Isoprenylcysteine Carboxyl Methyltransferase Activity Modulates Endothelial Cell Apoptosis

Abstract

Extracellular ATP, adenosine (Ado), and adenosine plus homocysteine (Ado/HC) cause apoptosis of cultured pulmonary artery endothelial cells through the enhanced formation of intracellular S-adenosylhomocysteine and disruption of focal adhesion complexes. Because an increased intracellular ratio of S-adenosylhomocysteine/S-adenosylmethionine favors inhibition of methylation, we hypothesized that Ado/HC might act by inhibition of isoprenylcysteine-O-carboxyl methyltransferase (ICMT). We found that N-acetyl-S-geranylgeranyl-l-cysteine (AGGC) and Nacetyl-S-farnesyl-l-cysteine (AFC), which inhibit ICMT by competing with endogenous substrates for methylation, caused apoptosis. Transient overexpression of ICMT inhibited apoptosis caused by Ado/HC, UV light exposure, or tumor necrosis factor-␣. Because the small GTPase, Ras, is a substrate for ICMT and may modulate apoptosis, we also hypothesized that inhibition of ICMT with Ado/HC or AGGC might cause endothelial apoptosis by altering Ras activation. We found that ICMT inhibition decreased Ras methylation and activity and the activation of the downstream signaling molecules Akt, ERK-1, and ERK-2. Furthermore, overexpression of wild-type or dominant active H-Ras blocked Ado/HC-induced apoptosis. These findings suggest that inhibition of ICMT causes endothelial cell apoptosis by attenuation of Ras GTPase methylation and activation and its downstream antiapoptotic signaling pathway. INTRODUCTIONVascular injury has been implicated in the pathogenesis of disorders such as sepsis and acute respiratory distress syndrome (ARDS). Endothelial cell apoptosis, or programmed cell death, may be important in vascular injury and repair. Apoptotic cells have been identified in increased quantities in the lungs of patients with ARDS, indicating that apoptosis occurs in this syndrome (Polunovsky et al., 1993). Apoptosis can be triggered by disruption of cell-extracellular matrix communication (anoikis) (Frisch and Francis, 1994) or by extracellular factors, such as lipopolysaccharide (Han and Wyche, 1994;Hoyt et al., 1995;Mebmer et al., 1999), tumor necrosis factor (TNF)-␣ (Polunovsky et al., 1994), or UV light (Chatterjee and Wu, 2001). We have previously demonstrated that increased extracellular ATP causes endothelial cell apoptosis after conversion to adenosine and uptake into cells. Moreover, apoptosis caused by intracellular adenosine was enhanced by homocysteine (Dawicki et al., 1997). In subsequent work, we found that increased concentrations of adenosine and homocysteine or inhibition of Sadenosylhomocysteine hydrolase resulted in enhanced levels of S-adenosylhomocysteine (SAH) (Rounds et al., 1998). Because enhanced intracellular concentrations of SAH may result in product inhibition of S-adenosylmethionine (SAM)-dependent methyltransferases (Perna et al., 1997) (Figure 1), we postulated that methyltransferase activity is important in the modulation of endothelial cell apoptosis.Among the methyltransferases is isoprenylcysteine-O-carboxyl methyltransferase (ICMT), the substrates ...

Role of elevated S-adenosylhomocysteine in rat hepatocyte apoptosis: Protection by betaine

“…Since the homeostatic levels of SAH are critically important on account of SAH being a potent productinhibitor of many SAM-dependent methyltransferases [58], we postulate a critical role of one or more liver methyltransferases in preventing hepatocyte apoptosis. Recent studies have shown that the carboxyl methylation reaction of small GTPases is a crucial activation step that facilitates these proteins to participate in anti-apoptotic signaling pathways [59]. We speculate that inhibition of the critical methyltransferase (such as isoprenyl cysteine methyltransferase) by elevated intracellular SAH levels may be responsible for adenosine-induced apoptosis in hepatocytes.…”

Involvement and mechanism of DGAT2 upregulation in the pathogenesis of alcoholic fatty liver disease

“…These modifi cations allow CAAX proteins to associate with cellular membranes and promote protein-protein interactions ( 34 ). The methylation reactions require SAM as a methyl group donor to produce methylated Ras, thus linking methionine metabolism to modulation of MEK/ERK1/2 activation.…”

“…The methylation reactions require SAM as a methyl group donor to produce methylated Ras, thus linking methionine metabolism to modulation of MEK/ERK1/2 activation. Indeed, intracellular SAH level is negatively related to ICMT activity ( 34 ). In addition, 3-Deazaadenosine, a potent inhibitor of S-adenosylhomocysteine hydrolase, whose inhibition induces intracellular SAH accumulation, prevents vascular smooth muscle cell proliferation and neointima formation by interfering with Ras methylation and thereby with mitogenic activation of ERK1/2 ( 36 ).…”

Inhibition of isoprenylcysteine carboxylmethyltransferase induces autophagic-dependent apoptosis and impairs tumor growth

“…Subsequent pharmacologic studies have also provided evidence that inhibition of Icmt-catalyzed methylation presents a potential approach to controlling cell prolifera-tion (Kramer et al, 2003;Anderson et al, 2005;WinterVann et al, 2005;Blum et al, 2008). To date, the most potent pharmacologic agent targeting Icmt is a compound termed as cysmethynil, originally identified in a screen of a small molecule library containing diverse scaffolds (Baron et al, 2007).…”