TUMOR-NECROSIS-FACTOR RECEPTORS IN NEUROBLASTOMA SKNBE CELLS AND THEIR REGULATION BY RETINOIC ACID

The human neuroblastoma cell line SKNBE can be differentiated either b y serum removal or by adding to the culture medium different morphogen s, for instance, retinoic acid (RA), cyclic AMP derivatives, and phorb ol esters. Both the differentiated and undifferentiated cells express the two types of membrane tumor necrosis factor (TNF) receptors (TNFRs ) of 55 and 75 kDa (p55 and p75 TNFR, respectively) and also their sol uble forms. After RA addition the number of the surface TNFRs per cell is increased approximately twofold, but the kinetics of expression ar e different, depending on the receptor type. The level of the mRNAs of 2.4 and 4.2 kb, which, respectively, encode the p55 and p75 TNFRs, is also increased during the time course of differentiation, and the kin etics of their expression are biphasic. In contrast, the number of TNF Rs and the level of their encoding mRNAs remain unchanged after exposu re of the cells to both a phorbol and a cyclic AMP derivative.