Palladin Mediates Stiffness-Induced Fibroblast Activation in the Tumor Microenvironment

Abstract

Mechanical properties of the tumor microenvironment have emerged as key factors in tumor progression. It has been proposed that increased tissue stiffness can transform stromal fibroblasts into carcinoma-associated fibroblasts. However, it is unclear whether the three to five times increase in stiffness seen in tumor-adjacent stroma is sufficient for fibroblast activation. In this study we developed a three-dimensional (3D) hydrogel model with precisely tunable stiffness and show that a physiologically relevant increase in stiffness is sufficient to lead to fibroblast activation. We found that soluble factors including CC-motif chemokine ligand (CCL) chemokines and fibronectin are necessary for this activation, and the combination of C-C chemokine receptor type 4 (CCR4) chemokine receptors and β1 and β3 integrins are necessary to transduce these chemomechanical signals. We then show that these chemomechanical signals lead to the gene expression changes associated with fibroblast activation via a network of intracellular signaling pathways that include focal adhesion kinase (FAK) and phosphoinositide 3-kinase (PI3K). Finally, we identify the actin-associated protein palladin as a key node in these signaling pathways that result in fibroblast activation.

Stromal dynamic reciprocity in cancer: intricacies of fibroblastic-ECM interactions

“…also affect fibroblastic activation [54], which too depends on actin-generated Rho activity [127]. Thus, stiffness and serum factors contribute to the transition of innate stromal cells into an active (i.e., myofibroblastic) phenotype [106,107,128]. When considering the in vivo tumor microenvironment, the ECM is classically much stiffer than its innate counterpart.…”

“…Typically the ECM is aligned in quantifiable organized type I collagen fiber patterns [14,15,129,130]. It also includes increased ECM cross-linking and fiber density [30,106,131-135]. …”

The MyMOMA domain of MYO19 encodes for distinct Miro‐dependent and Miro‐independent mechanisms of interaction with mitochondrial membranes

“…Palladin is an actin crosslinking protein originally characterized in the stress fibers of fibroblasts and cardiac myocytes (Parast & Otey, 2000). Palladin is a cytosolic Ig domain containing protein with multiple isoforms (Rachlin & Otey, 2006), and has multiple roles in organizing the actin cytoskeleton in many structures and cell types (Goicoechea, Arneman, & Otey, 2008;McLane & Ligon, 2015;Sun et al, 2017). To date little evidence exists for interactions with mitochondria.…”

Expression quantitative trait loci for PI3K/AKT pathway

“…[39] Furthermore, it was identified as a key node in focal adhesion kinase ( FAK ) and PI3K of the PI3K/AKT pathway. [40] Collagens are synthesized for a variety of human tissues by fibroblast which can be activated by FAK and PI3K . [40] This suggests the PALLD might ultimately induce COL4A1 and COL4A2 .…”

“…[40] Collagens are synthesized for a variety of human tissues by fibroblast which can be activated by FAK and PI3K . [40] This suggests the PALLD might ultimately induce COL4A1 and COL4A2 .…”