The
protein RPE65 has an important role in
retinoid processing and/or
retinoid transport in the eye.
Retinoids are involved in cell differentiation, embryogenesis and
carcinogenesis. Since the kidney is known as an important site for
retinoid metabolism, the expression of RPE65 in normal kidney and transformed kidney cells has been examined. The RPE65
mRNA was detected in transformed kidney cell lines including the human embryonic kidney cell line HEK293 and the African green monkey kidney cell lines COS-1 and COS-7 by reverse transcription PCR. In contrast, it was not detected in human primary kidney cells or monkey kidney tissues under the same PCR conditions. The RPE65
protein was also identified in COS-7 and HEK293 cells by Western blot analysis using a
monoclonal antibody to RPE65, but not in the primary kidney cells or kidney tissues. The RPE65
cDNA containing the full-length encoding region was amplified from HEK293 and COS-7 cells.
DNA sequencing showed that the RPE65
cDNA from HEK293 cells is identical to the RPE65
cDNA from the human retinal pigment epithelium. The RPE65 from COS-7 cells shares 98 and 99% sequence identity with human RPE65 at the
nucleotide and
amino acid levels, respectively. Moreover, the RPE65
mRNA was detected in three out of four renal
tumor cultures analyzed including
congenital mesoblastic nephroma and
clear cell sarcoma of the kidney. These results demonstrated that transformed kidney cells express this
retinoid processing
protein, suggesting that these transformed cells may have an alternative
retinoid metabolism not present in normal kidney cells.