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Journal of Lipid Research, Vol. 45, 1500-1509, August 2004
Copyright © 2004 by American Society for Biochemistry and Molecular Biology

Phosphatidylcholine deficiency upregulates enzymes of triacylglycerol metabolism in CHO cells

J. Matías Caviglia^*, I. Nelva T. de Gómez Dumm^*, Rosalind A. Coleman and R. Ariel Igal^1,*

^* Instituto de Investigaciones Bioquímicas de La Plata, Universidad Nacional de La Plata, 1900-La Plata, Argentina
Departments of Nutrition and Pediatrics, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599

¹ To whom correspondence should be addressed. e-mail: aigal{at}atlas.med.unlp.edu.ar

We studied the regulation of triacylglycerol (TAG) metabolism by phosphatidylcholine (PC) in CHO MT58 cells, which are deficient in PC synthesis because of a temperature-sensitive CTP:phosphocholine cytidylyltransferase. At the permissive growth temperature (34°C), these cells contained 49% less TAG and 30% less PC than wild-type CHO K1 cells. Treatment with dipalmitoylphosphatidylcholine normalized both the PC and TAG levels. Despite low TAG levels, the incorporation of [¹⁴C]oleate into TAG was increased in CHO MT58 cells. The in vitro de novo synthesis of TAG and the activity of diacylglycerol acyltransferase were 90% and 34% higher, respectively. Two other key enzyme activities in TAG synthesis, acyl-CoA synthetase and mitochondrial glycerol-3-phosphate acyltransferase (GPAT), increased by 48% and 2-fold, respectively, and mitochondrial GPAT mRNA increased by 4-fold. Additionally, TAG hydrolysis was accelerated in CHO MT58 cells, and in vitro lipolytic activity increased by 68%.

These studies suggest that a homeostatic mechanism increases TAG synthesis and recycling in response to PC deficiency. TAG recycling produces diacylglycerol and fatty acids that can be substrates for de novo PC synthesis and for lysophosphatidylcholine (lysoPC) acylation. In CHO MT58 cells, in which de novo PC synthesis is blocked, lysoPC acylation with fatty acid originating from TAG may represent the main pathway for generating PC.

Abbreviations: ACS, acyl-CoA synthetase; CT, CTP:phosphocholine cytidylyltransferase; DAG, diacylglycerol; DGAT, diacylglycerol O-acyltransferase; DPH, 1,6-diphenyl 1,3,5-hexatriene; DPPC, dipalmitoyl-phosphatidylcholine; GPAT, glycerol-3-phosphate acyltransferase; lysoPC, lysophosphatidylcholine; PC, phosphatidylcholine; TAG, triacylglycerol

Supplementary key words phosphatidylcholine metabolism • triacylglycerol synthesis • lipolysis • diacylglycerol acyltransferase • lipase

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