Fenretinide-induced neuronal differentiation of ARPE-19 human retinal pigment epithelial cells is associated with the differential expression of Hsp70, 14-3-3, pax-6, tubulin beta-III, NSE, and bag-1 proteins.

PURPOSE

We reported earlier that fenretinide can induce neuronal differentiation of ARPE-19 human retinal pigment epithelial cells in culture. The purpose of this study was to investigate the potential involvement of key proteins involved in gene transcription, signal transduction, cell cycle check point, differentiation, neuronal cell survival, and stress response in the neuronal differentiation of ARPE-19 cells by fenretinide.

METHODS

Cells in culture were treated with 1.0 microM fenretinide. Cells were analyzed using antibodies against pax-6, neuronal specific enolase (NSE), tubulin beta-III, 14-3-3, bag-1, and Hsp-70 proteins using immunocytochemistry, western blot and ELISA methodologies.

RESULTS

We found that pax-6 and NSE were both expressed in the control ARPE-19 cells. Fenretinide induced neuronal differentiation of ARPE-19 cells led to a decrease in pax-6 protein and an increase in tubulin beta-III protein expression after 5 days fenretinide treatment. There was a translocation of 14-3-3 from the cytoplasm to the nucleus, and an increase in nuclear expression of bag-1 after treatment. We also found a time-dependent increase in Hsp70 protein expression in ARPE-19 cells treated with fenretinide. D-407, another human retinal pigment epithelial cell line, but not either Y-79 or PC-12 cells, was also able to be induced into neuronal morphologies by fenretinide.

CONCLUSIONS

The fenretinide-induced neuronal differentiation of ARPE-19 cells is associated with an increase in expression of the neuronal specific protein tubulin beta-III, and a decrease in expression of the progenitor cell marker pax-6. Neuronal differentiation of ARPE-19 cells is also associated with nuclear translocation of 14-3-3, a protein involved in signal transduction, cell cycle check point and cell growth, and an increase in expression of bag-1, a protein involved in neuronal cell survival and axon elongation. These results suggest that ARPE-19 cells could be a progenitor cell line that can be differentiated into neuronal cells when treated with factors such as fenretinide.