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Phorbol Ester‐Induced Loss of Membrane Sialic Acid: Implications for Tumor Cytolysis by Natural Killer Cells
Author(s) -
Nabi Zeenat F.,
ZuckerFranklin Dorothea,
Baten Abdul
Publication year - 1989
Publication title -
journal of leukocyte biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.819
H-Index - 191
eISSN - 1938-3673
pISSN - 0741-5400
DOI - 10.1002/jlb.45.3.183
Subject(s) - sialic acid , cytolysis , biology , biochemistry , natural killer cell , cell , neuraminidase , cell culture , glycoprotein , microbiology and biotechnology , cytotoxicity , in vitro , enzyme , genetics
Freeze‐fracture analysis has shown that treatment of cells with phorbol myristate acetate (PMA) results in a loss of intramembranous particles (IMP) associated with the external leaflet of their plasma membranes. It has also been demonstrated that phorbol esters markedly enhance the sensitivity of tumor targets to natural killer (NK) cells, although the mechanism underlying this phenomenon has remained unexplained. Since the ability of NK cells to recognize neoplasms appears to be inversely related to the concentration of sialic acid on the target cell surface, it seemed possible that phorbols affect membrane glycoproteins which have terminal carbohydrates bearing sialic acid residues. To investigate whether phorbol treatment could be responsible for the loss of sialic acid, four tumor cell lines were examined before and after exposure to PMA. A reduction in surface sialic acid was established by four different methods: 1) standard thiobarbituric acid analysis of cell hydsrolysates, 2) metabolic labelling of cells with [ 3 H]‐mannosamine followed by treatment with neuraminidase, 3) chromatography of membrane extracts, and 4) freeze‐fracture analysis of lectin‐labelled intact cells. These observations suggest a mechanism whereby phorbols may facilitate NK‐cell‐mediated cytolysis. In addition, an entirely novel effect of these tumor‐producing agents may have been uncovered.