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

Abstract

Giant congenital nevi are associated with clinical complications such as neurocutaneous melanosis and melanoma. Virtually nothing is known about why some individuals develop these lesions. We previously identified the sonic hedgehog (Shh) pathway regulator Cdon as a candidate nevus modifier gene. Here we validate this by studying Cdon knockout mice, and go on to establishing the mechanism by which Shh exacerbates nevogenesis. Cdon knockout mice develop blue nevi without the need for somatic melanocyte oncogenic mutation. In a mouse model carrying melanocyte NRAS, we found that strain backgrounds that carry genetic variants that cause increased keratinocyte Shh pathway activity, as measured by Gli1 and Gli2 expression, develop giant congenital nevi. Shh components are also active adjacent to human congenital nevi. Mechanistically, this exacerbation of nevogenesis is driven via the release of the melanocyte mitogen endothelin-1 from keratinocytes. We then suppressed nevus development in mice using Shh and endothelin antagonists. Our work suggests an aspect of nevus development whereby keratinocyte cytokines such as endothelin-1 can exacerbate nevogenesis, and provides potential therapeutic approaches for giant congenital nevi. Furthermore, it highlights the notion that germline genetic variation, in addition to somatic melanocyte mutation, can strongly influence the histopathological features of melanocytic nevi.

Keratinocyte Cytokine Networks Associated with Human Melanocytic Nevus Development

“…Some of these have been shown to influence melanocytes via the increased production of keratinocyte cytokines (Table 1 and Figure 1d). For instance, perturbation of Ptch1 and Smo leads to increased Edn1 secretion in mice, whereas loss of Nfib leads to Edn2 up-regulation (Chang et al, 2013;Chitsazan et al, 2018). Inactivating mutations in ribosomal subunit genes leads to hyperpigmentation (McGowan et al, 2008;Terzian et al, 2011) via increased in Kitl expression and secretion from keratinocytes (Table 1).…”

“…Using a screen tool to detect natural genetic variation that modifies the density and histopathology of melanocytic nevi developing in a melanoma-prone mouse model, we found that nevus development was exacerbated in a cellextrinsic manner by keratinocytes. It involves up-regulation of Shh signaling and its downstream targets such as Gli transcription factors in keratinocytes and their subsequent secretion of the melanocyte mitogen Edn1 (Chitsazan et al, 2016(Chitsazan et al, , 2018. It is well known that nevi mostly carry cell intrinsic oncogenic mutations (e.g., BRAF, NRAS, GNAQ) that stimulate the MAPK pathway, but little is known about germline factors playing a role in nevus growth.…”

Giant Congenital Melanocytic Nevi: An Update and Emerging Therapies

“…These mutations affect the microtubule-associated protein kinase (MAPK) signal transduction pathway, leading to abnormal proliferation of embryonic melanoblasts [ 1 ]. Recent evidence suggests that Cdon, a regulator acting via the sonic hedgehog pathway, exacerbates the development of CMN in the context of an NRAS mutation by causing excessive release of endothelin-1 [ 5 ].…”

“…However, clinical studies to substantiate this claim are yet to be conducted. Use of endothelin-1 receptor antagonists has been proposed as a therapeutic approach for GCMN, based on evidence generated from preclinical studies [ 5 ].…”

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

“…Inbred CC mice used in combination with other mouse models (e.g., transgenic) have also been applied, for example, in the identification of a mutation in the Cdon gene that accelerates congenital navus growth (Chitsazan et al, 2016). The function of this gene has now been further investigated using knockout mouse models (Chitsazan et al, 2017). Simulations of the power and precision of genetic mapping with the CC population demonstrated superior performance relative to traditional or alternative strategies (Broman, 2005; Valdar et al, 2006; Ram et al, 2014; Ram and Morahan, 2017).…”