1-(Carboxymethylthio)tetradecane attenuates PDGF- and TPA-induced c-fos mRNA expression and increases the formation of phosphatidylethanolamine with a shift from less to more polar molecular species in C3H/10T1/2 cells

RACK1 regulates Ki-Ras-mediated signaling and morphological transformation of NIH 3T3 cells

Activating Ras mutations are involved in a significant fraction of human tumors. A suppressor screen using a retroviral mouse fibroblast cDNA library was performed to identify novel factors in Ras-mediated transformation. We identified a novel potent inhibitor of Ras-mediated morphological transformation encoded by a truncated version of the receptor for activated C-kinase (RACK1). The truncated protein, designated RACK1DeltaWD1, lacked the N-terminal 49 amino acids encoding the first of the 7 WD40 repeats in RACK1. RACK1DeltaWD1 expression restored contact inhibition, stress fiber formation and reduced ERK phosphorylation in Ki-Ras transformed NIH 3T3 cells. We demonstrate that truncated RACK1 is involved in complexes consisting of wild-type RACK1 and protein kinase C isoforms alpha, betaI and delta, compromising the transduction of an activated Ras signal to the Raf-MEK-ERK pathway. The cellular localization of RACK1DeltaWD1 differed from wtRACK1, indicating that signaling complexes containing the truncated version of RACK1 are incorrectly localized. Notably, 12-O-tetradecanoyl-13-phorbol acetate (TPA) mediated intracellular translocation of RACK1-interacting PKC alpha and delta was abrogated in RACK1DeltaWD1-expressing cells. Our data support a model where RACK1 acts as a key factor in Ki-Ras-mediated morphological transformation.

Chlorpromazine interaction with phosphatidylserines: A 13C and 31P solid-state NMR study

Chlorpromazine (CPZ), a cationic, amphiphilic phenothiazine derivative is widely used as an antipsychotic drug because it antagonizes dopaminergic receptors. (13)C and (31)P solid-state NMR techniques were employed on phospholipid bilayers with and without CPZ. Phosphatidylserine from pig brain (PBPS), 1-palmitoyl-2-oleoyl phosphatidylserine (POPS), synthetic 1,2-dipalmitoyl phosphatidylcholine (DPPC) and chlorpromazineHCl were used to make phospholipid bilayers containing two types of phospholipids: DPPC (60%)/PBPS (40%) as well as POPS and PBPS bilayers without and with 10% CPZ. CPZ is found to prefer binding to the phosphate of phosphatidylserine, but also binding to the carboxyl of the serine head group in the DPPC/PBPS/CPZ bilayer is present. (31)P-NMR spectra indicate an effect of acyl chain unsaturation on the anisotropic motion of the charged serine head group. This implies that the serine head group anisotropic motion is restricted by intermolecular rather than intramolecular effects. The degree of phospholipid acyl chain unsaturation determines part of the CPZ bilayer interaction. The PBPS bilayer has the 22:6 acyl chain at 34 mol% and the C(4)?C(5) group of this acyl appears to be a determinant for CPZ bilayer interdigitation.

Nuclear import of factors involved in signaling is inhibited in C3H/10T1/2 cells treated with tetradecylthioacetic acid

The non-beta-oxidisable tetradecylthioacetic acid (TTA) is incorporated into cellular membranes when C3H/10T1/2 cells are cultured in TTA-containing medium. We here demonstrate that this alteration in cellular membranes affect the nuclear translocation of proteins involved in signal transduction. Analysis of cellular fatty acid composition shows that TTA and TTA:1n-8 constitute approximately 40 mol% of total fatty acids in cellular/nuclear membranes. Activation of c-fos expression is significantly inhibited in TTA-treated cells but the enzymatic activation of mitogen activated protein kinase (ERK) is not affected. Immunofluorescence and confocal microscopy studies demonstrate that in mitogene-stimulated TTA-treated cells, the translocation of phosphorylated ERK1/2, protein kinase C alpha (PKC alpha), and PKC beta(1) from the cytoplasm into the nucleus is considerably decreased and delayed. Concomitant with a decreased nuclear import, ERK1/2 dephosphorylation is decreased in TTA-treated cells. There is no TTA-induced inhibition of nuclear import of proteins with a classical nuclear localization signal (NLS), as seen by in vitro nuclear import experiments of BSA fused to the NLS from SV40 large T, or in vivo studies of hnRNP A1 nuclear import. The expression levels of Importin alpha, Importin beta, Importin 7, and NTF2 are not altered in the TTA-treated cells. Taken together, our data indicate that TTA treatment causes changes in cellular fatty acid composition that negatively affect NLS-independent mechanisms of protein translocation through the nuclear pore complex.

Mitochondrial 3-hydroxy-3-methylglutaryl coenzyme A synthase and carnitine palmitoyltransferase II as potential control sites for ketogenesis during mitochondrion and peroxisome proliferation

3-Thia fatty acids are potent hypolipidemic fatty acid derivatives and mitochondrion and peroxisome proliferators. Administration of 3-thia fatty acids to rats was followed by significantly increased levels of plasma ketone bodies, whereas the levels of plasma non-esterified fatty acids decreased. The hepatic mRNA levels of fatty acid binding protein and formation of acid-soluble products, using both palmitoyl-CoA and palmitoyl-L-carnitine as substrates, were increased. Hepatic mitochondrial carnitine palmitoyltransferase (CPT) -II and 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) synthase activities, immunodetectable proteins, and mRNA levels increased in parallel. In contrast, the mitochondrial CPT-I mRNA levels were unchanged and CPT-I enzyme activity was slightly reduced in the liver. The CoA ester of the monocarboxylic 3-thia fatty acid, tetradecylthioacetic acid, which accumulates in the liver after administration, inhibited the CPT-I activity in vitro, but not that of CPT-II. Acetoacetyl-CoA thiolase and HMG-CoA lyase activities involved in ketogenesis were increased, whereas the citrate synthase activity was decreased. The present data suggest that 3-thia fatty acids increase both the transport of fatty acids into the mitochondria and the capacity of the beta-oxidation process. Under these conditions, the regulation of ketogenesis may be shifted to step(s) beyond CPT-I. This opens the possibility that mitochondrial HMG-CoA synthase and CPT-II retain some control of ketone body formation.