Abstract
The cytoplasmic creatine kinase (CKB) enzyme has a central role in the regeneration of ATP in the brain. We have shown previously that CKB mRNA levels in cultured primary rat brain astrocytes and oligodendrocytes are much higher than in primary neurons. It has been suggested that high CKB expression is essential for the energy-demanding functions of glial cells. Conversely, CKB may be repressed in most neuronal cells; however, CKB protein has previously been detected by immunohistochemistry in several distinct groups of neurons in the adult rodent brain. Presently, little is known of the factors responsible for the high CKB expression in glia and possible repression in neurons. In this report, we investigated if low CKB mRNA was characteristic of some established neuronal cell lines. CKB mRNA was found to be extremely low in mouse C1300 neuroblastomas NS20Y and N1E-115 but 10-fold higher in NG108-15, a hybrid cell composed of a C1300 neuroblastoma and a rat C6 glioma. Since we showed NG108-15 contained only rat CKB mRNA transcribed from the C6 glioma CKB gene, expression of CKB mRNA may be a manifestation of a glial property in NG108-15 cells. However, CKB mRNA expression in NG108-15 appeared not to be fully activated since it was still 5-fold lower than in (parental) C6 glioma and 10-fold lower than in cellular RNA from either total rat brain or cultured primary astrocytes. When neuronal differentiation was increased in NS20Y and N1E-115 by treating cells with prostaglandin E1 and theophylline, the extremely low CKB mRNA level was not significantly changed. In a comparative study, the CKB mRNA levels in NS20Y, N1E-115 and neuronal RT4-B8 and RT4-E5 cells (from the rat RT4 peripheral neurotumor) were at least 50-fold lower than that in C6 glioma and 100-fold lower than in cultured primary astrocytes. These cell lines may provide a system for the identification of factors involved in the possible repression of CKB in many neuronal cells.
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