Homozygous mdm2 SNP309 cancer cells with compromised transcriptional elongation at p53 target genes are sensitive to induction of p53-independent cell death
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Melissa Rosso1, Alla Polotskaia1, Jill Bargonetti1
1The Department of Biological Sciences Hunter College at The Belfer Research Building and The Graduate Center Biology PhD Program, CUNY, New York, NY 10021, USA
Jill Bargonetti, e-mail: [email protected]
Keywords: MDM2, p53, chromatin, transcription elongation, 8-amino-adenosine
Received: April 07, 2015 Accepted: September 07, 2015 Published: September 19, 2015
A single nucleotide polymorphism (T to G) in the mdm2 P2 promoter, mdm2 SNP309, leads to MDM2 overexpression promoting chemotherapy resistant cancers. Two mdm2 G/G SNP309 cancer cell lines, MANCA and A875, have compromised wild-type p53 that co-localizes with MDM2 on chromatin. We hypothesized that MDM2 in these cells inhibited transcription initiation at the p53 target genes p21 and puma. Surprisingly, following etoposide treatment transcription initiation occurred at the compromised target genes in MANCA and A875 cells similar to the T/T ML-1 cell line. In all cell lines tested there was equally robust recruitment of total and initiated RNA polymerase II (Pol II). We found that knockdown of MDM2 in G/G cells moderately increased expression of subsets of p53 target genes without increasing p53 stability. Importantly, etoposide and actinomycin D treatments increased histone H3K36 trimethylation in T/T, but not G/G cells, suggesting a G/G correlated inhibition of transcription elongation. We therefore tested a chemotherapeutic agent (8-amino-adenosine) that induces p53-independent cell death for higher clinically relevant cytotoxicity. We demonstrated that T/T and G/G mdm2 SNP309 cells were equally sensitive to 8-amino-adenosine induced cell death. In conclusion for cancer cells overexpressing MDM2, targeting MDM2 may be less effective than inducing p53-independent cell death.
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