Early activation of endogenous pp60src kinase activity during neuronal differentiation of cultured human neuroblastoma cells

Expression of the B cell-associated tyrosine kinase gene Lyn in primary neuroblastoma tumours and its modulation during the differentiation of neuroblastoma cell lines

The src-related intracellular protein tyrosine kinase Lyn is a signal transducing molecule for surface immunoglobulin M and is expressed predominantly in hemopoietic cells. We report here the expression of the lyn gene in human neuroblastoma. In surgical tumour samples lyn transcripts were found preferentially at early stages whereas they were barely detectable in highly malignant tumours. In a cloned human neuroblastoma cell line, Be(2)C, lyn mRNA levels increased during neuronal differentiation induced by retinoic acid. Lyn mRNA levels were undetectable and did not respond to retinoic acid in a glial-type neuroblastoma clone, SH-EP. Retinoic acid-induced glial differentiation was associated with a reduction of lyn transcripts in a clonal I-type neuroblastoma cell line, SH-IN, which shares properties of both neuronal- and glial-type clones. Like pp60c-src Lyn may be involved in a signalling pathway of neuroblasts committed to neuronal differentiation.

Novel serine phosphorylation occurs in the fibroblast form of pp60c-src from Y79 retinoblastoma cells

Two-dimensional tryptic peptide analysis showed that pp60c-src from the human retinoblastoma cell line Y79 gave a unique phosphopeptide, which was not found in human fibroblast RT59. There was no significant difference in the extent of phosphorylation of other peptides between the two cell lines. Only phosphoserine was detected in this phosphopeptide. Both the fibroblast form and the neuronal form of pp60c-src from Y79 cells had this unique peptide phosphorylated to the same extent. The phosphorylation site was inferred to be serine 97 by comparing the tryptic map and the arginyl-endopeptidase map. The specific protein kinase activity of pp60c-src from Y79 cells was nearly equal to that of RT59 pp60c-src. This unique serine phosphorylation in the fibroblast form was discussed in relation to the oncogenic change of Y79 cells.

Alcohols synergize with NGF to induce early differentiation of PC12 cells

The role of alcohols in affecting neuromorphogenesis was investigated in a single cell type, pheochromocytoma (PC12). The effect of ethanol at physiological concentrations in this system leads to enhanced morphological and functional differentiation in combination with nerve growth factor (NGF). PC12 cells treated with a suboptimal concentration of NGF (30 ng/ml) and an alcohol (87 mM) underwent rapid morphological differentiation which was dependent upon the side chain length of the alcohol MeOH less than EtOH less than PrOH less than BuOH. Pyrazole at either 5 or 10 mM had no effect on alcohol induced neurite extension. Assessment of the degree of differentiation promoted by the various alcohols was quantified by an increase in neurite extension, a decrease in the incorporation of [3H]thymidine, an increase in acetylcholine esterase (AChE) activity and immunostaining with neuron specific enolase. Thus, alcohols may function in a specific manner by interacting with transmembrane signalling pathways which promote gene expression and neuronal differentiation.

Divergent changes of chromogranin A/secretogranin II levels in differentiating human neuroblastoma cells

Human neuroblastoma cells were cultured either in the absence or presence of 12-O-tetradecanoylphorbol-13-acetate (TPA) known to induce neuronal differentiation. This treatment led to a marked increase in the concentration of secretogranin II but to a decrease of chromogranin A. Analogous changes were observed for the respective mRNAs. Thus during differentiation of these cells the biosynthesis of two vesicle constituents of large dense core vesicles is differentially regulated as determined both at the mRNA and the protein level. Levels of both synaptin/synaptophysin large dense core vesicles is differentially regulated as determined both at the mRNA and the protein level. Levels of both synaptin/synaptophysin and SV2 were also elevated but to a smaller degree than that of secretogranin II.