Triggering of cyclin degradation in interphase extracts of amphibian eggs by cdc2 kinase

The cell cycles of early Xenopus embryos consist of a rapid succession of alternating S and M phases. These cycles are controlled by the activity of a protein kinase complex (cdc2 kinase) which contains two subunits. One subunit is encoded by the frog homologue of the fission yeast cdc2+ gene, p34cdc2 and the other is a cyclin. The concentration of cyclins follows a sawtooth oscillation because they accumulate in interphase and are destroyed abruptly during mitosis. The association of cyclin and p34cdc2 is not sufficient for activation of cdc2 kinase, however; dephosphorylation of key tyrosine and threonine residues of p34cdc2 is necessary to turn on its kinase activity. The activity of cdc2 kinase is thus regulated by a combination of translational and post-translational mechanisms. The loss of cdc2 kinase activity at the end of mitosis depends on the destruction of the cyclin subunits. It has been suggested that this destruction is induced by cdc2 kinase itself, thereby providing a negative feedback loop to terminate mitosis. Here we report direct experimental evidence for this idea by showing that cyclin proteolysis can be triggered by adding cdc2 kinase to a cell-free extract of interphase Xenopus eggs.     

Dual role of cAMP duringDictyostelium development

cAMP plays an essential role duringDictyostelium development both outside and inside the cell. Membrane-bound receptors and adenylyl cyclase are responsible for sensing and producing extracellular cAMP, whereas a phosphodiesterase is responsible for maintaining a low basal level. The molecular events underlying this type of hormone like signalling, which are now beginning to be deciphered, will be presented, in the light of cAMP analogue studies. The importance of intracellular cAMP for cell differentiation has been demonstrated by the central role of the cAMP dependent protein kinase. Mutants as well as strains obtained by reverse genetics will be reviewed which lead to our current understanding of the role of intracellular cAMP in the differentiation of both stalk and spore cells.     

AIDS virus-specific cytotoxic T lymphocytes in lung disorders

Human immunodeficiency virus (HIV) is implicated in the development of AIDS (acquired immune deficiency syndrome). HIV infection leads to the generation of HIV-specific thymus-derived (T) lymphocytes in humans and apes. We describe an experimental system permitting the quantitative and systematic analysis of HIV-specific cytotoxic T lymphocytes (CTL). Functional, HIV-specific CTL are obtained by broncho-alveolar lavage (BAL) from the lungs of seropositive patients with lymphocytic alveolitis. These alveolar CTL: (1) recognize and kill HIV-infected alveolar macrophages in vitro under autologous, but not heterologous, conditions; (2) correspond to standard CTL as they express the CD3 and CD8 surface markers, but not the CD4 marker; and (3) are restricted by class I HLA transplantation antigens in their cytotoxic activities. We propose the hypothesis that interactions between HIV-specific CTL and infected macrophages induce major inflammatory reactions in seropositive patients.     

Effect of monensin and diabetes on asialoglycoprotein degradation in rat hepatocytes

We have studied the effects of two modulations — streptozotocin-induced diabetes in vivo, and the presence of the carboxylic proton ionophore monensin in vitro — on the degradation of³H-asialoorosomucoid ligand in isolated rat hepatocytes.The ligand was internalized by means of a synchronous wave procedure. Diabetes was associated with a marked decrease in the amount of total degraded radioactive ligand compared to that in normal cells (3.6% and 37.3% of internalized ligand respectively, at 60 min), together with increased secretion of degradation products into the incubation medium (87% and 46.3% of the total degraded ligand was secreted by diabetic and normal cells, respectively). Monensin induced similar effects in normal cells, but had no apparent effect in diabetic cells.