PHLDA3 activated by BARX2 transcription, suppresses the malignant development of esophageal squamous cell carcinoma by downregulating PI3K/AKT levels

BACKGROUND

Low pleckstrin homology-like domain family A, member 3 (PHLDA3) expression has been reported to be associated with cancer specificity and disease-free survival in esophageal squamous cell carcinoma (ESCC), and was an independent predictor of postoperative recurrence. However, the specific mechanisms involved are still unclear. This paper aimed to explore the role and its mechanisms of PHLDA3 in ESCC.

MATERIALS AND METHODS

PHLDA3 and BarH-like homeobox 2 (BARX2) expressions in ESCC were predicted by Gene Expression Profiling Interactive Analysis (GEPIA) analysis and determined by quantitative real-time polymerase chain reaction (qRT-PCR) and western Blot. Western blot detected the expression of proteins associated with migration, angiogenesis and phosphoinositide 3-kinase (PI3K)/protein kinase B (PKB/AKT) signaling pathway. The University of California Santa Cruz Genomics Institute (UCSC) database predicted that the relationship of BARX2 and PHLDA3 promoter and JASPAR identified the possible binding sites. Dual luciferase gene reporter verified PHLDA3 promoter activity, and the relationship of both was determined by chromatin immunoprecipitation (CHIP). Cell counting kit (CCK)-8, 5-ethynyl-2'-deoxyuridine (EDU) and colony formation were used to assess cell proliferation. Wound healing and transwell were used to detect cell migration and invasion ability. Tube formation assay was applied to assess angiogenesis. Mice were injected with transfected KYSE30 cells under the right axilla. Body weight and tumor volume and mass were recorded for each group of mice. Immunohistochemistry was performed to detect KI67 level in tumor tissues.

RESULTS

Both PHLDA3 and BARX2 were downregulated in ESCC. The upregulated PHLDA3 suppressed PI3K/AKT expression. In addition, BARX2 bound to the PHLDA3 promoter and transcriptionally activated PHLDA3. PHLDA3 overexpression inhibited ESCC cell proliferation, migration, invasion and angiogenesis, but this effect was reversed by BARX2 knockdown. In addition, BARX2 overexpression inhibited ESCC cell proliferation, migration, invasion and angiogenesis, but this effect was reversed by PHLDA3 knockdown.

CONCLUSION

PHLDA3 was transcriptionally activated by BARX2 and inhibited malignant progression of ESCC by downregulating PI3K/AKT levels.

Pleckstrin homology-like domain family A, member 3, a miR-19a-3p-regulated gene, suppresses tumor growth in osteosarcoma by downregulating the Akt pathway

Pleckstrin homology-like domain family A, member 3 (PHLDA3), is emerging as a critical regulator for multiple cancers. Nevertheless, the expression and role of PHLDA3 in osteosarcoma remain unknown. Herein, we purposed to elucidate the role of PHLDA3 in the progression and chemoresistance of osteosarcoma. According to the bioinformatics analysis, PHLDA3 expression was low in osteosarcoma patients, and low content was linked to poor prognosis. Additionally, activation of PHLDA3 suppressed osteosarcoma cell proliferation, migration, and chemoresistance, whereas PHLDA3 inhibition caused the opposite effects. Mechanistically, our data revealed that PHLDA3 negatively regulates the Akt/GSK3β signaling cascade in osteosarcoma. Furthermore, we found that miR-19a-3p might exert its oncogenic function by inhibiting PHLDA3 expression in osteosarcoma. These results demonstrated miR-19a-3p/ PHLDA3/ Akt/GSK3β axis has a pivotal role in osteosarcoma, and PHLDA3 is a prospective therapeutic target for treating osteosarcoma.

PHLDA3 inhibition protects against myocardial ischemia/reperfusion injury by alleviating oxidative stress and inflammatory response via the Akt/Nrf2 axis

Pleckstrin homology-like domain family A, member 3 (PHLDA3) has a particularly critical role in regulating cell survival under stress conditions. However, whether PHLDA3 plays a role in myocardial ischemia/reperfusion injury has not been studied. We aimed to assess the possible role of PHLDA3 in myocardial ischemia/reperfusion (I/R) injury. PHLDA3 expression was increased in myocardial tissue from rats with myocardial I/R injury and rat cardiomyocytes with hypoxia/reoxygenation (H/R) injury. PHLDA3 knockdown protected against myocardial I/R injury in vivo and H/R injury in vitro. Inhibition of PHLDA3 increased the activation of nuclear factor erythroid-derived 2-related factor 2 (Nrf2) associated with regulation of the Akt/glycogen synthase kinase-3β (GSK-3β) axis. Repression of Nrf2 reversed PHLDA3-inhibition-mediated cardioprotective effects. Taken together, our work demonstrates that PHLDA3 inhibition exerts a protective role in myocardial I/R injury via regulation of the Akt/GSK-3β/Nrf2 axis. We suggest PHLDA3 as an attractive target for developing treatments against myocardial I/R injury.

PHLDA3 is an important downstream mediator of p53 in squamous cell carcinogenesis

Squamous cell carcinomas (SCCs) are one of the most frequent solid cancer types in humans and are derived from stratified epithelial cells found in various organs. SCCs derived from various organs share common important properties including genomic abnormalities in the tumor suppressor gene p53. There is a carcinogen-induced mouse model of SCC which produces benign papilloma, some of which progress to advanced carcinoma and metastatic SCCs. These SCCs undergo key genetic alterations that are conserved between human and mice, including alterations in the genomic p53 sequence, and is therefore an ideal system to study the mechanisms of SCC tumorigenesis. Using this SCC model, we show that the PHLDA3 gene, a p53 target gene encoding an Akt repressor, is involved in the suppression of benign and metastatic tumor development. Loss of PHLDA3 induces an epithelial-mesenchymal transition (EMT) and can complement p53 loss in the formation of metastatic tumors. We also show that in human SCC patients, low PHLDA3 expression is associated with poorer prognosis. Collectively, this study identifies PHLDA3 as an important downstream molecule of p53 involved in SCC development and progression.

PHLDA3 exerts an antitumor function in prostate cancer by down-regulating Wnt/β-catenin pathway via inhibition of Akt

Pleckstrin homology-like domain family A, member 3 (PHLDA3) is a novel tumor-related protein that mediates carcinogenesis of multiple cancers. However, the relevance of PHLDA3 in prostate cancer has not been explored. The purpose of this work was to illustrate the possible roles and mechanisms of PHLDA3 in prostate cancer. Our data showed strikingly lower abundance of PHLDA3 in prostate cancer, and that low levels of PHLDA3 in prostate cancer patients was associated with reduced survival. PHLDA3 was also weakly expressed in prostate cancer cells, and demethylation treatment dramatically up-regulated the expression level of PHLDA3. Up-regulation of PHLDA3 restrained proliferation, induced G1 cell cycle arrest, suppressed epithelial-mesenchymal transition of prostate cancer cells. In addition, up-regulation of PHLDA3 increased the sensitivity of prostate cancer cells to docetaxel In-depth research into the mechanism elucidated that PHLDA3 overexpression decreased the phosphorylation of Akt and suppressed the activation of Wnt/β-catenin signaling. Overexpression of constitutively active Akt strikingly abolished PHLDA3-mediated inactivation of Wnt/β-catenin pathway. A xenograft assay revealed that prostate cancer cells with PHLDA3 overexpression displayed reduced tumorigenicity in vivo. Collectively, these data document that PHLDA3 exerts an outstanding cancer-inhibiting role in prostate cancer by down-regulating Wnt/β-catenin pathway via the inhibition of Akt. This work highlights PHLDA3 as a novel anticancer target for prostate cancer.

p53-PHLDA3-Akt Network: The Key Regulators of Neuroendocrine Tumorigenesis

p53 is a well-known tumor suppressor gene and one of the most extensively studied genes in cancer research. p53 functions largely as a transcription factor and can trigger a variety of antiproliferative programs via induction of its target genes. We identified PHLDA3 as a p53 target gene and found that its protein product is a suppressor of pancreatic neuroendocrine tumors (PanNETs) and a repressor of Akt function. PHLDA3 is frequently inactivated by loss of heterozygosity (LOH) and methylation in human PanNETs, and LOH at the PHLDA3 gene locus correlates with PanNET progression and poor prognosis. In addition, in PHLDA3-deficient mice, pancreatic islet cells proliferate abnormally and acquire resistance to apoptosis. In this article, we briefly review the roles of p53 and Akt in human neuroendocrine tumors (NETs) and describe the relationship between the p53-PHLDA3 and Akt pathways. We also discuss the role of PHLDA3 as a tumor suppressor in various NETs and speculate on the possibility that loss of PHLDA3 function may be a useful prognostic marker for NET patients indicating particular drug therapies. These results suggest that targeting the downstream PHLDA3-Akt pathway might provide new therapies to treat NETs.

Expression Analysis of GRHL3 and PHLDA3 in Head and Neck Squamous Cell Carcinoma

Background

Head and neck squamous cell carcinoma (HNSCC) includes a group of heterogeneous tumors with generally invasive behavior. The PI3K/AKT pathway plays an important role in the pathogenesis of HNSCC.

Methods

In the current study, we investigated the expression of two negative feedback regulators of the PI3K pathway, namely PHLDA3 and GRHL3, in 45 paired samples of HNSCC and adjacent non-cancerous tissues (ANCTs).

Results

While expression of GRHL3 was down-regulated in tumoral tissues compared with ANCTs by the factor 4.21, PHLDA3 expression levels were up-regulated by 5.99-times. Gender-based analysis revealed a significant down-regulation of GRHL3 gene expression level in male patients compared with the control samples and significant up-regulation of PHLDA3 gene expression level in both sexes compared with the control samples. Differences in the expressions of both genes were significant in patients aged more than 60 years, but not in the younger patients. Expression of GRHL3 was only down-regulated in patients with positive smoking history. Expression of GRHL3 was decreased in grades 2 and 3 samples compared with controls. There was a significant increase in transcript levels of PHLDA3 in stages II and III HNSCC samples compared with the controls group. ROC curve analysis indicated that the expression level of PHLDA3 could be a promising marker for the diagnosis of HNSCC patients with a sensitivity and specificity of 0.666 and 0.688, respectively. In addition, sensitivity and specificity of GRHL3 were 0.755 and 0.577, respectively.

Discussion

The current study indicates dysregulation of regulators of PI3K pathway in HNSCC and their potential application as putative biomarkers for this cancer.

A vicious partnership between AKT and PHLDA3 to facilitate neuroendocrine tumors

Pancreatic neuroendocrine tumors (PanNET) are rare cancers that generally have a poor prognosis. Accurate diagnosis and proper treatment of these tumors requires a better understanding of the molecular mechanisms underlying the development of PanNET. It has been shown that the mTOR inhibitor everolimus can improve the progression‐free survival of PanNET patients, suggesting that inhibition of the PI3K‐Akt‐mTOR pathway may suppress the progression of PanNET. PHLDA3 is a novel tumor suppressor protein that inhibits Akt activation by competition for binding to PIP₃. Our analysis of PanNET revealed frequent loss‐of‐heterozygosity and DNA methylation at the PHLDA3 locus, resulting in strong suppression of PHLDA3 transcription. Such alterations in the PHLDA3 gene were also frequently found in lung neuroendocrine tumors (NET), suggesting the possibility that various types of NET have in common the functional loss of the PHLDA3 gene.

Low PHLDA3 expression in oesophageal squamous cell carcinomas is associated with poor prognosis

BACKGROUND/AIM

Patients with oesophageal squamous cell carcinoma (ESCC) have a poor prognosis. Akt has been associated with malignant potential in several cancers, including ESCC. Pleckstrin homology-like domain, family A, member 3 (PHLDA3) has been identified as a direct target gene of p53 and as a potent inhibitor of Akt activation. The present study investigated the role of PHLDA3 expression and its ability to predict prognosis in patients with ESCC who did not receive induction therapy.

MATERIALS AND METHODS

The intensity of PHLDA3 expression was immunohistochemically analyzed in tumor and adjacent normal tissue samples from 84 patients with ESCC, 22 who underwent endoscopic submucosal dissection and 62 who underwent thoracic oesophagectomy.

RESULTS

High expression of PHLDA3 was observed in 60 (71.4%) patients and low expression in 24 (28.6%). Cancer-specific (p=0.029) and disease-free (p<0.001) survival rates were significantly lower in the PHLDA3 low-than in the PHLDA3 high-expression group, and low PHLDA3 expression was an independent predictor of postoperative recurrence (relative risk (RR)=0.38; 95% confidence interval (CI)=0.166-0.78; p=0.0074).

CONCLUSION

Low PHLDA3 expression in ESCC may be predictive of tumor recurrence suggesting that Akt activation may be a therapeutic target in ESCCs.