Deciphering the role of Gremlin1 signalling in colorectal cancer

Abstract

Gremlin1 (GREM1) is a secreted DAN-family cystine-knot glycoprotein that functions as a canonical antagonist of bone morphogenetic proteins (BMPs) and plays critical roles in embryonic development and tissue homeostasis. Dysregulation of GREM1 has been implicated in a range of human diseases, including renal and pulmonary fibrosis, inflammatory disorders, and multiple malignant tumors such as colorectal, lung, and cervical cancers. In colorectal cancer (CRC), GREM1 mRNA expression is markedly elevated and has been associated with the maintenance of intestinal crypt homeostasis. Classically, GREM1 binds extracellular BMP ligands, preventing their engagement with cognate BMP receptors and thereby attenuating BMP-dependent signalling and gene expression. Beyond this canonical function, some evidence suggests that GREM1 may also engage in non-canonical signalling through interactions with cell surface receptor tyrosine kinases. However, the molecular mechanisms underlying these processes remain poorly defined.

In this study, wild-type GREM1 (GREM1WT) and a BMP-binding-deficient mutant (GREM1MUT) were generated to distinguish BMP-dependent from BMP-independent signalling activities. GREM1 was found to be predominantly produced and secreted by intestinal fibroblasts and efficiently internalized by adjacent epithelial cells. Using CRC cell models lacking endogenous GREM1 mRNA expression, we systematically characterized GREM1 internalization, intracellular trafficking, and downstream signalling responses. Exogenous GREM1WT exhibited membrane association and efficient internalization, a process that was markedly enhanced by BMP ligands. In contrast, GREM1MUT displayed a pronounced defect in cellular uptake, indicating that BMP binding is critical for GREM1 internalization and subsequent intracellular trafficking. Biochemical analyses further revealed that recombinant GREM1 exists in both monomeric and dimeric forms, with biological activity closely linked to protein conformation and oligomeric state. Beyond canonical BMP antagonism, GREM1 was also found to mediate non-canonical signalling. Exogenous GREM1 robustly activated MAPK, Akt, and NF-kB signalling cascades in CRC cells in a BMP-independent manner that was nevertheless highly sensitive to extracellular context and recombinant protein integrity.

Collectively, this thesis demonstrates that GREM1 functions through coordinated canonical BMP-dependent and non-canonical BMP-independent mechanisms in CRC. BMP binding, protein conformation, and extracellular context jointly determine GREM1 cellular trafficking and signalling output. These findings extend the role of GREM1 from a simple extracellular BMP antagonist to a multifunctional, context-dependent signalling regulator in CRC, providing important mechanistic insight into GREM1-mediated pathways with potential therapeutic relevance.

Date of Award	Jul 2026
Original language	English
Awarding Institution	Queen's University Belfast
Supervisor	Derek Brazil (Supervisor) & Richard Williams (Supervisor)