C Terminus of Hsc70-interacting Protein Promotes Smooth Muscle Cell Proliferation and Survival through Ubiquitin-mediated Degradation of FoxO1

Abstract

Forkhead transcription factors (FoxOs) play a pivotal role in controlling cellular proliferation and survival. The cellular level of these factors is tightly regulated through the phosphoinositide 3-kinase/Akt and ubiquitin-mediated degradation. However, the ubiquitin ligases responsible for the degradation of FoxO1 and the relevance of this regulation to smooth muscle cell (SMC) proliferation and survival have not been fully identified. Here we showed that overexpression of C terminus of Hsc70-interacting protein (CHIP) promoted ubiquitination and degradation of FoxO1 in SMCs in response to tumor necrosis factor-␣. Both the U-box (containing ubiquitin ligase activity) and the charged (essential for FoxO1 binding) domains within CHIP were required for CHIP-mediated FoxO1 down-regulation. Moreover, interaction and ubiquitination of FoxO1 by CHIP depended on phosphorylation of FoxO1 at Ser-256. Furthermore, overexpression of CHIP repressed FoxO1-mediated transactivation and its proapoptotic function following tumor necrosis factor-␣ treatment. In contrast, knockdown of CHIP by small interfering RNA enhanced FoxO1-mediated transactivation and its effect on SMC proliferation and survival. Taken together, our data indicate that CHIP is a negative regulator of FoxO1 activity through ubiquitin-mediated degradation, and inhibition of CHIP may serve as a potential therapeutic target for reducing proliferative arterial diseases.The atherosclerotic lesion is characterized by the endothelial dysfunction, inflammation, and accumulation of vascular smooth muscle cells (SMCs), 3 foam cells, and matrix protein and lipids in the intima (1, 2). Although the pathogenic mechanisms of atherosclerosis and restenosis are complex, the balance between proliferation and apoptosis of vascular SMCs seems to be a major factor in the progression of these diseases (1, 2). Various growth factors and cytokines are known to be involved in these processes (3-6). One important pleiotropic cytokine is tumor necrosis factor-␣ (TNF-␣), which is believed to play a key role in modulating SMC proliferation, migration, survival, or apoptosis (3-6). TNF-␣ has been shown to promote cellular proliferation and survival via phosphoinositide 3-kinase (PI3K)/Akt and nuclear factor-B signaling pathways in several cell types (7-10). Activated Akt phosphorylates and regulates a number of downstream proapoptotic proteins, among which are the forkhead factors FoxO1, FoxO3a, and FoxO4 (formally known as FKHR, FKHRL1, and AFX, respectively) (11). The FoxO proteins are multifunctional transcription factors, which have important roles in regulating cellular differentiation, proliferation, survival in various cell lines, including cancer cells, fibroblasts, myoblasts, endothelial cells, and SMCs (3-6). Activated FoxO proteins modulate apoptosis through regulation of a number of proapoptotic proteins, inducing Bim, the TNF-related death inducing ligand, Fas ligand, and TNF-R1-associated death domain, which all are involved in apoptotic signaling (11)(12)(13)(14). Recent s...

Toll-Like Receptor-2 Ligand Peptidoglycan Upregulates Expression and Ubiquitin Ligase Activity of CHIP through JNK Pathway

“…In addition to its well-characterized three-tetratricopeptide repeats (TRP) domain that allows it to interact with chaperones such as Hsc70/Hsp70 and Hsp90, it also has charged domain, and U-box domain that confers E3 ubiquitin ligase activity and facilitates the polyubiquitination of chaperone substrates [13]. Studies have shown that CHIP plays important roles in the regulation of pathophysiological processes through promoting the degradation of various target proteins including cystic fibrosis transmembrane conductance regulator (CFTR), ErBB2, Foxo1, myocardin, Ask1, p53, Tau, and ataxin 1 proteins [27,28]. Several studies have demonstrated that the expression of CHIP at mRNA and protein levels is regulated by various factors.…”

Post-translational modifications of FOXO family proteins

“…C-terminus of Hsc70-interacting protein (CHIP) is highly expressed in the heart and blood vessels, and the C-terminus has a cochaperone/ubiquitin ligase with a dual function. Under the stimulus of TNF-α, CHIP promotes the smooth muscle cells to degrade and ubiquitination (110). Ring finger and WD repeat domain 2 (COP1), a ring-finger E3 ubiquitin ligase regulated by insulin, has a key role in survival of mammalian cells.…”

Expression Profiling Identifies Klf15 as a Glucocorticoid Target That Regulates Airway Hyperresponsiveness

“…By virtue of previously described functions in other muscle types, this analysis implicated numerous GR targets as novel candidates to modulate ASM function. For example, FOXO1 had been shown to regulate skeletal muscle atrophy and vascular smooth muscle (VSM) proliferation (34,35), but has not been studied in the lung or in ASM. Likewise, the GR targets, HES1, NR4A3, and MSX1, are transcription factors that have been implicated in smooth muscle biology (36-38), but have not been studied in ASM or asthma.…”