Wedegaertner PB. Characterization of subcellular localization and stability of a splice variant of G alpha i2.
BMC Cell Biol 2002;
3:12. [PMID:
12057015 PMCID:
PMC116600 DOI:
10.1186/1471-2121-3-12]
[Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2002] [Accepted: 05/31/2002] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND
Alternative mRNA splicing of alpha(i2), a heterotrimeric G protein alpha subunit, has been shown to produce an additional protein, termed salpha(i2). In the salpha(i2) splice variant, 35 novel amino acids replace the normal C-terminal 24 amino acids of alpha(i2). Whereas alpha(i2) is found predominantly at cellular plasma membranes, salpha(i2) has been localized to intracellular Golgi membranes, and the unique 35 amino acids of salpha(i2) have been suggested to constitute a specific targeting signal.
RESULTS
This paper proposes and examines an alternative hypothesis: disruption of the normal C-terminus of alpha(i2) produces an unstable protein that fails to localize to plasma membranes. salpha(i2) is poorly expressed upon transfection of cultured cells; however, radiolabeling indicated that alpha(i2) and salpha(i2) undergo myristoylation, a co-translational modification, equally well suggesting that protein stability rather than translation is affected. Indeed, pulse-chase analysis indicates that salpha(i2) is more rapidly degraded compared to alpha(i2). Co-expression of betagamma rescues PM localization and increases expression of salpha(i2). In addition, alpha(i2)A327S, a mutant previously shown to be unstable and defective in guanine-nucleotide binding, and alpha(i2)(1-331), in which the C-terminal 24 amino acids of alpha(i2) are deleted, show a similar pattern of subcellular localization as salpha(i2) (i.e., intracellular membranes rather than plasma membranes). Finally, salpha(i2) displays a propensity to localize to potential aggresome-like structures.
CONCLUSIONS
Thus, instead of the novel C-terminus of salpha(i2) functioning as a specific Golgi targeting signal, the results presented here indicate that the disruption of the normal C-terminus of alpha(i2) causes mislocalization and rapid degradation of salpha(i2).
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