Ca2+ and phorbol ester effect on the mast cell phosphoprotein induced by cromolyn

Area of Science:

• Immunology
• Cell Biology
• Biochemistry

Background:

• Stimulus-secretion coupling in mast cells is a complex process involving multiple phosphoproteins.
• The Fc epsilon RI receptor and other proteins undergo phosphorylation during mast cell activation and secretion.

Purpose of the Study:

• To investigate the specific protein kinase C (PKC) isozyme involved in the phosphorylation of a 78 kDa protein during mast cell secretion.
• To elucidate the role of calcium and PKC in the regulation of 78 kDa protein phosphorylation by disodium cromoglycate (cromolyn).

Main Methods:

• Mast cells were stimulated with compound 48/80 (C48/80) and disodium cromoglycate (cromolyn).
• Phosphorylation of specific protein bands, including a 78 kDa protein, was analyzed.
• Immunoprecipitation identified the 78 kDa protein as moesin. Western blot analysis was used to detect PKC isozymes.

Main Results:

• A 78 kDa protein band, identified as moesin, was phosphorylated as secretion waned after C48/80 stimulation and upon cromolyn treatment.
• Phosphorylation of the 78 kDa protein was insensitive to calcium and typical PKC activators but was inhibited by PKC inhibitors.
• Western blot analysis revealed the presence of PKC zeta, which fits the observed phosphorylation profile, suggesting its involvement.

Conclusions:

• The phosphorylation of moesin (78 kDa) during mast cell secretion is likely mediated by an atypical protein kinase C isozyme, specifically PKC zeta.
• This phosphorylation pathway appears to be independent of extracellular calcium and direct PKC activation, suggesting a unique regulatory mechanism.
• The findings provide new insights into the molecular mechanisms governing mast cell degranulation and the role of specific PKC isozymes.