Inhibition of non-small-cell lung cancer cell proliferation by Pbx1

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.

TRIM26 promotes non-small cell lung cancer survival by inducing PBX1 degradation

The transcription factor PBX1 is regarded as an oncogene in various cancers, but its role in non-small cell lung cancer (NSCLC) and the detailed mechanism is not known. In the present study, we found that PBX1 is downregulated in NSCLC tissues and inhibits NSCLC cell proliferation and migration. Subsequently, we performed an affinity purification-coupled tandem mass spectrometry (MS/MS) and found the ubiquitin ligase TRIM26 in the PBX1 immunoprecipitates. Moreover, TRIM26 binds to and mediates PBX1 for K48-linked polyubiquitination and proteasomal degradation. Noticeably, TRIM26 activity depends on its C-terminal RING domain when it is deleted TRIM26 loses its function towards PBX1. TRIM26 further inhibits PBX1 transcriptional activity and downregulates the PBX1 downstream genes, such as RNF6. Moreover, we found that overexpression of TRIM26 significantly promotes NSCLC proliferation, colony formation, and migration in contradiction to PBX1. TRIM26 is highly expressed in NSCLC tissues and predicts poor prognosis. Lastly, the growth NSCLC xenografts is promoted by overexpression of TRIM26 but is suppressed by TRIM26 knockout. In conclusion, TRIM26 is a ubiquitin ligase of PBX1 and it promotes while PBX1 inhibits NSCLC tumor growth. TRIM26 might be a novel therapeutic target for the treatment of NSCLC.

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.

Identifying General Tumor and Specific Lung Cancer Biomarkers by Transcriptomic Analysis

The bioinformatic pipeline previously developed in our research laboratory is used to identify potential general and specific deregulated tumor genes and transcription factors related to the establishment and progression of tumoral diseases, now comparing lung cancer with other two types of cancer. Twenty microarray datasets were selected and analyzed separately to identify hub differentiated expressed genes and compared to identify all the deregulated genes and transcription factors in common between the three types of cancer and those unique to lung cancer. The winning DEGs analysis allowed to identify an important number of TFs deregulated in the majority of microarray datasets, which can become key biomarkers of general tumors and specific to lung cancer. A coexpression network was constructed for every dataset with all deregulated genes associated with lung cancer, according to DAVID’s tool enrichment analysis, and transcription factors capable of regulating them, according to oPOSSUM´s tool. Several genes and transcription factors are coexpressed in the networks, suggesting that they could be related to the establishment or progression of the tumoral pathology in any tissue and specifically in the lung. The comparison of the coexpression networks of lung cancer and other types of cancer allowed the identification of common connectivity patterns with deregulated genes and transcription factors correlated to important tumoral processes and signaling pathways that have not been studied yet to experimentally validate their role in lung cancer. The Kaplan–Meier estimator determined the association of thirteen deregulated top winning transcription factors with the survival of lung cancer patients. The coregulatory analysis identified two top winning transcription factors networks related to the regulatory control of gene expression in lung and breast cancer. Our transcriptomic analysis suggests that cancer has an important coregulatory network of transcription factors related to the acquisition of the hallmarks of cancer. Moreover, lung cancer has a group of genes and transcription factors unique to pulmonary tissue that are coexpressed during tumorigenesis and must be studied experimentally to fully understand their role in the pathogenesis within its very complex transcriptomic scenario. Therefore, the downstream bioinformatic analysis developed was able to identify a coregulatory metafirm of cancer in general and specific to lung cancer taking into account the great heterogeneity of the tumoral process at cellular and population levels.

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.

PBX1 Increases the Radiosensitivity of Oesophageal Squamous Cancer by Targeting of STAT3

The radioresistance of oesophageal squamous cell carcinoma (OSCC) is a critical factor leading to a poor prognosis among patients. The expression of PBX1 is abnormally high in a broad range of human tissues, and this gene plays a key role in tumour proliferation. This research intended to explore the radiosensitization of OSCC by silencing PBX1. The OSCC cell lines KYSE450 and KYSE150 were subjected to PBX1 silencing and/or irradiation (IR). Cell proliferation, colony formation, and apoptosis were tested to evaluate the radiosensitization ability of PBX1 silencing. The levels of STAT3 and p-STAT3 in the OSCC cells were tested by Western blotting. Furthermore, KYSE150 cells with or without PBX1 silencing were xenografted into nude mice with or without radiation exposure. Concomitant PBX1 silencing and IR can obviously suppress growth and enhance radiosensitivity in OSCC cells and xenografts. Moreover, the downregulation of PBX1 inhibits the expression of STAT3 and p-STAT3. The downregulation of PBX1 may increase radiosensitivity in OSCC cells and xenografts via the PBX1/STAT3 pathway. Our findings demonstrate that PBX1 may be a potential target for promoting the effect of radiation therapy in OSCC 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.