Expression of the Brain Creatine Kinase Gene Is Low in Neuroblastoma Cell Lines

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 CI300 neuroblastomas NS20Y and N1E-115 but 10-fold higher in NG108-15, a hybrid cell composed of a Cl300 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.

Expression of the Brain Creatine Kinase Gene in Rat RT4 Peripheral Neurotumor Cell Lines and Its Modulation by Cell Confluence

“…In addition to high CKB expression in glial cells, a number of human tumors display elevated CKB [Gazdar et al, 1981;Kaye et al, 1987], However, our results would suggest that CKB is not elevated in all transformed cells, since CKB mRNA was undetectable in neuronal RT4-B8 cells, low in neuronal RT4-E5 cells and barely detectable in mouse Cl 300 neuroblastomas NS20Y and N1E-115 [Wilson et al, 1997], Since we have recently shown in transient transfection experiments that tran scription of rat CKB is significantly repressed by the p53wt, tumor suppressor protein but not mutant p53 [Zhao et al, 1994[Zhao et al, , 1996, increased CKB may be a charac teristic of tumor cells which have lost p53wt function. Future investigations with RT4 cells, in conjunction with studies of primary cultures of neuronal and glial cells, will assist in identify the protein factors [Hobson et al, , 1990 regulating CKB expression in the PNS and CNS.…”