Recoverin and Hsc 70 are found as autoantigens in patients with cancer-associated retinopathy.

PURPOSE To characterize retinal autoantigens in patients with cancer-associated retinopathy (CAR). METHODS The sera of 4 patients with CAR were examined by western blot analysis, and the proteins specifically probed were partially purified from bovine retinas and identified by Edman sequence analysis of the proteolytic peptides. RESULTS Western blot analysis demonstrated that soluble 23-kDa and 65-kDa proteins were probed by the serum of all the patients. The 23-kDa protein assumed an identical position to that of recoverin when the latter, previously identified as an autoantigen of CAR, was probed by its antibody. This strongly suggested that the 23-kDa antigen and recoverin are identical proteins. After partial purification of the 65-kDa protein from bovine retinas, the corresponding band in two-dimensional gel electrophoresis was cut out and subjected to in-gel digestion by endoproteinase Lys C. Edman sequencing of the proteolytic peptides purified on a high-performance liquid chromatography reverse-phase column identified the 65-kDa protein as the heat shock cognate protein 70 (hsc 70), a member of the heat shock protein (hsp) family involved in protein metabolism as chaperons under both stress and nonstress conditions. To estimate the relationship between the autoimmune responses against recoverin and hsc 70, the maximum serum dilutions required to identify recoverin and hsc 70 on western blot analysis were determined and found to be different among the patients. CONCLUSIONS These observations suggest that humoral autoimmune reactions against recoverin and hsc 70 might be involved in the pathogenesis of CAR.