Pannocytes, a unique type of rhombohedral cells, exist in the CPJ site and express high levels of transcriptional proto-oncogenes c-FOS, c-MYC, and c-JUN and express MMP-1, cathepsin B, and cathepsin L. Such expression may represent the early stage of mesenchymal cell differentiation; however, the role of pannocytes in bone destruction in RA remains to be elucidated (62, 63). The gene discussed is MMP1; the disease is rheumatoid arthritis.