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Cdc42 stimulates RNA splicing via the S6 kinase and a novel S6 kinase target, the nuclear cap-binding complex
K F Wilson1, W J Wu, R A Cerione
1Departments of Molecular Medicine and Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, USA.
Abstract:
Cdc42 is a low molecular weight GTP-binding protein that plays a key regulatory role in a variety of cellular activities. The importance of the coordination of different cell functions by Cdc42 is underscored by the fact that a constitutively active Cdc42 mutant induces cellular transformation. In this study, we describe a novel function for Cdc42: its ability to stimulate pre-messenger RNA splicing. This activity is dependent on cysteine 37 in the effector loop of Cdc42 but is not dependent on cell growth. A likely candidate protein for mediating the Cdc42 effects on pre-mRNA splicing is the nuclear RNA cap-binding complex (CBC), which plays a key role in an early step of cap-dependent RNA splicing. Activation of the CBC by Cdc42 can be inhibited by rapamycin. Additionally, phosphatidylinositol 3-kinase and the Cdc42 effector, pp70 S6 kinase, stimulate the RNA cap-binding activity of the CBC. S6 kinase may directly target the CBC in vivo as it can phosphorylate the 80-kDa subunit of the CBC, CBP80, at residues that are subject to a growth factor-dependent and rapamycin-sensitive phosphorylation in vivo. Together these data suggest the involvement of a Cdc42-S6 kinase pathway in the regulation of RNA splicing, mediated by an increase in capped RNA binding by the CBC, as well as raise the possibility that the effects of Cdc42 on cell growth may be due in part to its regulation of RNA processing.
Insights
The GTP-binding protein Cdc42 regulates RNA splicing by activating the nuclear RNA cap-binding complex (CBC). This Cdc42-S6 kinase pathway influences cell growth through RNA processing.
Area of Science:
- Molecular Biology
- Cellular Biology
- Biochemistry
Background:
- Cdc42 is a GTP-binding protein crucial for cellular functions.
- A constitutively active Cdc42 mutant can induce cellular transformation.
- Cdc42's role in coordinating cell functions is vital.
Purpose of the Study:
- To investigate a novel function of Cdc42 in regulating pre-messenger RNA (pre-mRNA) splicing.
- To identify the molecular mechanisms and protein interactions involved in Cdc42-mediated splicing.
- To explore the link between Cdc42, RNA processing, and cell growth.
Main Methods:
- Assessing Cdc42's effect on pre-mRNA splicing.
- Investigating the role of cysteine 37 in Cdc42's splicing activity.
- Examining the interaction between Cdc42 and the nuclear RNA cap-binding complex (CBC).
- Analyzing the effects of phosphatidylinositol 3-kinase and pp70 S6 kinase on CBC activity.
Main Results:
- Cdc42 stimulates pre-mRNA splicing, dependent on cysteine 37 but not cell growth.
- The nuclear RNA cap-binding complex (CBC) is a likely mediator of Cdc42's splicing activity.
- Cdc42 activation of CBC is rapamycin-sensitive.
- Phosphatidylinositol 3-kinase and S6 kinase activate CBC's RNA cap-binding activity.
- S6 kinase phosphorylates the CBC subunit CBP80 in a growth factor- and rapamycin-sensitive manner.
Conclusions:
- A Cdc42-S6 kinase pathway regulates RNA splicing via enhanced CBC binding to capped RNA.
- Cdc42's influence on cell growth may involve its regulation of RNA processing.
- This study reveals a novel role for Cdc42 in RNA metabolism.