May 2008
Volume 49, Issue 13
ARVO Annual Meeting Abstract  |   May 2008
Regulation of Transducin Homeostasis by Phosducin in Rod Photoreceptors
Author Affiliations & Notes
  • H. Song
    Biochemistry, WVU Health Sciences Center, Morgantown, West Virginia
  • M. Belcastro
    WVU Eye Institute, Morgantown, West Virginia
  • A. Jivotovskaya
    WVU Eye Institute, Morgantown, West Virginia
  • M. Sokolov
    WVU Eye Institute, Morgantown, West Virginia
  • Footnotes
    Commercial Relationships  H. Song, None; M. Belcastro, None; A. Jivotovskaya, None; M. Sokolov, None.
  • Footnotes
    Support  NIH Grant 5P20 RR15574 COBRE in Neuroscience
Investigative Ophthalmology & Visual Science May 2008, Vol.49, 1675. doi:
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      H. Song, M. Belcastro, A. Jivotovskaya, M. Sokolov; Regulation of Transducin Homeostasis by Phosducin in Rod Photoreceptors. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1675.

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      © ARVO (1962-2015); The Authors (2016-present)

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Purpose: : Homeostasis of heterotrimeric G protein, transducin, is essential for normal function and even survival of rod photoreceptor cells. We previously demonstrated that the deletion of phosducin (Pdc), a major protein partner of free transducin βγ subunits in photoreceptors, caused significant down-regulation of transducin βγ expression. Intriguingly, expression of Pdc itself was reported to be modulated by transducin α subunit. We have explored molecular mechanisms of this mutual co-regulation of Pdc and transducin expression.

Methods: : Expression levels of transducin α, β and γ subunits and Pdc were compared in the retinas of normal, Pdc knockout, and transducin α knockout mice, using quantitative RT-PCR and Western blotting. The rates of protein turnover were determined using metabolic labeling and pulse-chase assay. Similar analyses of transient co-expression of these proteins were conducted in cultured HEK 293 cells.

Results: : We confirmed that the knockout of Pdc reduced protein content of transducin βγ subunits in the retina by up to two fold, while the knockout of transducin α increased protein levels of Pdc by two fold. However no significant differences in the Ct values of transducin β, γ and Pdc were observed, indicating no change in the corresponding mRNA levels due to the Pdc or transducin α gene deletion. In the cell-culture, co-transfection of Pdc and transducin β subunit was required for the overexpression of transducin β, while the overexpression of transducin α appeared to be Pdc-independent. The studies of transducin βγ folding and assembly will be presented.

Conclusions: : Our data provide evidence that Pdc and two functional parts of transducin, α and βγ subunits, co-regulate each other’s protein levels. This regulation occurs on a post-translational, rather than a transcriptional level, and is based on a mutual stabilization of transducin βγ and Pdc. The model describing mechanisms of mutual co-regulation of transducin and Pdc expression will be presented.

Keywords: photoreceptors • protein structure/function • signal transduction 

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