Matrix Metalloprotease 1 (Mmp1) promotes cell fate change for epithelial-to-epithelial transition during regeneration after radiation damage in Drosophila

Ionizing radiation (IR) is used to treat cancer, but therapeutic failure occurs when surviving cancer cells change fate and regenerate tumors through acquired stem cell-like properties. While transcriptional mechanisms underlying cell fate plasticity have been characterized, the cellular processes enabling cell movement during tissue regeneration remain unclear. We reported previously that hinge cells of the Drosophila larval wing disc convert to pouch fate and translocate to help regenerate the pouch that suffers from more IR-induced apoptosis. We report here that IR increases the expression of extracellular proteins in the hinge, including secreted proteases and cell adhesion modulators. Functional validation using RNA interference revealed that secreted Matrix Metalloprotease 1 (Mmp1) and the related secreted protease homolog Scarface (Scaf) are required in hinge cells for IR-induced cell fate conversion and translocation. IR, we found, induces Mmp1 and scaf transcripts in hinge cells via cell-autonomous JNK signaling. Overexpression of Mmp1 specifically in the hinge was sufficient to elevate Mmp1 protein levels throughout the disc and induced cell fate change of both hinge and non-hinge cells but only in the context of irradiation. Confocal imaging in a time course demonstrated that cells undergoing fate conversion remain within the epithelial layer with little evidence for delamination or epithelial-mesenchymal transition (EMT). We propose that remodeling of the extracellular environment is a critical mechanism that enables cellular reorganization during tissue regeneration. Mmp enzymes are important for cancer biology because of their role in ECM remodeling, extracellular signaling, and EMT. Our findings demonstrate for the first time that Mmp1 is necessary and sufficient for one epithelial cell type to switch to another epithelial cell type after radiation damage. These results provide a mechanistic basis for radiation therapy-induced cell fate plasticity.