Induction of c-fos mRNA by lead in PC 12 cells.

Addition of lead acetate to PC 12 pheochromocytoma cells elicits induction of c-fos, an immediate early response gene. Induction of c-fos was concentration- and time-dependent: the lowest concentration of lead acetate tested that induced c-fos was 10 microM; induction was observed after a 30 min incubation and remained high after 90 min. Treatment with lead acetate and cycloheximide superinduced c-fos mRNA. Actinomycin D, an inhibitor of mRNA transcription, decreased the level of c-fos mRNA induced by lead acetate by almost 80%. Cadmium chloride and zinc chloride did not induce c-fos mRNA. Since the c-fos gene encodes a transcription factor, Pb2+ has the potential to deregulate the expression of other genes.

Phosphorylation of membrane proteins in erythrocytes treated with lead.

In immature rat microvessels, endothelial cells and glioma cells, exposure to lead results in an increase in the level of protein kinase C in membranes. In this paper we have extended these studies to human erythrocytes and, in addition, studied the phosphorylation of membrane proteins. A significant increase in the phosphorylation of membrane cytoskeletal proteins of molecular mass 120, 80, 52 and 45 kDa was observed in human erythrocytes treated for 60 min with lead acetate at concentrations greater than 100 nM. These same proteins were phosphorylated when erythrocytes were treated for 10 min with 50 nM phorbol 12-myristate 13-acetate (PMA). Similarly, protein kinase C activity was elevated and an increase in the amount of protein kinase C-alpha was observed in membranes from erythrocytes exposed to concentrations of lead acetate above 100 nM. No changes, however, in the activities of cAMP-dependent protein kinase, protein phosphatases I and IIA or casein kinase were observed. Phosphorylation of these membrane proteins stimulated by lead acetate or by PMA was not observed in erythrocytes depleted of protein kinase C by a 72-h treatment with 500 nM phorbol 12,13-dibutyrate. Finally, no changes in the levels of calcium or diacylglycerol were observed in erythrocytes stimulated with 100 nM lead acetate. These results indicate that, in erythrocytes, lead acetate stimulates the phosphorylation of membrane cytoskeletal proteins by a mechanism dependent on protein kinase C. Since levels of calcium or diacylglycerols did not increase, it appears that lead may activate the enzyme by a direct interaction.

Comparative analysis of virus-induced polypeptides of an avirulent and a virulent strain of avian reovirus.

Ten avian reovirus-specific polypeptides, ranging in molecular weight from 32,000 to 145,000, were identified in chicken embryo fibroblasts infected with virulent and attenuated strains. Time-course studies on the viral polypeptides indicated that all of these proteins could be detected as early as 16 hr postinfection (PI) for both strains of avian reoviruses. With the virulent strain 1733, protein production reached a plateau 24 hr PI, whereas with an attenuated strain S1133, production plateaued at 48 hr PI. Immunoprecipitation of labeled polypeptides from S1133 and 1733 strains with homologous and heterologous sera revealed that sera against strain 1733 recognizes sigma NS protein in both strains 1733 and S1133, whereas sera against strain S1133 recognizes this protein only in 1733, suggesting a difference in the primary structure or the conformation of that particular protein in both viruses. None of the polypeptides of avian reovirus were glycosylated or phosphorylated.