Keratinocyte Sonic Hedgehog Upregulation Drives the Development of Giant Congenital Nevi via Paracrine Endothelin-1 Secretion

How to Better Understand the Influence of Host Genetics on Developing an Effective Immune Response to Thoracic Cancers

Thoracic cancers pose a significant global health burden. Immune checkpoint blockade therapies have improved treatment outcomes, but durable responses remain limited. Understanding how the host immune system interacts with a developing tumor is essential for the rational development of improved treatments for thoracic malignancies. Recent technical advances have improved our understanding of the mutational burden of cancer cells and changes in cancer-specific gene expression, providing a detailed understanding of the complex biology underpinning tumor-host interactions. While there has been much focus on the genetic alterations associated with cancer cells and how they may impact treatment outcomes, how host genetics affects cancer development is also critical and will greatly determine treatment response. Genome-wide association studies (GWAS) have identified genetic variants associated with cancer predisposition. This approach has successfully identified host genetic risk factors associated with common thoracic cancers like lung cancer, but is less effective for rare cancers like malignant mesothelioma. To assess how host genetics impacts rare thoracic cancers, we used the Collaborative Cross (CC); a powerful murine genetic resource designed to maximize genetic diversity and rapidly identify genes associated with any biological trait. We are using the CC in conjunction with our asbestos-induced MexTAg mouse model, to identify host genes associated with mesothelioma development. Once genes that moderate tumor development and progression are known, human homologues can be identified and human datasets interrogated to validate their association with disease outcome. Furthermore, our CC-MexTAg animal model enables in-depth study of the tumor microenvironment, allowing the correlation of immune cell infiltration and gene expression signatures with disease development. This strategy provides a detailed picture of the underlying biological pathways associated with mesothelioma susceptibility and progression; knowledge that is crucial for the rational development of new diagnostic and therapeutic strategies. Here we discuss the influence of host genetics on developing an effective immune response to thoracic cancers. We highlight current knowledge gaps, and with a focus on mesothelioma, describe the development and application of the CC-MexTAg to overcome limitations and illustrate how the knowledge gained from this unique study will inform the rational design of future treatments of mesothelioma.

Editor’s Pick: Systemic Sclerosis: The Role of YAP/TAZ in Disease Pathogenesis

Systemic sclerosis (SSc) is a systemic autoimmune condition of unknown cause. Yes-Associated Protein/Tafazzin (YAP/TAZ) are transcriptional coactivators previously demonstrated to be involved in cellular stretch biology, and form the principal effector molecules of the Hippo signalling pathway. The association between YAP/TAZ and stretch is contingent upon their cytoplasmic localisation (with nuclear translocation, the cell adopts a relaxed state). The author weighs the evidence for a central role for YAP/TAZ signalling in scleroderma spanning the major clinical features of the condition. Several of the features unique to SSc are mediated by cytoplasmic localisation of YAP/TAZ, including the stretch phenotype (through binding to NF-2), arterial lumenal obliteration (through their binding to angiomotin), the promotion of hypergammaglobulinaemia (via feedback to the upstream Hippo signalling molecule Mammalian Ste20-like Kinase 1), and the induction of B-Lymphocyte-Induced Maturation Protein-1 leading to the adoption of Th2 lineage, prominent in SSc. One observes that the induction of the fibrotic phenotype of scleroderma is mediated through GLI1/GLI2 (the effector molecules of the Hedgehog pathway). GLI1/GLI2 are induced to reciprocally enter the nucleus when YAP/TAZ is intracytoplasmic. The latter explains the characteristically increased connective tissue growth factor 2 and endothelin-1 expression. In this article, the author references some examples of the role of YAP/TAZ in the biophysically similar condition nephrogenic systemic fibrosis and suggests a role of YAP/TAZ cytoplasmic sequestration in programmed cell death protein 1-ligand antagonist-induced scleroderma.

Advanced Genetic Approaches in Discovery and Characterization of Genes Involved With Osteoporosis in Mouse and Human

Osteoporosis is a complex condition with contributions from, and interactions between, multiple genetic loci and environmental factors. This review summarizes key advances in the application of genetic approaches for the identification of osteoporosis susceptibility genes. Genome-wide linkage analysis (GWLA) is the classical approach for identification of genes that cause monogenic diseases; however, it has shown limited success for complex diseases like osteoporosis. In contrast, genome-wide association studies (GWAS) have successfully identified over 200 osteoporosis susceptibility loci with genome-wide significance, and have provided most of the candidate genes identified to date. Phenome-wide association studies (PheWAS) apply a phenotype-to-genotype approach which can be used to complement GWAS. PheWAS is capable of characterizing the association between osteoporosis and uncommon and rare genetic variants. Another alternative approach, whole genome sequencing (WGS), will enable the discovery of uncommon and rare genetic variants in osteoporosis. Meta-analysis with increasing statistical power can offer greater confidence in gene searching through the analysis of combined results across genetic studies. Recently, new approaches to gene discovery include animal phenotype based models such as the Collaborative Cross and ENU mutagenesis. Site-directed mutagenesis and genome editing tools such as CRISPR/Cas9, TALENs and ZNFs have been used in functional analysis of candidate genes in vitro and in vivo. These resources are revolutionizing the identification of osteoporosis susceptibility genes through the use of genetically defined inbred mouse libraries, which are screened for bone phenotypes that are then correlated with known genetic variation. Identification of osteoporosis-related susceptibility genes by genetic approaches enables further characterization of gene function in animal models, with the ultimate aim being the identification of novel therapeutic targets for osteoporosis.

Keratinocyte Cytokine Networks Associated with Human Melanocytic Nevus Development

Melanocytes can group together in nevi, commonly thought to form because of intrinsic somatic mutations involving MAPK pathway activation. However, the role of the microenvironment, in particular keratinocytes, in nevogenesis is rarely studied. Melanocytes proliferate during the hair follicle growth phase and in some basal cell carcinomas, allowing us to construct keratinocyte gene expression clusters correlated with melanocyte activation. We asked whether such correlations are evident in the more subtle context of regulation of melanocyte behavior in normal skin. We considered genes which, when mutated in keratinocytes in mice, lead to nevogenesis. Across the human GTEx normal skin database, their expression was correlated with that of keratinocyte cytokines KITLG, HGF, FGF2, EDN1, and melanocyte markers. These cytokines have pleiotropic effects on melanocyte-specific and pigmentation genes and also influence mast cell gene expression. We show five classes of keratinocyte genes that, via germline genetic variation, influence melanocyte activity. These include genes involved in SHH signaling, structural keratins, ribosomal biogenesis, and stem cell governance. In agreement with the finding of KITLG linked to nevogenesis in human genome-wide association studies, we provide evidence that specific keratinocyte cytokines are components of networks that may drive or exacerbate nevus development.

Giant Congenital Melanocytic Nevi: An Update and Emerging Therapies

Giant congenital melanocytic nevi (GCMN) are a rare occurrence. Gain-of-function mutation in the NRAS gene is found to be associated with GCMN, causing abnormal proliferation of embryonic melanoblasts. The two major complications associated with GCMN are malignant melanoma and neurocutaneous melanosis. Treatment of GCMN has conventionally been surgical. However, the role of NRAS inhibitors and inactivation of nevus tissue by high hydrostatic pressure are being explored. We present a case of a 1-day-old neonate born with GCMN, along with a review of the literature.