Regulation of Extracellular Matrix Gene Expression by Desmosomal Cadherins

Desmosomes are protein complexes crucial for maintaining cell‐cell adhesion and integrity of tissues. These complexes are made up of proteins from three families: transmembranecadherins(Desmoglein and Desmocollin) linkadjacentcellsin the extracellular space, armadilloproteins (Plakophilin and Plakoglobin)stabilizethe intracellular plaque, and the cytolinker Desmoplakin (DP) connects the plaque to the intermediate filament network. Desmosomal proteins have also been shown to coordinate gene expression pathways required for processes such as proliferation, differentiation and cell migration. In particular, several lines of evidence have linked desmosomal proteins to gene expression of extracellular matrix (ECM) proteins. Loss of Plakophilin‐2 or Desmoplakin causes increases in expression of fibronectin and collagen, while in contrast, loss of plakoglobin results in a significant decrease in expression of fibronectin. These data indicate that individual components of the desmosomal complex control ECM gene expression via distinct cellular signaling networks. In our study, we sought to investigate the role of desmosomal cadherins in ECM gene expression, via use of A431 cells lacking either Desmoglein‐2 or Desmocollin‐2, generated via CRISPR‐mediated knock‐out (Dsg2 KO and Dsc2 KO, kindly provided by Dr. Daniel Conway, VCU). Compared to control cells, Dsg2 KO cells demonstrated a dramatic (~10‐fold) increase in expression of Fibronectin (Fn1), and relatively minor changes in expression of Collagen 1 (Col1a1) and Collagen 2 (Col2a1). In contrast, no major changes in expression of Fn1 was observed in Dsc2 KO cells. We show that loss of Dsg2 KO (but not Dsc2 KO) also caused a significant increase in expression of the pro‐fibrotic signaling molecule transforming growth factor beta 2 (Tgfb2), but not Tgfb1 or Tgfb3. Increased expression of Fn1, Col1a1, Col2a1 and Tgfb2 was also observed upon siRNA‐mediated knockdown of Dsg2 in A431 cells, verifying that these changes are not clone‐specific or due to off‐target CRISPR effects. While expression of other desmosomal proteins is unchanged in Dsg2 KO cells (mRNA and protein levels), the integrity of the junctional complex was expectedly perturbed, as observed via a significant increase in Triton‐solubility of Plakophilin‐2, Plakophilin‐3, Plakoglobin and Desmoplakin. Nevertheless, siRNA‐mediated knockdown of these proteins could not rescue Fn1 or Tgfb2 increases in Dsg2 KO cells, indicating that changes are not due to mislocalization of other desmosomal components. Taken together, our study highlights a novel role for Dsg2 in mediating ECM gene expression, adding significant insight into the mechanisms by which desmosomal cadherins control the adhesive behavior of cancer cells. Support or Funding Information NIH INBRE Developmental Research Grant