To determine the mechanism underlying CXCL7 dysregulation, we generated CXCL7 knockout mice as a model for OPLL, and investigated the expression and activities of proteins in the ubiquitin-proteasome system, such as ubiquitin C-terminal hydrolase1 (UCHL1) [14]. Here, PPBP is linked to ossification of the posterior longitudinal ligament of the spine.