Up-regulation of cullin7 promotes proliferation and migration of pulmonary artery smooth muscle cells in hypoxia-induced pulmonary hypertension

Abstract

It has well been demonstrated that E3 ubiquitin ligase cullin7 plays important roles in cancer cell growth control via down-regulating p53 expression. The noncanonical function or the pathogenic role of p53 has more recently been implicated in pulmonary vascular remodeling. Therefore, whether cullin7 participates in hypoxia-induced pulmonary vascular remodeling deserves to be elucidated. The present study found that hypoxia up-regulated the expression of cullin7 mRNA and protein in pulmonary arteries and pulmonary artery smooth muscle cells, and knockdown of cullin7 inhibited hypoxia-induced proliferation and migration of pulmonary artery smooth muscle cells and reversed hypoxia-induced inhibition of p53 expression. Notably, administration of proteasome inhibitor MG132 significantly inhibited the expression of cullin7 and up-regulated the expression of p53 in pulmonary arteries concomitantly with improvement of hypoxia-induced pulmonary vascular remodeling. Our study demonstrated that hypoxia induced up-regulation of cullin7 expression resulting to the proliferation and migration of pulmonary artery smooth muscle cells via down-regulating p53 expression, which contributed to pulmonary vascular remodeling.

Introduction

Pulmonary hypertension (PH) is an intractable disease characterized by the increase in pulmonary vascular resistance and pulmonary artery pressure (Lai et al., 2014). Increased mitotic fission, phenotypic switch and excessive ability of pulmonary artery smooth muscle cells (PASMCs) to proliferate have been recognized as important contributors to pulmonary vascular remodeling in PH (Lyle et al., 2017). Although the role of PASMCs in the pathogenesis of PH, the underlying molecular mechanisms are still not exactly understood.

The ubiquitin-proteasome pathway degrades 80% proteins. Firstly, the ubiquitin molecule is activated by the E1 activating enzyme, then the E2 conjugated enzyme “holds” the activated ubiquitin molecule, and finally the ubiquitined protein is covalently transferred to one or more lysine residues of the target protein by E3 ubiquitin ligase (Hershko and Ciechanover, 1998). This highly specific intracellular degradation mechanism is mainly determined by E3 ubiquitin ligases, in which cullin-ring ligase (CRL) mainly composed of cullin7 protein regulates approximately 20% of protein ubiquitination degradation (Deshaies and Joazeiro, 2009; Schulman and Harper, 2009). Recent studies have found that E3 ubiquitin ligase cullin7 plays important roles in cancer cell growth control (Chen and Yao, 2016; Guo et al., 2014; Xi et al., 2016; Zhang et al., 2016). Notably, over-expressed cullin7 promotes proliferation and invasion of breast and lung cancer cells by inhibiting p53 expression (Guo et al., 2014; Men et al., 2015). PH pathogenesis has many similarities with carcinogenesis (Courboulin et al., 2016). It has shown that MG132, an inhibitor of ubiquitin proteasome, inhibits proliferation of PASMCs and reduces the pulmonary vascular wall thickness in hypoxia/SU5416-induced PH in rats (Ibrahim et al., 2014; Li et al., 2011). Therefore, whether cullin7 could participate in pulmonary vascular remodeling in hypoxia-induced PH deserves to be elucidated.

The tumor-suppressive role of transcription factor p53 has been linked to cell cycle arrest, apoptosis, and senescence (Wang and Sun, 2010). The noncanonical function or the pathogenic role of p53 has more recently been implicated in pulmonary vascular disease (Jacquin et al., 2015; Mizuno et al., 2011; Mouraret et al., 2013). It has been shown that cullin7 promotes cell growth by binding to p53 to inhibit its function (Andrews et al., 2006). We therefore hypothesized that cullin7 could promote the proliferation and migration of PASMCs by down-regulating p53 expression, which contributes to hypoxia-induced pulmonary vascular remodeling.

This study is designed to explore the role of cullin7 in mediating hypoxia-induced pulmonary vascular remodeling and the underlying mechanisms. Our results demonstrated that hypoxia induced up-regulation of cullin7 expression resulting to the proliferation and migration of PASMCs by inhibiting p53 expression, which contributed to pulmonary vascular remodeling.