Phorbol ester and vasopressin activate phospholipase D in Leydig cells

Oleate Promotes Triple-Negative Breast Cancer Cell Migration by Enhancing Filopodia Formation through a PLD/Cdc42-Dependent Pathway

Breast cancer, particularly triple-negative breast cancer (TNBC), poses a global health challenge. Emerging evidence has established a positive association between elevated levels of stearoyl-CoA desaturase 1 (SCD1) and its product oleate (OA) with cancer development and metastasis. SCD1/OA leads to alterations in migration speed, direction, and cell morphology in TNBC cells, yet the underlying molecular mechanisms remain elusive. To address this gap, we aim to investigate the impact of OA on remodeling the actin structure in TNBC cell lines, and the underlying signaling. Using TNBC cell lines and bioinformatics tools, we show that OA stimulation induces rapid cell membrane ruffling and enhances filopodia formation. OA treatment triggers the subcellular translocation of Arp2/3 complex and Cdc42. Inhibiting Cdc42, not the Arp2/3 complex, effectively abolishes OA-induced filopodia formation and cell migration. Additionally, our findings suggest that phospholipase D is involved in Cdc42-dependent filopodia formation and cell migration. Lastly, the elevated expression of Cdc42 in breast tumor tissues is associated with a lower survival rate in TNBC patients. Our study outlines a new signaling pathway in the OA-induced migration of TNBC cells, via the promotion of Cdc42-dependent filopodia formation, providing a novel insight for therapeutic strategies in TNBC treatment.

The expression and cellular localization of phospholipase D isozymes in the developing mouse testis

To examine the involvement of phospholipase D (PLD) isozymes in postnatal testis development, the expression of PLD1 and PLD2 was examined in the mouse testis at postnatal weeks 1, 2, 4, and 8 using Western blot analysis and immunohistochemistry. The expression of both PLD1 and PLD2 increased gradually with development from postnatal week 1 to 8. Immunohistochemically, PLD immunoreactivity was detected in some germ cells in the testis and interstitial Leydig cells at postnatal week 1. PLD was mainly detected in the spermatocytes and residual bodies of spermatids in the testis after 8 weeks after birth. The intense immunostaining of PLD in Leydig cells remained unchanged by postnatal week 8. These findings suggest that PLD isozymes are involved in the spermatogenesis of the mouse testis.

Mechanisms of AVP-induced glucagon release in clonal alpha-cells in-R1-G9: involvement of Ca(2+)-dependent and -independent pathways

1. The mechanisms underlying AVP-induced increase in [Ca(2+)](i) and glucagon release in clonal alpha-cells In-R1-G9 were investigated. 2. AVP increased [Ca(2+)](i) and glucagon release in a concentration-dependent manner. After the administration of AVP, glucagon was released within 30 s, quickly reached the maximum within 2 min, and maintained a steady-state concentration for at least 15 min. 3. In Ca(2+)-containing medium, AVP increased [Ca(2+)](i) in a biphasic pattern; a peak followed by a sustained plateau. In Ca(2+)-free medium, the Ca(2+) response to AVP became monophasic with lower amplitude and no plateau. Both the basal and AVP-induced glucagon releases were lower in the absence than in the presence of extracellular Ca(2+). When [Ca(2+)](i) was stringently deprived by BAPTA, a Ca(2+) chelator, AVP still significantly increased glucagon release. 4. Pretreatment with thapsigargin, a microsomal Ca(2+) ATPase inhibitor, abolished both the Ca(2+) peak and sustained plateau. 5.AVP increased intracellular concentration of IP(3). 6. U-73122 (8 microM), a phospholipase C inhibitor, abolished AVP-induced increases in [Ca(2+)](i), but only reduced AVP-induced glucagon release by 39%. 7. Pretreatment with nimodipine, an L-type Ca(2+) channel blocker failed to alter AVP-induced glucagon release or increase in [Ca(2+)](i). 8. The results suggest that AVP causes glucagon release through both Ca(2+)-dependent and -independent pathways. For the Ca(2+)-dependent pathway, the G(q) protein activates phospholipase C, which catalyzes the formation of IP(3). IP(3) induces Ca(2+) release from the endoplasmic reticulum, which, in turn, triggers Ca(2+) influx. Both Ca(2+) release and Ca(2+) influx may contribute to AVP-induced glucagon release.

The subcellular localization of phospholipase D activities in rat Leydig cells

Rat Leydig cells contain a phospholipase D (PLD), which can be activated by vasopressin and phorbol ester. In order to clarify which Leydig cell organelles that express PLD activity, the subcellular localization of two differently regulated PLD activities was investigated by subcellular fractionation on a 40% (v/v) self-generating Percoll gradient. PLD activities in broken cells were estimated using radiolabeled didecanoylphosphatidylcholine as a substrate. Initial experiments revealed the presence of an oleate Mg2+ -activated PLD and a phosphatidylinositol 4,5-bisphosphate-activated PLD (PIP2-PLD) in the microsomal fraction of Leydig cells. The latter activity could be further stimulated by recombinant nonmyristoylated ADP ribosylating factor 1 (ARF1) plus GTPgammaS. The peak of oleate Mg2+ -PLD activity colocalized with the plasma membrane marker, whereas the highest specific activity of the PIP2-PLD activity was found in fractions with a slightly lower density than those containing the plasma membrane and trans-Golgi marker enzymes. In order to localize phorbol ester-stimulated PLD activity in intact Leydig cells, the cells were prelabeled with [14C]-palmitate and then stimulated for 15 min with 100 nM 4-beta-phorbol-12-myristate-13-acetate (PMA) in the presence of ethanol or butanol. The PLD product [14C]-phosphatidylethanol, expressed as the percentage of total labeled phospholipids in the fraction, was slightly increased in all Percoll fractions and showed a prominent peak in the fractions containing plasma membrane, trans-Golgi, and fractions of slightly lower density. The PMA-induced formation of [14C]-phosphatidylbutanol could be inhibited dose-dependently with brefeldin A suggesting that the activation of PLD by the phorbol ester was mediated by ARF.

Arf and RhoA regulate both the cytosolic and the membrane-bound phospholipase D from human placenta

In this paper we demonstrate for the first time that human placenta contains a cytosolic phospholipase D (PLD) activity. This activity had a pH optimum of 7.0 and was stimulated by PIP2 and inhibited by oleate. Furthermore, cytosolic PLD was stimulated by 30 microM GTP gamma S (6-14-fold) and by the small G proteins 1 microM mArf3 (2-fold) and 0.37 nM RhoA (2-fold). This is the first report to show RhoA activation of a cytosolic PLD. The activation by mArf3 was maintained after partial purification on DEAE Sepharose of the enzyme. We have previously reported the existence of a membrane-bound PLD from human placenta, which is stimulated by PIP2, but not by oleate (Vinggaard, A. M. & Hansen, H. S. (1995) Biochim. Biophys. Acta 1258, 169-176). Here we show that oleic acid and alpha-linolenic acid both dose-dependently inhibited solubilized membrane PLD (65% inhibition at 4 mM), whereas stearic acid (4 mM) had no effect. Thus, the presence of double bonds in the fatty acid is important for the inhibitory effect. Furthermore, placental membrane PLD was activated by 30 microM GTP gamma S (4-fold) and by mArf3 (1 microM) and RhoA (0.37 nM) by a factor of 3 and 2, respectively. The solubilized membrane phospholipase D was partially purified to a basal specific activity of 25-37 nmol/min/mg. This preparation was devoid of endogenous RhoA and Arf and could not be stimulated by GTP gamma S. However, mArf3 (1 microM) still activated this partially purified membrane PLD, whereas RhoA (0.37 nM) was not able to activate this PLD fraction. In conclusion, our results suggest that the human placenta contains a PLD that is located both in the cytosol and the membranes, and that is activated by PIP2, mArf3 and RhoA but inhibited by oleate.

ARF-regulated phospholipase D: a potential role in membrane traffic

Phospholipase D activity is stimulated rapidly upon occupation of cell-surface receptors. One of the intracellular regulators of phospholipase D activity has been identified as ADP ribosylation factor (ARF). ARF is a small GTP binding protein whose function has been elucidated in vesicular traffic. This review puts into context the connection between the two fields of signal transduction and vesicular transport.

Characterization and partial purification of phospholipase D from human placenta

We report the existence in the human placenta of a phosphatidylcholine-hydrolyzing phospholipase D (PLD) activity, which has been characterized and partially purified. Triton X-100 effectively solubilized PLD from the particulate fraction of human placenta in a dose-dependent manner. However, Triton X-100 caused decreasing enzyme activities. Maximum transphosphatidylation was obtained with 2% ethanol. The enzyme was found to have a pH optimum of 7.0-7.5 and an apparent Km of 33 mol% (or 0.8 mM). Ca2+ and Mg2+ was not required for the enzyme activity. Addition of phosphatidyl-4,5-bisphosphate, but not phosphatidylethanolamine, to the substrate mixture gave rise to a pronounced dose-dependent increase in PLD activity (EC50 = 0.3 mol%), suggesting a regulatory role of this phospholipid in PLD action. The enzyme was inhibited by sodium oleate when partly or fully substituting for octylglucoside in the substrate mixture. The PLD activity was enriched 15-fold by solubilization and purification on a DEAE-Sepharose column. N-Ethylmaleimide (10 mM) markedly inhibited the purified enzyme, indicating the presence of free thiol groups on PLD. Sphingosine (20 microM) and (+/-) propranolol (53 microM) had no direct effect on PLD activity. The present results form the basis for further purification of a PLD from human tissue.

Effect of prostaglandin E2 on phospholipase D activity in osteoblast-like MC3T3-E1 cells

Recent evidence indicates that phosphatidylcholine breakdown by phospholipase D (PLD) is an important cellular control mechanism. We investigated the signaling pathway participating in prostaglandin E2 (PGE2)-induced PLD activation in osteoblast-like MC3T3-E1 cells. PGE2 stimulated PLD activity, as measured by choline generated from phosphatidylcholine, just after the stimulation. The reaction reached a plateau 15 minutes later. PGE2 stimulated PLD activity in a dose-related manner and also increased inositol phosphate (IP) formation. However, the EC50 value for PGE2-induced IP formation is lower than that for PLD activation. 12-O-Tetradecanoylphorbol-13-acetate (TPA), a protein kinase C (PKC) activator, stimulated PLD activity, and a combination of PGE2 and TPA potentiated it in an additive manner. Although NaF, a heterotrimeric GTP-binding protein activator, significantly stimulated PLD activity, this effect was not augmented by combination with PGE2. PGE2-induced PLD activity was markedly suppressed by either chelating extracellular Ca2+ by EGTA or pertussis toxin. These findings suggest that osteoblasts might have at least two PLD activation mechanisms which involve PKC-dependent or -independent pathways. However, present results indicate that PKC is unlikely to be essential to PGE2-induced PLD activation. On the contrary, pertussis toxin-sensitive GTP-binding protein and extracellular Ca2+ might play important roles in the pathway of PGE2-induced PLD activation.

Activation of human endometrial phospholipase D by bradykinin

Bradykinin may act as a promoter of endometrial regeneration. In [3H]myristate-labelled endometrial stromal cells, bradykinin and tetradecanoylphorbol acetate (TPA) mediated activation of phospholipase D (PLD) as measured by the accumulation of [3H]phosphatidylbutanol ([3H]PtdBut). Kinetics of bradykinin-evoked PLD activation was rapid and transient, whereas the TPA response was relatively slow in onset. Bradykinin induced a dose-dependent (EC50 0.11 nM) [3H]PtdBut accumulation at concentrations at which it stimulated DNA synthesis. In [3H]inositol-labelled cells, bradykinin evoked a rapid increase in inositol phosphates which preceded the increase in [3H]PtdBut formation. Chronic pretreatment with 400 nM TPA abolished PLD activation to subsequent treatment with either TPA and bradykinin. Staurosporine, an inhibitor of protein kinase C, strongly inhibited (IC50 96 nM) TPA-induced [3H]PtdBut formation, but bradykinin-stimulated [3H]PtdBut accumulation was only partially inhibited (IC50 65 microM). The effect of bradykinin and TPA on PLD activity was synergistic, suggesting that the two agents may act via different mechanisms. These results suggest PKC-dependent and independent pathways are involved in bradykinin-induced PLD activation and that the mitogenic activity of this vasoactive peptide on endometrial stromal cells may in part be mediated via the PLD pathway. This may have significance both to implantation and endometrial cancer.

Effects of dexamethasone on steroidogenesis in Leydig cells from rats of different ages

The effects of 0.1 microM dexamethasone on cytochrome P450 content, 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) activity, and basal and LH-induced testosterone production of Leydig cells from rats 3, 5, 7 and 10 weeks old were examined. The cytochrome P450 content of Leydig cells from rats 3 weeks old was increased by treatment with dexamethasone for 22 h, while 3 beta-HSD activity was decreased. The cytochrome P450 content of Leydig cells from rats 5 weeks old was increased after 3 and 22 h of culture, while 3 beta-HSD activity was decreased after 22 and 44 h of treatment. The cytochrome P450 content of rats 7 weeks old was increased after 3 h of culture, while 3 beta-HSD activity was decreased after 22 and 44 h of culture. Leydig cells from rats 10 weeks old showed increased cytochrome P450 content upon dexamethasone treatment after 3 h. The activity of 3 beta-HSD was decreased after 44 h of treatment. In Leydig cells from rats 3 and 5 weeks old, dexamethasone decreased basal testosterone production after 22 h of treatment, but not after 44 h, and did not affect LH-induced testosterone production. Leydig cells from rats 7 weeks old showed decreased basal and LH-induced testosterone production, when treated with dexamethasone for 22 and 44 h. Basal testosterone production was unaffected by dexamethasone in rats 10 weeks old, while LH-induced testosterone production was decreased after 44 h of treatment. The effect of dexamethasone on testosterone secretion changed during development, as a transient, early effect on basal testosterone secretion was observed in Leydig cells from prepubertal and pubertal rats. These data suggest that dexamethasone affects Leydig cells differently, depending on the age of the rat, the older rats being more sensitive than the younger rats.

Localisation of bradykinin-like immunoreactivity and modulation of bradykinin-evoked phospholipase D activity by 17 beta-oestradiol in human endometrium

Bradykinin may act as a promoter of endometrial regeneration. Bradykinin-like immunoreactivity was detected immunocytochemically in the glandular epithelium and stroma of human endometrium. The staining was localized around the stroma and especially in the cells undergoing mitosis. Relatively weak staining was seen in the stromal cells of secretory endometrium, which was predominantly localised around the basal vacuoles of endometrial glands. During the late secretory phase, the intensity of staining was diminished throughout the endometrium: the glandular epithelium showed weak staining and stroma appeared negative. As phosphatidate, the product of phospholipase D pathway, may mediate cell proliferation, the effect of 17 beta-oestradiol on bradykinin-evoked phospholipase D activity assayed as accumulation of [3H]phosphatidylbutanol ([3H]PtdBut) was examined in [3H]myristic acid-labelled primary cultures of human endometrial stromal cells. Bradykinin induced a rapid accumulation of [3H]PtdBut in a time-dependent manner, indicating phospholipase D activation. Pretreatment of stromal cells with 17 beta-oestradiol enhanced the bradykinin-evoked phospholipase D activity. These results suggest that bradykinin-like immunoreactivity is strongly associated with proliferative stromal cells undergoing mitosis, a process that may be mediated by phospholipase D activation as the magnitude of this enzyme's activation in vitro appears to be regulated by 17 beta-oestradiol.

Agents that increase phosphatidic acid inhibit the LH-induced testosterone production

The results of the present study point to phosphatidic acid (PtdOH) as a possible intracellular messenger, which might be involved in local modulation of testicular testosterone production in vivo. Propranolol (27-266 microM) induced an increased level of [3H]PtdOH in isolated rat Leydig cells, prelabeled with [3H]myristate, and at the same time a strong dose-dependent inhibition of the acute testosterone production stimulated by luteinizing hormone (LH). The inhibition was not bypassed by the addition of dibutyryl-cAMP but was overcome, when 22(R)-hydroxycholesterol was added as a direct substrate for cytochrome P-450 side chain cleavage enzyme. Thus, the inhibition appears to be exerted at a point distal to cAMP-generation but before the first enzyme in the testosterone synthetic pathway. Treatment with other agents (4 beta-phorbol 12-myristate 13-acetate (PMA), A23187, and sphingosine) giving rise to increases in the PtdOH-level resulted in the inhibition of the LH-induced testosterone formation as well, thus indicating a connection between the two effects. Furthermore, we were able to demonstrate a highly significant correlation between the PtdOH-increase and the inhibition of the LH-stimulated testosterone production. This may suggest a causal relationship between these two parameters.

Insulin-stimulated hydrolysis of phosphatidylcholine by phospholipase C and phospholipase D in cultured rat hepatocytes

We have investigated the mechanism of action by which insulin increases phosphatidate (PA) and diacylglycerol (DAG) levels in cultured rat hepatocytes. Insulin initially stimulated phosphatidylcholine-dependent phospholipase D (PC-PLD) with a significant increase in both PA and intracellular as well as extracellular choline. The involvement of phospholipase D was confirmed by the formation of PC-derived phosphatidylethanol in the presence of ethanol. The DAG increase appeared to be biphasic. Only the early phase of DAG production was inhibited by propranolol, an inhibitor of the phosphatidate phosphatase (PAP) responsible for the conversion of PA into DAG, suggesting that initially the DAG increase is due to the PLD-PAP pathway. The delayed DAG increase was in parallel with increased intracellular and extracellular phosphocholine and probably derived directly from PC-PLC activity. Experiments performed in the presence of 1 microM phorbol 12-myristate 13-acetate (PMA) indicated that protein kinase C (PKC) mediated the insulin effect on PC-PLC, but not on PC-PLD. These findings were confirmed using the PKC inhibitors calphostin, H7 and staurosporine. The dual activation of these phospholipases with a biphasic elevation of DAG levels and activation of specific PKC isoenzymes could be necessary to elicit both early and delayed effects of insulin.

Phospholipase D: regulation and functional significance

PLD is a major route for hydrolysis of PC in most tissues, consistent with it playing an important role in signal transduction. The enzyme appears to be activated by a variety of different mechanisms in different tissues, suggesting there might be several different isoforms. Little, however, is known at present about its enzymology and molecular biology. There is little direct evidence to indicate the functional significance of PLD activation but an accumulation of indirect evidence links PLD with prolonged changes in cell function. In particular, two areas where there is strong evidence for a role for PLD are mitogenesis and leukocyte hyperresponsiveness. An important area for future work will be the investigation of how products from the PLD pathway exert these effects. Current evidence suggests an important role for Ca(2+)-independent PKC isoforms and probably also for novel cellular targets for the putative second messenger PA.

Regulation by dexamethasone of the 3 beta-hydroxysteroid dehydrogenase activity in adult rat Leydig cells

The effect of long-term in vitro treatment with dexamethasone, insulin and/or LH on the 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) activity and the testosterone level was examined in cultures of Leydig cells from adult rats. A rapid and simple method for measuring the 3 beta-HSD activity has been developed, in which the NADH, generated by 3 beta-HSD, reduced nitroblue tetrazolium to a product with absorption maximum at 560 nm. Km for the reaction was 8.1 microM and Vmax was 12.7 nmol/min x mg protein. Addition of 0.1 or 1 microM dexamethasone for 44 h decreased the 3 beta-HSD activity to 83% and the basal testosterone level to 64% of control value after 22 and 44 h of culture. Addition of 1 nM insulin inhibited the 3 beta-HSD activity to 90% after 44 h of culture, whereas the testosterone level was increased after 3 h. Addition of 0.1 ng/ml LH did not affect the 3 beta-HSD activity in Leydig cells from adult rats. Concomitant treatment of the cells with dexamethasone and insulin inhibited the 3 beta-HSD activity to 74%, indicating an additive effect, whereas no additive effect on the testosterone level was observed. The results demonstrate that the 3 beta-HSD activity can be measured in a rapid and reliable way by measuring the reduction of nitroblue tetrazolium. Furthermore, the results suggest that dexamethasone acts on 3 beta-HSD through a mechanism different from that of insulin, as an additive effect was observed.