Gorlin syndrome model with active GLI1 expression and higher sensitivity to SMO inhibitor

2 Views

07/14/23

Hajime made his first talk in the laboratory meeting in 2016.

Hajime Ikehara, Akihiro Umezawa 20160623091301

This study was published in Laboratory Investigation 2020 as an open access paper.
https://www.nature.com/articles/s41374-019-0346-2

ABSTRUCT
The hedgehog signaling pathway is a vital factor for embryonic development and stem cell maintenance. Dysregulation of its function results in tumor initiation and progression. The aim of this research was to establish a disease model of hedgehog-related tumorigenesis with Gorlin syndrome-derived induced pluripotent stem cells (GS-iPSCs). Induced neural progenitor cells from GS-iPSCs (GS-NPCs) shows constitutive high GLI1 expression and higher sensitivity to smoothened (SMO) inhibition compared to wild-type induced neural progenitor cells (WT-NPCs). The differentiation process from iPSCs to NPCs may have similarity in gene expression to Hedgehog signal related-carcinogenesis. Therefore, GS-NPCs may be useful for screening compounds to find effective drugs to control Hedgehog signaling activity.

INTRODUCTION
The hedgehog (Hh) signaling pathway plays an important role in embryogenesis and stem cell maintenance. Ectopic Hh signal up-regulation causes tumors such as basal cell carcinoma (BCC) and medulloblastoma. Hh signaling is also related to other malignancies such as breast cancer, pancreatic cancer, lung cancer, and prostate cancer. A lot of medications have been under research to establish treatment and prevention of Hh signaling pathway-related tumors. The Hh signaling pathway can be initiated by three ligands: desert hedgehog (DHH), Indian hedgehog(IHH) or sonic hedgehog (SHH). These proteins bind to the 12-pass transmembrane protein receptor PTCH1. Once ligand binding occurs, the PTCH1 receptor relieves its inhibitory action on smoothened (SMO), a 7-pass transmembrane G-protein-coupled signal transduction molecule, which then activates a signaling cascade resulting in the translocation of Gli transcription factors to the nucleus. In the absence of the ligand, SMO is normally localized in vesicles. When the pathway is activated, SMO localizes to the primary cilium on the cell membrane.

Gorlin syndrome (GS) or nevoid basal cell carcinoma syndrome (NBCCS; OMIM 109400) is a rare autosomal dominantly inherited disorder that is characterized by congenital anomalies and development of tumors such as basal cell carcinoma and medulloblastoma. GS is caused by mutations in the PTCH1 gene and is transmitted as an autosomal dominant trait with complete penetrance and variable expressivity. Haploinsufficiency of PTCH1 results in constitutive activation of the Hh signaling pathway. Multiple genes that influence embryogenesis and pluripotency are oncogenes that drive the development of tumors. Additionally, some mechanisms of tumorigenesis are similar to embryonic development. GS patients frequently develop medulloblastoma at a young age compared to patients with sporadic cases, because mutation of PTCH1 causes dysregulation of the Hh signaling pathway during development of the cerebellum, which can lead to medulloblastoma.

Ptch1+/- mice, an animal model of Gorlin syndrome, develop medulloblastoma in early life stages, and have BCC-like tumors in their skin from UV or radiation exposure. However, there are few reports of tumorigenesis models with human cells. Differences between human and other vertebrate hedgehog signaling pathways might make it difficult to precisely predict effects and side effects of a candidate drug to treat hedgehog pathway-related tumors.

Disease models using human induced pluripotent stem cells (iPSCs) have recently been described as a promising tool for the investigation of disease mechanisms and identification of new drugs. Cell functions with human cells and get organs that cannot be taken from live human body can now be analyzed to investigate the efficacy and safety of potential Hh signaling inhibitors. Vismodegib (CDC-044), inhibitor of SMO, is the first oral medicine that disrupts Hh pathway to be approved by the US Food and Drug Administration for treatment of advanced phase basal cell carcinoma in adults. But because of its many side effects, most of patients do not continue treatment27. Safer and more tolerable drugs are necessary.

In this study, we generated GS-iPSCs with a heterozygous mutation of PTCH1, and induced neural progenitor cells (NPCs) from GS-iPSCs. Neural progenitors from GS-iPSCs expressed GLI1, a downstream target gene of Hh signaling and exhibited sensitivity to Vismodegib, an SMO inhibitor. Induced neural progenitor cells from Gorlin syndrome iPSCs may therefore serve a good precancerous model for Hh related tumors.