K252a: a new blocker of the cell-cycle at G1 phase in a human hepatoma cell line

High Glucose Concentration Alters Cell Proliferation Dynamics in Human Hepatoma Cells

The aim of this study was to develop an in vitro model to investigate the molecular mechanisms of glucose-induced inhibition of cell proliferation. HuH7 cells were grown in the presence or absence of glucose for 7 days and cell proliferation was stimulated by exposure to thioacetamide. Lactate dehydrogenase leakage and 3H-thymidine incorporation were used as indices of toxicity and DNA synthesis, respectively. Cell cycle progression and protooncogene expression was monitored by flow cytometry and slot-blot analyses. Toxicity caused by thioacetamide regressed with time in the presence of 11 mM glucose (control). However, in the presence of 28 mM glucose, sustained toxicity was evident as mirrored by lactate dehydrogenase leakage. Peak DNA synthesis noted at 48 hours in the thioacetamide-treated group (11 mM glucose) was significantly diminished in the presence of 28 mM glucose. Increased c-myc expression was observed as early as 30 minutes in the thioacetamide-treated group. When cells were exposed to 28 mM glucose, c-myc expression was delayed and diminished. Methylation profile studies revealed no appreciable changes, but c-myc was significantly amplified in the control, thioacetamide-, and in the presence of 28 mM of glucose-treated groups which correlated with mRNA changes in these groups. In the glucose-pretreated group (28 mM) significant amplification of the c-myc gene was observed at later time points but there was no change in the mRNA expression, indicating that the expression was delayed. This study shows that high glucose concentrations diminish DNA synthesis and cell cycle progression normally stimulated by thioacetamide. It is concluded that high glucose concentration causes cell cycle arrest via perturbation in protooncogene expression and hence the use of high glucose concentrations in therapy should be carefully examined in situations where postsurgical healing and healing after xenobiotic-induced injury are encountered.

K252a induces cell cycle arrest and apoptosis by inhibiting Cdc2 and Cdc25c

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.