Cx58 is associated with the metastasis of non-small cell lung cancer via MEF2B/Cx58 axis

Abstract

Connexins (Cxs), also known as gap junction proteins, are structurally related transmembrane proteins and have been implicated in carcinogenesis. Although some evidence suggests that these proteins are tumor suppressors due to their reduced expression in cancers, recent research indicates their complicated roles in tumor progression during different stages, including metastasis. Here, we show that Cx58, which is upregulated in non-small cell lung cancer (NSCLC), is modulated by myocyte-enhancer binding factor 2B (MEF2B). Either Cx58 or MEF2B knockdown attenuates the migration and invasion of NSCLC cells by inducing cytoskeleton rearrangement. Additionally, the prometastatic role of Cx58 in NSCLC is demonstrated in vivo. In conclusion, our findings suggest that Cx58 is transcriptionally activated by MEF2B and is involved in the metastasis of NSCLC by regulating cytoskeleton organization. Targeting the MEF2B/Cx58 axis may be exploited as a modality for improving NSCLC therapy.

1. Introduction

Lung cancer remains the number one cause of cancer-related death, causing 1.8 million deaths worldwide each year [1]. Approximately 85% of lung cancers are diagnosed as non-small cell lung cancer (NSCLC) [2]. Great advances have been achieved in lung cancer treatment during the past two decades, especially with the recent use of tyrosine kinase inhibitors and immunotherapy in selected patients [3]. Nevertheless, only a minority of patients have obtained unprecedented survival benefits from the abovementioned new therapies. At present, the overall survival rate for NSCLC patients is still not optimistic, particularly for patients with metastatic NSCLC [4]. Metastasis accounts for the majority of non-small cell lung cancer-related deaths, but its role in cancer biology is poorly understood [2,4,5]. Thus, novel biomarkers and therapeutic targets are still urgently needed.

Connexins (Cxs), the primary structure of gap junctions, mediate direct cellular communication under various physiological and pathological conditions [6]. Gap junctional intercellular communication (GJIC) is essential for coordinating cell growth, cell differentiation, and tissue homoeostasis [7]. Over the past 50 years, a tremendous amount of data has been generated supporting the hypothesis that a lack of GJIC or reduced expression of Cxs is the structural hallmark of cancer cells [8–12]. Moreover, accumulating evidence has shown that the roles of Cxs in tumors depend on both Cx isoform expression and the tumor type or subtype. The complexity of cancer biology in multiple stages, including metastasis, makes the issue more complicated [7,13–16]. In addition, more recent data suggest that Cxs could have GJIC-independent functions, playing oncogenic and prometastatic roles in cancer development and metastasis [17–19]. There are 21 members in the human Cx family [20]. Extensive research has explored the link between lung cancer and members of the Cx family, including Cx43, Cx31.1, Cx26, and Cx45 [7,13,11]. However, few studies have focused on connexin58 (Cx58). Human Cx58, also known as gap junction alpha-9 protein (GJA9) or gap junction alpha-10 (GJA10) protein, was first identified by genome sequencing in 2003, and this protein has no mouse ortholog in the mouse genome [21,22]. Human Protein Atlas RNA-seq analysis of normal tissues revealed biased expression in the testis, skin and 6 other tissues [23]. Data from The Cancer Genome Atlas (TCGA) revealed significant upregulation of Cx58 mRNA expression in lung adenocarcinoma (3.01-fold) and lung squamous cell carcinoma (1.82-fold), compared with healthy tissue [24]. To date, in addition to mRNA analysis in lung cancer, few studies have investigated the relationship between Cx58 and cancer. Here, we found that the Cx58 protein level was much higher in lung cancer tissues than in adjacent normal lung tissues and that the expression level was positively related to metastatic potential, indicating that Cx58 might be associated with NSCLC metastasis. Moreover, the reduction in Cx58 in NSCLC cells impaired their migration and invasion ability in vitro and suppressed their lung metastasis potential in vivo.