Increased expression of immediate early response gene 3 protein promotes aggressive progression and predicts poor prognosis in human bladder cancer

Bladder cancer (BCa) was the fourth most common cancer in men and the twelfth most common cancer in women in United States in 2016 [1]. Although there have been great advances in bladder carcinogenesis, the mortality rate of BCa is still high, due to its complex etiology and insufficient therapeutic strategies. A multivariate analysis showed that an increasing death rate of BCa was associated with multiple environmental exposures, such as smoking, air pollution, well water, urban residence and mining employment [2]. Most of BCa occur as non-muscle-invasive cancer, but there are still approximately 25% of them have muscle-invasive or metastatic disease, which leads to a poor outcome [3]. Therefore, it is of great clinical significance to discover novel and efficient molecular markers to develop more accurate diagnosis and prognosis methods for BCa patients.

Immediate early response gene 3 (IER3), also known as IEX-1, Dif-2, gly96 or p22/PRG-1, is a stress-inducible gene, which is rapidly regulated by multiple factors, including transcription factors, inflammatory cytokines, viral infection, chemical carcinogens, growth factors and hormones [4]. Under a wide range of stress, IER3 activation exerts diverse effects in regulating cell apoptosis and cell cycle with its distinct domains [5]. Accumulating studies have reported that IER3 may be associated with various signaling pathways, such as Nuclear factor kappa B (NF-κB) pathway and Mitogen-activated protein kinase (MAPK) /Extracellular regulated protein kinases (ERK) pathway, and may functions either as an oncogene or a tumor suppressor [6‐8].

IER3 expression has been observed in a wide range of human epithelial tissues [9]. Growing evidence also shows that the aberrant expression of IER3 may be associated with prognosis in patients with multiple cancers [4]. However, the involvement of IER3 in BCa has not been elucidated. In this present study, we aimed to examine the expression pattern of IER3 protein in BCa tissues, and to evaluate its clinical significance in this malignancy.

IER3 was initially identified as a radiation-inducible protein in squamous carcinomas [13]. It has been demonstrated to response to quite distinct stress or cellular stimuli immediately. Among these stimulating factors, NF-κB, p53, SP1 and AP1 are well-known to be involved into tumor development [6]. Increasing evidence show that IER3 may play complex roles in cell apoptosis in different manners [4‐6]. In a mitochondria-dependent environment, IER3 up-regulated can reduce the production of intracellular reactive oxygen species by facilitating the degradation of the inhibitor of F1 catalytic sector, which can prevent apoptosis at its initial phase [14]. On the other hand, IER3 was identified to mediate the NF-κB signaling pathway by interacting with RelA/p65 subunit. This modification can contribute to inducing the expression of anti-apoptotic NF-κB target genes and then supporting cell apoptosis [15]. Besides the impact of IER3 on NF-κB signaling pathway, some studies indicated the IER3 might act as a regulator of ERK1/2 pathway. A phenomenon found by Letourneux et al. [16] showed that ERK activation led to IER3 phosphorylation. Simultaneously, the p-IER3 can enhance ERK phosphorylation by preventing its dephosphorylation factor B56-containing PP2A. The roles of IER3 sustaining ERK1/2 phosphorylation and promoting the tumor development were found in pancreatic cancer [17], lung adenocarcinoma [18] and Hodgkin lymphoma [19]. Moreover, IER3 were found to play crucial roles in regulating tumor growth. Han et al. [20] analyzed the clinical significance of IER3 expression in 77 ovarian carcinoma patients by using immunohistochemistry, and found a decreased expression of IER3 in ovarian carcinoma tissues compared to cystadenoma and borderline tumors tissues. They also indicated that the decreased expression of IER3 was associated with a short survival time of patients with this cancer. They subsequently showed a positive correlation between IER3 expression and anti-apoptotic activity of ovarian cancer cell. In breast cancer, estrogen was reported to effectively up-regulated the expression of IER3 [21]. Furthermore, Yang et al. [22] showed IER3 was overexpressed in invasive breast cancer tissues compared with preinvasive cancer tissues. In vitro experimental system, IER3 was found to reduce the apoptotic activity of T47D and MCF-7 cells. Akilov et al. [23] revealed that IER3 up-regulation in Sézary cells might result in decreased expression levels of reactive oxygen species; as a downstream target of TNF-α-induced pathway, IER3 could protect Sézary cells from TNF-α-induced apoptosis. Sasada et al. [24] found that IER3 protein showed high expression in 41 patients and low expression in 37 patients with pancreatic cancer; statistically, patients with IER3 overexpression had a significantly better survival than those with low expression. In colon cancer, Nambiar et al. [25] built two different mouse models with hyperplasic or dysplastic preneoplastic aberrant crypt foci (ACF). The gene expression analysis based on ACF lesions showed that IER3 expression was increased in low risk ACF mice compared to high risk ACF mice; further immunohistochemistry analysis showed the positive staining of IER3 in adjacent normal-appearing colonic while the negative staining in the tumor crypts from the same patients. These findings suggest that the aberrant expression of IER3 may be implicated into carcinogenesis, progression and patients’ outcome of various human cancers.

In present study, we determined that IER3 protein was overexpressed in the cytoplasm of cancer cells in BCa tissues specimens and that high IER3 protein expression was distinctly associated with high pathologic nodal stage. Notably, high IER3 protein expression also predicted poor overall survival in BCa patients.

Our findings suggest for the first time that the increased expression of IER3 protein may promote the aggressive progression of BCa. Importantly, IER3 may be a potential prognostic marker for BCa patients. Further investigations on molecular mechanisms underlying IER3 involvement in BCa are required.