Unpeaceful roles of mutant PAX proteins in cancer

The Role of the PAX Genes in Renal Cell Carcinoma

Renal cell carcinoma (RCC) is a significant oncological challenge due to its heterogeneous nature and limited treatment options. The PAX developmental gene family encodes nine highly conserved transcription factors that play crucial roles in embryonic development and organogenesis, which have been implicated in the occurrence and development of RCC. This review explores the molecular landscape of RCC, with a specific focus on the role of the PAX gene family in RCC tumorigenesis and disease progression. Of the various RCC subtypes, clear cell renal cell carcinoma (ccRCC) is the most prevalent, characterized by the loss of the von Hippel-Lindau (VHL) tumor suppressor gene. Here, we review the published literature on the expression patterns and functional implications of PAX genes, particularly PAX2 and PAX8, in the three most common RCC subtypes, including ccRCC, papillary RCC (PRCC), and chromophobe RCC (ChRCC). Further, we review the interactions and potential biological mechanisms involving PAX genes and VHL loss in driving the pathogenesis of RCC, including the key signaling pathways mediated by VHL in ccRCC and associated mechanisms implicating PAX. Lastly, concurrent with our update regarding PAX gene research in RCC, we review and comment on the targeting of PAX towards the development of novel RCC therapies.

Identification and function of the Pax gene Bmgsb in the silk gland of Bombyx mori

Paired box (Pax) genes are highly conserved throughout evolution, and the Pax protein is an important transcription factor of embryonic development. The Pax gene Bmgsb is expressed in the silk glands of silkworm, but its biological functions remain unclear. This study aimed to investigate the expression pattern of Bmgsb in the silk gland and explore its functions using RNA interference (RNAi). Here, we identified eight Pax genes in Bombyx mori. Phylogenetic analysis showed that the B. mori Pax genes were highly homologous to the Pax genes in other insects and highly evolutionarily conserved. The tissue expression profile showed that Bmgsb was expressed in the anterior silk gland and anterior part of the middle silk gland (AMSG). RNAi of Bmgsb resulted in defective development of the AMSG, and the larvae were mostly unable to cocoon in the wandering stage. RNA-seq analysis showed that the fibroin genes fib-l, fib-h and p25, cellular heat shock response-related genes and phenol oxidase genes were considerably upregulated upon Bmgsb knockdown. Furthermore, quantitative reverse transcription-PCR results showed that the fibroin genes and ubiquitin proteolytic enzyme-related genes were significantly upregulated in the AMSG after Bmgsb knockdown. This study provides a foundation for future research on the biological functions of B. mori Pax genes. In addition, it demonstrates the important roles of Bmgsb in the transcriptional regulation of fibroin genes and silk gland development.

Divergent transcriptional and transforming properties of PAX3-FOXO1 and PAX7-FOXO1 paralogs

The hallmarks of the alveolar subclass of rhabdomyosarcoma are chromosomal translocations that generate chimeric PAX3-FOXO1 or PAX7-FOXO1 transcription factors. Overexpression of either PAX-FOXO1s results in related cell transformation in animal models. Yet, in patients the two structural genetic aberrations they derived from are associated with distinct pathological manifestations. To assess the mechanisms underlying these differences, we generated isogenic fibroblast lines expressing either PAX-FOXO1 paralog. Mapping of their genomic recruitment using CUT&Tag revealed that the two chimeric proteins have distinct DNA binding preferences. In addition, PAX7-FOXO1 binding results in greater recruitment of the H3K27ac activation mark than PAX3-FOXO1 binding and is accompanied by greater transcriptional activation of neighbouring genes. These effects are associated with a PAX-FOXO1-specific alteration in the expression of genes regulating cell shape and the cell cycle. Consistently, PAX3-FOXO1 accentuates fibroblast cellular traits associated with contractility and surface adhesion and limits entry into S phase. In contrast, PAX7-FOXO1 drives cells to adopt an amoeboid shape, reduces entry into M phase, and causes increased DNA damage. Altogether, our results argue that the diversity of rhabdomyosarcoma manifestation arises, in part, from the divergence between the genomic occupancy and transcriptional activity of PAX3-FOXO1 and PAX7-FOXO1.

Rhabdomyosarcoma is a class of paediatric soft tissue cancers of genetic origin, but for which the causal links between genetic aberrations and tumour development remain to be deciphered. To answer this question, we focused on the products of two chromosomal translocations that generate the chimeric proteins PAX3-FOXO1 and PAX7-FOXO1. They are composed of the DNA-binding domains of the PAX3 or PAX7 proteins and a single portion of the FOXO1 protein. Several clinical parameters distinguish patients expressing PAX3-FOXO1 or PAX7-FOXO1 and we wondered if these differences could emanate from a different mode of action of the two chimeric proteins. Thus, we generated inducible human fibroblast cell lines expressing one or the other protein. We analysed some molecular and cellular characteristics of these cells 48 hours after induction of PAX3-FOXO1 or PAX7-FOXO1. As it was previously known for PAX3-FOXO1, we showed that PAX7-FOXO1 binds genomic DNA on cis-regulatory regions and activates them. Surprisingly, PAX7-FOXO1 only partially shares the DNA binding sites of PAX3-FOXO1 and its activation potential is stronger than that of PAX3-FOXO1. Thus, PAX3-FOXO1 and PAX7-FOXO1 generate partially divergent transcriptomic signatures, which include genes encoding regulators of cell morphology and cell cycle, two key oncogenic processes. In agreement, our data revealed specificities in these two processes that are either PAX3-FOXO1 or PAX7-FOXO1 dependent. Overall our results demonstrate a differential mode of action between the two chimeric proteins that could in turn participate in the heterogeneity of rhabdomyosarcoma manifestation.

Serial Xenotransplantation in NSG Mice Promotes a Hybrid Epithelial/Mesenchymal Gene Expression Signature and Stemness in Rhabdomyosarcoma Cells

Serial xenotransplantation of sorted cancer cells in immunodeficient mice remains the most complex test of cancer stem cell (CSC) phenotype. However, we have demonstrated in various sarcomas that putative CSC surface markers fail to identify CSCs, thereby impeding the isolation of CSCs for subsequent analyses. Here, we utilized serial xenotransplantation of unsorted rhabdomyosarcoma cells in NOD/SCID gamma (NSG) mice as a proof-of-principle platform to investigate the molecular signature of CSCs. Indeed, serial xenotransplantation steadily enriched for rhabdomyosarcoma stem-like cells characterized by enhanced aldehyde dehydrogenase activity and increased colony and sphere formation capacity in vitro. Although the expression of core pluripotency factors (SOX2, OCT4, NANOG) and common CSC markers (CD133, ABCG2, nestin) was maintained over the passages in mice, gene expression profiling revealed gradual changes in several stemness regulators and genes linked with undifferentiated myogenic precursors, e.g., SOX4, PAX3, MIR145, and CDH15. Moreover, we identified the induction of a hybrid epithelial/mesenchymal gene expression signature that was associated with the increase in CSC number. In total, 60 genes related to epithelial or mesenchymal traits were significantly altered upon serial xenotransplantation. In silico survival analysis based on the identified potential stemness-associated genes demonstrated that serial xenotransplantation of unsorted rhabdomyosarcoma cells in NSG mice might be a useful tool for the unbiased enrichment of CSCs and the identification of novel CSC-specific targets. Using this approach, we provide evidence for a recently proposed link between the hybrid epithelial/mesenchymal phenotype and cancer stemness.

Pseudolaric acid B inhibits PAX2 expression through Wnt signaling and induces BAX expression, therefore promoting apoptosis in HeLa cervical cancer cells

Objectives

Pseudolaric acid B (PAB) has been shown to inhibit the growth of various tumor cells, but the molecular details of its function are still unknown. This study investigated the molecular mechanisms by which PAB induces apoptosis in HeLa cells.

Methods

The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays were performed to investigate the effect of PAB treatment in various cervical cancer cell lines. Annexin V/propidium iodide staining combined with flow cytometry and Hoechst 33258 staining were used to assess PAB-induced apoptosis. Additionally, we performed bioinformatics analyses and identified a paired box 2 (PAX2) binding site on the BAX promoter. We then validated the binding using luciferase and chromatin immunoprecipitation assays. Finally, western blotting assays were used to investigate PAB effect on the Wnt signaling and the involved signaling molecules.

Results

PAB promotes apoptosis and downregulates PAX2 expression in HeLa cells in a time- and concentration-dependent manner. PAX2 binds to the promoter of BAX and inhibits its expression; therefore, PAX2 inhibition is associated with increased levels of BAX, which induces apoptosis of HeLa cells via the mitochondrial pathway. Additionally, PAB inhibits classical Wnt signaling.

Conclusion

PAB effectively inhibits Wnt signaling and PAX2 expression, and increases BAX levels, which induce apoptosis in HeLa cells. Therefore, PAB is a promising natural molecule for the treatment of cervical cancer.

PAX7 nucleotide variants and the risk of non-syndromic orofacial clefts in the Polish population

OBJECTIVE

The etiology of non-syndromic cleft lip with or without cleft palate (nsCL/P) is multifactorial, heterogeneous, and still not completely understood. The aim of the present study was to examine the associations between common and rare PAX7 nucleotide variants and the risk of this common congenital anomaly in a Polish population.

SUBJECTS AND METHODS

Eight top nsCL/P-associated PAX7 variants identified in our cleft genome-wide association study (GWAS) were selected for replication analysis in an independent group of patients and controls (n = 247 and n = 445, respectively). In addition, mutation screening of the PAX7 protein-coding region was conducted.

RESULTS

Analysis of the pooled data from the GWAS and replication study confirmed that common PAX7 nucleotide variants are significantly associated with the increased risk of nsCL/P. The strongest individual variant was rs1339062 (c.586 + 15617T > C) with a p-value = 2.47E-05 (OR = 1.4, 95%CI: 1.20-1.64). Sequencing analysis identified a novel synonymous PAX7 substitution (c.87G > A, p.Val29Val) in a single patient with nsCLP. This transition located in the early exonic position was predicted to disrupt potential splice enhancer elements.

CONCLUSION

Our study confirmed that PAX7 is a strong candidate gene for nsCL/P. Nucleotide variants of this gene contribute to the etiology of nsCL/P in the homogenous Polish population.

Loss of Barx1 promotes hepatocellular carcinoma metastasis through up-regulating MGAT5 and MMP9 expression and indicates poor prognosis

Metastasis is the major dominant reason for poor prognosis of hepatocellular carcinoma (HCC) after surgical treatment. However, the molecular mechanism of metastasis has not been well characterzied. Here, we report a novel function of Barx homeobox1 (Barx1) in inhibiting HCC invasion and metastasis. Barx1 expression is significantly decreased in human HCC tissues than in adjacent non-tumorous tissues and normal liver tissues. Low Barx1 expression is correlated with higher tumor-nodule-metastasis stage and indicates poor prognosis. Down-regulation of Barx1 promotes HCC migration, invasion and metastasis, whereas up-regulation of Barx1 inhibits HCC migration, invasion and metastasis. Mannosyl (alpha-1,6-)-glycoprotein beta-1,6-N-acetyl-glucosaminyltransferase 5 (MGAT5) and matrix metallopeptidase 9 (MMP9) are direct target genes of Barx1. Knockdown of Barx1 up-regulates MGAT5 and MMP9 expression in HCC cells with low metastatic capability, whereas over-expression of Barx1 suppresses their expression in HCC cells with high metastatic capability. Knockdown of both MGAT5 and MMP9 significantly decreases the invasion and metastasis abilities induced by Barx1 knockdown. Barx1 expression is negatively correlated with MGAT5 and MMP9 expression in human HCC tissues. Patients with low expression of Barx1 and high expression of MGAT5 or MMP9 are associated with poorer prognosis. Thus, loss of Barx1 represents a prognostic biomarker in human HCC patients.

An Examination of the Role of Transcriptional and Posttranscriptional Regulation in Rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is an aggressive family of soft tissue tumors that most commonly manifests in children. RMS variants express several skeletal muscle markers, suggesting myogenic stem or progenitor cell origin of RMS. In this review, the roles of both recently identified and well-established microRNAs in RMS are discussed and summarized in a succinct, tabulated format. Additionally, the subtypes of RMS are reviewed along with the involvement of basic helix-loop-helix (bHLH) proteins, Pax proteins, and microRNAs in normal and pathologic myogenesis. Finally, the current and potential future treatment options for RMS are outlined.