P100 - A NOVEL PROLIFERATION-ASSOCIATED NUCLEAR-PROTEIN SPECIFICALLY RESTRICTED TO CELL-CYCLE PHASE-S, PHASE-G(2), AND PHASE-M

By immunization with nuclear lysates of L428 cells, we raised a monocl onal mouse antibody, Ki-S2 (IgG(1)). In Western blots, this antibody r ecognizes a nuclear antigen with an apparent molecular mass of 100 kD, termed p100, Protein sequencing of p100 showed that this is a hithert o unknown protein. Immunohistochemical examination of cryostat and par affin sections of nearly all human tissue types and neoplasms showed t hat p100 was exclusively expressed in the nuclei of a fraction of prol iferating cells. Cell sorting and fluorescence-activated cell sorting analysis of stimulated peripheral blood mononuclear cells showed that p100 was exclusively expressed in proliferating cells from the transit ion G(1)/S until the end of cytokinesis. During mitosis, this protein is strictly associated with the spindle pole and with the mitotic spin dle, whereas during S and G(2), p100 is diffusely distributed througho ut the cell nucleus. Immediately after completion of cytokinesis, p100 was rapidly degraded. In L428 cells, p100 is phosphorylated at least during mitosis. It has a turnover time of about 1 hour. Studies on rou tinely processed paraffin sections of specimens of malignant lymphoma, benign and malignant nevocellular tumors, and breast cancer showed th at in all cases less than 40% of the Ki-67-positive growth fraction ex pressed p100. Thus, p100 might prove to be a more reliable measure of cellular proliferation and one that is more closely correlated to canc er prognosis, beyond its general biologic relevance as a cell cycle pr otein. (C) 1997 by The American Society of Hematology.