mithramycin-sk and Necrosis

The effects of mithramycin SK (MSK) and demycarosyl-3D-β-D-digitoxosyl-mithramycin SK (DIG-MSK; EC-8042), two novel analogs of the antitumor antibiotic mithramycin A, on gene transcription were examined in human HCT116 colon carcinoma cells by quantitative real-time PCR of 89 genes mainly involved in cell cycle control. Each one of the analogs down-regulated a different set of genes, while only five genes were down-regulated by both compounds. Moreover, other genes were significantly up-regulated, among them p21(WAF1)/CDKN1A which is involved in halting cells at the G1 and G2/M checkpoints. These results are rationalized in terms of MSK or DIG-MSK competition with various transcription factors for binding to consensus C/G-rich tracts encompassed in gene promoters. Changes in cell cycle distribution and protein levels after treatment with every analog were consistent with changes observed in gene expression.

Topics: Antineoplastic Agents; Apoptosis; Binding Sites; G1 Phase Cell Cycle Checkpoints; G2 Phase Cell Cycle Checkpoints; Genes, cdc; HCT116 Cells; Humans; Necrosis; Plicamycin; Real-Time Polymerase Chain Reaction; Transcription Factors; Transcription, Genetic

During a normal cell cycle, polyploidy and aneuploidy can be prevented by several checkpoints, which are mainly p53 dependent. Here, we show that treatment of HCT-116 (p53+/+) colon carcinoma cells with the novel antitumor antibiotic mithramycin SK (MSK) results in polyploidization and mitotic catastrophe, which occurs after a transient halt in G1 phase followed by the overtaking of the G2-M checkpoint when treated cells are incubated in a fresh drug-free medium. Cells reentering aberrant mitosis mainly died by necrosis, although active caspase-3 was observed. Our results indicate that a decrease in p53 RNA and protein levels, together with concomitant changes in the expression of other proteins such as p21WAF1, were involved in MSK-induced polyploidy. Furthermore, the effects of MSK on HCT-116 (p53+/+) cells cannot be attributed exclusively to the down-regulation of p53 by MSK, because these effects differed from those observed in MSK-treated HCT-116 (p53-/-) cells. The p53(-/-) cells died mainly from G2-M through early p53-independent apoptosis, which appeared to be mediated by caspase-2, although secondary necrosis was also observed.

Topics: Blotting, Western; Cell Death; Cell Proliferation; Cell Survival; Colonic Neoplasms; Cytokinesis; Gene Expression Regulation, Neoplastic; HCT116 Cells; Humans; Mitosis; Necrosis; Neoplasm Proteins; Plicamycin; Polyploidy; Transcription, Genetic; Tumor Stem Cell Assay; Tumor Suppressor Protein p53