p120, is up-regulated during the onset of growth and influences th e morphology of the nucleolus supports the notion that this protein co uld serve as a marker for proliferation in neoplastic cells, Lung canc er is characteristic in that different histological types show differe nt biological features, We attempted to evaluate the levels of p120 ex pression in resected human lung cancer tissues of different histologic al types and the relation of p120 expression and cell proliferation us ing human lung cancer cell lines, When 37 frozen specimens of human lu ng cancer and normal lung were stained with a p120 monoclonal antibody , the nucleoli of cancer cells were positively stained, whereas a few macrophages in normal lung revealed only weak staining, The labeling i ndex of p120 in squamous cell carcinoma (67.7 +/- 12.4%) was significa ntly higher than that in adenocarcinoma (35.3 +/- 12.6%) or in large c ell carcinoma (30.1 +/- 17.3%; P < 0.01). In six human lung cancer cel l lines and one normal lung fibroblast cell line cultured bt vitro, th ere was a significant correlation between S-phase fraction and p120 mR NA (r = 0.851, P < 0.02)/p120 protein (r = 0.869, P < 0.01) or between doubling time and p120 protein (r = -0.928, P < 0.01), In the context of the reports that indicate higher [H-3]thymidine incorporation and shorter doubling time in the squamous cell carcinoma, these results in dicate that p120 can be a marker for proliferation in human lung cance r cells in vivo and in vitro, and that it has an important function in the cell cycle of tumor proliferation.