Integrin-dependent recruitment of Src to ROS-producing endosomes in osteoarthritic cartilage.

Fibronectin (FN) fragments stimulate catabolic signaling, and, by binding to integrins, they induce chondrocytes to increase the production of matrix metalloproteinases, including MMP-13. In this issue of Science Signaling , Miao et al. reveal that internalization of a FN fragment, but not intact FN, by α5β1 integrin results in the formation of ROS-producing endosomes (redoxosomes) through which chondrocytes detect and respond to damaged matrix by producing more MMP-13.