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Gelsolin modulates phospholipase C activity in vivo through phospholipid binding
1Department of Physiology, University of Texas Southwestern Medical Center at Dallas 75235-9040, USA.
The Journal of Cell Biology
|August 25, 1997
Summary
Gelsolin and CapG proteins regulate cell signaling by competing for phosphatidylinositol 4,5-bisphosphate (PIP2). Overexpression inhibits PLCbeta activity, demonstrating cross-talk in signal transduction.
Area of Science:
- Cell Biology
- Biochemistry
- Signal Transduction
Background:
- Gelsolin and CapG are actin regulatory proteins sensitive to calcium (Ca2+) and PIP2.
- Changes in Ca2+ can alter their affinity for PIP2, impacting cellular signaling.
- These proteins may influence PIP2-dependent pathways by affecting substrate availability.
Purpose of the Study:
- To investigate the competitive interaction of gelsolin and CapG with phospholipase C (PLC) for PIP2.
- To determine the effect of gelsolin and CapG overexpression on PLCbeta and PLCgamma activity in various cellular contexts.
- To elucidate the role of PIP2 availability in regulating signal transduction cascades.
Main Methods:
- Experiments in live cells, semi-intact cells, and in vitro assays.
- Overexpression of gelsolin and CapG in cells.
- Stimulation of PLC activity using bradykinin and NaF.
- Washout and addback experiments with exogenous proteins.
- Analysis of protein-PIP2 competition by varying PIP2 concentrations.
Main Results:
- Overexpression of gelsolin and CapG significantly inhibited bradykinin-stimulated PLCbeta activity, even with direct G protein activation.
- Restoration of bradykinin responsiveness occurred when cytosolic proteins leaked from overexpressing cells.
- Exogenous gelsolin inhibited PLCbeta in a dose-dependent manner in permeabilized cells.
- In vitro, gelsolin and CapG showed both stimulatory and inhibitory effects on PLCbeta, with PIP2-binding domains being crucial for inhibition.
- Increasing PIP2 concentration mitigated inhibition, supporting a competitive mechanism.
- Gelsolin and CapG exhibited biphasic effects on PLCgamma, with less inhibition compared to PLCbeta.
Conclusions:
- Gelsolin and CapG act as competitors for PIP2, modulating PLC activity.
- Cellular cross-talk between PIP2-regulated proteins provides a mechanism for fine-tuning signal transduction.
- These interactions allow for both positive and negative regulation of signaling cascades based on PIP2 levels and availability.