Selective changes in the phosphorylation of endogenous proteins in subcellular fractions from cyclic AMP-induced differentiated neuroblastoma cells

Clinical biochemistry of neuron specific enolase

The soluble brain protein 14-3-2 first described by Moore and McGregor in 1965 is now known to be a cell specific isoenzyme of the glycolytic enzyme enolase (EC 4.2.1.11), designated neuron specific enolase (NSE). It is not only a marker for all types of neurons, but also for all neuroendocrine or paraneuronal cells. The appearance of NSE is a late event in neural differentiation, thus making NSE a useful index of neural maturation. The demonstration that tumors of the nervous system and of neuroendocrine origin contain NSE has promoted the study of NSE as a possible tumor marker. Immunocytochemistry has been used to identify NSE in cytologic preparations from several types of tumors, offering useful indications for differential diagnosis. NSE levels in serum from tumor patients are not useful in the diagnosis of early stage disease. However, serum NSE levels have been shown to be helpful in the identification of advanced small cell lung cancer, neuroblastoma and several other neoplasms. The main use of serum NSE is the monitoring of chemotherapy and the detection of a relapse in these cases.

Cyclic nucleotides in muscarinic regulation of DNA and RNA polymerase activity in cultured corneal epithelial cells of the rabbit

DNA and RNA polymerase activities in the purified nuclear fraction from cultured rabbit corneal epithelial cells were assayed over a range of substrate (labeled dTTP or UTP) concentrations using calf thymus DNA as template. Effects of carbamylcholine on polymerase activities were evaluated over a range of drug concentrations including those saturating muscarinic receptors. Carbamylcholine significantly (p less than 0.001) enhanced activity of both polymerases, both in nuclei incubated with the drug during assay and in nuclei from carbamylcholine-treated cells. Drug effects were blocked by atropine. Regression analysis of Hill plots for variation of polymerase activity with carbamylcholine concentration indicated half-maximal activity of both polymerases at approximately 1 microM carbamylcholine. Mechanisms by which carbamylcholine may alter polymerase activities are discussed in relation to effects of the drug on nuclear enzymes of cyclic nucleotide metabolism and on cyclic nucleotide-dependent protein phosphorylation.

Neuron-specific enolase in relation to differentiation in human neuroblastoma

The presence of the two forms of enolase, neuron-specific enolase (NSE) and non-neuronal enolase (NNE), have been examined in biopsy material of human neuroblastoma, ganglioneuroblastoma, ganglioneuroma and cultured neuroblastoma cells, after separation with ion exchange chromatography. The enolase activities were inhibited in the presence of NaCl but remained active in KCl, which were used in the chromatographic step. The relative NSE levels in the neuroblastoma tissues were found to be lower than in the histopathologically more differentiated forms of the tumour, i.e. ganglioneuroblastoma and ganglioneuroma. The human neuroblastoma in vitro cell lines SK-N-SH, SH-SY5Y, SK-N-MC and IMR-32 contained considerably lower relative levels of NSE compared to the levels in the neuroblastoma biopsies. After treatment of the cultured cells with nerve growth factor or dibutyryl-cAMP some cells showed morphological differentiation and concomitantly an increase in the NSE levels. The results indicate that NSE might be useful as a marker for differentiation in human neuroblastoma.

Evidence that the 40,000 Mr phosphoprotein influenced by high frequency synaptic stimulation is the alpha subunit of pyruvate dehydrogenase

We have previously shown that brief periods of high frequency synaptic stimulation of the rat hippocampus influence the endogenous phosphorylation of a 40,000 Mr brain protein (Browning et al.). The results of the present study demonstrate that this brain phosphoprotein is enriched in a purified mitochondrial fraction and co-migrates with the alpha-subunit of pyruvate dehydrogenase in sodium dodecyl sulfate polyacrylamide gels. Comparisons of total and partial proteolytic fingerprints indicate that the two proteins are essentially identical. In addition, the phosphorylation of the 40,000 Mr brain protein is sensitive to both dichloroacetate and magnesium as has been reported for pyruvate dehydrogenase. Taken together these data provide persuasive evidence that the brain protein is the alpha-subunit of pyruvate dehydrogenase and thereby raise the possibility that even very short periods of synaptic activity influence an enzyme of particular importance to mitochondrial metabolism in brain.