Esophageal squamous cell carcinoma (ESCC) is the most predominant histological type of esophageal malignancy, accounting for approximately 90% of the 456,000 cases of esophageal cancer incidence each year [1]. Despite extensive clinical efforts by researchers, ESCC patients still experience poor prognosis [2]. Statistically, the 5-year survival rate is less than 20% in developed countries and less than 5% in a number of developing countries [3]. In addition to the combination of 5-fluorouracil and platinum, paclitaxel, docetaxel and irinotecan are among the first-line therapies for patients with early ESCC [4]. The preferred treatment for advanced ESCC is neoadjuvant chemotherapy combined with radical surgery [5]. Unfortunately, more than 50% of ESCC patients have no significant response to surgery and most die of cancer recurrence [6]. Metastasis and recurrence remain the main cause of poor prognosis in ESCC [7]. Suppression of ESCC tumor malignant progression has been reported to result in a significant improvement in patient prognosis [8,9]. Regarding anti-angiogenic therapy, some tyrosine kinase inhibitors (TKIs) targeting the vascular endothelial growth factor receptor (VEGFR) have proven to be effective during the treatment of ESCC patients [4]. Therefore, further exploration of the mechanisms of ESCC tumor malignant progression and angiogenesis can reveal new possibilities for anticancer therapy.

Pleckstrin homology-like domain family A, member 3(PHLDA3) is a novel p53-regulated factor that exerts oncogenic effects by inhibiting PI3K/AKT activation [10,11]. And the PI3K/AKT pathway promotes proliferation, adhesion, migration, invasion and survival of cancer cells [12]. Recently, PHLDA3 has been described to inhibit tumor malignant progression by suppressing PI3K/AKT activation in a variety of cancers, including prostate cancer, pancreatic neuroendocrine tumors (PanNET), osteosarcoma [[13], [14], [15]]. Additionally, PI3K/AKT promotes angiogenesis in cancer [16]. As a negative regulator of PI3K/AKT, PHLDA3 may inhibit cancer angiogenesis by suppressing PI3K/AKT activation [11]. PHLDA3 expression has been found to be downregulated in ESCC and correlated with patient survival and prognosis [17]. However, the molecular mechanisms involved remain to be further elucidated.

BarH-like homeobox 2 (BARX2) is a cis structural factor of the Bar family that affects cell adhesion, migration, proliferation and differentiation by regulating gene expression [18]. Emerging investigation is in support of the idea that aberrant expression of Barx2 is inextricably linked to tumor development. For instance, BARX2 downregulation was associated with poor prognosis in multiple cancers, such as colorectal cancer, gastric cancer, and primary hepatocellular carcinoma [[19], [20], [21]]. However, upregulation of BARX2 inhibited the proliferation and invasion of gastric cancer cells [22]. Since BARX2 is located downstream of Wnt signaling and is involved in its mediated activities [23]. Wnt/β-catenin signaling functions in the angiogenic activity of endothelial cells (ECs) [24]. And PHLDA3 can downregulate the Wnt/β-catenin pathway by inhibiting Akt [13]. Consequently, we hypothesized that PHLDA3 is transcriptionally activated by BARX2 and functions in the malignant development and angiogenesis of ESCC.

In this study, we made an effort to investigate the expression of PHLDA3 and Barx2 in ESCC tissues and cells. In addition, the relationship between BARX2 and PHLDA3 was determined and the combined mechanism of both was analyzed for its effects in ESCC in vitro and in vivo. Data on the effect of PHLDA3 will inform its use as a biomarker for diagnosis and assessment of ESCC prognosis.