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The Journal of Neuroscience, February 6, 2008, 28(6):1444-1451; doi:10.1523/JNEUROSCI.5134-07.2008

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Cellular/Molecular
Role of Protein Phosphatase 2A in Regulating the Visual Signaling in Drosophila

Ning Wang,¹ Hung-Tat Leung,³ William L. Pak,³ Yonatan T. Carl,¹ Brian E. Wadzinski,¹ and Bih-Hwa Shieh^1,2

¹Department of Pharmacology, Center for Molecular Neuroscience, and ²Vision Research Center, Vanderbilt University, Nashville, Tennessee 37232, and ³Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907

Correspondence should be addressed to Dr. Bih-Hwa Shieh, Department of Pharmacology, 402 Robinson Research Building, Vanderbilt University Medical Center, Nashville, TN 37232-6600. Email: bih-hwa.shieh{at}vanderbilt.edu

Drosophila visual signaling, a G-protein-coupled phospholipase Cβ (PLCβ)-mediated mechanism, is regulated by eye-protein kinase C (PKC) that promotes light adaptation and fast deactivation, most likely via phosphorylation of inactivation no afterpotential D (INAD) and TRP (transient receptor potential). To reveal the critical phosphatases that dephosphorylate INAD, we used several biochemical analyses and identified protein phosphatase 2A (PP2A) as a candidate. Importantly, the catalytic subunit of PP2A, microtubule star (MTS), is copurified with INAD, and an elevated phosphorylation of INAD by eye-PKC was observed in three mts heterozygotes. To explore whether PP2A (MTS) regulates dephosphorylation of INAD by counteracting eye-PKC [INAC (inactivation no afterpotential C] in vivo, we performed ERG recordings. We discovered that inaC^P209 was semidominant, because inaC^P209 heterozygotes displayed abnormal light adaptation and slow deactivation. Interestingly, the deactivation defect of inaC^P209 heterozygotes was rescued by the mts^XE2258 heterozygous background. In contrast, mts^XE2258 failed to modify the severe deactivation of norpA^P16, indicating that MTS does not modulate NORPA (no receptor potential A) (PLCβ). Together, our results strongly indicate that dephosphorylation of INAD is catalyzed by PP2A, and a reduction of PP2A can compensate for a partial loss of function in eye-PKC, restoring the fast deactivation kinetics in vivo. We thus propose that the fast deactivation of the visual response is modulated in part by the phosphorylation of INAD.

Key words: PP2A; PKC; deactivation; TRP; INAD; reversible phosphorylation

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Received Oct. 5, 2007; revised Dec. 11, 2007; accepted Dec. 14, 2007.

Correspondence should be addressed to Dr. Bih-Hwa Shieh, Department of Pharmacology, 402 Robinson Research Building, Vanderbilt University Medical Center, Nashville, TN 37232-6600. Email: bih-hwa.shieh{at}vanderbilt.edu

This article has been cited by other articles:

				H. Lu, H.-T. Leung, N. Wang, W. L. Pak, and B.-H. Shieh Role of Ca2+/Calmodulin-dependent Protein Kinase II in Drosophila Photoreceptors J. Biol. Chem., April 24, 2009; 284(17): 11100 - 11109. [Abstract] [Full Text] [PDF]

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