Hematopoietic pre-B cell leukemia transcription factor interacting protein is overexpressed in gastric cancer and promotes gastric cancer cell proliferation, migration, and invasion

Comprehensive summary: the role of PBX1 in development and cancers

PBX1 is a transcription factor that can promote the occurrence of various tumors and play a reg-ulatory role in tumor growth, metastasis, invasion, and drug resistance. Furthermore, a variant generated by fusion of E2A and PBX1, E2A-PBX1, has been found in 25% of patients with childhood acute lymphoblastic leukemia. Thus, PBX1 is a potential therapeutic target for many cancers. Here, we describe the structure of PBX1 and E2A-PBX1 as well as the molecular mecha-nisms whereby these proteins promote tumorigenesis to provide future research directions for developing new treatments. We show that PBX1 and E2A-PBX1 induce the development of highly malignant and difficult-to-treat solid and blood tumors. The development of specific drugs against their targets may be a good therapeutic strategy for PBX1-related cancers. Furthermore, we strongly recommend E2A-PBX1 as one of the genes for prenatal screening to reduce the incidence of childhood hematological malignancies.

PBX1: a TALE of two seasons-key roles during development and in cancer

Pre-B cell leukemia factor 1 (PBX1) is a Three Aminoacid Loop Extension (TALE) homeodomain-containing transcription factor playing crucial roles in organ pattering during embryogenesis, through the formation of nuclear complexes with other TALE class and/or homeobox proteins to regulate target genes. Its contribution to the development of several organs has been elucidated mainly through the study of murine knockout models. A crucial role for human development has been recently highlighted through the discovery of different de novo pathogenic PBX1 variants in children affected by developmental defects. In the adult, PBX1 is expressed in selected tissues such as in the brain, in the gastro-intestinal and urinary systems, or in hematopoietic stem and progenitor cells, while in other organs is barely detectable. When involved in the t(1;19) chromosomal translocation it acts as an oncogene, since the resulting fusion protein drives pre-B cell leukemia, due to the induction of target genes not normally targeted by the native protein. Its aberrant expression has been associated to tumor development, progression, or therapy-resistance as in breast cancer, ovarian cancer or myeloproliferative neoplasm (MPN). On the other hand, in colorectal cancer PBX1 functions as a tumor suppressor, highlighting its context-dependent role. We here discuss differences and analogies of PBX1 roles during embryonic development and in cancer, focusing mainly on the most recent discoveries.

Research progress of PBX1 in developmental and regenerative medicine

Pre-B-cell leukemia transcription factor 1 (PBX1) proteins are a subfamily of evolutionarily conserved atypical homeodomain transcription factors belonging to the superfamily of triple amino acid loop extension homeodomain proteins. PBX family members play crucial roles in the regulation of various pathophysiological processes. This article reviews the research progress on PBX1 in terms of structure, developmental function, and regenerative medicine. The potential mechanisms of development and research targets in regenerative medicine are also summarized. It also suggests a possible link between PBX1 in the two domains, which is expected to open up a new field for future exploration of cell homeostasis, as well as the regulation of endogenous danger signals. This would provide a new target for the study of diseases in various systems.

Mechanistic Effects of Baicalein on Aqueous Humor Drainage and Intraocular Pressure

Elevated intraocular pressure (IOP) is a major risk factor for glaucoma that results from impeded fluid drainage. The increase in outflow resistance is caused by trabecular meshwork (TM) cell dysfunction and excessive extracellular matrix (ECM) deposition. Baicalein (Ba) is a natural flavonoid and has been shown to regulate cell contraction, fluid secretion, and ECM remodeling in various cell types, suggesting the potential significance of regulating outflow resistance and IOP. We demonstrated that Ba significantly lowered the IOP by about 5 mmHg in living mice. Consistent with that, Ba increased the outflow facility by up to 90% in enucleated mouse eyes. The effects of Ba on cell volume regulation and contractility were examined in primary human TM (hTM) cells. We found that Ba (1–100 µM) had no effect on cell volume under iso-osmotic conditions but inhibited the regulatory volume decrease (RVD) by up to 70% under hypotonic challenge. In addition, Ba relaxed hTM cells via reduced myosin light chain (MLC) phosphorylation. Using iTRAQ-based quantitative proteomics, 47 proteins were significantly regulated in hTM cells after a 3-h Ba treatment. Ba significantly increased the expression of cathepsin B by 1.51-fold and downregulated the expression of D-dopachrome decarboxylase and pre-B-cell leukemia transcription factor-interacting protein 1 with a fold-change of 0.58 and 0.40, respectively. We suggest that a Ba-mediated increase in outflow facility is triggered by cell relaxation via MLC phosphorylation along with inhibiting RVD in hTM cells. The Ba-mediated changes in protein expression support the notion of altered ECM homeostasis, potentially contributing to a reduction of outflow resistance and thereby IOP.

m6 A-mediated regulation of PBX1-GCH1 axis promotes gastric cancer proliferation and metastasis by elevating tetrahydrobiopterin levels

BACKGROUND

Methyltransferase 3 (METTL3)-mediated N6-methyladenosine (m6 A) RNA modification has been demonstrated to be a potential factor in promoting gastric cancer (GC). METTL3 regulates a series of signaling pathways by modifying various mRNAs. This study aimed to identify novel METTL3-mediated signaling pathways and explored possible targets for use in the clinical setting of gastric cancer.

METHODS

To investigate the proliferation and metastatic capacity of GC cell lines with METTL3 knockdown, a xenograft, lung metastasis, and popliteal lymph node metastasis model was used. The m6 A-modified RNA immunoprecipitation (Me-RIP) sequence was utilized to explore the target mRNAs of METTL3. Cell counting kit 8 and transwell assays were performed to investigate the promoting function of pre-B cell leukemia homeobox 1 (PBX1) and GTP cyclohydrolase 1 (GCH1). Western blotting and chromatin immunoprecipitation were employed to confirm the involvement of the METTL3-PBX1-GCH1 axis. ELISA and liquid chromatography-mass spectrometry were used to explore the biological function of tetrahydrobiopterin (BH4 ).

RESULTS

Knockdown of METTL3 suppressed xenograft tumor growth and lung/lymph node metastasis in vivo. Mechanistically, we found that METTL3 combined with and stabilized PBX1 mRNAs. Chromatin immunoprecipitation (ChIP) and further experiments suggested that PBX1 acted as a transcription factor inducing GCH1 expression. Moreover, the METTL3-PBX1-GCH1 axis increased BH4 levels in GC cells, thereby promoting tumor progression.

CONCLUSIONS

This study suggested that METTL3 enzymes promote tumor growth and lung/lymph node metastasis via METTL3-PBX1-GCH1 axis increasing BH4 levels in GC.

A novel chemical inhibitor suppresses breast cancer cell growth and metastasis through inhibiting HPIP oncoprotein

Increasing evidence suggests the pivotal role of hematopoietic pre-B-cell leukemia transcription factor (PBX)-interacting protein (HPIP/PBXIP1) in cancer development and progression, indicating that HPIP inhibition may be a promising target for cancer therapy. Here, we screened compounds inhibiting breast cancer cell proliferation with HPIP fused with green fluorescent protein as a reporter. A novel agent named TXX-1-10 derived from rimonabant, an antagonist of cannabinoid receptor 1 with anticancer effects, has been discovered to reduce HPIP expression and has greater inhibitory effects on breast cancer cell growth and metastasis in vitro and in vivo than rimonabant. TXX-1-10 regulates HPIP downstream targets, including several important kinases involved in cancer development and progression (e.g., AKT, ERK1/2, and FAK) as well as cell cycle-, apoptosis-, migration-, and epithelial-to-mesenchymal transition (EMT)-related genes. Consistent with the results of anticancer effects, genome-wide RNA sequencing indicated that TXX-1-10 has more significant effects on regulation of the expression of genes related to DNA replication, cell cycle, apoptosis, cell adhesion, cell migration, and invasion than rimonabant. In addition, TXX-1-10 significantly regulated genes associated with the cell growth and extracellular matrix organization, many of which were shown to be regulated by HPIP. Moreover, compared with rimonabant, TXX-1-10 greatly reduces blood-brain barrier penetrability to avoid adverse central depressive effects. These findings suggest that HPIP inhibition may be a useful strategy for cancer treatment and TXX-1-10 is a promising candidate drug for cancer therapy.

HPIP protooncogene differentially regulates metabolic adaptation and cell fate in breast cancer cells under glucose stress via AMPK and RNF2 dependent pathways

While cancer cells rewire metabolic pathways to sustain growth and survival under metabolic stress in solid tumors, the molecular mechanisms underlying these processes remain largely unknown. In this study, cancer cells switched from survival to death during the early to late phases of metabolic stress by employing a novel signaling switch from AMP activated protein kinase (AMPK)-Forkhead box O3 (FOXO3a)-hematopoietic PBX1-interacting protein (HPIP) to the ring finger protein 2 (RNF2)-HPIP-ubiquitin (Ub) pathway. Acute metabolic stress induced proto-oncogene HPIP expression in an AMPK-FOXO3a-dependent manner in breast cancer (BC) cells. HPIP depletion reduced cell survival and tumor formation in mouse xenografts, which was accompanied by diminished intracellular ATP levels and increased apoptosis in BC cells in response to metabolic (glucose) stress. Glutamine flux (¹³C-labeled) analysis further suggested that HPIP rewired glutamine metabolism by controlling the expression of the solute carrier family 1 member 5 (SLC1A5) and glutaminase (GLS) genes by acting as a coactivator of MYC to ensure cell survival upon glucose deprivation. However, in response to chronic glucose stress, HPIP was ubiquitinated by the E3-Ub ligase, RNF2, and was concomitantly degraded by the proteasome-mediated pathway, ensuring apoptosis. In support of these data, clinical analyses further indicated that elevated levels of HPIP correlated with AMPK activation in BC. Taken together, these data suggest that HPIP is a signal coordinator during metabolic stress and thus serves as a potential therapeutic target in BC.

Two decades of a protooncogene HPIP/PBXIP1: Uncovering the tale from germ cell to cancer

Hematopoietic PBX interacting protein (HPIP or pre-B-cell leukemia transcription factor interacting protein (PBXIP1) was discovered two decades ago as a corepressor of pre-B-cell leukemia homeobox (PBX) 1 with a vital functional role in hematopoiesis. Later it emerged as a potential biomarker of poor prognosis and tumorigenesis for more than a dozen different cancers. It regulates aggressive cancer phenotypes, cell proliferation, metastasis, EMT, etc. The anomaly in the regulation of HPIP is linked with physiological disorders like renal fibrosis, chronic kidney disease and osteoarthritis. Scientists have unraveled more than twenty interacting proteins of HPIP and its functional role in various physiological and cellular processes that involves normal neuronal development, embryogenesis, endometrium decidualization, and germ cell proliferation. Over the past 20 years, we have witnessed the emerging role of HPIP and its association with a myriad of cellular activities ranging from germ cell proliferation to cancer aggressiveness, modulating multitude of signaling cascades like TGF-β1, PI3K/AKT, Wnt, mTOR, and Sonic hedgehog signaling pathways. This review will give the current understanding of HPIP, in terms of its diverse functions, theoretical ideas, and further explore cellular links and promising areas that need to be investigated. We also provide a comprehensive overview of the transcript variants of HPIP and distinct sets of transcription factors regulating their expression, which may help to understand the role of HPIP in various cellular or physiological conditions.

The PAX6-ZEB2 axis promotes metastasis and cisplatin resistance in non-small cell lung cancer through PI3K/AKT signaling

Paired-box 6 (PAX6) is an important transcription factor required for the function of human neuroectodermal epithelial tissues. Previous studies have suggested that it is also expressed in several types of tumors and has an oncogenic role. However, little is known about its role in non-small cell lung cancer (NSCLC). Here, we found that PAX6 expression levels were upregulated in human lung cancer tissues and correlated with poor clinical outcomes. PAX6 overexpression significantly promoted NSCLC epithelial-to-mesenchymal transition (EMT) and metastasis, whereas its knockdown inhibited these processes. PAX6 is commonly correlated with EMT-mediated stem cell transformation, thereby inducing cisplatin resistance. Using the RT² Profiler PCR Array, we found that WNT5A, EGFR, and ZEB2 were differentially regulated in response to PAX6 modulation. In addition, PAX6 directly bound to the promoter region of ZEB2. ZEB2 knockdown significantly reduced the expression and function of PAX6. ZEB2 was upregulated upon PAX6 overexpression and downregulated upon PAX6 knockdown, whereas E-cadherin expression negatively correlated with PAX6 levels. Moreover, p-PI3K and p-AKT were significantly enhanced by PAX6, which was reversed by the addition of the PI3K-AKT inhibitor, LY294002. These data suggest that PAX6 can mediate E-cadherin downregulation through the PI3K/AKT signaling pathway by directly binding the promoter region of ZEB2, thereby mediating cell migration, stem cell transformation, and cisplatin resistance; and ultimately, affecting survival in NSCLC patients.

Alternative splicing links histone modifications to stem cell fate decision

BACKGROUND

Understanding the embryonic stem cell (ESC) fate decision between self-renewal and proper differentiation is important for developmental biology and regenerative medicine. Attention has focused on mechanisms involving histone modifications, alternative pre-messenger RNA splicing, and cell-cycle progression. However, their intricate interrelations and joint contributions to ESC fate decision remain unclear.

RESULTS

We analyze the transcriptomes and epigenomes of human ESC and five types of differentiated cells. We identify thousands of alternatively spliced exons and reveal their development and lineage-dependent characterizations. Several histone modifications show dynamic changes in alternatively spliced exons and three are strongly associated with 52.8% of alternative splicing events upon hESC differentiation. The histone modification-associated alternatively spliced genes predominantly function in G2/M phases and ATM/ATR-mediated DNA damage response pathway for cell differentiation, whereas other alternatively spliced genes are enriched in the G1 phase and pathways for self-renewal. These results imply a potential epigenetic mechanism by which some histone modifications contribute to ESC fate decision through the regulation of alternative splicing in specific pathways and cell-cycle genes. Supported by experimental validations and extended datasets from Roadmap/ENCODE projects, we exemplify this mechanism by a cell-cycle-related transcription factor, PBX1, which regulates the pluripotency regulatory network by binding to NANOG. We suggest that the isoform switch from PBX1a to PBX1b links H3K36me3 to hESC fate determination through the PSIP1/SRSF1 adaptor, which results in the exon skipping of PBX1.

CONCLUSION

We reveal the mechanism by which alternative splicing links histone modifications to stem cell fate decision.

miR‑152 regulates TGF‑β1‑induced epithelial‑mesenchymal transition by targeting HPIP in tubular epithelial cells

Renal fibrosis is a common pathological feature of chronic kidney diseases, and their development and progression are influenced by epigenetic modifications including aberrant microRNA (miRNA or miR) expression. miRNAs have been demonstrated to modulate the aggressiveness of various cancers and have emerged as possible therapeutic agents for the management of renal fibrosis. Transforming growth factor β1 (TGF‑β1)‑induced epithelial‑mesenchymal transition (EMT) of tubular epithelial cells serves a role in the initiation and progression of renal fibrosis. Furthermore, recent results indicated that the progression of EMT is reversible. The present study aimed to clarify the role of miR‑152 in EMT of the tubular epithelial cell line HK‑2, stimulated by TGF‑β1, using in vitro transfection with a miR‑152 mimic and to further investigate the underlying mechanism of miR‑152 activity. In the present study, miR‑152 expression was significantly reduced in TGF‑β1‑treated HK‑2 cells, accompanied by an increased expression of hematopoietic pre‑B‑cell leukemia transcription factor (PBX)‑interacting protein (HPIP). Additionally, miR‑152 overexpression inhibited TGF‑β1‑induced EMT and suppressed HPIP expression by directly targeting the 3' untranslated region of HPIP in HK‑2 cells. Furthermore, upregulation of HPIP reversed miR‑152‑mediated inhibitory effects on the EMT. Collectively, the results suggest that downregulation of miR‑152 initiates the dedifferentiation of renal tubules and progression of renal fibrosis, which may provide important targets for prevention strategies of renal fibrosis.

HPIP: a predictor of lymph node metastasis and poor survival in cervical cancer

Background

The aim of this study was to explore the relationships of HPIP expression status with the clinicopathological variables and survival outcomes of patients with cervical cancer (CC).

Methods

We compared the HPIP expression of 119 samples from CC tissues, 20 from cervical intraepithelial tissues, and 20 from normal cervical tissues by using immunohistochemical staining.

Results

It was observed that the ratio of elevated HPIP expression was higher in CC tissues than in cervical intraepithelial neoplasia (P=0.017) and normal cervical tissues (P=0.001). In addition, there was an association between HPIP and clinicopathological factors, such as histological grade (P<0.001), stromal infiltration (P=0.015), lymph node metastasis (P<0.001), lymphovascular space invasion (LVSI; P=0.026), and recurrence (P=0.029). Furthermore, multivariate Cox regression analysis revealed that high HPIP expression (P=0.027 and P=0.042) as well as the International Federation of Gynaecology and Obstetrics stage (P=0.003 and P=0.009), lymph node metastasis (P=0.031 and P=0.017), and LVSI (P=0.024 and P=0.046) were independent prognostic factors. In addition, we demonstrated that high HPIP expression (P=0.003) and LVSI (P<0.001) were independently related to lymph node metastasis.

Conclusion

Elevated HPIP expression may contribute to the progression and metastasis of CC and may also serve as a new biomarker to predict the prognosis of CC.

PCID: A Novel Approach for Predicting Disease Comorbidity by Integrating Multi-Scale Data

Disease comorbidity is the presence of one or more diseases along with a primary disorder, which causes additional pain to patients and leads to the failure of standard treatments compared with single diseases. Therefore, the identification of potential comorbidity can help prevent those comorbid diseases when treating a primary disease. Unfortunately, most of current known disease comorbidities are discovered occasionally in clinic, and our knowledge about comorbidity is far from complete. Despite the fact that many efforts have been made to predict disease comorbidity, the prediction accuracy of existing computational approaches needs to be improved. By investigating the factors underlying disease comorbidity, e.g., mutated genes and rewired protein-protein interactions (PPIs), we here present a novel algorithm to predict disease comorbidity by integrating multi-scale data ranging from genes to phenotypes. Benchmark results on real data show that our approach outperforms existing algorithms, and some of our novel predictions are validated with those reported in literature, indicating the effectiveness and predictive power of our approach. In addition, we identify some pathway and PPI patterns that underlie the co-occurrence between a primary disease and certain disease classes, which can help explain how the comorbidity is initiated from molecular perspectives.

Knockdown of HPIP Inhibits the Proliferation and Invasion of Head-and-Neck Squamous Cell Carcinoma Cells by Regulating PI3K/Akt Signaling Pathway

Hematopoietic pre-B-cell leukemia transcription factor (PBX)-interacting protein (HPIP/PBXIP1) is a corepressor for the transcription factor PBX. Previous studies showed that HPIP is frequently overexpressed in many tumors. However, the role of HPIP in head-and-neck squamous cell carcinoma (HNSCC) has not yet been determined. Thus, we decided to investigate the effects and mechanisms of HPIP in HNSCC. Our results demonstrated that HPIP is highly expressed in human HNSCC cell lines and provides the first evidence that knockdown of HPIP obviously inhibits proliferation and migration/invasion in HNSCC cells in vitro, as well as inhibits tumor growth in vivo. Furthermore, knockdown of HPIP significantly inhibits the expression of p-PI3K and p-Akt in human HNSCC cells. In conclusion, our study demonstrated that knockdown of HPIP significantly inhibits the proliferation and migration/invasion of HNSCC cells by suppressing the PI3K/Akt signaling pathway. Therefore, HPIP may be a novel potential therapeutic target for the treatment of HNSCC.

HPIP Silencing Prevents Epithelial-Mesenchymal Transition Induced by TGF-β1 in Human Ovarian Cancer Cells

Hematopoietic pre-B-cell leukemia transcription factor (PBX)-interacting protein (HPIP/PBXIP1) is a nucleo-cytoplasmic shuttling protein, and its expression is associated with cancer aggressiveness. However, the role of HPIP in ovarian cancer is still unclear. Here, we aimed to clarify the role of HPIP in epithelial–mesenchymal transition (EMT) process of ovarian cancer cells, stimulated by transforming growth factor (TGF)-β1. In this study, we found that HPIP was highly expressed in ovarian cancer cells, and TGF-β1 treatment induced HPIP expression in ovarian cancer cells. In addition, knockdown of HPIP suppressed TGF-β1-induced EMT and migration/invasion in ovarian cancer cells. Moreover, knockdown of HPIP significantly blocked the phosphorylated pattern of both PI3K and Akt induced by TGF-β1 in SKOV3 cells. In conclusion, the present study showed that HPIP silencing might prevent TGF-β1-induced EMT in ovarian cancer cells. Thus, HPIP may be a potential therapeutic target for the treatment of ovarian cancer.

HPIP promotes epithelial-mesenchymal transition and cisplatin resistance in ovarian cancer cells through PI3K/AKT pathway activation

PURPOSE

Hematopoietic PBX interacting protein (HPIP), a scaffold protein, is known to regulate the proliferation, migration and invasion in different cancer cell types. The aim of this study was to assess the role of HPIP in ovarian cancer cell migration, invasion and epithelial-mesenchymal transition (EMT), and to unravel the mechanism by which it regulates these processes.

METHODS

HPIP expression was assessed by immunohistochemistry of tissue microarrays containing primary ovarian tumor samples of different grades. OAW42, an ovarian carcinoma-derived cell line exhibiting a high HPIP expression, was used to study the role of HPIP in cell migration, invasion and EMT. HPIP knockdown in these cells was achieved using a small hairpin RNA (shRNA) approach. Cell migration and invasion were assessed using scratch wound and transwell invasion assays, respectively. The extent of EMT was assessed by determining the expression levels of Snail, Vimentin and E-cadherin using Western blotting. The effect of HPIP expression on AKT and MAPK activation was also investigated by Western blotting. Cell viabilities in response to cisplatin treatment were assessed using a MTT assay, whereas apoptosis was assessed by determining caspase-3 and PARP cleavage in ovarian carcinoma-derived SKOV3 cells.

RESULTS

We found that HPIP is highly expressed in high-grade primary ovarian tumors. In addition, we found that HPIP promotes the migration, invasion and EMT in OAW42 cells and induces EMT in these cells via activation of the PI3K/AKT pathway. The latter was found to lead to stabilization of the Snail protein and to repression of E-cadherin expression through inactivation of GSK-3β. We also found that HPIP expression confers cisplatin resistance to SKOV3 cells after prolonged exposure and that its subsequent knockdown decreases the viability of these cells and increases caspase-3 activation and PARP proteolysis in these cells following cisplatin treatment.

CONCLUSIONS

From these results we conclude that HPIP expression is associated with high-grade ovarian tumors and may promote their migration, invasion and EMT, a process that is associated with metastasis. In addition, we conclude that HPIP may serve as a potential therapeutic target for cisplatin resistant ovarian tumors.

Expression of HPIP in epithelial ovarian carcinoma: a clinicopathological study

Objectives

Hematopoietic pre-B-cell leukemia transcription factor (PBX)-interacting protein (HPIP) plays an important role in cancer invasion and metastasis. The aim of this study is to investigate the expression of HPIP in epithelial ovarian cancer (EOC).

Patients and methods

Immunohistochemical method was performed using 42 normal ovarian specimens and 145 specimens with EOC. The correlations of HPIP expression with the clinicopathological factors and prognosis of EOC patients were evaluated. Statistical analyses were performed using the chi-square test, multivariate Cox proportional hazard, and Kaplan–Meier method.

Results

HPIP expression in EOC was higher than that in normal tissues (P<0.001). HPIP expression was significantly associated with histological grade, International Federation of Gynecology and Obstetrics stage, and lymphatic metastasis of EOC (P<0.05). Patients with high HPIP expression had poorer overall survival and disease-free survival (P<0.001) compared with patients with low HPIP expression. Multivariate Cox analysis demonstrated that HPIP was an independent factor for overall survival and disease-free survival (P<0.05).

Conclusion

HPIP may be a valuable biomarker for predicting the prognosis of EOC patients and may serve as a potential target for cancer therapy.