Disruption of replication protein A/single-stranded DNA complexes during apoptosis in HL-60 cells

New insight into the molecular mechanisms of the biological effects of DNA minor groove binders

BACKGROUND

Bisbenzimides, or Hoechst 33258 (H258), and its derivative Hoechst 33342 (H342) are archetypal molecules for designing minor groove binders, and widely used as tools for staining DNA and analyzing side population cells. They are supravital DNA minor groove binders with AT selectivity. H342 and H258 share similar biological effects based on the similarity of their chemical structures, but also have their unique biological effects. For example, H342, but not H258, is a potent apoptotic inducer and both H342 and H258 can induce transgene overexpression in in vitro studies. However, the molecular mechanisms by which Hoechst dyes induce apoptosis and enhance transgene overexpression are unclear.

METHODOLOGY/PRINCIPAL FINDINGS

To determine the molecular mechanisms underlying different biological effects between H342 and H258, microarray technique coupled with bioinformatics analyses and multiple other techniques has been utilized to detect differential global gene expression profiles, Hoechst dye-specific gene expression signatures, and changes in cell morphology and levels of apoptosis-associated proteins in malignant mesothelioma cells. H342-induced apoptosis occurs in a dose-dependent fashion and is associated with morphological changes, caspase-3 activation, cytochrome c mitochondrial translocation, and cleavage of apoptosis-associated proteins. The antagonistic effect of H258 on H342-induced apoptosis indicates a pharmacokinetic basis for the two dyes' different biological effects. Differential global gene expression profiles induced by H258 and H342 are accompanied by unique gene expression signatures determined by DNA microarray and bioinformatics software, indicating a genetic basis for their different biological effects.

CONCLUSIONS/SIGNIFICANCE

A unique gene expression signature associated with H342-induced apoptosis provides a new avenue to predict and classify the therapeutic class of minor groove binders in the drug development process. Further analysis of H258-upregulated genes of transcription regulation may identify the genes that enhance transgene overexpression in gene therapy and promote recombinant protein products in biopharmaceutical companies.

DATA DEPOSITION

The microarray data reported in this article have been deposited in the Gene Expression Omnibus (GEO) database, www.ncbi.nlm.nih.gov/geo (accession no.GSE28616).

Hoechst 33342 alters luciferase gene expression in transfected BC3H-1 myocytes

BACKGROUND

Hoechst 33342 and Hoechst 33258 bind to the minor groove of DNA. Hoechst 33342 induces apoptosis in a variety of cell types by a mechanism that is associated with disruption of the formation of the TATA box-binding protein/DNA complex.

OBJECTIVE

To further investigate the role of Hoechst 33342 in gene regulation using BC3H-1 myocytes transfected with 4 different pGL3 luciferase reporter vectors constructed with or without the SV40 promoter and/or enhancer regions or with 2 synthetic Renilla luciferase vectors (phRL-null and phRL-TK).

METHODS

Luciferase messenger RNA content was measured by reverse transcriptase-polymerase chain reaction, and luciferase activity was measured by luminometry. The ability of transcription factors in nuclei prepared from BC3H-1 myocytes to bind to a [32P]-labeled 24-base pair oligonucleotide containing the TATA box-binding element was determined by a gel mobility shift assay.

RESULTS

In vivo, 4.4 and 8.9 microM of Hoechst 33342 (sublethal doses) increased luciferase enzyme activity in cells transfected with each of the 4 pGL3 luciferase reporter vectors and both of the Renilla luciferase vectors. Hoechst 33258 had no effect on luciferase enzyme activity. In vitro, Hoechst 33342 increased transcription factor binding to the 24-mer oligonucleotide containing the TATA box-binding element, which would be favorable to increased RNA polymerase II efficiency.

CONCLUSION

Hoechst 33342 stimulates luciferase activity by a pathway that is independent of the integrity of the promoters in the luciferase gene expression vectors used (pGL3 basic, pGL3 control, pGL3 enhancer, and pGL3 promoter vectors, phRL-null, or phRL-TK).

Apoptosis: biochemical aspects and clinical implications

Apoptosis and necrosis represent two distinct types of cell death. Apoptosis possesses unique morphologic and biochemical features which distinguish this mechanism of programmed cell death from necrosis. Extrinsic apoptotic cell death is receptor-linked and initiates apoptosis by activating caspase 8. Intrinsic apoptotic cell death is mediated by the release of cytochrome c from mitochondrial and initiates apoptosis by activating caspase 3. Cancer chemotherapy utilizes apoptosis to eliminate tumor cells. Agents which bind to the minor groove of DNA, like camptothecin and Hoechst 33342, inhibit topoisomerase I, RNA polymerase II, DNA polymerase and initiate intrinsic apoptotic cell death. Hoechst 33342-induced apoptosis is associated with disruption of TATA box binding protein/TATA box complexes, replication protein A/single-stranded DNA complexes, topoisomerase I/DNA cleavable complexes and with an increased intracellular concentration of E2F-1 transcription factor and nitric oxide concentration. Nitric oxide and transcription factor activation or respression also regulate the two apoptotic pathways. Some human diseases are associated with excess or deficient rates of apoptosis, and therapeutic strategies to regulate the rate of apoptosis include inhibition or activation of caspases, mRNA antisense to reduce anti-apoptotic factors like Bcl-2 and survivin and recombinant TRAIL to activate pro-apoptotic receptors, DR4 and DR5.