Abstract
| Language | English |
|---|---|
| Pages | 77-82 |
| Number of pages | 6 |
| Journal | FEBS Letters |
| Volume | 243 |
| Issue number | 1 |
| DOIs | |
| Publication status | Published - 1989 |
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Keywords
- adenylate cyclase
- Animals
- antigen-antibody complex
- cells
- GTP-binding proteins
- glucagon
- immune sera
- kinetics
- Llver
- phosphorylation
- rats
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Treatment of intact hepatocytes with either the phorbol ester TPA or glucagon elicits the phosphorylation and functional inactivation of the inhibitory guanine nucleotide regulatory protein Gi. / Pyne, N J; Murphy, G J; Milligan, G; Houslay, M D.
In: FEBS Letters, Vol. 243, No. 1, 1989, p. 77-82.Research output: Contribution to journal › Article
TY - JOUR
T1 - Treatment of intact hepatocytes with either the phorbol ester TPA or glucagon elicits the phosphorylation and functional inactivation of the inhibitory guanine nucleotide regulatory protein Gi
AU - Pyne, N J
AU - Murphy, G J
AU - Milligan, G
AU - Houslay, M D
PY - 1989
Y1 - 1989
N2 - The antiserum AS7 can specifically immunoprecipitate alpha-Gi from membrane extracts as well as from a mixture of purified alpha-Gi and alpha-Go as ascertained using [32P]ADP-ribosylated G-proteins. Using this antiserum to immunoprecipitate alpha-Gi from hepatocytes labelled with 32P it was evident that alpha-Gi was phosphorylated under basal (resting) conditions. Challenge of hepatocytes with the tumour promoting phorbol ester TPA, however, elicited a marked enhancement of the phosphorylation state of alpha-Gi. This was accompanied by the loss of inhibitory effect of Gi on adenylate cyclase, as judged by the inability of low concentrations of p[NH]ppG to inhibit forskolin-stimulated adenylate cyclase activity. Such actions were mimicked by treatment of hepatocytes with either glucagon or TH-glucagon, an analogue of glucagon which is incapable of activating adenylate cyclase and elevating intracellular cyclic AMP concentrations. Pre-treatment of hepatocytes with either glucagon, TPA or insulin did not affect the ability of pertussis toxin to cause the NAD+-dependent, [32P]ADP-ribosylation of alpha-Gi in membrane fractions isolated from such pre-treated hepatocytes. We suggest that protein kinase C can elicit the phosphorylation and functional inactivation of alpha-Gi in intact hepatocytes. As pertussis toxin only causes the ADP-ribosylation of the holomeric form of Gi, it may be that phosphorylation leaves alpha-Gi in its holomeric state.
AB - The antiserum AS7 can specifically immunoprecipitate alpha-Gi from membrane extracts as well as from a mixture of purified alpha-Gi and alpha-Go as ascertained using [32P]ADP-ribosylated G-proteins. Using this antiserum to immunoprecipitate alpha-Gi from hepatocytes labelled with 32P it was evident that alpha-Gi was phosphorylated under basal (resting) conditions. Challenge of hepatocytes with the tumour promoting phorbol ester TPA, however, elicited a marked enhancement of the phosphorylation state of alpha-Gi. This was accompanied by the loss of inhibitory effect of Gi on adenylate cyclase, as judged by the inability of low concentrations of p[NH]ppG to inhibit forskolin-stimulated adenylate cyclase activity. Such actions were mimicked by treatment of hepatocytes with either glucagon or TH-glucagon, an analogue of glucagon which is incapable of activating adenylate cyclase and elevating intracellular cyclic AMP concentrations. Pre-treatment of hepatocytes with either glucagon, TPA or insulin did not affect the ability of pertussis toxin to cause the NAD+-dependent, [32P]ADP-ribosylation of alpha-Gi in membrane fractions isolated from such pre-treated hepatocytes. We suggest that protein kinase C can elicit the phosphorylation and functional inactivation of alpha-Gi in intact hepatocytes. As pertussis toxin only causes the ADP-ribosylation of the holomeric form of Gi, it may be that phosphorylation leaves alpha-Gi in its holomeric state.
KW - adenylate cyclase
KW - Animals
KW - antigen-antibody complex
KW - cells
KW - GTP-binding proteins
KW - glucagon
KW - immune sera
KW - kinetics
KW - Llver
KW - phosphorylation
KW - rats
U2 - 10.1016/0014-5793(89)81221-9
DO - 10.1016/0014-5793(89)81221-9
M3 - Article
VL - 243
SP - 77
EP - 82
JO - FEBS Letters
T2 - FEBS Letters
JF - FEBS Letters
SN - 0014-5793
IS - 1
ER -