Biochemistry of the tale transcription factors PREP, MEIS, and PBX in vertebrates

MEIS2 suppresses breast cancer development by downregulating IL10

BACKGROUND

Breast cancer (BC) is the most commonly diagnosed female cancer. Homeobox protein MEIS2, a key transcription factor, is involved in the regulation of many developmental and cellular processes. However, the role of MEIS2 in the development of breast cancer is still unclear.

AIMS

We aimed to examine the role of myeloid ecotropic insertion site (MEIS2) in breast cancer and the association of MEIS2 with breast cancer clinical stages and pathological grades. We revealed the underlying mechanism by which MEIS2 affected breast cancer cell growth and tumor development.

METHODS AND RESULTS

Using human BC cell lines, clinical samples and animal xenograft model, we reveal that MEIS2 functions as a tumor suppressor in breast cancer. The expression of MEIS2 is inversely correlated with BC clinical stages and pathological grades. MEIS2 knockdown (MEIS2-KD) promotes while MEIS2 overexpression suppresses breast cancer cell proliferation and tumor development in vitro and in animal xenograft models, respectively. To determine the biological function of MEIS2, we screen the expression of a group of MEIS2 potential targeting genes in stable-established cell lines. Results show that the knockdown of MEIS2 in breast cancer cells up-regulates the IL10 expression, but MEIS2 overexpression opposed the effect on IL10 expression. Furthermore, the suppressive role of MEIS2 in breast cancer cell proliferation is associated with the IL10 expression and myeloid cells infiltration.

CONCLUSION

Our study demonstrates that the tumor suppressor of MEIS2 in breast cancer progression is partially via down regulating the expression of IL10 and promoting myeloid cells infiltration. Targeting MEIS2 would be a potentially therapeutic avenue for BC.

PBX1 as a novel master regulator in cancer: Its regulation, molecular biology, and therapeutic applications

PBX1 is a critical transcription factor at the top of various cell fate-determining pathways. In cancer, PBX1 stands at the crossroads of multiple oncogenic signaling pathways and mediates responses by recruiting a broad repertoire of downstream targets. Research thus far has corroborated the involvement of PBX1 in cancer proliferation, resisting apoptosis, tumor-associated neoangiogenesis, epithelial-mesenchymal transition (EMT) and metastasis, immune evasion, genome instability, and dysregulating cellular metabolism. Recently, our understanding of the functional regulation of the PBX1 protein has advanced, as increasing evidence has depicted a regulatory network consisting of transcriptional, post-transcriptional, and post-translational levels of control mechanisms. Furthermore, accumulating studies have supported the clinical utilization of PBX1 as a prognostic or therapeutic target in cancer. Preliminary results showed that PBX1 entails vast potential as a targetable master regulator in the treatment of cancer, particularly in those with high-risk features and resistance to other therapeutic strategies. In this review, we will explore the regulation, protein-protein interactions, molecular pathways, clinical application, and future challenges of PBX1.

Touch receptor end-organ innervation and function require sensory neuron expression of the transcription factor Meis2

Touch sensation is primarily encoded by mechanoreceptors, called low-threshold mechanoreceptors (LTMRs), with their cell bodies in the dorsal root ganglia. Because of their great diversity in terms of molecular signature, terminal endings morphology, and electrophysiological properties, mirroring the complexity of tactile experience, LTMRs are a model of choice to study the molecular cues differentially controlling neuronal diversification. While the transcriptional codes that define different LTMR subtypes have been extensively studied, the molecular players that participate in their late maturation and in particular in the striking diversity of their end-organ morphological specialization are largely unknown. Here we identified the TALE homeodomain transcription factor Meis2 as a key regulator of LTMRs target-field innervation in mice. Meis2 is specifically expressed in cutaneous LTMRs, and its expression depends on target-derived signals. While LTMRs lacking Meis2 survived and are normally specified, their end-organ innervations, electrophysiological properties, and transcriptome are differentially and markedly affected, resulting in impaired sensory-evoked behavioral responses. These data establish Meis2 as a major transcriptional regulator controlling the orderly formation of sensory neurons innervating peripheral end organs required for light touch.

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.

The advances of E2A-PBX1 fusion in B-cell acute lymphoblastic Leukaemia

The E2A-PBX1 gene fusion is a common translocation in B-cell acute lymphoblastic leukaemia. Patients harbouring the E2A-PBX1 fusion gene typically exhibit an intermediate prognosis. Furthermore, minimal residual disease has unsatisfactory prognostic value in E2A-PBX1 B-cell acute lymphoblastic leukaemia. However, the mechanism of E2A-PBX1 in the occurrence and progression of B-cell acute lymphoblastic leukaemia is not well understood. Here, we mainly review the roles of E2A and PBX1 in the differentiation and development of B lymphocytes, the mechanism of E2A-PBX1 gene fusion in B-cell acute lymphoblastic leukaemia, and the potential therapeutic approaches.

CircDHRS3 inhibits prostate cancer cell proliferation and metastasis through the circDHRS3/miR-421/MEIS2 axis

Prostate cancer is the most prevalent type of cancer among men worldwide. The importance of circular RNA (circRNA) in prostate cancer and its connection to malignancy has been steadily recognized. circRNA expression was obtained by circRNA sequencing of prostate cancer. circRNA and its function were further analysed. The results were verified by qRT-PCR, RIP assay, FISH, RNA pulldown, WB, CCK-8, colony formation assay and wound-healing assay. BALB/c Nude mice were used for xenograft hosts. Low expression of circDHRS3 was assessed in prostate cancer. Overexpression of circDHRS3 inhibited prostate cancer growth and migration in vitro. Additionally, miR-421 was shown to be the downstream target of circDHRS3, as shown by fluorescence in situ hybridization and dual-luciferase experiments. The rescue assay results for the PC3 and Du145 cell lines demonstrated that circDHRS3 inhibits prostate cancer cell lines' ability to proliferate and metastasize by modulating MEIS2 expression through the circDHRS3/miR-421/MEIS2 axis. In vivo investigations confirmed that the overexpression of circDHRS3 could inhibit both the lung and bone metastasis of prostate cancer cells. circDHRS3 has the potential to become a biomarker and a targeted therapeutic site for prostate cancer, particularly in the malignant stage. Our study indicates that circDHRS3 inhibits prostate cancer cell proliferation and metastasis through the circDHRS3/miR-421/MEIS2 axis.

A novel pathogenic variant c.262delA in PBX1 causing oligomeganephronia identified using whole-exome sequencing and a literature review

Oligomeganephronia (OMN) is a rare congenital renal hypoplasia reported more often in children than in adults. The diagnosis of OMN relies on renal biopsy and exhibits a significant reduction in the number of glomeruli and pronounced glomerular hypertrophy. Here, we report the case of an 8-year-old boy with recurrent proteinuria and abnormal external ears. A renal biopsy revealed large and rare glomeruli. The histological findings confirmed the diagnosis of OMN. Whole-exome sequencing of the patient revealed a new pathogenic variant in PBX1 (hg19, NM_002585, c.262delA, p.Thr88Glnfs*3). The PBX1 gene encodes a transcription factor whose pathogenic variants can result in congenital renal and urinary system anomalies, with or without hearing loss, abnormal ears, and developmental retardation (CAKUTED). This is the first report to detect PBX1 pathogenic variants in children with OMN, a novel phenotype of human PBX1 pathogenic variants. We performed functional prediction analyses of deletions in the corresponding structural domains. We summarized 27 cases of PBX1 single pathogenic variants reported between 2003 and 2023 in terms of truncating and missense pathogenic variants, which can deepen our understanding of the PBX1 structural domain and expand our knowledge of the PBX1 genotype and phenotype.

Molecular Mechanisms of Lupus Susceptibility Allele PBX1D

Pre-B cell leukemia homeobox 1 (PBX1) controls chromatin accessibility to a large number of genes in various cell types. Its dominant negative splice isoform, PBX1D, which lacks the DNA and Hox-binding domains, is expressed more frequently in the CD4+ T cells from lupus-prone mice and patients with systemic lupus erythematosus than healthy control subjects. PBX1D overexpression in CD4+ T cells impaired regulatory T cell homeostasis and expanded inflammatory CD4+ T cells. In this study, we showed that PBX1 message expression is downregulated by activation in CD4+ T cells as well as in B cells. PBX1D protein was less stable than the normal isoform, PBX1B, and it is degraded through the ubiquitin-proteasome-dependent pathway. The DNA binding domain lacking in PBX1D has two putative ubiquitin binding sites, K292 and K293, that are predicted to be in direct contact with DNA. Mutation of K292-293 reduced PBX1B stability to a level similar to PBX1D and abrogated DNA binding. In addition, contrary to PBX1B, PBX1D is retained in the cytoplasm without the help of the cofactors MEIS or PREP1, indicating a different requirement for nuclear translocation. Overall, these findings suggest that multiple post-transcriptional mechanisms are responsible for PBX1D loss of function and induction of CD4+ T cell inflammatory phenotypes in systemic lupus erythematosus.

PBX3 promotes pentose phosphate pathway and colorectal cancer progression by enhancing G6PD expression

Metabolic reprogramming is a hallmark of cancers crucial for fulfilling the needs of energy, building blocks, and antioxidants to support tumor cells' rapid proliferation and to cope with the harsh microenvironment. Pre-B-cell leukemia transcription factor 3 (PBX3) is a member of the PBX family whose expression is up-regulated in various tumors, however, whether it is involved in tumor cell metabolic reprogramming remains unclear. Herein, we report that PBX3 is a positive regulator of glucose-6-phosphate dehydrogenase (G6PD), the rate-limiting enzyme in the pentose phosphate pathway (PPP). PBX3 promoted G6PD transcriptional activity in tumor cells by binding directly to its promoter, leading to PPP stimulation and enhancing the production of nucleotides and NADPH, a crucial reductant, thereby promoting nucleic acid and lipid biosynthesis while decreasing intracellular reactive oxygen species levels. The PBX3/G6PD axis also promoted tumorigenic potential in vitro and in vivo. Collectively, these findings reveal a novel function of PBX3 as a regulator of G6PD, linking its oncogenic activity with tumor cell metabolic reprogramming, especially PPP. Furthermore, our results suggested that PBX3 is a potential target for metabolic-based anti-tumor therapeutic strategies.

Phosphorylation of PBX2, a novel downstream target of mTORC1, is determined by GSK3 and PP1

Mechanistic target of rapamycin complex 1 (mTORC1) is a serine-threonine kinase that is activated by extracellular signals, such as nutrients and growth factors. It plays a key role in the control of various biological processes, such as protein synthesis and energy metabolism by mediating or regulating the phosphorylation of multiple target molecules, some of which remain to be identified. We have here reanalysed a large-scale phosphoproteomics data set for mTORC1 target molecules and identified pre-B cell leukemia transcription factor 2 (PBX2) as such a novel target that is dephosphorylated downstream of mTORC1. We confirmed that PBX2, but not other members of the PBX family, is dephosphorylated in an mTORC1 activity-dependent manner. Furthermore, pharmacological and gene knockdown experiments revealed that glycogen synthase kinase 3 (GSK3) and protein phosphatase 1 (PP1) are responsible for the phosphorylation and dephosphorylation of PBX2, respectively. Our results thus suggest that the balance between the antagonistic actions of GSK3 and PP1 determines the phosphorylation status of PBX2 and its regulation by mTORC1.

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.

Meis2 controls skeletal formation in the hyoid region

A vertebrate skull is composed of many skeletal elements which display enormous diversity of shapes. Cranial bone formation embodies a multitude of processes, i.e., epithelial-mesenchymal induction, mesenchymal condensation, and endochondral or intramembranous ossification. Molecular pathways determining complex architecture and growth of the cranial skeleton during embryogenesis are poorly understood. Here, we present a model of the hyoid apparatus development in Wnt1-Cre2-induced Meis2 conditional knock-out (cKO) mice. Meis2 cKO embryos develop an aberrant hyoid apparatus—a complete skeletal chain from the base of the neurocranium to lesser horns of the hyoid, resembling extreme human pathologies of the hyoid-larynx region. We examined key stages of hyoid skeletogenesis to obtain a complex image of the hyoid apparatus formation. Lack of Meis2 resulted in ectopic loci of mesenchymal condensations, ectopic cartilage and bone formation, disinhibition of skeletogenesis, and elevated proliferation of cartilage precursors. We presume that all these mechanisms contribute to formation of the aberrant skeletal chain in the hyoid region. Moreover, Meis2 cKO embryos exhibit severely reduced expression of PBX1 and HAND2 in the hyoid region. Altogether, MEIS2 in conjunction with PBX1 and HAND2 affects mesenchymal condensation, specification and proliferation of cartilage precursors to ensure development of the anatomically correct hyoid apparatus.

The TALE never ends: A comprehensive overview of the role of PBX1, a TALE transcription factor, in human developmental defects

PBX1 is a highly conserved atypical homeodomain transcription factor (TF) belonging to the TALE (three amino acid loop extension) family. Dimerized with other TALE proteins, it can interact with numerous partners and reach dozens of regulating sequences, suggesting its role as a pioneer factor. PBX1 is expressed throughout the embryonic stages (as early as the blastula stage) in vertebrates. In human, PBX1 germline variations are linked to syndromic renal anomalies (CAKUTHED). In this review, we summarized available data on PBX1 functions, PBX1-deficient animal models, and PBX1 germline variations in humans. Two types of genetic alterations were identified in PBX1 gene. PBX1 missense variations generate a severe phenotype including lung hypoplasia, cardiac malformations, and sexual development defects (DSDs). Conversely, truncating variants generate milder phenotypes (mainly cryptorchidism and deafness). We suggest that defects in PBX1 interactions with various partners, including proteins from the HOX (HOXA7, HOXA10, etc.), WNT (WNT9B, WNT3), and Polycomb (BMI1, EED) families are responsible for abnormal proliferation and differentiation of the embryonic mesenchyme. These alterations could explain most of the defects observed in humans. However, some phenotype variability (especially DSDs) remains poorly understood. Further studies are needed to explore the TALE family in greater depth.

An example of parenchymal renal sparing in the context of complex malformations due to a novel mutation in the PBX1 gene

INTRODUCTION

PBX1 encodes the pre-B cell leukemia factor 1, a Three Amino acid Loop Extension (TALE) transcription factor crucial to regulate basic developmental processes. PBX1 loss-of-function variants have been initially described in association with renal malformations in both isolated and syndromic forms.

CASE REPORT

Herein, we report a male infant presenting multiple organ malformations (cleidosternal dysostosis, micrognathia, left lung hypoplasia, wide interatrial defect, pulmonary hypertension, total anomalous pulmonary venous return, intestinal malrotation) and carrying the heterozygous de novo c.868C > T (p.Arg290Trp) variant in PBX1. This novel variant affects the highly conserved homeodomain of the protein, leading to a non-conservative substitution and consequently altering its tridimensional structure and DNA-binding capacity.

CONCLUSION

So far, PBX1 has been reported in association with a broad spectrum of renal anomalies. However, given the role of this gene in many different developing processes, whole-exome sequencing can detect mutations in PBX1 even in patients with different phenotypes, not necessarily involving the renal primordium. This report presents a novel PBX1 variant with a predicted strong deleterious effect. The mutation leads to a non-conservative substitution in a very highly conserved domain of the protein, thus altering its tertiary structure and DNA-binding capacity.

Identifying the Potential Roles of PBX4 in Human Cancers Based on Integrative Analysis

PBX4 belongs to the pre-B-cell leukemia homeobox (PBX) transcription factors family and acts as a transcriptional cofactor of HOX proteins participating in several pathophysiological processes. Recent studies have revealed that the dysregulation of PBX4 is closely related to multiple diseases, especially cancers. However, the research on PBX4’s potential roles in 33 cancers from the Cancer Genome Atlas (TCGA) is still insufficient. Therefore, we performed a comprehensive pan-cancer analysis to explore the roles of PBX4with multiple public databases. Our results showed that PBX4 was differentially expressed in 17 types of human cancer and significantly correlated to the pathological stage, tumor grade, and immune and molecular subtypes. We used the Kaplan–Meier plotter and PrognoScan databases to find the significant associations between PBX4 expression and prognostic values of multiple cancers. It was also found that PBX4 expression was statistically related to mutation status, DNA methylation, immune infiltration, drug sensitivity, and immune checkpoint blockade (ICB) therapy. Additionally, we found that PBX4 was involved in different functional states of multiple cancers from the single-cell resolution perspective. Enrichment analysis results showed that PBX4-related genes were enriched in the cell cycle process, MAPK cascade, ncRNA metabolic process, positive regulation of GTPase activity, and regulation of lipase activity and mainly participated in the pathways of cholesterol metabolism, base excision repair, herpes simplex virus 1 infection, transcriptional misregulation in cancer, and Epstein–Barr virus infection. Altogether, our integrative analysis could help in better understanding the potential roles of PBX4 in different human cancers.

The transcription factor PREP1(PKNOX1) regulates nuclear stiffness, the expression of LINC complex proteins and mechanotransduction

Mechanosignaling, initiated by extracellular forces and propagated through the intracellular cytoskeletal network, triggers signaling cascades employed in processes as embryogenesis, tissue maintenance and disease development. While signal transduction by transcription factors occurs downstream of cellular mechanosensing, little is known about the cell intrinsic mechanisms that can regulate mechanosignaling. Here we show that transcription factor PREP1 (PKNOX1) regulates the stiffness of the nucleus, the expression of LINC complex proteins and mechanotransduction of YAP-TAZ. PREP1 depletion upsets the nuclear membrane protein stoichiometry and renders nuclei soft. Intriguingly, these cells display fortified actomyosin network with bigger focal adhesion complexes resulting in greater traction forces at the substratum. Despite the high traction, YAP-TAZ translocation is impaired indicating disrupted mechanotransduction. Our data demonstrate mechanosignaling upstream of YAP-TAZ and suggest the existence of a transcriptional mechanism actively regulating nuclear membrane homeostasis and signal transduction through the active engagement/disengagement of the cell from the extracellular matrix.

The transcription factor PREP1 binds to promoter regions of SUN1, SUN2 and LAP2 genes and promotes nuclear stiffness, and its depletion results in impaired mechanotransduction.

Genetic Regulation of Vertebrate Forebrain Development by Homeobox Genes

Forebrain development in vertebrates is regulated by transcription factors encoded by homeobox, bHLH and forkhead gene families throughout the progressive and overlapping stages of neural induction and patterning, regional specification and generation of neurons and glia from central nervous system (CNS) progenitor cells. Moreover, cell fate decisions, differentiation and migration of these committed CNS progenitors are controlled by the gene regulatory networks that are regulated by various homeodomain-containing transcription factors, including but not limited to those of the Pax (paired), Nkx, Otx (orthodenticle), Gsx/Gsh (genetic screened), and Dlx (distal-less) homeobox gene families. This comprehensive review outlines the integral role of key homeobox transcription factors and their target genes on forebrain development, focused primarily on the telencephalon. Furthermore, links of these transcription factors to human diseases, such as neurodevelopmental disorders and brain tumors are provided.

HOX and PBX gene dysregulation as a therapeutic target in glioblastoma multiforme

BACKGROUND

Glioblastoma multiforme (GBM) is the most common high-grade malignant brain tumour in adults and arises from the glial cells in the brain. The prognosis of treated GBM remains very poor with 5-year survival rates of 5%, a figure which has not improved over the last few decades. Currently, there is a modest 14-month overall median survival in patients undergoing maximum safe resection plus adjuvant chemoradiotherapy. HOX gene dysregulation is now a widely recognised feature of many malignancies.

METHODS

In this study we have focused on HOX gene dysregulation in GBM as a potential therapeutic target in a disease with high unmet need.

RESULTS

We show significant dysregulation of these developmentally crucial genes and specifically that HOX genes A9, A10, C4 and D9 are strong candidates for biomarkers and treatment targets for GBM and GBM cancer stem cells. We evaluated a next generation therapeutic peptide, HTL-001, capable of targeting HOX gene over-expression in GBM by disrupting the interaction between HOX proteins and their co-factor, PBX. HTL-001 induced both caspase-dependent and -independent apoptosis in GBM cell lines.

CONCLUSION

In vivo biodistribution studies confirmed that the peptide was able to cross the blood brain barrier. Systemic delivery of HTL-001 resulted in improved control of subcutaneous murine and human xenograft tumours and improved survival in a murine orthotopic model.

Annotation of Hox cluster and Hox cofactor genes in the Asian citrus psyllid, Diaphorina citri, reveals novel features

Hox genes and their cofactors are essential developmental genes specifying regional identity in animals. Hox genes have a conserved arrangement in clusters in the same order in which they specify identity along the anterior-posterior axis. A few insect species have breaks in the cluster, but these are exceptions. We annotated the 10 Hox genes of the Asian citrus psyllid Diaphorina citri, and found a split in its Hox cluster between the Deformed and Sex combs reduced genes - the first time a break at this position has been observed in an insect Hox cluster. We also annotated D. citri orthologs of the Hox cofactor genes homothorax, PKNOX and extradenticle and found an additional copy of extradenticle in D. citri that appears to be a retrogene. Expression data and sequence conservation suggest that the extradenticle retrogene may have retained the original extradenticle function and allowed divergence of the parental extradenticle gene.

Downstream of the HOX genes: explaining conflicting tumour suppressor and oncogenic functions in cancer

The HOX genes are a highly conserved group of transcription factors that have key roles in early development, but which are also highly expressed in most cancers. Many studies have found strong associative relationships between the expression of individual HOX genes in tumours and clinical parameters including survival. For the majority of HOX genes, high tumour expression levels seem to be associated with a worse outcome for patients, and in some cases this has been shown to result from the activation of pro-oncogenic genes and pathways. However, there are also many studies that indicate a tumour suppressor role for some HOX genes, sometimes with conclusions that contradict earlier work. In this review, we have attempted to clarify the role of HOX genes in cancer by focusing on their downstream targets as identified in studies that provide experimental evidence for their activation or repression. On this basis, the majority of HOX genes would appear to have a pro-oncogenic function, with the notable exception of HOXD10, which acts exclusively as a tumour suppressor. HOX proteins regulate a wide range of target genes involved in metastasis, cell death, proliferation, and angiogenesis, and activate key cell signalling pathways. Furthermore, for some functionally related targets, this regulation is achieved by a relatively small subgroup of HOX genes.

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.

Transcriptional Regulation and Implications for Controlling Hox Gene Expression

Hox genes play key roles in axial patterning and regulating the regional identity of cells and tissues in a wide variety of animals from invertebrates to vertebrates. Nested domains of Hox expression generate a combinatorial code that provides a molecular framework for specifying the properties of tissues along the A–P axis. Hence, it is important to understand the regulatory mechanisms that coordinately control the precise patterns of the transcription of clustered Hox genes required for their roles in development. New insights are emerging about the dynamics and molecular mechanisms governing transcriptional regulation, and there is interest in understanding how these may play a role in contributing to the regulation of the expression of the clustered Hox genes. In this review, we summarize some of the recent findings, ideas and emerging mechanisms underlying the regulation of transcription in general and consider how they may be relevant to understanding the transcriptional regulation of Hox genes.

Dynamic Expression of the Homeobox Factor PBX1 during Mouse Testis Development

Members of the pre-B-cell leukemia transcription factor (PBX) family of homeoproteins are mainly known for their involvement in hematopoietic cell differentiation and in the development of leukemia. The four PBX proteins, PBX1, PBX2, PBX3 and PBX4, belong to the three amino acid loop extension (TALE) superfamily of homeoproteins which are important transcriptional cofactors in several developmental processes involving homeobox (HOX) factors. Mutations in the human PBX1 gene are responsible for cases of gonadal dysgenesis with absence of male sex differentiation while Pbx1 inactivation in the mouse causes a failure in Leydig cell differentiation and function. However, no data is available regarding the expression profile of this transcription factor in the testis. To fill this knowledge gap, we have characterized PBX1 expression during mouse testicular development. Real time PCRs and Western blots confirmed the presence Pbx1 mRNA and PBX1 protein in different Leydig and Sertoli cell lines. The cellular localization of the PBX1 protein was determined by immunohistochemistry and immunofluorescence on mouse testis sections at different embryonic and postnatal developmental stages. PBX1 was detected in interstitial cells and in peritubular myoid cells from embryonic life until puberty. Most interstitial cells expressing PBX1 do not express the Leydig cell marker CYP17A1, indicating that they are not differentiated and steroidogenically active Leydig cells. In adults, PBX1 was mainly detected in Sertoli cells. The presence of PBX1 in different somatic cell populations during testicular development further supports a direct role for this transcription factor in testis cell differentiation and in male reproductive function.

PBX1-directed stem cell transcriptional program drives tumor progression in myeloproliferative neoplasm

PBX1 regulates the balance between self-renewal and differentiation of hematopoietic stem cells and maintains proto-oncogenic transcriptional pathways in early progenitors. Its increased expression was found in myeloproliferative neoplasm (MPN) patients bearing the JAK2V617F mutation. To investigate if PBX1 contributes to MPN, and to explore its potential as therapeutic target, we generated the JP mouse strain, in which the human JAK2 mutation is induced in the absence of PBX1. Typical MPN features, such as thrombocythemia and granulocytosis, did not develop without PBX1, while erythrocytosis, initially displayed by JP mice, gradually resolved over time; splenic myeloid metaplasia and in vitro cytokine independent growth were absent upon PBX1 inactivation. The aberrant transcriptome in stem/progenitor cells from the MPN model was reverted by the absence of PBX1, demonstrating that PBX1 controls part of the molecular pathways deregulated by the JAK2V617F mutation. Modulation of the PBX1-driven transcriptional program might represent a novel therapeutic approach.

MEIS1 in Hematopoiesis and Cancer. How MEIS1-PBX Interaction Can Be Used in Therapy

Recently MEIS1 emerged as a major determinant of the MLL-r leukemic phenotype. The latest and most efficient drugs effectively decrease the levels of MEIS1 in cancer cells. Together with an overview of the latest drugs developed to target MEIS1 in MLL-r leukemia, we review, in detail, the role of MEIS1 in embryonic and adult hematopoiesis and suggest how a more profound knowledge of MEIS1 biochemistry can be used to design potent and effective drugs against MLL-r leukemia. In addition, we present data showing that the interaction between MEIS1 and PBX1 can be blocked efficiently and might represent a new avenue in anti-MLL-r and anti-leukemic therapy.

PKNOX2 regulates myofibroblast functions and tubular cell survival during kidney fibrosis

The number of patients with chronic kidney disease (CKD) is increasing worldwide. When kidneys are exposed to severe injury, tubular cell death occurs and kidney fibrosis progresses by activating fibroblasts and myofibroblasts (referred to as (myo)fibroblasts), leading to CKD; however, the pathological and molecular mechanisms underlying CKD, including kidney fibrosis, remain obscure. In the present study, we focused on a transcription factor PBX/Knotted Homeobox 2 (PKNOX2) in kidney fibrosis. The transcript and protein expression of PKNOX2 was upregulated in fibrotic kidneys after unilateral ureteral obstruction (UUO). Importantly, immunofluorescence microscopic analysis revealed that the number of PKNOX2-expressing myofibroblasts was increased, whereas the expression of PKNOX2 was decreased in proximal tubular epithelial cells after UUO. In (myo)fibroblasts, PKNOX2 was induced by TGF-β1. Knockdown of PKNOX2 using shRNA lentiviral system reduced the viability of (myo)fibroblasts either in the presence or absence of TGF-β1, accompanied by increased apoptosis. Moreover, PKNOX2 knockdown decreased TGF-β1-induced migration of myofibroblasts and differentiation of fibroblasts into myofibroblasts. Significantly, knockdown of PKNOX2 also decreased the viability and increased apoptosis of tubular epithelial cells. Collectively, PKNOX2 regulates the function of (myo)fibroblasts and the viability of proximal tubular epithelial cells in progression of kidney fibrosis.

The Mandibular and Hyoid Arches-From Molecular Patterning to Shaping Bone and Cartilage

The mandibular and hyoid arches collectively make up the facial skeleton, also known as the viscerocranium. Although all three germ layers come together to assemble the pharyngeal arches, the majority of tissue within viscerocranial skeletal components differentiates from the neural crest. Since nearly one third of all birth defects in humans affect the craniofacial region, it is important to understand how signalling pathways and transcription factors govern the embryogenesis and skeletogenesis of the viscerocranium. This review focuses on mouse and zebrafish models of craniofacial development. We highlight gene regulatory networks directing the patterning and osteochondrogenesis of the mandibular and hyoid arches that are actually conserved among all gnathostomes. The first part of this review describes the anatomy and development of mandibular and hyoid arches in both species. The second part analyses cell signalling and transcription factors that ensure the specificity of individual structures along the anatomical axes. The third part discusses the genes and molecules that control the formation of bone and cartilage within mandibular and hyoid arches and how dysregulation of molecular signalling influences the development of skeletal components of the viscerocranium. In conclusion, we notice that mandibular malformations in humans and mice often co-occur with hyoid malformations and pinpoint the similar molecular machinery controlling the development of mandibular and hyoid arches.

The Hox protein conundrum: The "specifics" of DNA binding for Hox proteins and their partners

Homeotic genes (Hox genes) are homeodomain-transcription factors involved in conferring segmental identity along the anterior-posterior body axis. Molecular characterization of HOX protein function raises some interesting questions regarding the source of the binding specificity of the HOX proteins. How do HOX proteins regulate common and unique target specificity across space and time? This review attempts to summarize and interpret findings in this area, largely focused on results from in vitro and in vivo studies in Drosophila and mouse systems. Recent studies related to HOX protein binding specificity compel us to reconsider some of our current models for transcription factor-DNA interactions. It is crucial to study transcription factor binding by incorporating components of more complex, multi-protein interactions in concert with small changes in binding motifs that can significantly impact DNA binding specificity and subsequent alterations in gene expression. To incorporate the multiple elements that can determine HOX protein binding specificity, we propose a more integrative Cooperative Binding model.

GATA4 Controls Epithelial Morphogenesis in the Developing Stomach to Promote Establishment of Glandular Columnar Epithelium

BACKGROUND & AIMS

The transcription factor GATA4 is broadly expressed in nascent foregut endoderm. As development progresses, GATA4 is lost in the domain giving rise to the stratified squamous epithelium of the esophagus and forestomach (FS), while it is maintained in the domain giving rise to the simple columnar epithelium of the hindstomach (HS). Differential GATA4 expression within these domains coincides with the onset of distinct tissue morphogenetic events, suggesting a role for GATA4 in diversifying foregut endoderm into discrete esophageal/FS and HS epithelial tissues. The goal of this study was to determine how GATA4 regulates differential morphogenesis of the mouse gastric epithelium.

METHODS

We used a Gata4 conditional knockout mouse line to eliminate GATA4 in the developing HS and a Gata4 conditional knock-in mouse line to express GATA4 in the developing FS.

RESULTS

We found that GATA4-deficient HS epithelium adopted a FS-like fate, and conversely, that GATA4-expressing FS epithelium adopted a HS-like fate. Underlying structural changes in these epithelia were broad changes in gene expression networks attributable to GATA4 directly activating or repressing expression of HS or FS defining transcripts. Our study implicates GATA4 as having a primary role in suppressing an esophageal/FS transcription factor network during HS development to promote columnar epithelium. Moreover, GATA4-dependent phenotypes in developmental mutants reflected changes in gene expression associated with Barrett's esophagus.

CONCLUSIONS

This study demonstrates that GATA4 is necessary and sufficient to activate the development of simple columnar epithelium, rather than stratified squamous epithelium, in the embryonic stomach. Moreover, similarities between mutants and Barrett's esophagus suggest that developmental biology can provide insight into human disease mechanisms.

A Computer-Based Methodology to Design Non-Standard Peptides Potentially Able to Prevent HOX-PBX1-Associated Cancer Diseases

In the last decades, HOX proteins have been extensively studied due to their pivotal role in transcriptional events. HOX proteins execute their activity by exploiting a cooperative binding to PBX proteins and DNA. Therefore, an increase or decrease in HOX activity has been associated with both solid and haematological cancer diseases. Thus, inhibiting HOX-PBX interaction represents a potential strategy to prevent these malignancies, as demonstrated by the patented peptide HTL001 that is being studied in clinical trials. In this work, a computational study is described to identify novel potential peptides designed by employing a database of non-natural amino acids. For this purpose, residue scanning of the HOX minimal active sequence was performed to select the mutations to be further processed. According to these results, the peptides were point-mutated and used for Molecular Dynamics (MD) simulations in complex with PBX1 protein and DNA to evaluate complex binding stability. MM-GBSA calculations of the resulting MD trajectories were exploited to guide the selection of the most promising mutations that were exploited to generate twelve combinatorial peptides. Finally, the latter peptides in complex with PBX1 protein and DNA were exploited to run MD simulations and the ΔGbinding average values of the complexes were calculated. Thus, the analysis of the results highlighted eleven combinatorial peptides that will be considered for further assays.

Amyloid-like Prep1 peptides exhibit reversible blue-green-red fluorescence in vitro and in living cells

PREP1-based peptides form amyloid-like aggregates endowed with an intrinsic blue-green-red fluorescence with an unusual sharp maximum at 520 nm upon excitation with visible light under physiological conditions. The peptide PREP1[117-132], whose sequence does not contain aromatic residues, presents a pH-dependent and reversible fluorescence, in line with its structural transition from β-sheet rich aggregates to α-helix structures. These findings further demonstrate that the non-canonical fluorescence exhibited by amyloids is an articulated phenomenon.

The cooperation of cis-elements during M-cadherin promoter activation

M-cadherin is a skeletal muscle-specific transmembrane protein mediating the cell-cell adhesion of myoblasts during myogenesis. It is expressed in the proliferating satellite cells and highly induced by myogenic regulatory factors (MRFs) during terminal myogenic differentiation. Several conserved cis-elements, including 5 E-boxes, 2 GC boxes, and 1 conserved downstream element (CDE) were identified in the M-cadherin proximal promoter. We found that E-box-3 and -4 close to the transcription initiation site (TIS) mediated most of its transactivation by MyoD, the strongest myogenic MRF. Including of any one of the other E-boxes restored the full activation by MyoD, suggesting an essential collaboration between E-boxes. Stronger activation of M-cadherin promoter than that of muscle creatine kinase (MCK) by MyoD was observed regardless of culture conditions and the presence of E47. Furthermore, MyoD/E47 heterodimer and MyoD ∼ E47 fusion protein achieved similar levels of activation in differentiation medium (DM), suggesting high affinity of MyoD/E47 to E-boxes 3/4 under DM. We also found that GC boxes and CDE positively affected MyoD mediated activation. The CDE element was predicted to be the target of the chromatin-modifying factor Meis1/Pbx1 heterodimer. Knockdown of Pbx1 significantly reduced the expression level of M-cadherin, but increased that of N-cadherin. Using ChIP assay, we further found significant reduction in MyoD recruitment to M-cadherin promoter when CDE was deleted. Taken together, these observations suggest that the chromatin-modifying function of Pbx1/Meis1 is critical to M-cadherin promoter activation before MyoD is recruited to E-boxes to trigger transcription.

Roles of the HOX Proteins in Cancer Invasion and Metastasis

Invasion and metastasis correspond to the foremost cause of cancer-related death, and the molecular networks behind these two processes are extremely complex and dependent on the intra- and extracellular conditions along with the prime of the premetastatic niche. Currently, several studies suggest an association between the levels of HOX genes expression and cancer cell invasion and metastasis, which favour the formation of novel tumour masses. The deregulation of HOX genes by HMGA2/TET1 signalling and the regulatory effect of noncoding RNAs generated by the HOX loci can also promote invasion and metastasis, interfering with the expression of HOX genes or other genes relevant to these processes. In this review, we present five molecular mechanisms of HOX deregulation by which the HOX clusters products may affect invasion and metastatic processes in solid tumours.

DamID identifies targets of CEH-60/PBX that are associated with neuron development and muscle structure in Caenorhabditis elegans

Transcription factors govern many of the time- and tissue-specific gene expression events in living organisms. CEH-60, a homolog of the TALE transcription factor PBX in vertebrates, was recently characterized as a new regulator of intestinal lipid mobilization in Caenorhabditis elegans. Because CEH-60's orthologs and paralogs exhibit several other functions, notably in neuron and muscle development, and because ceh-60 expression is not limited to the C. elegans intestine, we sought to identify additional functions of CEH-60 through DNA adenine methyltransferase identification (DamID). DamID identifies protein-genome interaction sites through GATC-specific methylation. We here report 872 putative CEH-60 gene targets in young adult animals, and 587 in L2 larvae, many of which are associated with neuron development or muscle structure. In light of this, we investigate morphology and function of ceh-60 expressing AWC neurons, and contraction of pharyngeal muscles. We find no clear functional consequences of loss of ceh-60 in these assays, suggesting that in AWC neurons and pharyngeal muscle, CEH-60 function is likely more subtle or redundant with other factors.

Mapping the native interaction surfaces of PREP1 with PBX1 by cross-linking mass-spectrometry and mutagenesis

Both onco-suppressor PREP1 and the oncogene MEIS1 bind to PBX1. This interaction stabilizes the two proteins and allows their translocation into the nucleus and thus their transcriptional activity. Here, we have combined cross-linking mass-spectrometry and systematic mutagenesis to detail the binding geometry of the PBX1-PREP1 (and PBX1-MEIS1) complexes, under native in vivo conditions. The data confirm the existence of two distinct interaction sites within the PBC domain of PBX1 and unravel differences among the highly similar binding sites of MEIS1 and PREP1. The HR2 domain has a fundamental role in binding the PBC-B domain of PBX1 in both PREP1 and MEIS1. The HR1 domain of MEIS1, however, seem to play a less stringent role in PBX1 interaction with respect to that of PREP1. This difference is also reflected by the different binding affinity of the two proteins to PBX1. Although partial, this analysis provides for the first time some ideas on the tertiary structure of the complexes not available before. Moreover, the extensive mutagenic analysis of PREP1 identifies the role of individual hydrophobic HR1 and HR2 residues, both in vitro and in vivo.

Identification and characterization of cytotoxic amyloid-like regions in human Pbx-regulating protein-1

The ability of many proteins to fold into well-defined structures has been traditionally considered a prerequisite for fulfilling their functions. Protein folding is also regarded as a valuable loophole to escape uncontrolled and harmful aggregations. Here we show that the PBX-regulating protein-1 (PREP1), an important homeodomain transcription factor involved in cell growth and differentiation during embryogenesis, is endowed with an uncommon thermostability. Indeed, circular dichroism analyses indicate that it retains most of its secondary structure at very high temperatures. These findings have important implications for PREP1 functions since it is a stabilizing factor of its partner PBX1. Predictive analyses suggest that the observed PREP1 thermostability could be related to the presence of aggregation-prone regions. Interestingly, synthetic peptides corresponding to these regions exhibit a remarkable propensity to form toxic β-rich amyloid-like aggregates in physiological conditions. On this basis, we suggest that PREP1 stability is an effective way to prevent or limit the formation of harmful aggregates. Notably, one of these PREP1 fragments (residues 117-132) is able to reversibly switch from α-helical to β-rich states depending on the environmental conditions. The chameleon conformational behavior of this peptide makes it an ideal system to study this intriguing and widespread structural transition.

MEIS-mediated suppression of human prostate cancer growth and metastasis through HOXB13-dependent regulation of proteoglycans

The molecular roles of HOX transcriptional activity in human prostate epithelial cells remain unclear, impeding the implementation of new treatment strategies for cancer prevention and therapy. MEIS proteins are transcription factors that bind and direct HOX protein activity. MEIS proteins are putative tumor suppressors that are frequently silenced in aggressive forms of prostate cancer. Here we show that MEIS1 expression is sufficient to decrease proliferation and metastasis of prostate cancer cells in vitro and in vivo murine xenograft models. HOXB13 deletion demonstrates that the tumor-suppressive activity of MEIS1 is dependent on HOXB13. Integration of ChIP-seq and RNA-seq data revealed direct and HOXB13-dependent regulation of proteoglycans including decorin (DCN) as a mechanism of MEIS1-driven tumor suppression. These results define and underscore the importance of MEIS1-HOXB13 transcriptional regulation in suppressing prostate cancer progression and provide a mechanistic framework for the investigation of HOXB13 mutants and oncogenic cofactors when MEIS1/2 are silenced.

PBX1 is a valuable prognostic biomarker for patients with breast cancer

Pre-B-cell leukemia transcription factor (PBX) proteins have important roles in the development of numerous organs. To date, four members of the PBX family have been identified to be involved in human cancer but little is known about their expression patterns and precise functions in breast cancer (BC) progression. The aim of the present study was to determine whether they have the potential to be prognostic biomarkers in patients with BC. The expression patterns of PBXs were evaluated using Oncomine, Cancer Cell Line Encyclopedia and Gene expression-based Outcome for Breast cancer Online algorithm analyses. The prognostic value of PBX1 was determined by Kaplan-Meier plotter analysis. It was observed that, among all PBX family members, only PBX1 was significantly upregulated in BC vs. normal tissues. Meta-analysis in the Oncomine database revealed that PBX1 was significantly upregulated in invasive breast carcinoma stroma, ductal breast carcinoma, invasive lobular breast carcinoma, invasive mixed breast carcinoma and male breast carcinoma compared with normal tissues. In addition, PBX1 was significantly correlated with forkhead box protein A1. Subtype analysis indicated that PBX1 overexpression was associated with luminal-like and hormone receptor-sensitive subtypes. In the survival analysis, a high expression level of PBX1 was associated with poor prognosis of patients with estrogen receptor (ER)-positive, luminal A and luminal B subtypes of BC. The results of the present study indicate that PBX1 may serve as a specific biomarker and essential prognostic factor for ER-positive, luminal A and luminal B subtypes of BC.

The effects of environmental stressors on candidate aging associated genes

BACKGROUND

Aging is defined as a biological and physical complex process that is characterized by the increase in susceptibility to diseases and eventually death. Aging may occur at different rates between and within species, especially or (it varies) among the long-lived ones. Here, we ask whether this diversity (e.g. aging phenotype) stems from genetic or environmental factors or as a combination between the two (epigenetics). Epigenetics play a central role in controlling changes in gene expression during aging. DNA methylation is the most abundant epigenetic modification among vertebrates and is essential to mammalian development.

MATERIALS AND METHODS

In this study, we utilized the HELPtag assay to identify five candidate genes that were significantly hyper- or hypo-methylated across four different age groups in mice. The candidate genes were annotated using ensemble and their expression was further tested in vitro using the murine RAW 264.7 cell line to examine the effect of three environmental stressors (UV radiation, Hypoxia and fasting) on their expression. RNA was extracted at different time points followed by cDNA synthesis. Changes in gene expression were evaluated using qRT-PCR.

RESULTS

We show that fasting and UV radiation reduced the viability of RAW264.7 cells. We also found a significant change in three candidate genes' expression levels during fasting (TOP2B, RNF13 and MRPL4). Furthermore, we found a significant change in the four candidate genes' expression levels following UVC treatment (TOP2B, RNF13, PKNOX1 and CREB5) and yet no changes were recorded in hypoxic conditions.

CONCLUSION

Our results suggest that the model we used was a fitting model for the assessment of environmental stressors on candidate gene expression. In addition, we established a cellular response to the environment via changes in gene expression.

The transcriptional regulator MEIS2 sets up the ground state for palatal osteogenesis in mice

Haploinsufficiency of Meis homeobox 2 (MEIS2), encoding a transcriptional regulator, is associated with human cleft palate, and Meis2 inactivation leads to abnormal palate development in mice, implicating MEIS2 functions in palate development. However, its functional mechanisms remain unknown. Here we observed widespread MEIS2 expression in the developing palate in mice. Wnt1Cre -mediated Meis2 inactivation in cranial neural crest cells led to a secondary palate cleft. Importantly, about half of the Wnt1Cre ;Meis2f/f mice exhibited a submucous cleft, providing a model for studying palatal bone formation and patterning. Consistent with complete absence of palatal bones, the results from integrative analyses of MEIS2 by ChIP sequencing, RNA-Seq, and an assay for transposase-accessible chromatin sequencing identified key osteogenic genes regulated directly by MEIS2, indicating that it plays a fundamental role in palatal osteogenesis. De novo motif analysis uncovered that the MEIS2-bound regions are highly enriched in binding motifs for several key osteogenic transcription factors, particularly short stature homeobox 2 (SHOX2). Comparative ChIP sequencing analyses revealed genome-wide co-occupancy of MEIS2 and SHOX2 in addition to their colocalization in the developing palate and physical interaction, suggesting that SHOX2 and MEIS2 functionally interact. However, although SHOX2 was required for proper palatal bone formation and was a direct downstream target of MEIS2, Shox2 overexpression failed to rescue the palatal bone defects in a Meis2-mutant background. These results, together with the fact that Meis2 expression is associated with high osteogenic potential and required for chromatin accessibility of osteogenic genes, support a vital function of MEIS2 in setting up a ground state for palatal osteogenesis.

PBX1 acts as terminal selector for olfactory bulb dopaminergic neurons

Neuronal specification is a protracted process that begins with the commitment of progenitor cells and culminates with the generation of mature neurons. Many transcription factors are continuously expressed during this process but it is presently unclear how these factors modify their targets as cells transition through different stages of specification. In olfactory bulb adult neurogenesis, the transcription factor PBX1 controls neurogenesis in progenitor cells and the survival of migrating neuroblasts. Here, we show that, at later differentiation stages, PBX1 also acts as a terminal selector for the dopaminergic neuron fate. PBX1 is also required for the morphological maturation of dopaminergic neurons and to repress alternative interneuron fates, findings that expand the known repertoire of terminal-selector actions. Finally, we reveal that the temporal diversification of PBX1 functions in neuronal specification is achieved, at least in part, through the dynamic regulation of alternative splicing. In Caenorhabditis elegans, PBX/CEH-20 also acts as a dopaminergic neuron terminal selector, which suggests an ancient role for PBX factors in the regulation of terminal differentiation of dopaminergic neurons.

HOX genes function in Breast Cancer development

Breast cancer develops in the mammary glands during mammalian adulthood and is considered the second most common type of human carcinoma and the most incident and mortal in the female population. In contrast to other human structures, the female mammary glands continue to develop after birth, undergoing various modifications during pregnancy, lactation and involution under the regulation of hormones and transcription factors, including those encoded by the HOX clusters (A, B, C, and D). Interestingly, HOX gene deregulation is often associated to breast cancer development. Within the HOXB cluster, 8 out of the 10 genes present altered expression levels in breast cancer with an impact in its aggressiveness and resistance to hormone therapy, which highlights the importance of HOXB genes as potential therapeutic targets used to overcome the limitations of tamoxifen-resistant cancer treatments. Here, we review the current state of knowledge on the role of HOX genes in breast cancer, specially focus on HOXB, discussing the causes and consequences of HOXB gene deregulation and their relevance as prognostic factors and therapeutic targets.

Inherited Eye Diseases with Retinal Manifestations through the Eyes of Homeobox Genes

Retinal development is under the coordinated control of overlapping networks of signaling pathways and transcription factors. The paper was conceived as a review of the data and ideas that have been formed to date on homeobox genes mutations that lead to the disruption of eye organogenesis and result in inherited eye/retinal diseases. Many of these diseases are part of the same clinical spectrum and have high genetic heterogeneity with already identified associated genes. We summarize the known key regulators of eye development, with a focus on the homeobox genes associated with monogenic eye diseases showing retinal manifestations. Recent advances in the field of genetics and high-throughput next-generation sequencing technologies, including single-cell transcriptome analysis have allowed for deepening of knowledge of the genetic basis of inherited retinal diseases (IRDs), as well as improve their diagnostics. We highlight some promising avenues of research involving molecular-genetic and cell-technology approaches that can be effective for IRDs therapy. The most promising neuroprotective strategies are aimed at mobilizing the endogenous cellular reserve of the retina.

PBX3 in Cancer

PBX3 is a homeodomain-containing transcription factor of the pre-B cell leukemia (PBX) family, members of which have extensive roles in early development and some adult processes. A number of features distinguish PBX3 from other PBX proteins, including the ability to form specific and stable interactions with DNA in the absence of cofactors. PBX3 has frequently been reported as having a role in the development and maintenance of a malignant phenotype, and high levels of PBX3 tumor expression have been linked to shorter overall survival in cancer. In this review we consider the similarities and differences in the function of PBX3 in different cancer types and draw together the core signaling pathways involved to help provide a better insight into its potential as a therapeutic target.

Recapitulating developmental mechanisms for retinal regeneration

Degeneration of specific retinal neurons in diseases like glaucoma, age-related macular degeneration, and retinitis pigmentosa is the leading cause of irreversible blindness. Currently, there is no therapy to modify the disease-associated degenerative changes. With the advancement in our knowledge about the mechanisms that regulate the development of the vertebrate retina, the approach to treat blinding diseases through regenerative medicine appears a near possibility. Recapitulation of developmental mechanisms is critical for reproducibly generating cells in either 2D or 3D culture of pluripotent stem cells for retinal repair and disease modeling. It is the key for unlocking the neurogenic potential of Müller glia in the adult retina for therapeutic regeneration. Here, we examine the current status and potential of the regenerative medicine approach for the retina in the backdrop of developmental mechanisms.

CEH-60/PBX regulates vitellogenesis and cuticle permeability through intestinal interaction with UNC-62/MEIS in Caenorhabditis elegans

The onset of sexual maturity involves dramatic changes in physiology and gene expression in many animals. These include abundant yolk protein production in egg-laying species, an energetically costly process under extensive transcriptional control. Here, we used the model organism Caenorhabditis elegans to provide evidence for the spatiotemporally defined interaction of two evolutionarily conserved transcription factors, CEH-60/PBX and UNC-62/MEIS, acting as a gateway to yolk protein production. Via proteomics, bimolecular fluorescence complementation (BiFC), and biochemical and functional readouts, we show that this interaction occurs in the intestine of animals at the onset of sexual maturity and suffices to support the reproductive program. Our electron micrographs and functional assays provide evidence that intestinal PBX/MEIS cooperation drives another process that depends on lipid mobilization: the formation of an impermeable epicuticle. Without this lipid-rich protective layer, mutant animals are hypersensitive to exogenous oxidative stress and are poor partners for mating. Dedicated communication between the hypodermis and intestine in C. elegans likely supports these physiological outcomes, and we propose a fundamental role for the conserved PBX/MEIS interaction in multicellular signaling networks that rely on lipid homeostasis.

MEIS2C and MEIS2D promote tumor progression via Wnt/β-catenin and hippo/YAP signaling in hepatocellular carcinoma

Background

MEIS2 has been identified as one of the key transcription factors in the gene regulatory network in the development and pathogenesis of human cancers. Our study aims to identify the regulatory mechanisms of MEIS2 in hepatocellular carcinoma (HCC), which could be targeted to develop new therapeutic strategies.

Methods

The variation of MEIS2 levels were assayed in a cohort of HCC patients. The proliferation, clone-formation, migration, and invasion abilities of HCC cells were measured to analyze the effects of MEIS2C and MEIS2D (MEIS2C/D) knockdown with small hairpin RNAs in vitro and in vivo. Chromatin immunoprecipitation (ChIP) was performed to identify MEIS2 binding site. Immunoprecipitation and immunofluorescence assays were employed to detect proteins regulated by MEIS2.

Results

The expression of MEIS2C/D was increased in the HCC specimens when compared with the adjacent noncancerous liver (ANL) tissues. Moreover, MEIS2C/D expression negatively correlated with the prognosis of HCC patients. On the other hand, knockdown of MEIS2C/D could inhibit proliferation and diminish migration and invasion of hepatoma cells in vitro and in vivo. Mechanistically, MESI2C activated Wnt/β-catenin pathway in cooperation with Parafibromin (CDC73), while MEIS2D suppressed Hippo pathway by promoting YAP nuclear translocation via miR-1307-3p/LATS1 axis. Notably, CDC73 could directly either interact with MEIS2C/β-catenin or MEIS2D/YAP complex, depending on its tyrosine-phosphorylation status.

Conclusions

Our studies indicate that MEISC/D promote HCC development via Wnt/β-catenin and Hippo/YAP signaling pathways, highlighting the complex molecular network of MEIS2C/D in HCC pathogenesis. These results suggest that MEISC/D may serve as a potential novel therapeutic target for HCC.

Homeobox gene Meis1 modulates cardiovascular regeneration

Regeneration of cardiomyocytes, endothelial cells and vascular smooth muscle cells (three major lineages of cardiac tissues) following myocardial infarction is the critical step to recover the function of the damaged heart. Myeloid ecotropic viral integration site 1 (Meis1) was first discovered in leukemic mice in 1995 and its biological function has been extensively studied in leukemia, hematopoiesis, the embryonic pattering of body axis, eye development and various genetic diseases, such as restless leg syndrome. It was found that Meis1 is highly associated with Hox genes and their cofactors to exert its regulatory effects on multiple intracellular signaling pathways. Recently with the advent of bioinformatics, biochemical methods and advanced genetic engineering tools, new function of Meis1 has been found to be involved in the cell cycle regulation of cardiomyocytes and endothelial cells. For example, inhibition of Meis1 expression increases the proliferative capacity of neonatal mouse cardiomyocytes, whereas overexpression of Meis1 results in the reduction in the length of cardiomyocyte proliferative window. Interestingly, downregulation of one of the circular RNAs, which acts downstream of Meis1 in the cardiomyocytes, promotes angiogenesis and restores the myocardial blood supply, thus reinforcing better regeneration of the damaged heart. It appears that Meis1 may play double roles in modulating proliferation and regeneration of cardiomyocytes and endothelial cells post-myocardial infarction. In this review, we propose to summarize the major findings of Meis1 in modulating fetal development and adult abnormalities, especially focusing on the recent discoveries of Meis1 in controlling the fate of cardiomyocytes and endothelial cells.

Nuclear localization of Meis1 in dermal papilla promotes hair matrix cell proliferation in the anagen phase of hair cycle

The dermal papilla (DP) is a key mesenchymal compartment of hair follicles that orchestrates mesenchymal-epithelial interaction regulating hair growth cycles. In the present study, we demonstrate that a TALE-family transcription factor, Meis1, is selectively localized in the nucleus of the DP in the anagen phase of the hair cycle. By using an ex vivo organ culture of vibrissae follicles, conditional Meis1 loss causes retardation in hair growth, accompanied by defects in cell proliferation of hair matrix cells. This cell proliferation defect is partly rescued by the addition of culture supernatants derived from Meis1-sufficient but not -deficient DP cells. These findings indicate that nuclear Meis1 in DP activate genes involved in secretion of some unknown factors, which promote proliferation of hair matrix cells in the anagen phase of the hair cycle.