Posttranslational Modifications in Conserved Transcription Factors: A Survey of the TALE-Homeodomain Superclass in Human and Mouse

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.

The neuronal transcription factor MEIS2 is a calpain-2 protease target

Tight control over transcription factor activity is necessary for a sensible balance between cellular proliferation and differentiation in the embryo and during tissue homeostasis by adult stem cells, but mechanistic details have remained incomplete. The homeodomain transcription factor MEIS2 is an important regulator of neurogenesis in the ventricular-subventricular zone (V-SVZ) adult stem cell niche in mice. We here identify MEIS2 as direct target of the intracellular protease calpain-2 (composed of the catalytic subunit CAPN2 and the regulatory subunit CAPNS1). Phosphorylation at conserved serine and/or threonine residues, or dimerization with PBX1, reduced the sensitivity of MEIS2 towards cleavage by calpain-2. In the adult V-SVZ, calpain-2 activity is high in stem and progenitor cells, but rapidly declines during neuronal differentiation, which is accompanied by increased stability of MEIS2 full-length protein. In accordance with this, blocking calpain-2 activity in stem and progenitor cells, or overexpression of a cleavage-insensitive form of MEIS2, increased the production of neurons, whereas overexpression of a catalytically active CAPN2 reduced it. Collectively, our results support a key role for calpain-2 in controlling the output of adult V-SVZ neural stem and progenitor cells through cleavage of the neuronal fate determinant MEIS2.

N6 -Methyladenosine mRNA modification regulates transcripts stability associated with cotton fiber elongation

N6 -Methyladenosine (m6 A) is the most abundant methylation modification in eukaryotic mRNA. The discovery of the dynamic and reversible regulatory mechanism of m6 A has greatly promoted the development of m6 A-led epitranscriptomics. However, the characterization of m6 A in cotton fiber is still unknown. Here, we reveal the potential link between m6 A modification and cotton fiber elongation by parallel m6 A-immunoprecipitation-sequencing (m6 A-seq) and RNA-seq analysis of fibers from the short fiber mutants Ligonliness-2 (Li2 ) and wild-type (WT). This study demonstrated a higher level of m6 A in the Li2 mutant, with the enrichment of m6 A modifications in the stop codon, 3'-untranslated region and coding sequence regions than in WT cotton. In the correlation analysis between genes containing differential m6 A modifications and differentially expressed genes, we identified several genes that could potentially regulate fiber elongation, including cytoskeleton, microtubule binding, cell wall and transcription factors (TFs). We further confirmed that the methylation of m6 A affected the mRNA stability of these fiber elongation-related genes including the TF GhMYB44, which showed the highest expression level in the RNA-seq data and m6 A methylation in the m6 A-seq data. Next, the overexpression of GhMYB44 reduces fiber elongation, whereas the silencing of GhMYB44 produces longer fibers. In summary, these results uncover that m6 A methylation regulated the expression of genes related to fiber development by affecting mRNA's stability, ultimately affecting cotton fiber elongation.

Hox function and specificity – A tissue centric view

Since their discovery, the Hox genes, with their incredible power to reprogram the identity of complete body regions, a phenomenon called homeosis, have captured the fascination of many biologists. Recent research has provided new insights into the function of Hox proteins in different germ layers and the mechanisms they employ to control tissue morphogenesis. We focus in this review on the ectoderm and mesoderm to highlight new findings and discuss them with regards to established concepts of Hox target gene regulation. Furthermore, we highlight the molecular mechanisms involved the transcriptional repression of specific groups of Hox target genes, and summarize the role of Hox mediated gene silencing in tissue development. Finally, we reflect on recent findings identifying a large number of tissue-specific Hox interactor partners, which open up new avenues and directions towards a better understanding of Hox function and specificity in different tissues.

PBX4 functions as a potential novel oncopromoter in colorectal cancer: a comprehensive analysis of the PBX gene family

Pre-B-cell leukaemia (PBX) is a transcription factor family (PBX1, PBX2, PBX3 and PBX4) that regulates important cellular functions and has been identified to be involved in human cancers. This study aimed to explore the expression of PBX genes and their clinical significance in colorectal cancer (CRC). We analysed the differential expression of PBX genes in CRC vs. normal tissue, using the Cancer Genome Atlas (TCGA) (https://portal.gdc.cancer.gov/) and ONCOMINE platform (https://www.oncomine.org/). The UALCAN (http://ualcan.path.uab.edu/) interactive OMICS web-server was used to evaluate the epigenetic regulation of PBX genes via their promoter methylation status. We found that only PBX4 was upregulated whereas PBX1 and PBX3 were downregulated (644 tumour vs. 51 normal samples) (P<0.001). The methylation status of PBX4 promoter appeared to be decreased (P=1.4e-07) whereas the methylation status of PBX1 and PBX3 promoters was increased (P=3.8e-04 and P=3.2e-07, respectively) in cancer vs. normal samples. To determine the prognostic value of PBXs, we conducted a Kaplan-Meier survival analysis and multivariable COX regression. We observed that high PBX4 expression was associated with increased risk for a worse overall survival (OS) in the TCGA CRC patient cohort (n=639), (HR 1.46, 95% CI 1.14-1.88, P=0.003) adjusted for age, gender, tumour location and metastases. We conducted in vitro gene expression modulation experiments to investigate the impact of PBX4 overexpression in CRC cell (HCT116) growth. Additionally, we evaluated the RNA expression of epithelial-mesenchymal transition (EMT) and angiogenesis markers. In vitro studies showed that PBX4 overexpression increased CRC cell proliferation (P<0.001) and upregulated the expression of EMT markers VIM, CDH1, CDH2, ZEB1, SNAI1 (P<0.05) and angiomarker VEGFA (P<0.0001). Lastly, through the Cistrome data browser (http://dbtoolkit.cistrome.org/) we investigated putative transcriptional regulators and we performed gene set enrichment analysis in Enrichr server (https://maayanlab.cloud/Enrichr/) to identify related biological processes. Nineteen factors were identified to be putative regulators of PBX4 and gene set enrichment analysis showed that biological processes related to cell cycle and cell proliferation were enriched (GO:0051726: CDK8, JUN, JUND, and IRF1, P=0.001). In conclusion, our study identified PBX4 as a potential novel oncopromoter in CRC and its overexpression was found to be associated with increased risk for worse survival rate.