The emerging roles of WBP2 oncogene in human cancers

Abstract

WW domain-binding protein 2 (WBP2) is an emerging oncoprotein. Over the past decade, WBP2 surfaced as a key node connecting key signaling pathways associated with ER/PR, EGFR, PI₃K, Hippo, and Wnt in cancer. In addition to the oncogenic functions of WBP2, this review discusses the latest research regarding the multilevel regulation and modes of action of WBP2 and how they can be exploited for molecular medicine. In translational research, evidence supports the role of WBP2 as a biomarker for early detection, prognosis, and companion diagnostics in breast cancer. Finally, we envision new trends in WBP2 research in the space of molecular etiology of cancer, targeted therapeutics, and precision medicine.

Fig. 1. Schematic timeline of WBP2 historical background.

WBP2’s interactions with Yes-associated Protein (YAP) [2], Neural precursor cell expressed, developmentally downregulated 4 E3 ubiquitin-protein ligase (Nedd4) [64], paired box 8 (Pax8) [94], progesterone receptor (PR) [5], TAZ [12], E6-associated protein (E6AP) [5], WW domain-containing oxidoreductase (WWOX) [65], estrogen receptor (ER) [4], β-catenin [13], and itchy E3 ubiquitin-protein ligase (ITCH) [13] identified from 1995 to 2016, with the corresponding signaling pathways including Hippo [12], steroid receptor [4, 5], EGFR [10], and Wnt [11].

Fig. 2. WBP2’s modes of action in cancer.

Wnt pathway: WBP2 transcriptionally regulates the TINK expression gene positively through GPS1 and JNK/c-Jun proteins. WBP2-induced Wnt3A-mediated Wnt signaling pathway activation results in an increased β-catenin expression, which in interaction with WBP2, TNIK, and TCF proteins elevates the expression of Axin2 protein. Hippo pathway: Upon inactivation of the Hippo signaling pathway, YAP, and TAZ oncoproteins enter the nucleus and interact with WBP2 to increase the transcription of downstream oncogenic genes. PI₃K pathway: WBP2 interacts with ENO1 and Homer3, resulting in modulating the ENO1-PI₃K/Akt signaling pathway. The overall outcome of WBP2 involvement in various pathways is increased cell growth and proliferation, invasion, and metastasis.

Fig. 3. WBP2 regulation in breast cancer.

Various modes of WBP2 regulation in breast cancer are Transcriptional: WBP2 is regulated at the transcriptional level through insulin-induced USF-1 transcription factor phosphorylation. Phosphorylated and activated USF-1 enhances the transcription of the WBP2 gene. Post-transcriptional: WBP2 is intensively regulated at the posttranscriptional level through direct binding of miR-613, miR-485, and miR-206 to the WBP2 3′-UTR. Post-translational: Cross talk between Wnt and EGFR signaling pathways phosphorylates and protects WBP2 from ITCH E3-ubiquitin ligase-mediated degradation. This phosphorylation is important for the WBP2/β-catenin cooperation to drive TCF-mediated transcription, as previously shown in Fig. 2. The EGFR/ER signaling pathways cross talk also leads to WBP2 phosphorylation, thereby promoting its translocation to the nucleus to transcriptionally drive the expression of ER/PR-responsive genes.

Fig. 4. Structure of WBP2 protein.

The N-terminal GRAM domain is followed by three PPxY (PY) motifs in the C-terminal region. PPxY is described as P = Proline, x = any amino acid, and Y = Tyrosine. These PY motifs recognize and interact with the WW domain(s) of target proteins, including YAP, Taz Nedd4, and WWOX. Tyr 192 and Tyr 231 are the phosphorylation sites, which are important in regulating the WBP2 activity. The GRAM domain might be important for the integrity and full function of the protein [48].

Fig. 5. WBP2 signaling network and rational drug design.

The ability of WBP2 in activating a myriad of oncogenic functions through PI₃K/Akt, EGFR, ER, and Hippo proposes a multilayer targeting approach in WBP2-positive cancer cases for downregulating WBP2 and thereby its oncogenic properties. Decoy oligonucleotides against the USF-1 oncogenic transcription factor could block WBP2 expression at the transcriptional level. miRNA mimics could further repress the expression of WBP2 by targeting its 3′UTR. WBP2’s functions could be controlled at the protein level via designing therapeutic biologics such as aptamers and therapeutic peptides as well as small molecules against WBP2’s C-terminal region.

Fig. 6. Comparative overview of the expression levels of WBP2 mRNA versus protein in human cancers.

The RNA expression was obtained from RNA-seq data of The Cancer Genome Atlas (TCGA) [95]. The 15 human cancers were sorted and scored in terms of the WBP2 RNA level from 15 (the highest expression) to 1 (the lowest expression). The protein expression was obtained from The Human Protein Atlas database [96]. Similarly, the sorting and scoring method was carried out for human cancers in terms of WBP2 protein level. Scatter plot was used to show the RNA and protein scores for each cancer. Cancers with high level of WBP2 mRNA such as glioma, melanoma, and thyroid showed low protein expression level, while pancreatic and colorectal cancers with high level of WBP2 protein display low mRNA expression. The unit for the RNA-seq data is reads per kilobase of transcript per million mapped reads (FPKM). This unit represents the relative expression of the WBP2 transcript proportional to the number of cDNA fragments that originate from it. The protein expression data is based on the percentage of the patients who have medium or high expression of WBP2 in each cancer.

Fig. 7. The potential WBP2 signaling pathway network.

In silico analysis of the gene copy number variation (CNV) of normal versus breast cancer tissues in The Cancer Genome Atlas (TCGA) [95] database reveals that the upregulation of WBP2 was associated with the amplification of chromosome 17q. Enrichment analysis of the list of genes in the amplified region of chromosome 17q using the PANTHER gene ontology database uncovered a network of key signaling pathways associated with WBP2.