Increased human polo-like kinase-1 expression in gliomas.

PLK-1 (polo-like kinase) belongs to the family of serine/threonine kinases and is involved in spindle formation, centrosome cycles and chromosome segregation. Hence, the kinase is tightly linked to cell proliferation. We could detect immunohistochemically highly expressed PLK protein in astrocytic tumours depending on the grade of anaplasia, in commercially available human glioma cell lines (U87MG, U118MG, U138MG), in one immortalized cell culture derived from a glioblastoma patient and in a primary culture derived from a glioblastoma patient. The highest labelling of PLK-1 was demonstrated in glioblastomas. There was a significant correlation between the PLK expression and the nuclear immunoreactivity of MIB-1. PLK-mRNA, found in all tumour specimens investigated emphasizes the close correlation to proliferation and growth. Furthermore, the relation of the PLK-1 expression to the Mitogen-activated Protein Kinase Cascades was studied by applying various highly specific inhibitors. While all inhibitors minimized the cell density, only the PLCy inhibitor clearly lead to a reduced PLK-1 expression in the three cell lines U87MG, U118MG, U138MG.