Doxorubicin and 5-fluorouracil induced accumulation and transcriptional activity of p53 are independent of the phosphorylation at serine 15 in MCF-7 breast cancer cells

Abstract

The chemotherapeutic agents doxorubicin (dox) or 5-fluorouracil (5FU) are used to treat cancer cells as they cause irreparable DNA damage, inducing these aberrant cells to undergo cell death. The mediator of this process is presumed to be in part the tumor suppressor p53 which regulates genes involved in DNA repair and cell death. When MCF-7 breast cancer cells are treated with these drugs, we observed that the level of p53 and the p53 negative regulator, Mdm2, increased, as seen by others. But contrary to some reports, we observed minimal phosphorylation of p53 at serine 15 in MCF-7 cells after drug treatment. Interestingly, we determined that there was differential regulation of the kinases ATM and Chk2 with the drug treatments, likely the cause for the lack of phosphorylation of p53. We found a dramatic drop in p53 DNA binding affinity for p21 and other gene response elements (RE) after drug treatment. To determine if the p53 that accumulated in the drug treated cells was functionally active, we monitored changes in the protein products of two p53-regulated genes following drug treatment with and without the addition of a p53-specific siRNA. In response to 5FU, both p21 and Mdm2 proteins increased and that increase was alleviated if a p53-specific siRNA was added. This effect was not seen with the addition of dox. Thus, the phosphorylation at serine 15 is not necessary for the functional activation of this transcription factor. We propose a new model for the regulation of p53, Mdm2, and MdmX after drug treatment.

Doxorubicin attenuates CHIP-guarded HSF1 nuclear translocation and protein stability to trigger IGF-IIR-dependent cardiomyocyte death

“…With elevated concentrations of DOX, p53 and caspase-3 activation was markedly increased to induce apoptosis (Figure 1a). 30, 31, 32 Interestingly, IGF-IIR expression was strongly upregulated, implying that the IGF-IIR signaling pathway may be involved in DOX-induced cardiomyocyte death.…”

Anacardic acid inhibits pancreatic cancer cell growth, and potentiates chemotherapeutic effect by Chmp1A - ATM - p53 signaling pathway

“…AA regulates various signaling pathways for its activities; association with p53 in breast and prostate cancer [ 20 , 24 ], inhibition of Src/FAK/Rho GTPase to block angiogenesis in prostate cancer [ 24 ], and correlation with ATM in squamous cell carcinoma cells of lung [ 25 ]. As for chemotherapeutics, 5-FU was shown to activate p53 [ 26 ] and ATM in colorectal cancer [ 27 ], and GEM to activate p53 in breast cancer [ 20 ]. In addition, we have shown that Chmp1A activates ATM and p53 in pancreatic cancer cells [ 10 – 12 ].…”

The Roles of p53 in Mitochondrial Dynamics and Cancer Metabolism: The Pendulum between Survival and Death in Breast Cancer?

“…Under homeostatic conditions, cellular p53 protein levels are low due to its short half-life and continual degradation by the HDM2 ubiquitin ligase [ 160 , 161 ]. Due to the large proportion of breast carcinomas retaining wt-p53, radiotherapy and chemotherapy agents such as doxorubicin are successful in reactivating p53 via the DNA damage pathway, inducing cell cycle arrest and cell death [ 25 , 26 , 27 ]. In line with its classical role as a tumor suppressor, novel anti-HDM2 (human double minute 2) agents target HDM2, stabilize p53, and reactivate the p53 signaling pathway to kill cancer cells [ 27 , 162 , 163 , 164 ].…”

“…Common treatment regimes for breast cancer include surgical ablation, adjuvant or neoadjuvant chemotherapy, radiotherapy, and endocrine therapy, with the therapeutic strategy dependent on the stage and type of cancer [ 24 ]. Radiotherapy and chemotherapy induce DNA damage, inducing cell cycle arrest and apoptosis [ 25 , 26 , 27 , 28 ]. Endocrine therapy, including Tamoxifen and Fulvestrant, blocks the ERα receptor, which in turn represses aberrant estrogen signaling [ 21 ].…”