Splice Isoforms of Phosducin-like Protein Control the Expression of Heterotrimeric G Proteins

• Published in: The Journal of biological chemistry Vol. 288; no. 36; pp. 25760 - 25768
• Main Authors: Gao, Xueli, Sinha, Satyabrata, Belcastro, Marycharmain, Woodard, Catherine, Ramamurthy, Visvanathan, Stoilov, Peter, Sokolov, Maxim
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 06.09.2013; American Society for Biochemistry and Molecular Biology
• Subjects: Alternative Splicing - physiology; Animals; Carrier Proteins - genetics; Carrier Proteins - metabolism; Chaperone; Chaperonin; Gene Expression Regulation, Enzymologic - physiology; HEK293 Cells; Heterotrimeric G Proteins; Heterotrimeric GTP-Binding Proteins - biosynthesis; Heterotrimeric GTP-Binding Proteins - genetics; Humans; Mice, Transgenic; Molecular Chaperones; Nerve Tissue Proteins - genetics; Nerve Tissue Proteins - metabolism; Phosducin-like Protein; Photoreceptors; Protein Assembly; Protein Isoforms - genetics; Protein Isoforms - metabolism; Protein Stability; Protein Structure and Folding; Retina; RNA Splicing; Chaperonin; RNA Splicing; Chaperone; Heterotrimeric G Proteins; Photoreceptors; Retina; Protein Assembly; Phosducin-like Protein
• ISSN: 0021-9258; 1083-351X; 1083-351X
• DOI: 10.1074/jbc.M113.486258

Heterotrimeric G proteins play an essential role in cellular signaling; however, the mechanism regulating their synthesis and assembly remains poorly understood. A line of evidence indicates that the posttranslational processing of G protein β subunits begins inside the protein-folding chamber of the chaperonin containing t-complex protein 1. This process is facilitated by the ubiquitously expressed phosducin-like protein (PhLP), which is thought to act as a CCT co-factor. Here we demonstrate that alternative splicing of the PhLP gene gives rise to a transcript encoding a truncated, short protein (PhLPs) that is broadly expressed in human tissues but absent in mice. Seeking to elucidate the function of PhLPs, we expressed this protein in the rod photoreceptors of mice and found that this manipulation caused a dramatic translational and posttranslational suppression of rod heterotrimeric G proteins. The investigation of the underlying mechanism revealed that PhLPs disrupts the folding of Gβ and the assembly of Gβ and Gγ subunits, events normally assisted by PhLP, by forming a stable and apparently inactive tertiary complex with CCT preloaded with nascent Gβ. As a result, the cellular levels of Gβ and Gγ, which depends on Gβ for stability, decline. In addition, PhLPs evokes a profound and rather specific down-regulation of the Gα transcript, leading to a complete disappearance of the protein. This study provides the first evidence of a generic mechanism, whereby the splicing of the PhLP gene could potentially and efficiently regulate the cellular levels of heterotrimeric G proteins. Background: Heterotrimeric G proteins are essential for biological signaling; however, the mechanism of their biosynthesis remains poorly understood. Results: Long and short splice isoforms of phosducin-like protein stimulate and inhibit production of G proteins in the cell. Conclusion: Both G protein α and βγ functional units are subject to the regulation. Significance: We describe a potential mechanism for regulating the cellular levels of G proteins.