Phospholipase D

Activation of Mi, M3, and M5 mAChRs does not only lead to the generation of IP3 followed by the mobilization of intracellular Ca2+, but also results in the stimulation of phospholipase A2, phospholipase D, and various tyrosine kinases. Similarly, M2 and M4 receptor activation does not only mediate the inhibition of adenylyl cyclase, but also induces other biochemical responses including augmentation of phospholipase A2 activity. Moreover, the stimulation of different mAChR subtypes is also linked to the activation of different classes of mitogen-activated protein kinases (MAP kinases), resulting in specific effects on gene expression and cell growth or differentiation. 

Phosphatidic acid is glycerol esterified at the sn-1 and sn-2 positions to two fatty acids and at the sn-3 position to phosphoric acid. It is a product of phospholipase D action that is also an intermediate in the biosynthesis of phosphatidylseiine and phosphatidylinositol. 

Phospholipase D is widely distributed in bacteria, fungi, plants and animals, and is present in almost all mammalian cells [3]. In mammals, it occurs as alternatively spliced products of two genes (PLD1 andPLD2) (Fig. 3). Most mammalian cells express different levels of both isoforms. Both PLD1 and PLD2 have four conserved sequences (I-IV), and sequences I and IV contain the HXKX4D (HKD) motif that is characteristic of the PLD superfamily, which includes bacterial endonucleases, phospholipid synthases, viral envelope... 

Exton JH (2002) Phospholipase D - structure, regulation and function. Rev Physiol Biochem Pharmacol 144 1-94... 

A subfamily of Rho proteins, the Rnd family of small GTPases, are always GTP-bound and seem to be regulated by expression and localization rather than by nucleotide exchange and hydrolysis. Many Rho GTPase effectors have been identified, including protein and lipid kinases, phospholipase D and numerous adaptor proteins. One of the best characterized effector of RhoA is Rho kinase, which phosphorylates and inactivates myosin phosphatase thereby RhoA causes activation of actomyosin complexes. Rho proteins are preferred targets of bacterial protein toxins ( bacterial toxins). 

Therefore, it is currently believed that anandamide is formed from membrane phospholipids (Fig. 4) through a pathway that involves (1) a trans-acylation of the amino group of phosphatidylethanolamine with arachidonate from the sn-1 position of phosphatidylcholine and (2) a D-type phosphodiesterase activity on the resulting A-arachidonylphosphati-dylethanolamide (NAPE). Synthesis of anandamide is presumably regulated at the levels of both enzymes, the A-acyltranferase and the phospholipase D, by stimuli that raise intracellular calcium or by receptors linked with cAMP and PKA. It has been shown that anandamide is formed when neurons are depolarized and, therefore, the intracellular calcium ion levels are elevated (Cadas, 1996). 

Figure 6 Anandamide metabolism NAPE, N-arachidonylphosphatidyl-ethanol-amides PLD, phospholipase D AEA, anandamide AC, anandamide carrier protein AT, anandamide transporter AEAase, anandamide amidase AA, arachidonic acid.

Martelli AM, Bortul R, Bareggi R, et al. The pro-apoptotic drug camptothecin stimulates phospholipase D activity and diacylglycerol production in the nucleus of HL-60 human promyelocytic leukemia cells. Cancer Res 1999 59 3961-3967. 

Choline-containing phospholipids Phospholipase D Choline oxidase 51... 

Choline-containing phospholipids have been determined in human serum using an IMER consisting of coimmobilized phospholipase D and choline oxidase [51]. Recently, immobilized glutamate oxidase was used to determine L-glutamic acid in culture media [52],... 

Ahn SJ, Yoon MS, Hyuk S, Han W, Yoon YD, Han JS, Noh DY (2003) Phospholipase C-protein kinase C mediated phospholipase D activation pathway is involved in tamoxifen induced apoptosis. J Cell Biochem 89(3) 520-528... 

Eisen SF, Brown HA (2002) Selective estrogen receptor (ER) modulators differentially regulate phospholipase D catalytic activity in ER-negative breast cancer cells. Mol Pharmacol 62(4) 911-920... 

Fiucci G, Czarny M, Lavie Y, Zhao D, Berse B, Blusztajn JK, Liscovitch M (2000) Changes in phospholipase D isoform activity and expression in multidrug-resistant human cancer cells. Int J Cancer 85 882-888... 

Kiss Z (1994) Tamoxifen stimulates phospholipase D activity by an estrogen receptor-independent mechanism. FEBS Lett 355 173-177... 

Uchida N, Okamura S, Kuwano H (1999) Phospholipase D activity in human gastric carcinoma. Anticancer Res 19 671-675... 

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