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J. Biol. Chem., Vol. 263, Issue 18, 8658-8665, Jun, 1988
S Grinstein, JD Smith, R Onizuka, RK Cheung, EW Gelfand and S Benedict
It has been suggested that an intracellular alkalinization, resulting from
stimulation of Na+/H+ exchange, is a necessary step and perhaps the signal
leading to cellular proliferation in cells stimulated by mitogens. This
hypothesis was tested by measuring the early stages of the proliferative
cascade in cells where antiport activity was precluded by omission of Na+
or by the addition of potent amiloride analogs. To circumvent possible
nonspecific effects due to long incubations under these conditions, an
early response to mitogens, the increased level of c-fos mRNA, was
monitored. In rat thymic lymphocytes, the increase in the level of c-fos
RNA induced by the combination of 12-O-tetradecanoylphorbol 13-acetate and
ionomycin was unaffected by inhibition of the antiport with 5-(N-ethyl-N-
propyl)amiloride. Increased c-fos RNA was also observed in the absence of
Na+ and when alkalinization was prevented by means of nigericin. Similar
results were obtained with phytohemagglutinin-stimulated human T
lymphocytes. Moreover, although the lectin stimulated the antiport in these
cells, an alkalinization was not observed, due to the concomitant
occurrence of an acidifying process. It was concluded that the stimulation
of the Na+/H+ antiport that accompanies the addition of mitogens is neither
sufficient nor necessary for the initiation of cellular proliferation.
Activation of Na+/H+ exchange and the expression of cellular proto- oncogenes in mitogen- and phorbol ester-treated lymphocytes
Department of Biochemistry, University of Toronto, Canada.
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