Linking Extracellular Matrix Agrin to the Hippo Pathway in Liver Cancer and Beyond

Abstract

In addition to the structural and scaffolding role, the extracellular matrix (ECM) is emerging as a hub for biomechanical signal transduction that is frequently relayed to intracellular sensors to regulate diverse cellular processes. At a macroscopic scale, matrix rigidity confers long-ranging effects contributing towards tissue fibrosis and cancer. The transcriptional co-activators YAP/TAZ, better known as the converging effectors of the Hippo pathway, are widely recognized for their new role as nuclear mechanosensors during organ homeostasis and cancer. Still, how YAP/TAZ senses these "stiffness cues" from the ECM remains enigmatic. Here, we highlight the recent perspectives on the role of agrin in mechanosignaling from the ECM via antagonizing the Hippo pathway to activate YAP/TAZ in the contexts of cancer, neuromuscular junctions, and cardiac regeneration.

Keywords: Hippo pathway; YAP/TAZ; agrin; cardiac regeneration; extracellular matrix; liver cancer; mechanotransduction; neuromuscular junctions.

Figure 1

Cartoon showing the different forms of Agrin.

Figure 2

Role of agrin in maintaining YAP localization under altered Extracellular matrix ECM and cell geometrical shapes.

Figure 3

Coordinated mechanotransduction network involving agrin and YAP in liver cancer. Elevated agrin levels enhance ECM stiffness and remodeling in the liver by activating YAP. Soluble agrin binds to Lrp4/MuSK and integrins in liver cancer cells and stabilizes focal adhesions by activating Focal adhesion kinase-Integrin linked kinase- p21-Activated kinase (FAK-ILK-PAK1) axis. This activated mechanosignalling pathway inhibits the core Hippo components Merlin and LATS1/2 kinases. Further, agrin mediated mechanosignalling enhances cellular contractility and confer matrix stiffness by “mechano-activating” YAP mediated transcription. Together, agrin and YAP mediate changes in the cellular microenvironment that cumulatively enhance proliferation, migration and liver tumorigenesis.

Figure 4

Agrin stimulates integrin-FAK-ILK-PAK1 mechanosignalling pathway to antagonize the Hippo pathway and activate YAP/TAZ mediated gene transcription.

Figure 5

Survival analysis of HCC patients (TCGA datasets) with high or low level of agrin (AGRN) and glypican 3 (GPC3).

Figure 6

Interactive mapping of Agrin and YAP/TAZ expression profiles across different cancer types. (A) Tumor map patterns of AGRN and YAP1 mRNA expression (generated by UCSC tumor map using the TCGA_TARGET_GTEX dataset). The expression patterns of AGRN and YAP1 mRNA are closely matched in several cancer types (Color coded). The panels on the extreme right indicate the relative expression levels of AGRN, YAP1 and WWTR1 (TAZ) in liver cancer (LIHC). The intensity map of expression is indicated below. (B) Correlation between AGRN and YAP1/WWTR1 mRNA across cancer cell lines (Cancer Cell Encyclopedia-Novartis/Broad Institute dataset). (C) Correlation between agrin and YAP target gene expressions across cancer cell lines.

Figure 7

Concerted agrin and YAP activity in the maintenance of NMJs and promoting cardiac regeneration. (A) Agrin secretion from motor nerve terminal activates Lrp4-MuSK signaling. This potentiates YAP and possibly β-catenin activity in the nucleus of muscle cells, thereby, aggregating Acetylcholine receptors (AchR) and propagating nerve impulse to the muscle cells. (B) Though adult hearts have minimal agrin expression compared to that during neonatal stages, stimulation with recombinant agrin has protective values against myocardial infarction (MI) in adult mice hearts. Mechanistically, agrin binds to and inhibits dystroglycan complex, thereby, shifting YAP into the nucleus to engage cardiomyocyte proliferation and regeneration.