Correlation between secretion and phospholipase D activation in differentiated HL60 cells

Area of Science:

• Cell biology
• Biochemistry
• Immunology

Background:

• Receptor-directed agonists like fMetLeuPhe, C5a, ATP, and UTP trigger phospholipase D (PLD) activation and cellular secretion in differentiated HL60 cells.
• The PLD pathway generates phosphatidic acid (PA), a key signaling molecule implicated in cellular responses.

Purpose of the Study:

• To investigate the role of PLD activation and its product, PA, in agonist-evoked secretion.
• To elucidate the signaling mechanisms underlying secretion triggered by various agonists in HL60 cells.

Main Methods:

• Utilizing differentiated and streptolysin-O-permeabilized HL60 cells.
• Employing ethanol to divert PLD activity from PA production to phosphatidylethanol (PEt) synthesis.
• Stimulating cells with agonists (fMetLeuPhe, C5a, ATP, UTP), GTP[S], and Ca2+ to assess secretion and PLD activation.

Main Results:

• Diverting PA production to PEt significantly inhibited secretion induced by ATP, UTP, fMetLeuPhe, and C5a.
• In permeabilized cells, fMetLeuPhe, GTP[S], and Ca2+ activated PLD and secretion, with activation being reduced when agonists were added after permeabilization.
• The inhibitory effect of ethanol on secretion was observed regardless of the stimulus (Ca2+, fMetLeuPhe, or GTP[S]) in permeabilized cells.

Conclusions:

• PLD activation is crucial for initiating secretion evoked by various agonists.
• The generated PA acts as a second messenger, initiating the secretory process.
• While PA is essential for initiating secretion, it is not directly involved in the exocytosis mechanism itself.