Aberrant expression of photoreceptor-specific calcium-binding protein (recoverin) in cancer cell lines

Cancer-associated retinopathy (CAR) is an ocular manifestation of a paraneo plastic syndrome whereby immunological reactions to retinal am antigens abe rrantly expressed in tumor cells lead to the degeneration of retinal photor eceptor cells. In our previous study (H. Ohguro et al. Invest, Ophthalmol, Vis. Sci., 40: 82-89, 1999), recoverin, a retina-specific calcium-binding p rotein, and heat shock cognate protein 70 (hsc 70) were identified as autoa ntigens recognized by sera from patients with CAR. Therefore, we suggested that autoimmune reactions against both recoverin and hsc 70 might be involv ed in the pathogenesis of CAR. To elucidate the initial step of the molecul ar pathology of CAR, we examined the expression of recoverin and hsc 70 by reverse transcription-PCR and Western blot using cell lines of several kind s of cancers, including lung small cell carcinoma, lung adenocarcinoma, gas tric cancer, pancreatic cancer, breast cancer, uterine cervical cancer, end ometrial cancer, and leukemia. Recoverin was expressed in 21 of the 31 canc er cell lines. The expression levels of hsc 70 were significantly higher in cancer cell lines than in noncancerous cell lines. However, no difference in the expression levels of hsc 70 was observed between recoverin-positive and -negative cell lines. Immunofluorescence labeling by the affinity-purif ied recoverin antibody revealed the immunoreactivity to recoverin as a gran ular pattern within the cancer cells. Long adenocarcinoma A549 cells, which did not express recoverin, exhibited a significant reduction in cell proli feration upon transfection with human recoverin cDNA, Taken together, our p resent data suggest that the retina-specific calcium-binding protein recove rin is expressed in more than 50% of a variety of cancer cells and may play a significant role in the cell proliferation of these tumor cells.