Immunohistochemical determination of protein kinase C expression and proliferative activity in human brain tumors

Protein kinase C (PKC), the major receptor for phorbol ester tumor promotors, is a phospholipid- and calcium-dependent phosphorylating enzyme which plays an important role in the intracellular signal transduction necessary for a variety of basic cellular functions including the control of cell proliferation. To determine the expression of PKC in human neurogenic tumors we investigated 121 tumors of the human nervous system by means of immunohistochemistry using the monoclonal antibody C5. The results were compared with immunohistochemical staining for intermediate filament proteins, desmoplakins, and the proliferation-associated nuclear antigen Ki-67. Besides strong staining of normal and reactive astrocytes, C5 immunoreactivity was consistently observed in tumor cells of all types of gliomas. However, the fraction of C5 positive tumor cells varied between the different tumor types with astrocytomas and subependymomas demonstrating the strongest immunoreactivity. In the other gliomas, especially those of higher malignancy, a considerable heterogeneity in C5 expression could be observed. There was a tendency for the percentage of C5 immunostained tumor cells being lower in high-grade gliomas compared to low-grade ones and comparison with Ki-67 staining frequently revealed an inverse relationship between proliferative activity and C5 immunoreactivity. Besides the gliomas we found 3 of 7 neurinomas and 6 of 18 meningiomas which were partially C5 positive. All other tumors investigated including medulloblastomas and metastatic carcinomas were C5 negative. Our results thus indicate that immunohistochemistry for PKC using the monoclonal antibody C5 could be an useful aid for histopathological tumor classification in neuro-oncology.