Overexpression of DDR1 contributes to gastric cancer progression by inhibiting the Hippo pathway

Gastric cancer (GC) is a prevalent and devastating disease with a poor prognosis. The lack of biomarkers for early detection and effective targeted therapeutics for GC patients represents two major challenges. Through isobaric tags for relative and absolute quantitation (iTRAQ) coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS) phosphoproteomic analysis of 14 GC and gastric epithelial cell lines, we discovered the discoidin domain receptor tyrosine kinase 1 (DDR1) as a top potential drug target out of 40 tyrosine kinases detected along with over 1000 phosphoproteins profiled. The DDR1 protein and mRNA levels were upregulated in GC cells concurrent with DDR1 gene amplification. Immunohistochemistry staining of more than 200 clinical samples revealed that DDR1 was overexpressed in approximately 41% and 48% of the intestinal and diffuse types of GC cases, respectively, compared with only 3.5% in normal tissues. Higher DDR1 expression was associated with poor prognosis. In cellular models, DDR1 overexpression led to accelerated proliferation, invasion, and malignant transformation, putatively via inhibition of the Hippo pathway and consequent activation of YAP-TEAD target gene expression. Notably, DDR1-overexpressing GC cells exhibited high vulnerability to selective DDR1 inhibitors. The present study provides preclinical support for the application of DDR1-selective inhibitors in DDR1-overexpressing GC.