The PNPLA-family phospholipases involved in glycerophospholipid homeostasis of HeLa cells.
Mammalian cells maintain the glycerophospholipid (GPL) compositions of their membranes nearly constant. To achieve this, GPL synthesis and degradation must be coordinated. There is strong evidence that A-type phospholipases (PLAs) are key players in homeostatic degradation of GPLs, but the identities of the PLAs involved have not been established. However, some members of the Patatin-like phospholipase domain-containing proteins (PNPLAs) have been implicated. Accordingly, we knocked down all the PNPLAs significantly expressed in human HeLa cells using RNA interference and then determined whether the turnover of the major glycerophospholipids is affected by using mass spectrometry and metabolic labeling with stable isotope-labeled precursors. Knockdown of PNPLA9, PNPLA6 or PNPLA4 significantly (30-50%) reduced the turnover of phosphatidylcholine, -ethanolamine and -serine. In a notable contrast, turnover of phosphatidylinositol was not significantly affected by the knockdown of any PNPLA. Depletion of PNPLA9 and PNPLA4 also inhibited G0/G1 to S cell cycle progression, which could thus be regulated by GPL turnover. These results strongly suggest that PNPLA9, -6 and -4 play a key role in GPL turnover and homeostasis in human cells. A hypothetical model suggesting how these enzymes could recognize the relative concentration of the different GPLs is proposed.
Faculty of Medicine, Department of Biochemistry and Developmental Biology, University of Helsinki, PL 63, 00014 Helsinki, Finland. Electronic address: martin@lipidsci.com.
Martin
M
Hermansson
Faculty of Medicine, Department of Biochemistry and Developmental Biology, University of Helsinki, PL 63, 00014 Helsinki, Finland.
Satu
S
Hänninen
Faculty of Medicine, Department of Biochemistry and Developmental Biology, University of Helsinki, PL 63, 00014 Helsinki, Finland.
Kati
K
Hokynar
Faculty of Medicine, Department of Biochemistry and Developmental Biology, University of Helsinki, PL 63, 00014 Helsinki, Finland. Electronic address: pentti.somerharju@helsinki.fi.
Pentti
P
Somerharju
D002453:Cell Cycle / Q000235:genetics; D002462:Cell Membrane / Q000201:enzymology / Q000235:genetics; D005786:Gene Expression Regulation; D055785:Gene Knockdown Techniques; D020404:Glycerophospholipids / Q000235:genetics* / Q000378:metabolism; D006367:HeLa Cells; D006706:Homeostasis; D006801:Humans; D008049:Lipase / Q000096:biosynthesis / Q000235:genetics*; D010713:Phosphatidylcholines / Q000096:biosynthesis; D010740:Phospholipases / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D000217:Acyltransferases
D020404:Glycerophospholipids; D008049:Lipase; D010713:Phosphatidylcholines; D010740:Phospholipases; C586915:PNPLA6 protein, human; D000217:Acyltransferases; C091246:PNPLA4 protein, human
Ca(2+)-independent phospholipase A2; Degradation; Lipid metabolism; Phospholipid; Turnover