HuR Regulates p21 mRNA Stabilization by UV Light

Abstract

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.

Distinct Domains of AU-Rich Elements Exert Different Functions in mRNA Destabilization and Stabilization by p38 Mitogen-Activated Protein Kinase or HuR

“…HuR has been found to interact with several AREs in vitro and in cells, and its overexpression induced stabilization of mRNAs for vascular endothelial growth factor (23), nitric oxide synthase II (35), eotaxin (1), and different ARE-containing reporter RNAs (14,15,33). Furthermore, suppression of HuR amounts by antisense RNA or small interfering RNA approaches inhibited stabilization induced by hypoxia (23), cytokines (35), or UV light (43) or during cell cycle progression (42). Most recently, constitutively active MK2 (41), as well as stimuli known to activate the p38/MK2 pathway (H 2 O 2 [41] and TNF-␣ [1]), was found to induce cytoplasmic accumulation of HuR.…”

“…HuR is a ubiquitously expressed member of the human ELAV family of RNA binding proteins (24) whose functional role in the stabilization of several ARE-containing mRNAs has been established (15,23,33,35,42,43). It also plays a role in the nuclear export of mRNA (17) and in control of translation (20,26).…”

Cytoplasmic Expression of HuR is Related to Cyclooxygenase-2 Expression in Colon Cancer

“…Recent studies have shown that mitogenic-activated protein kinase-2 increased cytoplasmic translocation of HuR and the stability of ARE-containing mRNAs (19). The translocation of HuR to the cytoplasm can be induced by stress caused by agents such as UV light, DNA damaging agents or T cell activation, while AMP-activated kinase can inhibit the translocation of HuR to the cytoplasm (20)(21)(22).…”

The Role of Human Antigen R, an RNA-binding Protein, in Mediating the Stabilization of Toll-Like Receptor 4 mRNA Induced by Endotoxin

“…14 HuR is a ubiquitous protein belonging to the embryonic lethal abnormal vision family of RNA-binding proteins, predominantly nuclear proteins, which shuttle between the nucleus and cytoplasm. HuR regulates cyclin A, cyclin B1, 15 and p21 16 mRNA stability during cell proliferation. AUF1, a member of the heteronuclear ribonucleoprotein (hnRNP) family (also known as hnRNP D), is another RNA-binding protein, which exists in four isoforms (37, 40, 42, and 45 kDa).…”