Oncogenic potential of ATAD2 in stomach cancer and insights into the protein-protein interactions at its AAA + ATPase domain and bromodomain

Chordin-Like 2: A Possible Therapeutic Target for Gastric Cancer by Affecting Cell Cycle and Proliferation

PURPOSE

This study aimed to examine the role of chordin-like 2 (CHRDL2) in gastric cancer.

METHODS

The Gene Expression Omnibus (GEO) and the Cancer Genome Atlas (TCGA) datasets were screened and the differentially expressed gene CHRDL2 was identified. The CHRDL2 expression was examined in the Human Protein Atlas and TCGA. Clinical data on gastric cancer were evaluated for their association with CHRDL2 by using TCGA and KM-plotter databases. The possible relationship amongst CHRDL2, immune cells, and related genes was investigated via the TIMER database. Enrichment analysis was performed using GO and KEGG pathways to explore the mechanisms.

RESULTS

Screening of databases revealed that CHRDL2 was a differentially expressed gene. An increase in cytoplasmic CHRDL2 expression was found in cancer tissues compared with the surrounding normal tissues. The data, together with those from TCGA and the KM-plotter databases, showed that patients with gastric cancer with high level of CHRDL2 have worse prognosis than those with low expression. A strong correlation was found between CHRDL2 expression and T stage, race, pathological grade, and pathological type according to clinical data analysis. CHRDL2 expression is linked to immune infiltration, as shown by the TIMER database. The data suggested that CHRDL2 plays a pivotal role in the tumor microenvironment of gastric cancer and might help tumor cells evade the immune system. Gene set enrichment analysis showed that CHRDL2 is involved in the chemokine signaling route, the intestinal immune network, the MAPK pathway, cell cycle, and the PI3K-Akt signaling system that are associated with the pathological processes of gastric cancer.

CONCLUSION

Patients with gastric cancer with decreased CHRDL2 levels have dramatically improved OS, PFS, and PPS. CHRDL2 plays a pivotal role in enabling tumor cell immune evasion in tumor microenvironment, suggesting a function of this gene in the development of gastric cancer and its immune infiltration. Interfering with CHRDL2 may slow down the development of this malignancy by affecting cell cycle and apoptosis pathways.

Tumor-Promoting ATAD2 and Its Preclinical Challenges

ATAD2 has received extensive attention in recent years as one prospective oncogene with tumor-promoting features in many malignancies. ATAD2 is a highly conserved bromodomain family protein that exerts its biological functions by mainly AAA ATPase and bromodomain. ATAD2 acts as an epigenetic decoder and transcription factor or co-activator, which is engaged in cellular activities, such as transcriptional regulation, DNA replication, and protein modification. ATAD2 has been reported to be highly expressed in a variety of human malignancies, including gastrointestinal malignancies, reproductive malignancies, urological malignancies, lung cancer, and other types of malignancies. ATAD2 is involved in the activation of multiple oncogenic signaling pathways and is closely associated with tumorigenesis, progression, chemoresistance, and poor prognosis, but the oncogenic mechanisms vary in different cancer types. Moreover, the direct targeting of ATAD2’s bromodomain may be a very challenging task. In this review, we summarized the role of ATAD2 in various types of malignancies and pointed out the pharmacological direction.

MicroRNA-217 modulates pancreatic cancer progression via targeting ATAD2

AIMS

Pancreatic cancer is a fatal disease across the world with 5 years survival rate less than 10%. ATAD2, a valid cancer drug-target, is overexpressed in pancreatic malignancy with high oncogenic potential. However, the mechanism of the upregulated expression of ATAD2 in pancreatic cancer is unknown. Since microRNAs (miRNAs) could potentially control target mRNA expressions, and are involved in cancer as tumor-suppressors, oncomiR or both, we examine the possibility of miRNA-mediated regulation of ATAD2 in pancreatic cancer cells (PCCs).

MAIN METHODS

Our in-silico approach first identifies hsa-miR-217 as a candidate regulator for ATAD2 expression. For further validation, luciferase reporter assay is performed. We overexpress hsa-miRNA-217 and assess cellular viability, migration, apoptosis and cell cycle progression in three different PCCs (BxPC3, PANC1, and MiaPaCa2).

KEY FINDINGS

We find hsa-miRNA-217 has potential binding site at the 3'UTR of ATAD2. Luciferase assay confirms that ATAD2 is a direct target of hsa-miR-217. Overexpression of hsa-miR-217 drastically downregulates ATAD2 expression in PCCs, thus, corroborating binding studies. The elevated expression of hsa-miRNA-217 diminishes cell proliferation and migration as well as induces apoptosis and cell cycle arrest in PCCs. Finally, siRNA mediated ATAD2 knockdown or overexpression of hsa-miRNA-217 in PCCs showed inactivation of the AKT signaling pathway. Therefore, hsa-miR-217 abrogates pancreatic cancer progression through inactivation of the AKT signaling pathway and this might be partly due to miR-217 mediated suppression of ATAD2 expression.

SIGNIFICANCE

The application of hsa-miR-217 mimic could be a promising therapeutic strategy for the treatment of pancreatic cancer patients in near future.

The association between bromodomain (BrD) proteins and cancer stemness in different solid tumor types

Cancer stemness, which covers the stem cell‐like molecular traits of cancer cells, is essential for tumor development, progression and relapse. Both transcriptional and epigenetic aberrations are essentially connected with cancer stemness. The engagement of bromodomain (BrD) proteins—a family of epigenetic factors—has been presented in the pathogenesis of several tumor types, although their association with cancer stemness remains largely unknown. Here, we harnessed TCGA and GEO databases and used several bioinformatic tools (ie, Oncomine, PrognoScan, GEPIA2, TIMER2.0, TISIDB, GSEA, R2 platform) to characterize the association between the BrD family members' expression and cancer stemness in solid tumors. Our results demonstrate that significant upregulation of ATAD2 and SMARCA4, and downregulation of SMARCA2 is consistently associated with enriched cancer stem cell‐like phenotype, respectively. Especially, higher‐grade tumors that display stem cell‐like properties overexpress ATAD2. In contrast to most BrD members, the gene expression profiles of ATAD2^HIGH expressing tumors are strongly enriched with known markers of stem cells and with specific targets for c‐Myc transcription factor. For other BrD proteins, the association with cancer de‐differentiation status is rather tumor‐specific. Our results demonstrate for the first time the relation between distinct BrD family proteins and cancer stemness across 27 solid tumor types. Specifically, our approach allowed us to discover a robust association of high ATAD2 expression with cancer stemness and reveal its' versatility in tumors. As bromodomains are attractive targets from a chemical and structural perspective, we propose ATAD2 as a novel druggable target for de‐differentiated tumors, especially those overexpressing MYC.