Phosphatidic acid (PA)-preferring phospholipase A1 regulates mitochondrial dynamics.

Recent studies have suggested that phosphatidic acid (PA), a cone-shaped phospholipid that can generate negative curvature of lipid membranes, participates in mitochondrial fusion. However, precise mechanisms underling the production and consumption of PA on the mitochondrial surface are not fully understood. Phosphatidic acid-preferring phospholipase A1 (PA-PLA1)/DDHD1 is the first identified intracellular phospholipase A1 and preferentially hydrolyzes PA in vitro. Its cellular and physiological functions have not been elucidated. In this study, we show that PA-PLA1 regulates mitochondrial dynamics. PA-PLA1, when ectopically expressed in HeLa cells, induced mitochondrial fragmentation, whereas its depletion caused mitochondrial elongation. The effects of PA-PLA1 on mitochondrial morphology appear to counteract those of MitoPLD, a mitochondrion-localized phospholipase D that produces PA from cardiolipin. Consistent with high levels of expression of PA-PLA1 in testis, PA-PLA1 knock-out mice have a defect in sperm formation. In PA-PLA1-deficient sperm, the mitochondrial structure is disorganized, and an abnormal gap structure exists between the middle and principal pieces. A flagellum is bent at that position, leading to a loss of motility. Our results suggest a possible mechanism of PA regulation of the mitochondrial membrane and demonstrate an in vivo function of PA-PLA1 in the organization of mitochondria during spermiogenesis.

The intracellular phospholipase A1 protein family.

Abstract Phospholipase A1 is an enzyme that hydrolyzes phospholipids, producing 2-acyl-lysophospholipids and fatty acids. The intracellular phospholipase A1 (iPLA1) protein family is a relatively recently discovered lipid-metabolizing enzyme family. Lower eukaryotes, such as yeasts and nematodes, and plants have only one iPLA1 protein, whereas mammals have three iPLA1 family proteins (PA-PLA1/DDHD1/iPLA1α, p125/Sec23IP/iPLA1ß and KIAA0725p/DDHD2/iPLA1γ). Mammalian iPLA1 proteins are localized in different cellular compartments, and two of them, p125 and KIAA0725p, have been implicated in membrane trafficking events. Recent gene targeting studies on several organisms showed that iPLA1 family proteins are involved in various physiological functions, including plant shoot gravitropism, epithelial stem cell differentiation and spermiogenesis. In this review, we describe the features of iPLA1 family proteins and recent progress regarding our understanding of their physiological functions.

p125/Sec23-interacting protein (Sec23ip) is required for spermiogenesis.

p125/Sec23ip is a phospholipase A(1)-like protein that interacts with Sec23, a coat component of COPII vesicles that bud from endoplasmic reticulum exit sites. To understand its physiological function, we produced p125 knockout mice. The p125 knockout mice grew normally, but males were subfertile. Sperm from p125-deficient mice had round heads and lacked the acrosome, an organelle containing the enzymes responsible for fertilization. p125 was found to be expressed at stages I-XII of spermatogenesis, similar to the expression pattern of proteins involved in acrosome biogenesis. These results suggest that p125 plays an important role in spermiogenesis.

Golgi-localized KIAA0725p regulates membrane trafficking from the Golgi apparatus to the plasma membrane in mammalian cells.

Mammals have three members of the intracellular phospholipase A(1) protein family (phosphatidic acid preferring-phospholipase A(1), p125, and KIAA0725p). In this study, we showed that KIAA0725p is localized in the Golgi, and is rapidly cycled between the Golgi and cytosol. Catalytic activity is important for targeting of KIAA0725p to Golgi membranes. RNA interference experiments suggested that KIAA0725p contributes to efficient membrane trafficking from the Golgi apparatus to the plasma membrane, but is not involved in brefeldin A-induced Golgi-to-endoplasmic reticulum retrograde transport.