Cellular responses to excess phospholipid.

Area of Science:

• Cell Biology
• Biochemistry
• Molecular Biology

Background:

• Phosphatidylcholine (PtdCho) is a crucial membrane phospholipid in mammalian cells.
• CDP:phosphocholine cytidylyltransferase (CCT) regulates PtdCho synthesis.
• Cellular PtdCho levels are tightly controlled despite synthesis variations.

Purpose of the Study:

• To investigate the mechanisms cells employ to regulate PtdCho levels when synthesis is artificially increased.
• To identify the degradation pathways for excess PtdCho.
• To understand the role of phospholipase A2 in maintaining phospholipid homeostasis.

Main Methods:

• Enforced expression of CCT to increase PtdCho synthesis.
• Metabolic labeling to track PtdCho turnover.
• Exposure to exogenous lysophospholipids to stimulate phospholipid synthesis.
• Use of bromoenol lactone to inhibit phospholipase A2 activity.
• Synthesis of alkylacyl-PtdCho to block degradation.

Main Results:

• Elevated CCT activity led to increased PtdCho degradation to glycerophosphocholine (GPC), not accumulation.
• GPC was primarily secreted extracellularly.
• Calcium-independent phospholipase A2 was implicated in GPC formation.
• Inhibition of GPC formation by bromoenol lactone and the accumulation of non-degradable alkylacyl-PtdCho resulted in inhibited cell proliferation.
• Excess PtdCho also led to overproduction and exit of glycerophosphoethanolamine (GPE).

Conclusions:

• Mammalian cells actively degrade excess PtdCho to GPC to maintain membrane phospholipid homeostasis.
• Phospholipase A2 plays a critical role in this degradation pathway.
• Disruption of this balance can lead to impaired cell proliferation.