J. Biol. Chem., Vol. 255, Issue 17, 8103-8108, 09, 1980
Mechanism of cyclic AMP effect on nutrient transport in Chinese hamster ovary cells. A genetic approach
A LeCam, MM Gottesman and I Pastan
The effect of 8-bromo cyclic adenosine 3':5'-monophosphate (8-Br-cAMP) on
sugar and amino acid transport was investigated in wild-type Chinese
hamster ovary (CHO) cells and in mutants selected for resistance to cAMP
inhibition of cell growth. In wild type cells, both 3-O-methyl-D- glucose
and alpha-aminoisobutyric acid transport were decreased in cells treated
for 24 h with 8-Br-cAMP; kinetic analysis indicated that a decrease in
Vmax, without a significant change in Km, accounted for the lower transport
capacity of 8-Br-cAMP treated cells. Among the different transport systems
contributing to amino acid entry, "alanine" preferring transport system
(system A) appeared to be specifically affected. The sensitivity of
transport processes to 8-Br-cAMP was tested in three cAMP-resistant cell
lines. When tested for their capacity to phosphorylate histones in crude
extracts, one strain had apparently normal amounts of protein kinase
activity, one strain had a decreased enzyme sensitivity to cAMP, and one
strain had little or no enzyme activity. In all three mutants, no effect of
8-Br-cAMP on 3-O- methyl glucose and alpha-aminoisobutyric acid transport
could be observed, regardless of the level of cAMP-dependent protein kinase
activity. These data do not indicate whether the effect of cAMP on nutrient
transport in CHO cells is the cause or consequence of growth inhibition.
However, they support the conclusion that, in CHO cells, the presence of a
normally functioning cAMP-dependent protein kinase appears to be necessary
but may not be sufficient to observe the effects of cAMP on nutrient
transport as well as cell shape and cell growth.
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