Expression of a G protein subunit, alpha i-1, in Balb/c 3T3 cells leads to agonist-specific changes in growth regulation
Cellular receptors for many hormones, neurotransmitters, and growth factors are coupled to intracellular effector enzymes or ion channels through a set of heterotrimeric G proteins. In order to determine whether isoforms of G protein alpha subunits contribute differentially to mitogenic responses, w...
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Veröffentlicht in: | The Journal of biological chemistry 1991-10, Vol.266 (30), p.20276-20282 |
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Zusammenfassung: | Cellular receptors for many hormones, neurotransmitters, and growth factors are coupled to intracellular effector enzymes
or ion channels through a set of heterotrimeric G proteins. In order to determine whether isoforms of G protein alpha subunits
contribute differentially to mitogenic responses, we introduced an alpha subunit isoform, alpha i-1, into Balb/c 3T3 cells
that normally lack this subtype. Balb/c 3T3 cells transfected with a plasmid containing cDNA encoding alpha i-1 expressed
the alpha i-1 protein as judged both by the appearance of immunoreactive alpha i-1 protein on Western blots and by two-dimensional
analysis of the proteins [32P]ADP-ribosylated by pertussis toxin. The amount of alpha i-1 expressed is less than the amount
of alpha subunits endogenously present in these cells. Expression of alpha i-1 in the transfected cells slightly blunts stimulation
of adenylylcyclase by GTP, guanosine 5'-3-O-(thio)triphosphate, or forskolin, but has no major effect on the ability of thrombin
to inhibit the enzyme. In contrast, the expression of alpha i-1 has significant effects on cell growth and on the mitogenic
response to thrombin. The alpha i-1-transfected cells have a doubling time that is twice as long as control cells transfected
with the same plasmid without a cDNA insert. Despite their slower growth, thymidine incorporation in response to thrombin
is greater in transfected than in control cells. Thrombin-stimulated DNA synthesis is sensitive to inhibition by pertussis
toxin and is 5-fold more sensitive to inhibition by pertussis toxin in transfected cells than in control cells. The changes
are receptor-specific since the mitogenic response to platelet-derived growth factor is indistinguishable between control
and transfected cells. These studies suggest that the alpha i subunit composition of the cell may have profound effects on
its growth and its response to stimulation through a specific cell surface receptor. |
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ISSN: | 0021-9258 1083-351X |
DOI: | 10.1016/S0021-9258(18)54919-X |