Mitogenic action of lysophosphatidic acid and phosphatidic acid on fibroblasts. Dependence on acyl-chain length and inhibition by suramin

Abstract

Lysophosphatidic acid (LPA) is a naturally occurring phospholipid with growth-factor-like activities [van Corven, Groenink, Jalink, Eichholtz & Moolenaar (1989) Cell 45, 45-54]. We have examined various structural analogues of LPA for their ability to stimulate DNA synthesis in quiescent fibroblasts. When the acyl-chain length is varied, the rank order of mitogenic potency is: 1-oleoyl LPA congruent to 1-palmitoyl LPA greater than 1-myristoyl LPA greater than 1-lauroyl LPA greater than 1-decanoyl LPA; the last compound shows almost no activity over the concentration range tested (1-100 microM). An ether-linked LPA (1-O-hexadecylglycerol 3-phosphate) has much decreased mitogenic activity as compared with the ester-linked analogue at concentrations less than 25 microM, and becomes cytotoxic at higher concentrations. Hexadecylphosphate, which lacks a glycerol backbone, has negligible activity. On a molar basis, diacyl phosphatidic acid (PA) is about equally potent as the corresponding LPA analogue, showing similar acyl-chain-length dependence; the data argue against the possibility that the mitogenic action of PA is due to contaminating traces of LPA. Although the short-chain analogues of LPA and PA fail to antagonize the action of long-chain (L)PAs, the polyanionic drug suramin inhibits LPA- and PA-induced, DNA synthesis in a reversible and dose-dependent manner, at concentrations [IC50 (concn. giving 50% inhibition) approximately 70 microM] that do not affect epidermal-growth-factor-induced DNA synthesis. Suramin appears to act in the early G0/G1 phase of the cell cycle, blocking immediate responses to LPA such as phosphoinositide hydrolysis. We conclude that both LPA and PA can function as growth-promoting phospholipids, with the fatty acid chain length being a major determinant of mitogenic potency.

The role of phosphatidic acid in platelet-derived growth factor-induced proliferation of rat hepatic stellate cells

“…In support of this observation we have recently reported that PDGF but not TGF-␣ activates PLC and PLD in HSCs with a dose response similar to that for thymidine incorporation. 22 A role for this production of PA in PDGF-induced HSC proliferation is suggested by the mitogenic effect of exogenously added PA, which is consistent with its previously reported effects in rat and mouse fibroblasts, 13,14 human A431 carcinoma cells, 23 and human mesangial cells. 24 Assessing the precise contribution of PLD/PA to PDGF-induced HSC mitogenesis ideally requires specific PLD inhibitors that are currently unavailable.…”

“…In fibroblast cell lines, PLD activation has been implicated in PDGF-stimulated proliferation 13 and exogenous PA has been shown to induce DNA synthesis. 13,14 However, as yet, information on this signal cascade in HSCs is restricted to a report of PDGF-induced phosphoinositide hydrolysis by PLC-␥ 15 and a more recent study reporting the interaction of PLC-␥ with focal adhesion kinase, suggesting a role in cell adhesion and migration. 16 The initial aim of the studies described in this report was, therefore, to investigate the role of the lipid-derived second messenger PA in PDGF-induced proliferation of HSCs.…”

Lysophosphatidic acid inhibits gap-junctional communication and stimulates phosphorylation of connexin-43 in WB cells: possible involvement of the mitogen-activated protein kinase cascade

“…Thus photoaffinity-labelling studies with a LPA analogue have identified a binding protein of apparent molecular mass 38-40 kDa in a range of cell types, including fibroblasts [6]. Binding of LPA to this protein was inhibited by suramin, a polysulphonated naphthylurea derivative that also blocks the biological response of intact cells to LPA [7]. The initiating events in LPA-induced mitogenesis are not established, but rapid responses include inhibition of G-protein-linked adenylate cyclase [3], activation of both inositol lipid hydrolysis by phospholipase C [8] and phosphatidylcholine hydrolysis by phospholipase D [9], and activation of p2Iras [10].…”

Phorbol ester selectively stimulates the phospholipase D-mediated hydrolysis of phosphatidylethanolamine in multidrug-resistant MCF-7 human breast carcinoma cells

“…These data indicate that MCF-7/MDR cells contain a PtdEtn-specific PLD activity which can be selectively stimulated by PMA, sphingosine and H202* The hydrolysis of phospholipids by hormone-and phorbol ester-stimulated phospholipase D (PLD) results in the formation of phosphatidic acid [17,18]. Phosphatidic acid can serve as a messenger molecule with the potential to regulate cell growth [19][20][21][22][23][24], exocytosis [25][26][27][28][29][30], as well as other cellular processes (reviewed in [31]). In view of the emerging role of PLD in signal transduction, it is important to characterize the regulatory properties of PLD and to identify the phospholipid pools which can serve as substrates.…”