Pre-B-cell leukemia transcription factor 1 regulates expression of valosin-containing protein, a gene involved in cancer growth

The NRF2-p97-NRF2 negative feedback loop

p97 is a ubiquitin-targeted ATP-dependent segregase that regulates proteostasis, in addition to a variety of other cellular functions. Previously, we demonstrated that p97 negatively regulates NRF2 by extracting ubiquitylated NRF2 from the KEAP1-CUL3-RBX1 E3 ubiquitin ligase complex, facilitating proteasomal destruction. In the current study, we identified p97 as an NRF2-target gene that contains a functional ARE, indicating the presence of an NRF2-p97-NRF2 negative feedback loop that maintains redox homeostasis. Using CRISPR/Cas9 genome editing, we generated endogenous p97 ARE-mutated BEAS-2B cell lines. These p97 ARE-mutated cell lines exhibit altered expression of p97 and NRF2, as well as a compromised response to NRF2 inducers. Importantly, we also found a positive correlation between NRF2 activation and p97 expression in human cancer patients. Finally, using chronic arsenic-transformed cell lines, we demonstrated a synergistic effect of NRF2 and p97 inhibition in killing cancer cells with high NRF2 and p97 expression. Our study suggests dual upregulation of NRF2 and p97 occurs in certain types of cancers, suggesting that inhibition of both NRF2 and p97 could be a promising treatment strategy for stratified cancer patients.

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.

The regulation of PBXs and their emerging role in cancer

Pre‐B‐cell leukaemia transcription factor (PBX) proteins are a subfamily of evolutionarily conserved, atypical homeodomain transcription factors that belong to the superfamily of three amino acid loop extension (TALE) homeodomain proteins. Members of the PBX family play crucial roles in regulating multiple pathophysiological processes, such as the development of organs, congenital cardiac defects and carcinogenesis. The dysregulation of PBXs has been shown to be closely associated with many diseases, particularly cancer. However, the detailed mechanisms of PBX dysregulation in cancer progression are still inconclusive. In this review, we summarize the recent advances in the structures, functions and regulatory mechanisms of PBXs, and discuss their underlying mechanisms in cancer progression. We also highlight the great potential of PBXs as biomarkers for the early diagnosis and prognostic evaluation of cancer as well as their therapeutic applications. The information reviewed here may expand researchers’ understanding of PBXs and could strengthen the clinical implication of PBXs in cancer treatment.

PBX1: a key character of the hallmarks of cancer

Pre-B-cell leukemia homeobox transcription factor 1 (PBX1) was first identified as part of a fusion protein resulting from the chromosomal translocation t(1;19) in pre-B cell acute lymphoblastic leukemias. Since then, PBX1 has been associated with important developmental programs, and its expression dysregulation has been related to multifactorial disorders, including cancer. As PBX1 overexpression in many cancers is correlated to poor prognosis, we sought to understand how this transcription factor contributes to carcinogenesis, and to organize PBX1's roles in the hallmarks of cancer. There is enough evidence to associate PBX1 with at least five hallmarks: sustaining proliferative signaling, activating invasion and metastasis, inducing angiogenesis, resisting cell death, and deregulating cellular energetics. The lack of studies investigating a possible role for PBX1 on the remaining hallmarks made it impossible to defend or refute its contribution on them. However, the functions of some of the PBX1's transcription targets indicate a potential engagement of PBX1 in the avoidance of immune destruction and in the tumor-promoting inflammation hallmarks. Interestingly, PBX1 might be a player in tumor suppression by activating the transcription of some DNA damage response genes. This is the first review organizing PBX1 roles into the hallmarks of cancer. Thus, we encourage future studies to uncover the PBX1's underlying mechanisms to promote carcinogenesis, for it is a promising diagnostic and prognostic biomarker, as well as a potential target in cancer treatment.

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.

Interleukin-6 induced overexpression of valosin-containing protein (VCP)/p97 is associated with androgen-independent prostate cancer (AIPC) progression

Though Androgen deprivation therapy (ADT) is effective initially, numerous patients become resistant to it and develop castration resistant PCa (CRPC). Cytokines promotes ligand independent activation of AR. Interleukin-6 (IL-6) levels are elevated in CRPC patients and regulate AR activity. However, progression to CRPC is not fully understood. In this study, we analyzed differential protein expression in LNCaP cells treated with IL-6 using proteomics. Results revealed altered expression of 27 proteins and Valosin-containing protein (VCP)/p97 plays a predominant role in co-regulation of altered proteins. Interestingly, IL-6 induced VCP expression through Pim-1 via STAT3 is AR independent there by suggesting a role for VCP in CRPC. Transfection of LNCaP cells for VCP overexpression showed an increased cell proliferation, migration, and invasion where as its inhibition by NMS-873 showed the reverse effect causing cell death. Mechanistic studies demonstrate that cell death occurs due to apoptosis by endoplasmic reticulum (ER) stress, elevated cell cycle inhibitors p21, p27kip1, and active PARP and reduced Bcl-2. VCP promotes cell invasion and migration by altering E-cadherin and Vimentin levels inversely triggering EMT of PCa cells. VCP immunostaining revealed no staining in BPH but strong staining in PCa. This study determines VCP may play an important role in progression to CRPC and it can be a favorable target with to develop new therapies to treat ADT resistant prostate cancer.

VCP mutations are not a major cause of familial amyotrophic lateral sclerosis in the UK

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease causing loss of motor neurons in the spinal cord, brain stem and cerebral cortex. Mutations in the Valosin containing protein (VCP) gene have recently been identified in Familial ALS (FALS) patients, accounting for ~1% of all FALS cases. In order to study the frequency of VCP mutations in UK FALS patients, we have screened the exons known to harbour mutations together with 3' and 5' UTR sequences. No coding changes were identified in this UK cohort and no common polymorphisms were associated with FALS. However, we identified an imperfect hexanucleotide expansion (8 repeats), c.-221_-220insCTGCCACTGCCACTGCCG, in the 5'UTR of a FALS case and a 7-repeat hexanucleotide repeat in a Sporadic ALS case (SALS) that were not present in 219 UK controls. Subsequent screening of sequence data from 1844 controls (1000 genomes Phase 3) revealed the presence of the 7-repeat (0.3%) and a single individual with an 8-repeat containing a homogeneous insert [CTGCCG]3 but no individuals with the heterogeneous insert found in FALS ([CTGCCA]2[CTGCCG]). Two novel single base pair substitutions, c.-360G>C and c.2421+94C>T, were found in FALS cases in the 5' and 3' UTRs respectively. The hexanucleotide expansion and c.-360G>C were predicted to be pathogenic and were found in FALS cases harbouring C9orf72 expansions. The SALS case with a 7 repeat lacked a C9orf72 expansion. We conclude that VCP mutations are not a major cause of FALS in the UK population although novel rare variations in the 5' UTR of the VCP gene may be pathogenic.

A tumorigenic factor interactome connected through tumor suppressor microRNA-198 in human pancreatic cancer

PURPOSE

The majority of pancreatic cancers overexpress mesothelin (MSLN), which contributes to enhanced proliferation, invasion, and migration. However, the MSLN regulatory network is still unclear. Here, we investigated the regulation of a panel of tumorigenic factors and explored the potential of MSLN-regulated miR-198 treatment in vivo.

EXPERIMENTAL DESIGN

The expression and functional regulation of the tumorigenic factors MSLN, NF-κB, and the homeobox transcription factors (TF) POU2F2 (OCT-2), Pre-B-cell leukemia homeobox factor 1 (PBX-1), valosin-containing protein (VCP), and miR-198 were studied in pancreatic cancer cell lines, patient tumor samples, and xenograft pancreatic cancer mouse models.

RESULTS

We found that miR-198 is downregulated in pancreatic cancer and is involved in an intricate reciprocal regulatory loop with MSLN, which represses miR-198 through NF-κB-mediated OCT-2 induction. Furthermore, miR-198 repression leads to overexpression of PBX-1 and VCP. The dysregulated PBX-1/VCP axis leads to increased tumorigenicity. Reconstitution of miR-198 in pancreatic cancer cells results in reduced tumor growth, metastasis, and increased survival through direct targeting MSLN, PBX-1, and VCP. Most interestingly, reduced levels of miR-198 in human tissue samples are associated with upregulation of these tumorigenic factors (MSLN, OCT-2, PBX-1, VCP) and predict poor survival. Reduced miR-198 expression links this tumor network signature and prognosticates poor patient outcome. High miR-198 disrupts the network and predicts better prognosis and increased survival.

CONCLUSIONS

miR-198 acts as a central tumor suppressor and modulates the molecular makeup of a critical interactome in pancreatic cancer, indicating a potential prognostic marker signature and the therapeutic potential of attacking this tumorigenic network through a central vantage point.

Interaction between salt-inducible kinase 2 (SIK2) and p97/valosin-containing protein (VCP) regulates endoplasmic reticulum (ER)-associated protein degradation in mammalian cells

Salt-inducible kinase 2 (SIK2) is an important regulator of cAMP response element-binding protein-mediated gene expression in various cell types and is the only AMP-activated protein kinase family member known to interact with the p97/valosin-containing protein (VCP) ATPase. Previously, we have demonstrated that SIK2 can regulate autophagy when proteasomal function is compromised. Here we report that physical and functional interactions between SIK2 and p97/VCP underlie the regulation of endoplasmic reticulum (ER)-associated protein degradation (ERAD). SIK2 co-localizes with p97/VCP in the ER membrane and stimulates its ATPase activity through direct phosphorylation. Although the expression of wild-type recombinant SIK2 accelerated the degradation and removal of ERAD substrates, the kinase-deficient variant conversely had no effect. Furthermore, down-regulation of endogenous SIK2 or mutation of the SIK2 target site on p97/VCP led to impaired degradation of ERAD substrates and disruption of ER homeostasis. Collectively, these findings highlight a mechanism by which the interplay between SIK2 and p97/VCP contributes to the regulation of ERAD in mammalian cells.

P97/CDC-48: proteostasis control in tumor cell biology

P97/CDC-48 is a prominent member of a highly evolutionary conserved Walker cassette - containing AAA+ATPases. It has been involved in numerous cellular processes ranging from the control of protein homeostasis to membrane trafficking through the intervention of specific accessory proteins. Expression of p97/CDC-48 in cancers has been correlated with tumor aggressiveness and prognosis, however the precise underlying molecular mechanisms remain to be characterized. Moreover p97/CDC-48 inhibitors were developed and are currently under intense investigation as anticancer drugs. Herein, we discuss the role of p97/CDC-48 in cancer development and its therapeutic potential in tumor cell biology.

Expression level of pre-B-cell leukemia transcription factor 2 (PBX2) as a prognostic marker for gingival squamous cell carcinoma

OBJECTIVE

In this study, we investigated the interrelationship between clinicopathologic findings and pre-B-cell leukemia transcription factor 2 (PBX2) expression in gingival squamous cell carcinoma (GSCC).

METHODS

Expression level of PBX2 was immunohistochemically examined in 66 GSCC subjects (30 men and 36 women) with ages ranging from 42 to 85 (median 64.5) years, in which staining intensity in tumor cells was categorized as either weaker (level 1) or equal to/stronger (level 2) than that in the endothelial cells.

RESULTS

PBX2 expression is correlated with valosin-containing protein (VCP) expression. Univariate and multivariate analyses revealed a high level of PBX2 expression to be a poor prognosticator for disease-free survival (DFS) and overall survival (OS), and PBX2 expression was an independent prognostic factor for both DFS and OS in GSCC.

CONCLUSIONS

PBX2 expression level in GSCC is prognostic. PBX2 may be a useful marker to identify the potential for progression in GSCC.

VCP/p97, down-regulated by microRNA-129-5p, could regulate the progression of hepatocellular carcinoma

Valosin containing protein (VCP)/p97 plays various important roles in cells. Moreover, elevated expression of VCP in hepatocellular carcinoma (HCC) is correlated with increased incidence of recurrence. But the role of VCP in HCC progression in vitro and in vivo is unclear. And there are few reports about the regulation mechanism on the expression of VCP in HCC. In this study, it was identified that the level of VCP was frequently increased in human HCC tissues. In addition, down-regulation of VCP with siRNAs could dramatically suppress the genesis and progression of tumor in vivo. It was found that miR-129-5p directly inhibited the expression of VCP in several HCC cell lines. Meanwhile, the level of VCP in HCC tissues was negatively associated with the level of miR-129-5p. Our further investigation showed that the enhanced expression of miR-129-5p also suppressed tumor growth in vivo. Moreover, it was revealed that miR-129-5p could inhibit the degradation of IκBα and increase the apoptosis and reduce the migration of HCC cells by suppressing the expression of VCP. Our results revealed that the expression of VCP was directly regulated by miR-129-5p and this regulation played an important role in the progression of HCC.

Role of Meis1 in mitochondrial gene transcription of pancreatic cancer cells

Pre-B-cell leukemia transcription factor (PBX)/three-amino-acid loop extension (TALE) class transcription factors [PBX1-4, Meis homeobox (Meis) 1-3, pbx/knotted 1 homeobox (Prep) 1, 2] are involved in tumorigenesis and metastasis. To investigate further the function of PBX/TALE class transcription factors, mRNA expression profile after downregulation of each mRNA expression by siRNA transfection in pancreatic cancer cell line, Panc-1, was examined. Downregulation of Meis1 resulted in downregulation of mitochondrial genes, but those of PBX1 and PBX2 did not. Quantitative reverse transcription polymerase chain reaction confirmed downregulation of mitochondrial genes by Meis1 siRNA transfection. Chromatin immunoprecipitation assay revealed the binding of Meis1 to the mitochondrial promoter region that contained the putative Meis1 binding site. Luciferase reporter assay showed the increase of luciferase activity of a construct containing the Meis1 binding site compared with that with shorter fragment without Meis1 binding region. These findings indicate that Meis1 works as a transcription factor for mitochondrial genes in pancreatic cancer cells.

Regulation of PBX3 expression by androgen and Let-7d in prostate cancer

Background

The pre-leukemia transcription factor 3 (PBX) is part of the PBX family of transcription factors, which is known to regulate genes involved in differentiation of urogenital organs and steroidogenesis. This is of interest with regard to prostate cancer progression as regulation of steroidogenesis is one of the mechanisms involved in the development of castration-resistant prostate cancer. In light of this we wanted to investigate the possible involvement of androgen regulation of PBX3 expression in prostate cancer.

Results

In this study, we show that PBX3 is post-transcriptionally regulated by androgen in prostate cancer cells and that the effect might be independent of the androgen receptor. Furthermore, PBX3 was identified as a target of Let-7d, an androgen regulated microRNA. Let-7d was down-regulated in malignant compared to benign prostate tissue, whereas up-regulation of PBX3 expression was observed.

Conclusions

We demonstrate that PBX3 is up-regulated in prostate cancer and post- transcriptionally regulated by androgen through Let-7d.

The Hox genes and their roles in oncogenesis

Hox genes, a highly conserved subgroup of the homeobox superfamily, have crucial roles in development, regulating numerous processes including apoptosis, receptor signalling, differentiation, motility and angiogenesis. Aberrations in Hox gene expression have been reported in abnormal development and malignancy, indicating that altered expression of Hox genes could be important for both oncogenesis and tumour suppression, depending on context. Therefore, Hox gene expression could be important in diagnosis and therapy.

Pbx1 is a downstream target of Evi-1 in hematopoietic stem/progenitors and leukemic cells

Ecotropic viral integration site-1 (Evi-1) is a nuclear transcription factor, which is essential for the proliferation/maintenance of hematopoietic stem cells (HSCs). Aberrant expression of Evi-1 has been frequently found in myeloid leukemia, and is associated with a poor patient survival. Recently, we reported candidate target genes of Evi-1 shared in HSCs and leukemic cells using gene expression profiling analysis. In this study, we identified Pbx1, a proto-oncogene in hematopoietic malignancy, as a target gene of Evi-1. Overexpression of Evi-1 increased Pbx1 expression in hematopoietic stem/progenitor cells. An analysis of the Pbx1 promoter region revealed that Evi-1 upregulates Pbx1 transcription. Furthermore, reduction of Pbx1 levels through RNAi-mediated knockdown significantly inhibited Evi-1-induced transformation. In contrast, knockdown of Pbx1 did not impair bone marrow transformation by E2A/HLF or AML1/ETO, suggesting that Pbx1 is specifically required for the maintenance of bone marrow transformation mediated by Evi-1. These results indicate that Pbx1 is a target gene of Evi-1 involved in Evi-1-mediated leukemogenesis.

Interaction of intestinal and pancreatic transcription factors in the regulation of CFTR gene expression

The tissue-specific regulation of the cystic fibrosis transmembrane conductance regulator gene (CFTR) is coordinated by intronic and extragenic cis-acting elements that influence its transcriptional activity. The promoter apparently lacks sequences to drive cell type-specific expression. We previously identified a number of intronic elements that were associated with DNase I hypersensitive sites (DHS) and bound the hepatocyte nuclear factor 1 (HNF1) transcription factor. Moreover, we demonstrated the likely involvement of HNF1 in the regulation of CFTR expression in vivo. Here we investigate DHS in introns 16 and 17a of the CFTR gene, which are evident in intestinal and pancreatic cell lines, and determine the transcription factors that interact with these sites. Of particular interest were factors known to interact with HNF1 in coordinated expression of genes in the gastrointestinal tract. We demonstrate that though sequences within these DHS bind HNF1, CDX2, and PBX1 in vitro, only PBX1 show a robust in vivo interaction. These data contribute to our understanding of the complexity of cell-type-specific CFTR regulatory mechanisms.

Prognostic significance of pre B cell leukemia transcription factor 2 (PBX2) expression in non-small cell lung carcinoma

Previous studies on the mammary carcinoma cell line have shown that the pre B cell leukemia transcription factor 1 (PBX1) was a transcription factor for valosin-containing protein (VCP), which is involved in invasion and metastasis of cancers. The roles of PBX1 and PBX2, a highly homologous transcription factor to PBX1, for expression of VCP were examined in the cell lines from non-small cell lung cancer (NSCLC). The effects of PBX1 and PBX2 on VCP expression were examined with siRNA in A549 and PC14 NSCLC cell lines. Expression levels of PBX2 and VCP were immunohistochemically examined and compared with each other in 206 NSCLC cases. Subsequently, significance of PBX expression in clinical behavior of NSCLC patients was evaluated. Expression levels of VCP mRNA significantly decreased when PBX2 but not PBX1 expression was knocked down in NSCLC cell lines. Immunohistochemically, staining intensity of PBX2 was correlated with that of VCP in clinical samples. Then correlation of PBX2 expression and clinical behavior of NSCLC patients was evaluated. Univariate analysis revealed high expression levels of PBX2 and VCP to be poor prognosticators for overall and disease-free survival. Multivariate analysis revealed that high expression of VCP but not PBX2 to be an independent prognostic factor. PBX2 is a transcription factor for VCP in NSCLC. Because high levels of PBX2 expression correlated with prognosis of NSCLC, PBX2 could be a target molecule for treatment of NSCLC.

Neurotrophin 3/TrkC-regulated proteins in the human medulloblastoma cell line DAOY

Medulloblastoma (MB) is the most common malignant childhood brain tumor and high neurotrophin (NP) receptor TrkC mRNA expression was identified as a powerful independent predictor of favorable survival outcome. In order to determine downstream effector proteins of TrkC signaling, the MB cell line DAOY was stably transfected with a vector containing the full-length TrkC cDNA sequence or an empty vector control. A proteomic approach was used to search for expressional changes by two mass spectrometric methods and immunoblotting for validation of significant results. Multiple time points for up to 48 h following NP-3-induced TrkC receptor activation were chosen. Thirteen proteins from several pathways (nucleoside diphosphate kinase A, stathmin, valosin-containing protein, annexin A1, dihydropyrimidinase-related protein-3, DJ-1 protein, glutathione S-transferase P, lamin A/C, fascin, cofilin, vimentin, vinculin, and moesin) were differentially expressed and most have been shown to play a role in differentiation, migration, invasion, proliferation, apoptosis, drug resistance, or oncogenesis. Knowledge on effectors of TrkC signaling may represent a first useful step for the identification of marker candidates or reflecting probable pharmacological targets for specific treatment of MB.

E74-like factor 2 regulates valosin-containing protein expression

Enhanced expression of valosin-containing protein (VCP) correlates with invasion and metastasis of cancers. To clarify the transcription mechanism of VCP, human and mouse genomic sequence was compared, revealing a 260 bp DNA sequence in the 5'-flanking region of VCP gene to be highly conserved between the two, in which binding motif of E74-like factor 2/new Ets-related factor (ELF2/NERF) was identified. Chromatin immunoprecipitation assay showed binding of ELF2/NERF to the 5'-flanking region of VCP gene. Knock-down of ELF2/NERF by siRNA decreased expression level of VCP. Viability of cells under tumor necrosis factor-alpha treatment significantly reduced in ELF2/NERF-knock-down breast cancer cell line. Immunohistochemical analysis on clinical breast cancer specimens showed a correlation of nuclear ELF2/NERF expression with VCP expression and proliferative activity of cells shown by Ki-67 immunohistochemistry. These findings indicate that ELF2/NERF promotes VCP transcription and that ELF2/NERF-VCP pathway might be important for cell survival and proliferation under cytokine stress.