A Younes

Memorial Sloan-Kettering Cancer Center, New York City, New York, United States

Are you A Younes?

Claim your profile

Publications (5)49.44 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: We previously reported that protein kinase C (PKC) stimulation through phorbol ester (TPA) treatment enhances the effects of all-trans retinoic acid (RA) on immunophenotypic differentiation and RA nuclear receptor (RAR) activation in the multipotential human teratocarcinoma (TC) cell line NTera-2/clone D1 (abbreviated NT2/D1). This study extends prior work in NT2/D1 cells by demonstrating that PKC pathway activation is an early effect of RA treatment which regulates RAR transcriptional activity. RA activated the PKC pathway prior to induction of RAR-beta expression at 6 h, which is an established early marker of RAR activation in NT2/D1 cells. RA caused a transient 1.3-fold increase in intracellular diacylglycerol (DG) at 2 min and a translocation of the gamma isozyme of PKC (PKC-gamma) within 5 min. Transient co-transfection studies provided evidence that PKC pathway activation plays a role in the regulation of RAR-beta expression. In these studies a constitutively active PKC-gamma augmented the RA-mediated transactivation of a luciferase reporter containing the native RAR-beta promoter which has a retinoic-acid-response element (RARE). These findings reveal that PKC pathway activation is an early step in RA-mediated human TC differentiation and that PKC-gamma can potentiate the effects of RA on RAR transcriptional activation.
    Biochimica et Biophysica Acta 12/1993; 1179(2):203-7. DOI:10.1016/0167-4889(93)90142-C · 4.66 Impact Factor
  • S Mathias · A Younes · C C Kan · I Orlow · C Joseph · R N Kolesnick ·
    [Show abstract] [Hide abstract]
    ABSTRACT: The mechanism of interleukin-1 (IL-1) signaling is unknown. Tumor necrosis factor-alpha uses a signal transduction pathway that involves sphingomyelin hydrolysis to ceramide and stimulation of a ceramide-activated protein kinase. In intact EL4 thymoma cells, IL-1 beta similarly stimulated a rapid decrease of sphingomyelin and an elevation of ceramide, and enhanced ceramide-activated protein kinase activity. This cascade was also activated by IL-1 beta in a cell-free system, demonstrating tight coupling to the receptor. Exogenous sphingomyelinase, but not phospholipases A2, C, or D, in combination with phorbol ester replaced IL-1 beta to stimulate IL-2 secretion. Thus, IL-1 beta signals through the sphingomyelin pathway.
    Science 02/1993; 259(5094):519-22. DOI:10.1126/science.8424175 · 33.61 Impact Factor

    Biomedecine [?] Pharmacotherapy 12/1992; 46(5-7). DOI:10.1016/0753-3322(92)90159-5 · 2.02 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Previous studies have suggested a role for protein kinase C (PKC) during induction of murine erythroleukemia cell (MELC) differentiation by hexamethylene bisacetamide (HMBA) (Melloni, E., Pontremoli, S., Viotti, P. L., Patrone, M., Marks, P. A., and Rifkind, R. A. (1989) J. Biol. Chem. 264, 18414-18418). The present studies assess the effect of HMBA on the content of 1,2-diacylglycerol (DG), the physiologic activator of PKC, in MELC variants. Exposure of parental Sc9 cells to HMBA induced a rapid rise and fall in DG content. The DG level increased within seconds from 225 pmol.10(6) cells-1 to a maximum of 305 pmol.10(6) cells-1 at 5 min. Thereafter, DG content fell reaching control levels at 30 min and 46% of control at 4 h. Similar DG elevations were detected in HMBA-resistant, phorbol ester-resistant, and vincristine-resistant MELC lines. Early DG elevation was followed by the characteristic rapid fall in both the phorbol ester-resistant and vincristine-resistant lines, both of which differentiate rapidly in response to HMBA. In contrast, in an HMBA-resistant MELC the DG level failed to fall for at least 10 h. Selection of HMBA-resistant cells for vincristine resistance restores both HMBA sensitivity and the rapid fall in DG content. Addition of a synthetic DG, 1-oleyl-2-acetyl glycerol (OAG), along with HMBA and every 2 h for the next 48 h blocked differentiation, as measured by accumulation of benzidine-reactive cells or by the commitment assay in methyl-cellulose. However, if addition of OAG was delayed for just a few minutes, until endogenous DG levels began to fall, differentiation was no longer inhibited. Rapid elevation of DG content is the earliest reported event during HMBA action and a subsequent fall in the DG content appears to be a critical step in the process of commitment to terminal differentiation.
    Journal of Biological Chemistry 12/1992; 267(33):23463-6. · 4.57 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Prior studies demonstrated that ceramide was phosphorylated by a novel Ca(2+)-dependent kinase distinct from diacylglycerol (DG) kinase in human myelogenous leukemia (HL-60) cells (Kolesnick, R. N., and Hemer, M. R. (1990) J. Biol. Chem. 265, 10900-10904). The present studies were initiated to determine whether mammalian DG kinase purified to homogeneity possessed phosphotransferase activity toward ceramide. A high molecular weight rat brain DG kinase demonstrated Mg(2+)-(but not Ca(2+)-) dependent DG kinase activity and did not phosphorylate ceramide in the presence of either cation. In contrast, ceramide served as a competitive inhibitor with an inhibition constant (Ki) 2-6-fold greater than the Km for DG. Inhibition was noncompetitive with respect to ATP and Mg2+. A cell-permeable ceramide, N-octanoyl sphingosine (C8-cer), was used to study effects of ceramide on DG kinase in intact HL-60 cells. C8-cer induced dose- and time-dependent increases in cellular DG levels. As little as 1 microM C8-cer increased DG from a basal level of 103 to 177 pmol.10(6) cells-1, and a maximal 2.9-fold elevation to 292 pmol.10(6) cells-1 occurred with 10 microM C8-cer. DG elevation was detected after 1 min, maximal by 7.5 min, and sustained for 30 min. The DG elevation was accompanied by a reduction in 32P incorporation in phosphatidic acid in cells short term-labeled with [32P]orthophosphoric acid, consistent with inhibition of DG kinase. In contrast, a similar elevation in the DG level induced by exogenous phospholipase C increased 32P incorporation into phosphatidic acid. C8-cer was not metabolized to sphingomyelin, indicating that DG was not generated through the phosphatidylcholine:ceramide cholinephosphotransferase reaction. DG elevation after C8-cer or phospholipase C treatment was sufficient to redistribute protein kinase C from cytosol to membrane. These findings provide evidence that ceramide may serve as a competitive inhibitor of DG kinase.
    Journal of Biological Chemistry 02/1992; 267(2):842-7. · 4.57 Impact Factor

Publication Stats

430 Citations
49.44 Total Impact Points


  • 1992-1993
    • Memorial Sloan-Kettering Cancer Center
      • Department of Medicine
      New York City, New York, United States
    • Cornell University
      Итак, New York, United States