Dual role for guanine nucleotides in stimulus-secretion coupling

Area of Science:

• Cell Biology
• Immunology
• Biochemistry

Background:

• Mast cells and neutrophils are key immune cells involved in inflammatory responses.
• Cellular secretion is a critical process regulated by intracellular signaling pathways.
• Calcium ions (Ca2+) and guanine triphosphate (GTP) are known modulators of cellular functions.

Purpose of the Study:

• To investigate the role of cytosol composition in mast cell and neutrophil secretion.
• To elucidate the signaling pathways triggered by GTP in the stimulus-secretion sequence.
• To differentiate the mechanisms of Ca2+-dependent and Ca2+-independent secretion.

Main Methods:

• Making mast cells and neutrophils permeable to allow manipulation of cytosol.
• Stimulating secretion using elevated intracellular calcium (Ca2+) concentrations.
• Inducing secretion using stable analogs of guanine triphosphate (GTP) in the absence of Ca2+.

Main Results:

• Secretion from both mast cells and neutrophils can be triggered by elevated cytosol Ca2+ (approx. 10-6 M).
• Mast cell secretion and neutrophil beta-glucuronidase release (not lysozyme) are triggered by GTP independently of Ca2+.
• GTP interacts with two intracellular guanine nucleotide regulatory proteins (Np and Ne) in the stimulus-secretion pathway.

Conclusions:

• GTP plays a dual role in the stimulus-secretion pathway, acting on distinct N proteins.
• GTP activates polyphosphoinositide phosphodiesterase via Np, generating inositol phosphates and diacylglycerol.
• GTP directly triggers exocytosis via Ne, independent of Ca2+ and protein kinase C, highlighting a novel signaling mechanism.