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Early RB94-produced cytotoxicity in cancer cells is independent of caspase activation or 50 kb DNA fragmentation

Abstract

RB94, which lacks the N-terminal 112 amino-acid residues of the full-length retinoblastoma protein (RB110) is a more potent inhibitor of cancer cell growth than RB110, being cytotoxic to all cancer cell lines studied, independent of their genetic abnormalities. Although we initially thought RB94-induced cell death was caspase-dependent, such caspase activation now appears to be a late event. Cells that remained attached 48 h after transduction with Ad-RB94 showed, among other changes, nuclear enlargement, peripheral nuclear chromatin condensation and often micronucleation. In addition, the cells were TdT-mediated dUTP nick end labeling (TUNEL) positive but showed no cleavage of caspase 3 or 9. Only after the cells detached was cleavage of both caspase 3 and 9 observed. These TUNEL-positive cells showed neither cytochrome c mitochondrial translocation usually found in typical apoptotic cells nor DNA laddering indicative of oligonucleosomal DNA fragmentation. In addition, although 50 kb DNA fragmentation was produced in these TUNEL-positive cells, which was dependent on apoptosis-inducing factor (AIF), inhibiting this fragmentation by siAIF did not inhibit TUNEL formation or cytotoxicity. As RB94 will soon be used for gene therapy further understanding the molecular basis of these early changes in killing cancer cells is one of our particularly important present goals.

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Abbreviations

Ad-RB110:

adenoviral-mediated RB110

Ad-RB94:

adenoviral-mediated RB94

AIF:

apoptosis-inducing factor

Dox:

doxycycline

FIGE:

field-inversion gel electrophoresis

HMW:

high molecular weight

kb:

kilobase

MOI:

multiplicity of infection

RB:

retinoblastoma

RB110:

full-length wild-type RB protein of 110 kDa

RB94:

RB protein of 94 kDa

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Acknowledgements

This study was supported by Grant CA-097127 from the National Cancer Institute to WFB and a Career Development Award to JZ from The GU SPORE in Bladder Cancer CA-091846.

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Correspondence to W F Benedict.

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Zhou, J., Zhang, XQ., Ashoori, F. et al. Early RB94-produced cytotoxicity in cancer cells is independent of caspase activation or 50 kb DNA fragmentation. Cancer Gene Ther 16, 13–19 (2009). https://doi.org/10.1038/cgt.2008.54

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