A metabolite of an antineoplastic ether phospholipid may inhibit transmembrane signalling via protein kinase C

Abstract

In our search for the mechanisms by which the drug 1-O-alkyl-2-O-methylglycero-3-phosphocholine (AMG-PC) inhibits tumor growth and metastasis, we have detected a metabolite, 1-O-alkyl-2-O-methylglycerol (AMG), in membranes of MO4 mouse fibrosarcoma cells grown in the presence of the drug. Synthetic AMG inhibited the activation of highly purified human protein kinase C by diacylglycerol in the presence of phosphatidylserine. Furthermore, AMG also inhibited the receptor-specific binding of 3H-phorbol-12,13-dibutyrate to human HL-60 promyeloid leukemia cells in a dose-dependent fashion. AMG-PC was not effective or much less so in these assays. We suggest that interaction of the metabolite AMG with protein kinase C may inhibit stimulus-response coupling in tumor cells and may thus potentially contribute to the mechanism by which AMG-PC exerts its anticancer activities.

A pseudosubstrate peptide inhibits protein kinase C‐mediated phosphorylation in permeabilized Rat‐1 cells

“…It will now be of interest to verify the proposed role of PKC in these processes. The approach reported here may provide a novel tool to study the involvement of PKC in cellular processes, in addition to more conventional approaches like PKC down-regulation by long-term pretreatment with phorbol ester 1271 and the use of specific inhibitors such as staurosporin [28] and 1 -O-alkyl-2-0-methylglycerol [29].…”

“…Examination of the amino acid sequence of PKC revealed that the regulatory domain of the enzyme contains a sequence (residues [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36]) that fulfills most of the requirements for a PKC phosphorylation site. It contains a number of basic amino acid residues [9], but with an alanine residue instead of the phosphate acceptor serine.…”

Alkyllysophospholipid ET‐18‐OCH3 acts as an activator of protein kinase C in HL‐60 cells

“…The inhibition was described as competitively with respect to PS and to the activation by diacylglyerol or TPA. The lack of inhibitory action of ET-18-0CH3 on PK-C activity when added as separate liposomes (method (iii)) is remarkable and might explain the findings of Van Blitterswijk et al [20] who found no inhibition of PK-C by the ether lipid when added as separate liposomes. Even more striking is the effect of ET-I8-0CH3 when incorporated in the PS and diolein liposomes (method (ii)).…”

Purification, cDNA‐cloning and expression of human diacylglycerol kinase

“…unpublished results), obtained after affinity column chromatochraphy on immobilized PS [22]. 1"o investlgate tl~.c po~;sibility whether PKC could itself phosphorylatc tlle physiological activator, DG, the separation of the two activities was the original aim, Upon homogenization of WBC, 90e/o of the DG kinase activity was recovered in the cytosol fraction, whick displayed a 2-fold higher specific activity than the microsomal fraction.…”

“…1). These fractions were devoid of PKC activity (measured as descibed in [22]). In a similar rnanner, DG kinase was also purified from pig brain cytosol (results not shown).…”