The Extracellular Matrix Receptor Discoidin Domain Receptor 1 Regulates Collagen Transcription by Translocating to the Nucleus

Significance Statement The receptor discoidin domain receptor 1 (DDR1) is activated by collagen, upregulated in injured kidneys, and contributes to kidney fibrosis, but how DDR1 controls fibrosis is poorly understood. The authors show that upon collagen stimulation, DDR1 translocates to the nucleus. To do this, DDR1 must bind with SEC61B, a component of the Sec61 translocon, as well as with nonmuscle myosin IIA and β -actin. In the nucleus, DDR1 binds to chromatin to increase the transcription of collagen IV, a major collagen upregulated in fibrosis. The study reveals a novel mechanism whereby collagen-activated DDR1 moves to the nucleus to increase the production of profibrotic molecules. Background The discoidin domain receptor 1 (DDR1) is activated by collagens, upregulated in injured and fibrotic kidneys, and contributes to fibrosis by regulating extracellular matrix production, but how DDR1 controls fibrosis is poorly understood. DDR1 is a receptor tyrosine kinase (RTK). RTKs can translocate to the nucleus via a nuclear localization sequence (NLS) present on the receptor itself or a ligand it is bound to. In the nucleus, RTKs regulate gene expression by binding chromatin directly or by interacting with transcription factors. Methods To determine whether DDR1 translocates to the nucleus and whether this event is mediated by collagen-induced DDR1 activation, we generated renal cells expressing wild-type or mutant forms of DDR1 no longer able to bind collagen. Then, we determined the location of the DDR1 upon collagen stimulation. Using both biochemical assays and immunofluorescence, we analyzed the steps involved in DDR1 nuclear translocation. Results We show that although DDR1 and its natural ligand, collagen, lack an NLS, DDR1 is present in the nucleus of injured human and mouse kidney proximal tubules. We show that DDR1 nuclear translocation requires collagen-mediated receptor activation and interaction of DDR1 with SEC61B, a component of the Sec61 translocon, and nonmuscle myosin IIA and β -actin. Once in the nucleus, DDR1 binds to chromatin to increase the transcription of collagen IV, a major collagen upregulated in fibrosis. Conclusions These findings reveal a novel mechanism whereby activated DDR1 translates to the nucleus to regulate synthesis of profibrotic molecules.