Ubiquitin carboxyl terminal hydrolyase L1-suppressed autophagic degradation of p21WAF1/Cip1 as a novel feedback mechanism in the control of cardiac fibroblast proliferation.

Xiaoming Zhang,Weiwei Wu,Lei Shao,Fang Wang,Linmao Lv,Taixing Cui,Xing Li Wang,Linlin Guo,Huanjie Li,Dongqi Tang,Ting Niu,Wenjuan Wang,Qingyun Qin,Paul J Galardy

doi:10.1371/journal.pone.0094658

Abstract

AimsDeubiquitinating enzymes (DUBs) appear to be critical regulators of a multitude of processes such as proliferation, apoptosis, differentiation, and inflammation; however, the potential roles of DUBs in the heart remain to be determined. This study was aimed to explore the role of a DUB, ubiquitin carboxyl terminal hydrolyase L1 (UCH-L1) in maladaptive cardiac remodeling and dysfunction.Methods and ResultsMaladaptive cardiac remodeling and dysfunction were induced in mice by transverse aortic constriction (TAC). UCH-L1 expression was transiently increased and then declined near to the basal level while impairment of cardiac function proceeded. The upregulation of UCH-L1 was observed in cardiac myocytes and fibroblasts. In primary culture of cardiac fibroblasts, UCH-L1 was upregulated by platelet-derived growth factor (PDGF)-BB and PDGF-DD. Adenoviral overexpession of UCH-L1 inhibited the PDGF-induced cardiac fibroblast proliferation without affecting the activation of mitogen activated protein kinases (MAPKs), Akt, and signal transducers and activators of transcription 3 (STAT3). Further signaling dissection revealed that PDGF-BB posttranscriptional upregulated p21WAF1/Cip1 protein expression, which was inhibited by rapamycin, an activator of autophagy via suppressing mammalian target of rapamycin (mTOR), rather than MG132, a proteasome inhibitor. Overexpression of UCH-L1 enhanced PDGF-BB-induced mTOR phosphorylation and upregulation of p21WAF1/Cip1 protein expression while suppressed autophagic flux in cardiac fibroblasts.ConclusionUCH-L1 facilitates PDGF-BB-induced suppression of autophagic degradation of p21WAF1/Cip1 proteins in cardiac fibroblasts, which may serve as a novel negative feedback mechanism in the control of cardiac fibroblast proliferation contributing to cardiac fibrosis and dysfunction.

Highlights

Since ubiquitin (Ub) was discovered in the early 1970’s, the ubiquitination proteasome system (UPS) which consists of ubiquitin-activating enzymes (E1s), ubiquitin-conjugating enzymes (E2s), ubiquitin ligases (E3s), proteasomes, and deubiquitinating enzymes (DUBs) has emerged as a critical regulator in virtually all aspects of cell biology [1,2,3,4]
ubiquitin carboxyl terminal hydrolyase L1 (UCH-L1) facilitates platelet-derived growth factor (PDGF)-BB-induced suppression of autophagic degradation of p21WAF1/Cip1 proteins in cardiac fibroblasts, which may serve as a novel negative feedback mechanism in the control of cardiac fibroblast proliferation contributing to cardiac fibrosis and dysfunction
These results indicate that UCH-L1 expression are enhanced in the heart during the earlier stage of cardiac adaptive hypertrophy and declined in the process of maladaptive responses to the sustained hemodynamic stress, suggesting that UCH-L1 might play a critical role in the regulation of maladaptive cardiac remodeling and the transition of cardiac hypertrophy to heart failure

Summary

Introduction

Since ubiquitin (Ub) was discovered in the early 1970’s, the ubiquitination proteasome system (UPS) which consists of ubiquitin-activating enzymes (E1s), ubiquitin-conjugating enzymes (E2s), ubiquitin ligases (E3s), proteasomes, and deubiquitinating enzymes (DUBs) has emerged as a critical regulator in virtually all aspects of cell biology [1,2,3,4]. The process of ubiquitination is catalyzed by the sequential action of E1, E2, and E3 and DUBs mediate the removal and processing of ubiquitin. Approximately 100 functional DUBs are coded in human genome. Only one DUB, A20/ tumor necrosis factor alpha induced protein 3 (TNFAIP3), has been extensively studies in the heart. While A20 appears to be a key negative regulator of maladaptive cardiac remodeling and dysfunction induced by pressure overload or myocardial infarction [10,11], up-regulations of a few other DUBs including ubiquitin-specific protease 5 (USP5), USP20, and ubiquitin carboxyl terminal hydrolyase L1 (UCH-L1) in failed hearts have been observed [5]. The pathophysiological relevance of these DUBs in the heart remains unknown

Methods

Results

Discussion

Conclusion