Synthesis of the p53 tumor suppressor and its subsequent activation following DNA damage are critical for its protection against tumorigenesis. We previously discovered an internal ribosome entry site (IRES) at the 5= untranslated region of the p53 mRNA. However, the connection between IRES-mediated p53 translation and p53's tumor suppressive function is unknown. In this study, we identified two p53 IRES trans-acting factors, translational control protein 80 (TCP80), and RNA helicase A (RHA), which positively regulate p53 IRES activity. Overexpression of TCP80 and RHA also leads to increased expression and synthesis of p53. Furthermore, we discovered two breast cancer cell lines that retain wild-type p53 but exhibit defective p53 induction and synthesis following DNA damage. The levels of TCP80 and RHA are extremely low in both cell lines, and expression of both proteins is required to significantly increase the p53 IRES activity in these cells. Moreover, we found cancer cells transfected with a shRNA against TCP80 not only exhibit decreased expression of TCP80 and RHA but also display defective p53 induction and diminished ability to induce senescence following DNA damage. Therefore, our findings reveal a novel mechanism of p53 inactivation that links deregulation of IRES-mediated p53 translation with tumorigenesis.O ne of the most important tumor suppressors identified thus far is p53. Under normal conditions, p53 is inactive, and its cellular levels are low. In response to various genotoxic or cytotoxic stress, including DNA damage, p53 becomes activated (1). The activated p53 causes cell growth arrest or apoptosis, allowing damaged cells to self-repair or be eliminated. In this manner, p53 protects against malignant transformation of normal cells (2, 3). Activation of p53 involves both accumulation and posttranslational modification. It is thought that the control of p53 induction or accumulation occurs mainly at the translational and posttranslational levels (1). Although levels of p53 are known to be regulated by the ubiquitin ligase mouse double minute 2 (MDM2), now there is clear evidence showing that enhanced p53 translation is essential for its induction following DNA damage (4). More specifically, the 5= untranslated region (5= UTR) of p53 mRNA was found to be a major site for regulation of p53 translation (5, 6). The mechanism underlying translational regulation of p53 induction via its 5= UTR has started to emerge.Cap-dependent initiation of protein translation is used by the majority of mRNAs, since almost all eukaryotic mRNAs have an N 7 -methylguanosine cap structure at their 5= ends. Eukaryotic translation initiation factor 4E (eIF-4E), a translation initiation protein that binds to the cap structure, initiates the process (7). In situations where cap-dependent translation is impaired, including apoptosis or DNA damage, cap-independent protein translation, mediated by an internal ribosomal entry site (IRES) that does not require the participation of eIF-4E, is needed in eukaryotes for the synthe...
Synthesis of the p53 tumor suppressor increases following DNA damage. This increase and subsequent activation of p53 are essential for the protection of normal cells against tumorigenesis. We previously discovered an internal ribosome entry site (IRES) that is located at the 5′-untranslated region (UTR) of p53 mRNA and found that the IRES activity increases following DNA damage. However, the mechanism underlying IRES-mediated p53 translation in response to DNA damage is still poorly understood. In this study, we discovered that translational control protein 80 (TCP80) has increased binding to the p53 mRNA in vivo following DNA damage. Overexpression of TCP80 also leads to increased p53 IRES activity in response to DNA damage. TCP80 has increased association with RNA helicase A (RHA) following DNA damage and overexpression of TCP80, along with RHA, leads to enhanced expression of p53. Moreover, we found that MCF-7 breast cancer cells with decreased expression of TCP80 and RHA exhibit defective p53 induction following DNA damage and diminished expression of its downstream target PUMA, a proapoptotic protein. Taken together, our discovery of the function of TCP80 and RHA in regulating p53 IRES and p53 induction following DNA damage provides a better understanding of the mechanisms that regulate IRES-mediated p53 translation in response to genotoxic stress.
The ability of cancer cells to produce lactate through aerobic glycolysis is a hallmark of cancer. In this study, we established a positional isotopic labeling and LC-MS-based method that can specifically measure the conversion of glucose to lactate in glycolysis. We show that the rate of aerobic glycolysis is closely correlated with glucose uptake and lactate production in breast cancer cells. We also found that the production of [3-13C]lactate is significantly elevated in metastatic breast cancer cells and in early stage metastatic mammary tumors in mice. Our findings may enable the development of a biomarker for the diagnosis of aggressive breast cancer.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.