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M. Massaro–Giordano, M. Montanari, C.M. Marshall, A. Gambone, C. Cinti, G. Tosi, A. Giordano, M. Macaluso; pRb2/p130 and PAI–2 Interaction in the Cytoplasm and Nucleus of Normal Human Corneal and Conjunctival Cells . Invest. Ophthalmol. Vis. Sci. 2005;46(13):2114.
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Purpose: Under physiological conditions, the expression of the human plasminogen activator inhibitor type–2 (PAI–2) gene is maintained at low to undetectable levels in most cells. The molecular mechanisms regulating the PAI–2 basal levels are unknown. However, we previously showed the PAI–2 and the pRb2/p130 proteins are able to bind in vivo the same fragment of the PAI–2 proximal promoter, and suggested that these proteins could play a role in controlling PAI–2 transcription. Methods: Here we investigate the significance of PAI–2 and pRb2/p130 interactions in normal cornea and conjunctiva cells. We performed immunoprecipitation experiments using nuclear and cytoplasmic fractions from cycling normal cornea and conjunctiva cells. Results: We found that both proteins interact in the nuclear and cytoplasmic fractions of conjunctiva cells, whereas in the cornea cells pRb2/p130 and PAI–2 interact only in the cytoplasm. Conclusions: Our hypothesis is that the pRb2/p130–PAI–2 interaction is controlled by a biochemical balance between pRb2/p130 and PAI–2 proteins. Then, we suggest that the transcription of the PAI–2 gene is controlled by a feedback loop triggered by the PAI–2 concentration in the nucleus. Our goal will be to understand, in a physiological setting, the biochemical and biological significance of the pRb2/p130–PAI–2 interaction, and how they carry out the molecular signals regulating this mechanism.
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