The Innate Immune Response in Melanoma Phenotype Switching

Holden, Melissa and Unterholzner, Leonie and Mort, Richard (2025) The Innate Immune Response in Melanoma Phenotype Switching. Masters thesis, Biomedical and Life Sciences.

Text (The Innate Immune Response in Melanoma Phenotype Switching)
The_Innate_Immune_Response_in_Melanoma_Phenotype_Switching_2025.pdf - Published Version
Restricted to Repository staff only until 1 October 2030.
Download (3MB)

Abstract

Melanoma is highly heterogenous tumour that is capable of switching between various phenotypes and transcriptional states, allowing them to adapt to varying conditions within the tumour microenvironment (TME). This plasticity is termed phenotype switching and enables melanoma cells to transition along a trajectory from a mesenchymal state, with high invasiveness to a melanocytic state, associated with proliferation. This process is characterised by changes in gene expression levels, most notably microphthalmia-associated transcription factor (MITF). These shifts in phenotypes underpin melanoma’s ability to metastasise, survive in unfavourable conditions and evade therapeutics and immune surveillance. Furthermore, during the epithelial-to-mesenchymal transition (EMT)-like process cells undergo several mechanical and physical stresses, such as rearrangements in the extracellular matrix and cytoskeleton through cell-cell adhesion. Such stresses can lead to genome instability and DNA damage through the formation of reactive oxygen species, triggering activation of innate immune signalling pathways including DNA-sensing, RNA-sensing and inflammasome activation. An important DNA-sensing pathway is the cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway. cGAS detects cytosolic double stranded (ds)DNA, triggering a cascade that produces type-I interferons and pro-inflammatory cytokines for the recruitment of immune cells to the tumour site. Similarly, RNA-sensing pathways, mediated by retinoic acid-inducible gene I (RIG-I) and anti-melanoma differentiation-associated gene 5 (MDA5) detect cytoplasmic RNA, amplifying the immune response such as the production of C-X-C motif ligand 10 (CXCL10). Inflammasome activations are also pivotal within innate immunity. Inflammasomes are multiprotein complexes that can detect various stimuli and promote the cleavage and production of pro-inflammatory cytokines, such as interleukin (IL) IL-1 and IL-18. However, melanoma cells have developed mechanisms to suppress these innate immune pathways, therefore evading immune surveillance and allowing for tumour progression and metastasis. Melanocyte and melanoma development are regulated by a number of transcriptional networks, with Gli-similar (Glis) transcription factors (TF) emerging as regulators in these mechanisms. Glis1, Glis2 and Glis3 are found in the family of Kruppel-like zinc finger proteins and can bind to DNA to modulate the transcription of target genes. From this study, RNA sequencing data suggests KO of Glis genes can differentially regulate immune and developmental pathways by altering genes such as Absent in Melanoma (AIM2), Nfkb2 and Adam12. Furthermore, immunological tests showed significant suppression of cytokine and chemokine production after stimulation by DNA or RNA due to reduced presence of key proteins involved in innate immune pathways, such as STING. Interplay between phenotype switching, Glis TFs and suppression of innate immune signalling emphasises the complexity of melanoma biology. Investigating these processes further could allow for new therapeutic targets, aimed at restoring activation of the innate immune pathways, whilst addressing melanoma’s plasticity.