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J.W. Lee, K. Nishiyama, K.G. Shadrach, T. Tamura, J.G. Hollyfield; Nuclear Export of TIP120A in Retinal Pigment Epithelium . Invest. Ophthalmol. Vis. Sci. 2003;44(13):400.
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Purpose: TIP120A is reported to be a nucleus transcription factor, but little has been investigated about TIP120A in retinal pigment epithelium (RPE). We have previously reported the presence of TIP120A in RPE cells, and more recently we have recognized TIP120A in the interphotoreceptor matrix, the extracellular space facing RPE cells. We have also discovered that TIP120A is localized in the cytoplasm as well as in the nucleus in RPE cells, while it is generally localized only in the nucleus of non-RPE cells. In this study, we investigate the capacity of TIP120A to export from the nucleus to the cytoplasm or to shuttle between these compartments Methods: Human donor eye tissue and transformed RPE-type cell lines (RPE-J cells and ARPE-19 cells) were analyzed by RT-PCR for TIP120A mRNA. To determine the biochemical localization of TIP120A, subcelluar fractionation of RPE cells was performed, and then the fractionated cell samples were blotted for TIP120A. Immunohistochemistry for TIP120A was also done on donor ocular tissue containing RPE cells and cultured RPE cells. Results: The mRNA for TIP120A is clearly present in human donor RPE cells as well as transformed RPE cell lines. Western blotting for TIP120A also indicated that TIP120A protein exists in RPE cell lines. Immunohistochemistry data showed that TIP120A is localized not only in the nucleus but also in the cytoplasm in donor RPE cells and RPE culture cell lines. Furthermore, it was shown that the deduced amino acid sequence of TIP120A possesses three potential nuclear export signals. Conclusions: The present data suggests that TIP120A is a nuclear export-type transcription regulating molecule, and that it is exported from the nucleus to the cytoplasm. Such export or shuttling of TIP120A may be a unique feature of RPE cells. Additional studies are planned to determine the mechanism underlying the nuclear export of TIP120A in RPE cells.
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