Modulation of human platelet-activating factor receptor gene expression by protein kinase C activation

Area of Science:

• Immunology
• Molecular Biology
• Cell Biology

Background:

• Platelet-activating factor receptor (PAF-R) plays a crucial role in inflammatory responses.
• Understanding the regulation of PAF-R expression is vital for controlling inflammatory processes.

Purpose of the Study:

• To investigate the effects of Phorbol 12-myristate 13-acetate (PMA) on the early and late regulation of PAF-R expression in human monocytes.
• To elucidate the molecular mechanisms underlying PMA-induced PAF-R down-regulation.

Main Methods:

• Treatment of human monocytes with PMA and assessment of [3H]WEB 2086 binding and Scatchard analysis.
• Flow cytometry using anti-PAF-R antibodies to quantify surface receptor expression.
• Analysis of PAF-R mRNA expression levels and stability.
• Inhibition studies using protein kinase C (PKC) inhibitors (H-7, calphostin C) and activation with a diacylglycerol analogue.

Main Results:

• PMA treatment caused a rapid reduction in PAF-R binding sites within minutes, primarily by decreasing the number of receptors.
• Significant down-regulation of surface PAF-R expression was observed after 4 hours, reaching 80-90% by 24 hours.
• PMA rapidly decreased PAF-R mRNA levels, preceding the decline in surface receptor expression.
• PKC inhibition blocked PMA-induced down-regulation, while PKC activation mimicked the effect.
• The decrease in PAF-R mRNA was attributed to reduced mRNA stability, not altered gene transcription.

Conclusions:

• PAF-R gene expression in human leukocytes is regulated by a protein kinase C (PKC)-dependent pathway.
• PMA-induced down-regulation of PAF-R involves post-transcriptional destabilization of its mRNA.
• These findings provide insights into the molecular mechanisms controlling inflammatory mediator receptor expression.