REVIEW article

Front. Cell Dev. Biol., 23 September 2021

Sec. Molecular and Cellular Oncology

Volume 9 - 2021 | https://doi.org/10.3389/fcell.2021.709069

Long Non-coding RNA Double Homeobox A Pseudogene 8: A Novel Oncogenic Propellant in Human Cancer

  • 1. State Key Laboratory for Diagnosis and Treatment of Infectious Diseases, National Clinical Research Center for Infectious Diseases, Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases, The First Affiliated Hospital, College of Medicine, Zhejiang University, Hangzhou, China

  • 2. Department of Oncological Surgery, The First Affiliated Hospital, College of Medicine, Zhejiang University, Hangzhou, China

  • 3. Division of Hepatobiliary and Pancreatic Surgery, Department of Surgery, The First Affiliated Hospital, College of Medicine, Zhejiang University, Hangzhou, China

Abstract

A growing number of studies are reporting important roles played by long non-coding RNAs (lncRNAs) in various pathological and physiological processes. LncRNAs are implicated in numerous genomic regulatory functions at different levels, including regulation of transcription, post-transcriptional processes, genomic stability, and epigenetic genome modifications. Double homeobox A pseudogene 8 (DUXAP8), a novel lncRNA, has been reported to be involved in many cancers, including gastric, colorectal, esophageal, bladder, oral, ovarian, lung, and pancreatic cancers as well as hepatocellular carcinoma (HCC). DUXAP8 plays specific oncogenic roles via numerous malignancies promoting pathways. DUXAP8 is frequently dysregulated in multiple cancers, acting as a sponge to downregulate various tumor-suppressing microRNA activities. In this review, we comprehensively explore DUXAP8 expression and prognosis across cancer types, and systematically summarize current evidence concerning the functions and molecular mechanisms of DUXAP8 in tumorigenesis and progression. We conclude that DUXAP8 is a potential biomarker and therapeutic target for multiple cancers.

Introduction

Cancers collectively represent a life-threatening disease with major impact on public health (the second leading cause of death worldwide). An estimated 18.1 million new cancer cases and 9.6 million deaths occurred in 2018 (). The predicted number of new cancer patients is projected to be 14 million in 2035 ().

The human genome project has revealed that there are approximately 20,000–25,000 protein-coding genes in the human genome that account for 2% of the total human genome sequence (). Genetic mutations associated with diseases are commonly located in non-coding regions of the human genome (; ). The majority of the human genome is not protein-coding, and other transcriptionally active regions were originally considered to be transcriptional noise. As such, they attracted little attention (; ; ). Recent studies have demonstrated that expression of the non-coding RNAs produced by these regions is systematically altered in cancers, and displays potential correlations with protein coding gene expression, demonstrating the importance of long non-coding RNAs (lncRNAs) in tumor formation, development, and progression (; ). As lncRNAs are highly enriched in the genome, they are dynamically regulated in cell-, tissue-, and development-specific manners ().

Double homeobox A pseudogene 8 (DUXAP8), according to the HUGO Gene Nomenclature Committee, is a newly identified lncRNA located on 22q11.1. DUXAP8 is approximately 2,307 bp long. Recent studies have reported that DUXAP8 mRNA is substantially upregulated in many cancer tissues, including pancreatic, bladder, colon, lung, ovarian, and breast cancers (; ; ; ; ; ; ), as well as thyroid, hepatocellular and renal cell carcinomas (RCCs) (; ; ), and glioma, compared to corresponding non-tumor tissues. Emerging literature supports that overexpressed lncRNA DUXAP8 might function as a sponge in cancer tissues, targeting tumor suppressive microRNAs, thereby facilitating target oncogene signaling pathway activity and promoting tumor development and progression.

In this review, we comprehensively summarize tissue and developmental stage-specific lncRNA DUXAP8 mRNA expression and systematically describe DUXAP8-associated regulatory mechanisms based on current literature.

The Transcriptional Level of Double Homeobox A Pseudogene 8 Across Pancancer

To characterize mRNA expression levels of DUXAP8 in 33 different cancers, we developed gene expression profiling interactive analysis 2 (GEPIA2) and determined that DUXAP8 displays markedly different expression levels among cancers.

We observed that DUXAP8 produces relatively high transcripts per million (TPM) in bladder urothelial carcinoma (BLCA), cholangiocarcinoma (CHOL), esophageal carcinoma (ESCA), head and neck squamous cell carcinoma (HNSC), kidney renal clear cell carcinoma (KIRC), liver hepatocellular carcinoma (LIHC), lung adenocarcinoma (LUAD), lung squamous cell carcinoma (LUSC), ovarian serous cystadenocarcinoma (OV), skin cutaneous melanoma (SKCM), stomach adenocarcinoma (STAD), thymoma (THYM), uterine corpus endometrial carcinoma (UCEC), and uterine carcinosarcoma (UCS) tissues compared to corresponding normal tissues. We also observed low DUXAP8 TPM in acute myeloid leukemia (LAML) and testicular germ cell tumors (TGCT) compared to normal tissues (Figure 1).

FIGURE 1

These results indicate that upregulated DUXAP8 expression in tumor tissues compared with adjacent normal tissues might be a useful indicator in cancer diagnosis.

Long Non-coding RNA Double Homeobox A Pseudogene 8 Displays Potential as a Novel and Broadly Useful Biomarker for Cancer Prognosis

To further explore the prognostic role of DUXAP8 expression levels in cancers, we used the GEPIA2 survival analysis module and found that high DUXAP8 mRNA expression correlated with poor overall survival in seven cancers. Specifically, patients with high DUXAP8 expression levels had a shorter survival time than patients with low DUXAP8 expression levels in breast invasive carcinoma (BRCA) (p = 0.041), colon adenocarcinoma (COAD) (p = 0.0094), HNSC (p = 0.047), KIRC (p = 7.6e−6), kidney renal papillary cell carcinoma (KIRP) (p = 0.0057), LIHC (P = 0.0038), and UCEC (p = 0.03) (Figure 2). In summary, high DUXAP8 expression was positively associated with shorter survival times and worse prognosis. These results indicate that in most tumor tissues, high DUXAP8 expression has potential as a novel prognostic indicator of cancer progression.

FIGURE 2

Associations Between Long Non-coding RNA Double Homeobox A Pseudogene 8 and Clinical Characteristics Based on Current Literature

Double homeobox A pseudogene 8 expression was upregulated in various cancers, such as bladder cancer, hepatocellular carcinoma (HCC), colorectal cancer (CRC), lung cancers, oral cancers, gastric cancer, ovarian cancer, pancreatic cancer, neuroblastoma, and pancreatic cancer. The association between the clinical characteristics and DUXAP8 expression was listed in Table 1.

TABLE 1

Cancer typesClinical tumor tissuesExpression levelClinical characteristicsReferences
Bladder cancer31 pairsupregulatedHigh DUXAP8 expression indicating poor prognosis and advanced tumor stages
HCCTCGA databaseupregulatedHigh DUXAP8 expression indicating poor prognosis
HCC55 pairsupregulatedHigh DUXAP8 expression indicating poor prognosis
HCC50 pairsupregulatedHigh DUXAP8 expression is associated with larger tumor size, tumor stages, and distant metastasis
HCCTCGA databaseupregulatedHigher DUXAP8 expression had poor prognosis
HCCTCGA databaseupregulatedHigh DUXAP8 was positively correlated with elder patients (year over 60), advanced stages (stage III/IV), and vascular invasion
HCCHCC microarray profilesupregulatedHigher DUXAP8 was detected in stage II/III HCC samples compared to stage I HCC. High DUXAP8 expression predicted poor OS and correlated with lymph nodes metastasis, and tumor stages
CRC127 pairsupregulatedHigh DUXAP8 was correlated with shorter OS
CRCupregulatedCRC patients in stage I-II presented a lower level of DUXAP8 than those in stage III-IV, and patients with larger tumor size remained higher DUXAP8 expression
CRC30CRC patientsupregulatedHigh DUXAP8 expression indicating poor prognosis
RCC5 public RCC microarray gene profiling datasetsupregulatedHigh DUXAP8 expression indicating poor prognosis; ;
Lung adenocarcinoma45 patientsupregulatedHigh DUXAP8 expression was associated with advanced tumor stages, larger tumor sizes, and metastasis
Non-small cell lung cancer43 patientsupregulatedDUXAP8 was upregulated and associated with low overall survival in NSCLC patients
Non-small cell lung cancer66 pairsupregulatedhigh expression of DUXAP9 is closely associated with advanced tumor stages, larger tumor sizes, lymph node metastasis, and associated with shorter overall survival
Non-small cell lung cancer54 patientsupregulatedHigh expression of DUXAP8 was associated with advanced tumor stages, larger tumor sizes, lymph node metastases, and poor prognosis.
Non-small cell lung cancer78 pair of patientsupregulatedIncreased DUXAP8 expression was associated with poor prognosis
Oral cancerGDC Data Portal and Gene Expression Omnibus (GEO) datasetsupregulatedHigh expressed DUXAP8 was associated with shorter OS time
Gastric cancer72 pairsupregulatedHigh DUXAP8 was associated with advanced tumor stages, larger tumor size, lymphatic metastasis, and poor prognosis
Ovarian cancer33 pairsupregulatedHigh DUXAP8 expression indicating poor prognosis
Pancreatic cancer24 pairedupregulatedDUXAP8 was significantly upregulated in pancreatic cancer tissues
Pancreatic cancer58 patientsupregulatedHigh DUXAP8 expression obtained larger tumor size and TNM stages, and associated with shorter overall survival time
NeuroblastomaGene Expression Omnibus (GEO) databaseupregulatedHigh DUXAP8 was higher in NB tumor tissues in T4 stage than that in T1 stage. High DUXAP8 was associated with poor prognosis

The clinical information of double homeobox A pseudogene 8 (DUXAP8) in pan-cancers.

Bladder Cancer

Bladder cancer has become one of the most common cancers worldwide. More than 2 million woman were diagnosed patients were diagnosed, and more than 0.6 million death in 2018 (). LncRNAs have been identified as novel essential regulators of various human cancers. DUXAP8 is reportedly upregulated in bladder cancer tissues (; ). Researchers have detected substantially elevated lncRNA DUXAP8 expression in bladder cancer tissues compared with adjacent normal tissues (). High DUXAP8 expression is correlated with shorter overall survival time. Advanced stage bladder cancer patients frequently have higher DUXAP8 mRNA expression levels than stage I and stage II patients ().

Hepatocellular Carcinoma

Hepatocellular carcinoma is among the most common malignant tumor types, and has a poor prognosis in part due to late diagnosis (). The molecular mechanisms underlying HCC pathogenesis have not been comprehensively elucidated (). Emerging evidence suggests that lncRNAs are widely expressed and might function as promising therapeutic targets and prognostic indicators of various diseases and cancers (; ). DUXAP8 expression is markedly upregulated in HCC tumor tissues compared to that in corresponding normal tissues (; ; ; ; ). and found that higher DUXAP8 expression is strongly associated with poor prognosis in HCC (). They also showed that DUXAP8 RNA affects mitotic nuclear division, histone binding, regulation of cell cycle phase transitions, oxidative phosphorylation, cell division, and the tricarboxylic acid cycle, indicating that DUXAP8 can act as an oncogene in HCC progression (). also showed that DUXAP8 is substantially upregulated in HCC tissues, and found that DUXAP8 was markedly elevated in advanced stage III/IV tumors compared with stage I/II tumors (). applied GEPIA and found that DUXAP8 was upregulated in HCC tissues. They also correlated upregulated DUXAP8 expression with larger tumor size, more advanced tumor stage, and distant metastases. Patients with higher DUXAP8 expression were associated with shorter overall survival times (). discovered that DUXAP8 was considerably upregulated in elderly patients (>60 years), tumors in advanced stages (stage III/IV), and during vascular invasion. Similarly, they found upregulated DUXAP8 expression in stage II/III HCC samples relative to stage I HCC samples, and saw an association with poor prognosis ().

Colorectal Cancer

Colorectal cancer is the third most common malignancy. Involvement of a variety of genetic and epigenetic changes has been reported in CRC initiation and progression (; ). LncRNAs have been reported to play important roles in epigenetic alterations, revealing their potential as novel targets for CRC prevention and treatment (; ). found that CRC patients in stages I-II presented with lower levels of tumor DUXAP8 than those in stage III-IV, and patients with larger tumor sizes expressed higher levels of DUXAP8. Another study demonstrated increased DUXAP8 expression in CRC tissues compared with paracarcinoma tissues, and showed that high DUXAP8 expression was indicative of shorter overall survival time (). These data suggest the carcinogenic potential of DUXAP8 in CRC.

Renal Cell Carcinoma

Renal cell carcinoma remains one of the most lethal urological malignancies (). Epigenetic modifications are common in RCC, suggesting that these modifications play an important role in RCC initiation and progression (). Researchers have discovered that many lncRNAs are upregulated and associated with poor prognosis in RCC (). Many researchers have investigated public RNA sequencing data and microarray gene profiling data from RCC patients, and found that DUXAP8 was markedly upregulated in RCC tumor tissues compared with adjacent para-tumor tissues (; ; ). They have also shown that increased DUXAP8 expression correlates with poor prognosis in RCC (; ; ).

Lung Cancer

Lung cancer is the leading cause of cancer-related deaths worldwide (). LncRNAs are a new class of cancer regulators that govern fundamental biochemical and cellular processes in lung cancer (). DUXAP8 expression is substantially increased in LUAD tumor tissues. High DUXAP8 expression is closely associated with advanced tumor stages, larger tumor sizes, and metastasis (; ; ). have also revealed that DUXAP8 is notably increased in non-small-cell lung cancer (NSCLC) tissues, and is associated with lymph node metastases and advanced tumor stages. analyzed tumor tissue and normal tissue from 78 pairs of patients, and found that DUXAP8 was notably increased in tumor tissues compared with normal tissues. Elevated DUXAP8 expression has been positively correlated with tumor size, lymph node metastasis, tumor stage, shorter survival time, and shorter progression-free survival time (; ).

Ovarian Cancer

Double homeobox A pseudogene 8 is markedly upregulated in ovarian cancer, where elevated expression is associated with shorter overall survival time (; ).

Oral, Esophageal, Gastric, and Colon Cancers

Digestive tract cancers are a group of malignant cancers that together represent the most common cause of cancer-related deaths worldwide (; ). DUXAP8 is substantially upregulated in oral cancer tissues compared to normal tissues (). Increased DUXAP8 expression is negatively associated with overall patient survival time (). In esophageal cancer, DUXAP8 expression level is closely related to clinical stage, lymph node metastasis, and overall survival (; ). Increased DUXAP8 expression has also been detected in gastric cancer tissues compared to corresponding normal tissues (). In colon cancer research, elevated DUXAP8 expression has been positively correlated with advanced stages, lymph node metastasis, and shorter overall survival time ().

Double Homeobox A Pseudogene 8 in Ovarian and Pancreatic Cancers

Double homeobox A pseudogene 8 expression was markedly upregulated in tumor tissues compared to corresponding adjacent pancreatic tissue samples (; ). Increased DUXAP8 expression was also found to closely associate with larger tumor size, advanced stage, and shorter overall survival time ().

Double Homeobox A Pseudogene 8 in Other Cancers

Studies have also revealed that DUXAP8 is substantially upregulated in neuroblastoma and papillary thyroid carcinoma tissues compared to corresponding adjacent normal tissues (). Levels of DUXAP8 detected in neuroblastoma tumor tissues have been higher in T4 stage than in T1 stage, and elevated DUXAP8 expression is associated with worse prognosis ().

Double Homeobox A Pseudogene 8 Regulatory Mechanism in Cancer Initiation and Tumor Progression

Double Homeobox A Pseudogene 8 is markedly upregulated in various cancer tissues, which plays an important role in cancer initiation and progression. In this review, we comprehensively summarize existing research on DUXAP8 functional roles in various cancers, such as bladder cancer, HCC, CRC, RCC, NSCLC, esophageal cancer, oral cancer, gastric cancer, neuroblastoma, thyroid carcinoma, and breast cancer.

A mechanism of regulation is illustrated in Figure 3. In bladder, have demonstrated that DUXAP8 downregulated phosphatase level and facilitated tumor cell progression. have demonstrated that DUXAP8 knockdown in bladder cancer cells can inhibit tumor cell invasion and induce tumor cell apoptosis. In a study by , DUXAP8 acted as an oncogene when expressed at elevated levels, promoting and maintaining multiple malignant phenotypes by sequestering miR-485-5p to regulate the DUXAP8/Forkhead box M1 axis. demonstrated that DUXAP8 could sequester miR-422a, thus enhancing pyruvate dehydrogenase kinase isozyme 2 (PDK2) expression in HCC cell lines and promoting HCC malignant phenotypes. also demonstrated that DUXAP8 knockdown substantially inhibited the proliferation, migration, and invasion abilities of HCC cell lines. DUXAP8 can also sequester miR-490-5p, activating budding uninhibited by benzimidazole-1 (BUB1) expression and facilitating tumor proliferation and invasion (). Increased DUXAP8 expression allows it to sequester miR-577, enhancing the levels of ras-related protein 14 and promoting tumor proliferation and invasion (). demonstrated that DUXAP8 knockdown may suppress the proliferative, migratory, and invasive abilities of CRC cells. Specifically, in an in vitro study, increased DUXAP8 apparently potentiated the expression of lysine-specific histone demethylase 1A (LSD1) and Enhancer of zeste homolog 2 (EZH2), thereby accelerating CRC cell malignant activities. reported that increased DUXAP8 expression activates CRC cell proliferation and inhibits apoptosis, and that DUXAP8 interacts with EZH2 and H3K27me3. These studies suggest that DUXAP8 displays potential as a novel therapeutic target for CRC. Reports indicate that in RCC, DUXAP8 pseudogenes promote tumor growth via suppression of the miR-29c-3p, collagen type I alpha 1 (COL1A1)/COL1A2 axis in RCC (). have shown that DUXAP8 knockdown markedly inhibited RCC cell invasion abilities. have demonstrated that increased DUXAP8 lncRNA might promote RCC cell proliferation and invasion by regulating the miR-126/cell death abnormal-axis. In lung cancer, increased DUXAP8 promotes cancer proliferation and suppresses apoptosis by targeting miR-26b-5p (). found that DUXAP8 knockout substantially inhibited cell invasion, whereas DUXAP8 overexpression promoted cell invasion. Another study demonstrated that increased DUXAP8 expression might promote lung cancer cell growth, metastasis, and glycolysis. Mechanistically, increased DUXAP8 expression inhibited miR-409-3p expression to upregulate HK2 and LDHA expression (). In NSCLC, increased DUXAP8 could inhibit tumor growth and metastasis through reciprocal regulation of miR-498 and TRIM44 in vivo (). DUXAP8 acts as an oncogene, facilitating tumor cell proliferation, migration, and invasion by interacting with EZH2 and LSD1 to suppress their activities (). In oral cancer, increased DUXAP8 promotes tumor proliferation, migration, and invasion by activating the EZH2/Kruppel-like factor 2 (KLF2) axis (). In esophageal cancer, DUXAP8 knockdown may inhibit tumor proliferation, migration, and invasion (; ). In gastric cancer regulatory mechanisms, increased DUXAP8 expression promotes tumor cell proliferation and tumorigenesis, partly through epigenetic silencing of pleckstrin homology domain-containing family O member 1 transcription by binding to polycomb-repressive complex 2 (). Marked upregulation of DUXAP8 in colon cancer tissues compared with peritumor tissues has also been validated, and has been associated with tumor stage (III/IV) and larger tumor sizes (). In colon cancer cells, DUXAP8 accelerated malignant progression by targeting LSD1 and EZH2 (). demonstrated that DUXAP8 is involved in ovarian cancer proliferation, migration, and invasion. Increased DUXAP8 promotes yes-associated protein 1 (YAP1) expression by inhibiting miR-590-5p expression in ovarian cancer cells (). In pancreatic cancer, DUXAP8 promotes the migration and invasion of pancreatic cancer cells by sequestering miR-448 and focal adhesion kinase (). Another study demonstrated that DUXAP8 regulates pancreatic cancer cell proliferation, migration, and invasion through epigenetic silencing of CDKN1A and KLF2 expression (). Studies have also revealed that DUXAP8 exacerbates the malignancy of neuroblastoma cells via a miR-29/nucleolar protein 4 like axis in vivo (). In papillary thyroid carcinoma, DUXAP8 binding of miR-223-3p upregulates CXC chemokine receptor 4 signaling (). Specifically, increased DUXAP8 expression was positively associated with SOS1, c-Myc, and CCND1 expression. DUXAP8 is also markedly upregulated in breast cancer. Increased oncogenic DUXAP8 function in sequestering miR-29a-3b enhances oncogene suppressor APC domain containing 2 expression and its corresponding oncogenic signaling pathways (). These studies may provide novel insights into the etiology of cancers, and valuable lncRNA candidates for further investigation of lncRNA roles in cancer progression.

FIGURE 3

Conclusion and Further Perspectives

Expression of the novel lncRNA DUXAP8 has been described in various cancers. DUXAP8 levels are substantially upregulated in tumor tissues compared with adjacent normal tissues. High DUXAP8 expression correlates with shorter overall survival time and worse prognosis. Higher DUXAP8 levels indicate larger tumor sizes and advanced tumor stages. Aberrant DUXAP8 expression is closely related to many clinicopathological parameters. Therefore, in clinical applications, DUXAP8 displays potential as a novel indicator for the early diagnosis and prediction of tumor progression and outcome. However, DUXAP8 mRNA expression has not been fully characterized in blood and other biological samples. With the development of advanced technologies, the expression landscape of DUXAP8 in patient body fluids will soon be described. DUXAP8 is also involved in multiple mechanisms regulating cancer initiation and progression, indicating strong potential for DUXAP8 as a therapeutic target. In conclusion, DUXAP8 is a promising cancer indicator and therapeutic target for cancer.

Publisher’s Note

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

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Author contributions

CX and JJ designed the study. CX drafted the manuscript. XC and JJ revised the manuscript. All authors read and approved the final manuscript.

Funding

This work was supported by the Zhejiang Provincial Natural Science Foundation (LQ20H030005 and LQ18H160012), the Zhejiang Health Technology Project (2020KY126), the Zhejiang Health Technology Project (2019RC153), and Teaching Reform Project of First Affiliated Hospital, School of Medicine, the Zhejiang University (zyjg202011).

Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

References

Summary

Keywords

lncRNA, DUXAP8, cancer, molecular mechanism, tumorigenesis

Citation

Xue C, Cai X and Jia J (2021) Long Non-coding RNA Double Homeobox A Pseudogene 8: A Novel Oncogenic Propellant in Human Cancer. Front. Cell Dev. Biol. 9:709069. doi: 10.3389/fcell.2021.709069

Received

13 May 2021

Accepted

03 September 2021

Published

23 September 2021

Volume

9 - 2021

Edited by

Aamir Ahmad, University of Alabama at Birmingham, United States

Reviewed by

Qingbin Cui, University of Toledo, United States; Miaomiao Xue, First Affiliated Hospital of Zhengzhou University, China

Updates

Copyright

*Correspondence: Junjun Jia,

This article was submitted to Molecular and Cellular Oncology, a section of the journal Frontiers in Cell and Developmental Biology

Disclaimer

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.

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