PROTEIN-KINASE C-DEPENDENT PHOSPHORYLATION IS INVOLVED IN RESISTANCE TO TUMOR NECROSIS FACTOR-ALPHA-INDUCED CYTOTOXICITY IN A HUMAN MONOCYTOID CELL-LINE
Le. Sampson et al., PROTEIN-KINASE C-DEPENDENT PHOSPHORYLATION IS INVOLVED IN RESISTANCE TO TUMOR NECROSIS FACTOR-ALPHA-INDUCED CYTOTOXICITY IN A HUMAN MONOCYTOID CELL-LINE, Biochemical journal, 292, 1993, pp. 289-294
To investigate the mechanism underlying resistance to tumour necrosis
factor-alpha (TNFalpha)-induced cytotoxicity, we have developed a huma
n hybrid cell line, designated A10, derived from the fusion of human U
-937 monocytoid cells and human monocytes, which expressed large numbe
rs of TNFalpha receptors and yet remained highly resistant to TNFalpha
. However, in the presence of the protein kinase C (PKC) inhibitors RO
-31-7549 or RO-318220 (donated by Roche), these cells became sensitive
to TNFalpha-induced cytotoxicity, suggesting that PKC activity is req
uired for protective mechanisms. On investigation of protein phosphory
lation in TNFalpha-stimulated permeabilized A10 cells, a rapid increas
e in serine/threonine phosphorylation of phosphoproteins of molecular
masses 130, 90, 80, 65 and 42 kDa was found. Subsequently, we found a
similar pattern of increased phosphorylation following stimulation of
A10 cells with mezerein, a phorbol ester derivative which activates PK
C, a serine/threonine kinase. The theory that activation of PKC was re
sponsible for increased phosphorylation was confirmed by a dose-depend
ent inhibition of the TNFalpha-induced protein phosphorylation by the
PKC inhibitors RO-31-7549 and RO-31-8220. The possible link between th
e TNFalpha-stimulated early protein phosphorylation events and the mai
ntenance of protective mechanisms against TNFalpha-induced cytotoxicit
y is discussed.