ABSTRACT
The indole carbazole K252a has been shown in previous studies to inhibit the platelet-derived growth factor signal transduction pathway in gliomas. Because K252a has nonspecific effects on protein kinase function, we studied its effect on cyclin-dependent kinases (CDK) and cell cycle blockade in glioma cells. K252a blocked T98G cells at the G1/S and G2/M checkpoints. Consistent with cell cycle arrest, K252a was shown to hypophosphorylate Rb, upregulate p21, and decrease Cdc2 and Cdc25c activity. Finally, cell cycle arrest in T98G cells resulted in apoptosis as determined by cell morphology and DNA laddering. K252a is a useful tool for studying the effects of CDK inhibition and cell cycle blockade in tumor cells.
Subject(s)
Apoptosis/drug effects , CDC2 Protein Kinase/antagonists & inhibitors , Carbazoles/pharmacology , Cell Cycle Proteins/antagonists & inhibitors , Cell Cycle/drug effects , Blotting, Western , CDC2 Protein Kinase/metabolism , Cell Cycle Proteins/metabolism , Cell Size/drug effects , DNA Fragmentation/drug effects , Dose-Response Relationship, Drug , Enzyme Activation/drug effects , Enzyme Inhibitors/pharmacology , Flow Cytometry , Glioma , Histones/metabolism , Humans , Indole Alkaloids , Phosphorylation/drug effects , Protein Kinase Inhibitors , Protein Kinases/metabolism , Proto-Oncogene Proteins p21(ras)/metabolism , Retinoblastoma Protein/metabolism , Tumor Cells, Cultured , Up-Regulation/drug effects , ras-GRF1ABSTRACT
The dual signal hypothesis of apoptosis holds that a common signal can activate both apoptotic and proliferative pathways. The fate of a cell is dependent on which of these two pathways predominates. In the MAPK family of kinases, ERK and JNK have been proposed to mediate apoptosis whereas the PI3K-stimulated kinase, Akt/PKB, has been shown to inhibit apoptosis. The object of this study was to determine the role of these kinases in a glioma model of apoptosis. We have previously shown that K252a induces apoptosis and inhibits kinase activity. In this study we confirm these results and show that the protein tyrosine phosphatase inhibitor sodium vanadate activates ERK, JNK and Akt/PKB, but does not stimulate proliferation. Vanadate did protect T98G cells from K252a-induced apoptosis, an effect that was abolished by addition of the PI3K inhibitor wortmannin. This suggests that PI3K and Akt/PKB may be responsible for mediating vanadate's protective effect on glioma cells. We conclude that the intracellular balance between protein phosphorylation pathways is a critical determinant of both cell proliferation and cell death.
Subject(s)
Apoptosis/drug effects , Glioma/enzymology , Glioma/pathology , Protein Serine-Threonine Kinases , Proto-Oncogene Proteins/metabolism , Vanadates/pharmacology , Androstadienes/pharmacology , Apoptosis/physiology , Calcium-Calmodulin-Dependent Protein Kinases/metabolism , Cell Cycle/drug effects , Cell Division/drug effects , Enzyme Activation/drug effects , Enzyme Inhibitors/pharmacology , Humans , Phosphatidylinositol 3-Kinases/metabolism , Phosphoinositide-3 Kinase Inhibitors , Phosphorylation , Protein Tyrosine Phosphatases/antagonists & inhibitors , Proto-Oncogene Proteins c-akt , Tumor Cells, Cultured , Up-Regulation/drug effects , WortmanninABSTRACT
Apoptosis is a carefully regulated process involved in developmental and immunological events. The alteration of apoptotic pathways is important in the establishment and progression of neoplasia. Apoptosis allows for the orderly removal of excess cells but, in contrast to necrosis, it is not an inflammatory process. Many of the molecular components and effectors of apoptosis have been described. In this review the authors briefly discuss the current understanding of apoptosis in the context of the two prevailing hypotheses, the "conflicting signal" and "dual signal" theories.
ABSTRACT
We report a case of bilateral synovial cysts of the thoracic spine. The patient presented with progressive, lower-extremity weakness and hypesthesia, culminating in complete paraplegia. This rare lesion should be considered when confronted with a patient with thoracic cord compression.
