AJP - Cell Physiology, Vol 258, Issue 6 C1044-C1050, Copyright © 1990 by American Physiological Society
Induction of Na(+)-K(+)-ATPase and its subunit mRNAs by serum in a rat liver cell line
A. Bhutada, C. Perez, D. Y. Chon and F. Ismail-Beigi
Department of Medicine, College of Physicians and Surgeons, Columbia University, New York, New York 10032.
Addition of serum to confluent Clone 9 cells increased the protein, RNA,
and DNA content per plate of cells; the increments became manifest within
3-6 h and were sustained for the 48-h duration of study. After the addition
of serum, Na(+)-K(+)-ATPase activity was stimulated 1.25- and 1.45-fold at
6 and 12 h, respectively. In cells preincubated in the absence of serum for
24 h, addition of serum increased the abundances of Na(+)-K(+)-ATPase
subunit mRNAs, mRNA alpha 1 and mRNA beta, coordinately by approximately 2-
and 2.7-fold at 3 h, an effect that preceded the stimulation of
Na(+)-K(+)-ATPase activity. The serum-induced increments in subunit mRNA
abundances were further enhanced by the combined presence of serum and
cycloheximide; mRNA alpha 1 and mRNA beta abundances were also augmented by
cycloheximide alone (approximately 2.5- and 9.2-fold at 6 h, respectively).
In cells incubated in the absence of serum, the half-lives of mRNA alpha 1
and mRNA beta, estimated from decrements in their abundances after the
addition of actinomycin D, were 12 and 10 h, respectively. These data
demonstrate that serum enhances Na(+)-K(+)-ATPase subunit mRNA abundance
and enzyme activity in Clone 9 cells. Comparison of the estimated
half-lives of Na(+)-K(+)-ATPase subunit mRNAs with the observed increments
in their abundances at 3 h suggests that the serum-induced increases in
mRNA alpha 1 and mRNA beta abundances are in large part due to enhanced
synthesis of these mRNAs.
