Oncogenes in rheumatoid arthritis

The evolving knowledge of the actions and interactions of (proto)oncogenes in cancer has deeply influenced the understanding of other nonmalignant diseases. In RA, the longstanding pathohistologic evidence of transformed-appearing synovial cells at the site of bone and cartilage attachment and joint destruction can now be explained in terms of alterations of cell regulation, cell cycle, and apoptotically triggered cell death. The detection of upregulated oncogenes and their gene products at these sites supported the hypothesis of an aberrant synovial cell type invading the joint. Interestingly, there are hints that this transformation of synovial cells may require more than one activated oncogene. A model was introduced by Carson and Ribero in 1993. In this model, a primary stimulus affects the cell and leads to the enhanced transcription of an oncogene (i.e., c-myc). A second stimulus activates other oncogenes and determines if this cell (i.e., a synovial fibroblast) proliferates (marked by the presence of bcl-2 mRNA) or undergoes apoptosis (marked by fas mRNA and Fas expression at the cell surface). This co-upregulation might explain why some investigators could not detect a significant upregulation of oncogenes in cultured synovial fibroblasts devoid of their normal milieu. Based on the results of the specific activity of Fas and perforin and recent data from our laboratory, we have modified Carson's model to include these data. As there exists an established retroviral model in which the tax sequence of the HTLV retrovirus initiates central oncogene transcription similar to those activated in RA, the retroviral particles, which do not resemble any other known retrovirus but are detectable in the synovial fluid, might well be an important stimulus in the pathogenesis of RA. To simplify the puzzling events of oncogene interactions in RA, we have summarized the data and propose that an oncogene network acts as a pathogenic mechanism in the synoviocytes of the rheumatoid joint. Similar to the "cytokine network" regulating the T-cell-dependent pathway, the "oncogene network" is presumably the major T-cell-independent pathway in RA (Fig. 4).