Insulin induces the phosphorylation of nucleolin. A possible mechanism of insulin-induced RNA efflux from nuclei.
Insulin induces the serine phosphorylation of the nucleolar protein nucleolin at subnanomolar concentrations in differentiated 3T3-442A cells. The stimulation is biphasic with phosphorylation reaching a maximum at 10 pM insulin and then declining to only 40% of basal levels at insulin concentrations of 1 microM. These changes are rapid, reaching half-maximal after 4 min and maximal after 15 min of incubation. The cell-permeable casein kinase II inhibitor 5,6-dichlorobenzimidazole-riboside prevents the insulin-stimulated phosphorylation of nucleolin suggesting that casein kinase II may mediate this effect of the hormone. Insulin-like growth factor 1 mimics the action of insulin on dephosphorylation of nucleolin at nanomolar concentrations suggesting that the latter effect may be mediated by insulin-like growth factor 1 receptors. Insulin treatment of 3T3-442A cells also results in a stimulation of RNA efflux from isolated, intact cell nuclei. The dose dependence of insulin-induced nucleolin phosphorylation and insulin-stimulated RNA efflux from intact cell nuclei are almost identical. Insulin induces an increase in the RNA efflux at subnanomolar concentrations in 3T3-442A adipocytes, while high (micromolar) concentrations of insulin inhibited the efflux of RNA. These data indicate that insulin regulates the phosphorylation/dephosphorylation of nucleolin, possibly via stimulation of casein kinase II, and this may play a role in regulation of the RNA efflux from nuclei.
Csermely
P
P
Research Division, Joslin Diabetes Center, Boston, Massachusetts 02215.
Schnaider
T
T
Cheatham
B
B
Olson
M O
MO
Kahn
C R
CR
D016475:3T3 Cells; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D002454:Cell Differentiation; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000302:isolation & purification / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D007328:Insulin / Q000494:pharmacology*; D007700:Kinetics; D051379:Mice; D009687:Nuclear Proteins / Q000302:isolation & purification / Q000378:metabolism*; D010710:Phosphates / Q000378:metabolism; D010750:Phosphoproteins / Q000302:isolation & purification / Q000378:metabolism*; D010761:Phosphorus Radioisotopes; D010766:Phosphorylation; D012313:RNA / Q000378:metabolism*; D016601:RNA-Binding Proteins; D013997:Time Factors; D000097796:Nucleolin
D000596:Amino Acids; D004268:DNA-Binding Proteins; D007328:Insulin; D009687:Nuclear Proteins; D010710:Phosphates; D010750:Phosphoproteins; D010761:Phosphorus Radioisotopes; D012313:RNA; D016601:RNA-Binding Proteins; D000097796:Nucleolin