Impairment of a distinct cancer-associated fibroblast population limits tumour growth and metastasis

Abstract

Profiling studies have revealed considerable phenotypic heterogeneity in cancer-associated fibroblasts (CAFs) present within the tumour microenvironment, however, functional characterisation of different CAF subsets is hampered by the lack of specific markers defining these populations.Here we show that genetic deletion of the Endo180 (MRC2) receptor, predominantly expressed by a population of matrix-remodelling CAFs, profoundly limits tumour growth and metastasis; effects that can be recapitulated in 3D co-culture assays. This impairment results from a CAFintrinsic contractility defect and reduced CAF viability which, coupled with the lack of phenotype in the normal mouse, demonstrates that upregulated Endo180 expression by a specific, potentially targetable CAF subset is required to generate a supportive tumour microenvironment. Further, characterisation of a tumour subline selected via serial in vivo passage for its ability to overcome these stromal defects provides important insight into how tumour cells adapt to a non-activated stroma in the early stages of metastatic colonisation.There is extensive functional evidence implicating cancer-associated fibroblasts (CAFs) in tumour progression, via their ability to deposit and remodel the extracellular matrix (ECM), to secrete pro-tumourigenic factors and by modulating the immune compartment 1-5 . However, there is also evidence that stromal fibroblasts can play a role in restraining tumour growth, for example by acting as a desmoplastic barrier to tumour cell invasion and by the recruitment of anti-tumour immune cells 6 .Consideration of how to limit the pro-tumourigenic functions of CAFs, whilst retaining their anti-tumourigenic role, has been hampered by a lack of understanding of the heterogeneity of CAFs within solid tumours and the paucity of specific markers to identify and functionally analyse different CAF subpopulations. Progress in addressing these shortcomings has come from a number of studies reporting single cell Page 3 of 47 sequencing of CAFs or analysis of CAF subsets which has revealed the diversity of fibroblast populations and provided important clues as to their origin and functional properties 7-14 .In this study, we explore the functional role of a CAF receptor, Endo180 (also known as uPARAP) encoded by the MRC2 gene. The 180 kDa Endo180 receptor comprises an N-terminal cysteine-rich domain, a fibronectin type II (FNII) domain that has been shown to bind collagens 15-19 , 8 C-type lectin-like domains (CTLDs), of which only CTLD2 displays Ca 2+ -dependent binding of sugars 20 , a single pass transmembrane domain and a cytoplasmic domain that interacts with components of the clathrin-mediated internalisation machinery to drive constitutive recycling between the plasma membrane and intracellular endosomes 21,22 . Although Endo180 is expressed by some sarcomas 23 , glioblastomas 24 and metaplastic breast cancers 25 , in most solid tumours of epithelial origin, expression of Endo180 is predominantly restricted to CAFs with little or no expressio...

Photoimmunotherapy retains its anti-tumor efficacy with increasing stromal content in heterotypic pancreatic cancer spheroids

“…This suggests that the stroma may have both tumorsuppressing and tumor-promoting roles and that by destroying the stroma, critical mechanisms of tumor growth and metastasis are diminished 8,9,58 . Emerging data suggests that the high heterogeneity and plasticity in PCAFs where targeting of specific PCAF sub-populations may provide survival benefits [59][60][61][62] . Moreover, EGFR expression has been reported to increase with the activation of CAFs, making them a viable target for EGFR-specific PIT 63 .…”