Inhibition of a Golgi Complex Lysophospholipid Acyltransferase Induces Membrane Tubule Formation and Retrograde Trafficking

Abstract

Recent studies have suggested that formation of Golgi membrane tubules involves the generation of membrane-associated lysophospholipids by a cytoplasmic Ca2+-independent phospholipase A2 (PLA2). Herein, we provide additional support for this idea by showing that inhibition of lysophospholipid reacylation by a novel Golgi-associated lysophosphatidylcholine acyltransferase (LPAT) induces the rapid tubulation of Golgi membranes, leading in their retrograde movement to the endoplasmic reticulum. Inhibition of the Golgi LPAT was achieved by 2,2-dimethyl-N-(2,4,6-trimethoxyphenyl)dodecanamide (CI-976), a previously characterized antagonist of acyl-CoA cholesterol acyltransferase. The effect of CI-976 was similar to that of brefeldin A, except that the coatomer subunit β-COP remained on Golgi-derived membrane tubules. CI-976 also enhanced the cytosol-dependent formation of tubules from Golgi complexes in vitro and increased the levels of lysophosphatidylcholine in Golgi membranes. Moreover, preincubation of cells with PLA2 antagonists inhibited the ability of CI-976 to induce tubules. These results suggest that Golgi membrane tubule formation can result from increasing the content of lysophospholipids in membranes, either by stimulation of a PLA2 or by inhibition of an LPAT. These two opposing enzyme activities may help to coordinately regulate Golgi membrane shape and tubule formation.

Inhibition of Membrane Tubule Formation and Trafficking by Isotetrandrine, an Antagonist of G-protein-regulated Phospholipase A2 Enzymes

“…Previous studies have provided evidence that membrane tubule formation from the Golgi complex and endosomes requires the generation of curve-inducing LPLs by the direct action of a cytoplasmic Ca 2ϩ -independent PLA 2 enzyme on membrane phospholipids (de Figueiredo et al, 1998Polizotto et al, 1999;Drecktrah et al, 2003). Here we provide evidence for a previously unsuspected role for heterotrimeric G-proteins in the regulation of PLA 2 -mediated membrane tubule formation.…”

“…In particular, LPLs on the cytoplasmic surfaces of organelle membranes could contribute to the generation of outward bending, thus initiating tubule formation (Burger, 2000;Huijbregts et al, 2000;Huttner and Schmidt, 2002;Brown et al, 2003). Support for this idea was provided by studies showing that inhibition of LPL reacylation by a Golgi-associated lysophospholipid acyltransferase (LPAT) also leads to increased tubule formation and retrograde trafficking (Drecktrah et al, 2003). These studies suggest that LPATs function to negatively influence membrane tubulation by limiting the accumulation of LPLs.…”

Identification of an Insulin-regulated Lysophospholipase with Homology to Neuropathy Target Esterase

“…Due to their inverted cone shape LysoPLs influence membrane curvature and, consequently, also the formation and fission of vesicles (36,37). It was shown that increasing the ratio of LysoPL/PL in the outer leaflet of a membrane causes an outward curvature that at its most extreme leads to tubule formation (37). Phospholipases A 2, which generate LysoPLs, play critical roles in multiple membrane trafficking events.…”

Membrane lipids and vesicular traffic

“…by coats) may induce large-scale sorting by specifically including the unsaturated lipids in the forming bud. In this way, highly curved retrograde tubules [20] could also release unsaturated lipids from the Golgi. Whether a similar sorting reaction occurs on the cytosolic surface, excluding the cytosolically oriented phosphatidylserine from the retrograde pathway, remains to be determined, as the lipid organization on the cytosolic side of lumenal sphingolipid-cholesterol domains is unknown.…”

“…Lipid transport between ER and Golgi. A bidirectional vesicular transport pathway connects the ER and Golgi, although tubulation is also observed [20]. Cholesterol spontaneously exchanges between membranes.…”