Expression of the cyclin-dependent kinase inhibitor p21 is highly induced by many stresses, including exposure to short-wavelength UV light (UVC), which increases p21 mRNA stability. Investigation into the mechanisms underlying this stabilization process revealed that proteins present in cytoplasmic lysates of human RKO colorectal carcinoma cells formed complexes with p21 mRNA that were inducible by treatment with UVC and other stress agents. The ubiquitous Elav-type RNA-binding protein HuR was identified within the p21 mRNA-protein complexes, as antibodies recognizing HuR supershifted these complexes and revealed HuR-immunoreactive proteins complexing with p21 mRNA on Western blots. Lowering of endogenous HuR levels through expression of antisense HuR decreased p21 RNA-protein complexes, greatly reduced the UVC inducibility and half-life of p21 mRNA, and prevented UVC-mediated induction of luciferase activity in p21 3 untranslated region-containing reporter constructs. Our findings indicate that HuR plays a major role in regulating stress-induced p21 expression by enhancing p21 mRNA stability and that these effects are coupled to HuR's elevated presence in the cytoplasm.
Mitogen-activated protein (MAP) kinase phosphatase 1 (MKP-1) has been shown to play a critical role in mediating the feedback control of MAP kinase cascades in a variety of cellular processes, including proliferation and stress responsiveness. Although MKP-1 expression is induced by a broad array of extracellular stimuli, the mechanisms mediating its induction remain poorly understood. Here we show that MKP-1 mRNA was potently induced by arsenite and ultraviolet light and modestly increased by heat shock and hydrogen peroxide. Interestingly, arsenite also dramatically induces phosphorylation-acetylation of histone H3 at a global level which precedes the induction of MKP-1 mRNA. The transcriptional induction of MKP-1, histone H3 modification, and elevation in MKP-1 mRNA in response to arsenite are all partially prevented by the p38 MAP kinase inhibitor SB203580, suggesting that the p38 pathway is involved in these processes. Finally, analysis of the DNA brought down by chromatin immunoprecipitation (ChIP) reveals that arsenite induces phosphorylation-acetylation of histone H3 associated with the MKP-1 gene and enhances binding of RNA polymerase II to MKP-1 chromatin. ChIP assays following exposure to other stress agents reveal various degrees of histone H3 modification at the MKP-1 chromatin. The differential contribution of p38 and ERK MAP kinases in mediating MKP-1 induction by different stress agents further illustrates the complexity and versatility of stress-induced MKP-1 expression. Our results strongly suggest that chromatin remodeling after stress contributes to the transcriptional induction of MKP-1.The mitogen-activated protein (MAP) kinases play a central role in orchestrating many short-and long-term changes in the cell in response to extracellular stimuli (50). To date, three major MAP kinase subfamilies have been well characterized in mammalian cells: the extracellular signal-regulated kinase (ERK), the c-Jun N-terminal kinases/stress-activated protein kinase (JNK/SAPK), and p38 (11,40,50). Thus far, numerous proteins with a wide spectrum of biological functions have been identified as the targets of MAP kinase cascades, including protein kinases, cytoskeletal components, phospholipase A2, stalhmin, and the Na ϩ /H ϩ antipump NHE1 (6,23,42). In addition to the proteins that function on the membrane or in the cytoplasm, MAP kinases also play a crucial role in regulating gene transcription. Upon activation, MAP kinases translocate from the cytoplasm to the nucleus, where they phosphorylate and activate a multitude of transcription factors, including c-Myc, c-Jun, c-Fos, Elk-1, and ATF-2, ultimately resulting in enhanced gene transcription (8,24,58). The fact that a broad variety of extracellular signals conscript MAP kinase cascades to convey their specific messages suggests that MAP kinase cascades serve a myriad of purposes and the cascades need to be tightly controlled.The activities of all MAP kinases are regulated through reversible phosphorylation of two different amino acid residues (threonine ...
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.