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15-HETE: selective incorporation into inositol phospholipids of MDCK cells
R A Girton1, A A Spector, J A Gordon
1Department of Internal Medicine, University of Iowa College of Medicine, Iowa City 52242.
Abstract:
The interaction of 15-hydroxyeicosatetraenoic acid (15-HETE) and cultured MDCK renal tubular epithelial cells was investigated to determine whether incorporation of this lipoxygenase product will affect polyphosphoinositide formation. MDCK cells were incubated with 1 microM [3H]-15-HETE for 15 to 120 minutes. Maximum uptake occurred between 15 and 30 minutes, and after 60 minutes, 70% of the incorporated 15-HETE was present in the phosphatidylinositol (PI) fraction. Some 15-HETE was also incorporated into phosphatidylinositol-4-monophosphate (PIP) and phosphatidylinositol-4,5-bisphosphate (PIP2). However, even though more 15-HETE than arachidonic acid was incorporated into PI, the fractional amount of 15-HETE present in the polyphosphoinositides was smaller than arachidonic acid. Therefore, although 15-HETE is selectively channeled into PI, conversion of PI species containing 15-HETE to PIP and PIP2 is relatively impaired. This suggests that either PI containing 15-HETE is a less effective substrate for phosphorylation, or PI containing arachidonic acid is a preferred substrate. MDCK cells converted 15-HETE to polar metabolites that were released into the extracellular fluid. This process may constitute a renal tubular mechanism for the clearance of 15-HETE and related lipoxygenase products.
Insights
15-hydroxyeicosatetraenoic acid (15-HETE) is incorporated into kidney cells, primarily phosphatidylinositol (PI). However, its conversion to polyphosphoinositides is impaired, suggesting a clearance mechanism for 15-HETE.
Area of Science:
- Renal Physiology
- Lipid Metabolism
- Cell Biology
Background:
- 15-hydroxyeicosatetraenoic acid (15-HETE) is a lipoxygenase product with potential roles in renal function.
- Polyphosphoinositides (PI, PIP, PIP2) are critical signaling lipids in cellular processes.
- Understanding 15-HETE's interaction with renal cells is key to elucidating its physiological impact.
Purpose of the Study:
- To investigate the incorporation and metabolism of 15-HETE in cultured Madin-Darby canine kidney (MDCK) renal tubular epithelial cells.
- To determine if 15-HETE affects polyphosphoinositide formation and metabolism.
- To explore potential renal mechanisms for 15-HETE clearance.
Main Methods:
- MDCK cells were incubated with radiolabeled [3H]-15-HETE.
- Lipid analysis was performed to quantify 15-HETE incorporation into different phospholipid fractions (PI, PIP, PIP2).
- Metabolites of 15-HETE were analyzed in the extracellular fluid.
Main Results:
- Maximum uptake of 15-HETE occurred within 15-30 minutes.
- 70% of incorporated 15-HETE was found in the phosphatidylinositol (PI) fraction after 60 minutes.
- Despite preferential incorporation into PI, conversion of 15-HETE-containing PI to PIP and PIP2 was impaired compared to arachidonic acid.
Conclusions:
- MDCK cells selectively channel 15-HETE into PI, but its subsequent phosphorylation to PIP and PIP2 is inefficient.
- This suggests that PI containing 15-HETE may be a poor substrate for phosphorylation, or PI with arachidonic acid is preferred.
- MDCK cells metabolize and release 15-HETE, indicating a potential renal clearance pathway for this lipoxygenase product.