Regulation of transmembrane signal transduction of insulin-like growth factor II by competence type growth factors or viral ras p21.
In BALB/c 3T3 cells pretreated with platelet-derived growth factor (PDGF) and epidermal growth factor (EGF) (primed-competent cells), insulin-like growth factors I and II (IGF-I and IGF-II) bind to their own receptors (IGF-IR and IGF-IIR) and stimulate calcium influx and DNA synthesis by a mechanism involving a 40-kDa pertussis toxin substrate. In contrast, these IGFs do not act on unprimed quiescent cells. In this study, the 40-kDa pertussis toxin substrate was identified as Gi-2 alpha using anti-G protein antibodies. We analyzed the quality of signal transduction from IGF-II to Gi-2 alpha. There was no difference in the amount of Gi-2 alpha between quiescent and primed-competent cells, and both of these cells had similar Kd values and numbers of IGF-II-binding sites. Whereas IGF-II did not alter pertussis toxin-catalyzed ADP-ribosylation of Gi-2 alpha in quiescent cells, IGF-II reduced the pertussis toxin substrate activity by 35-50% via the IGF-IIR in primed-competent cells. The action of IGF-II lasted for up to 3 h when IGF-II was present in the medium, and it disappeared when IGF-II was removed. These results suggest that the signaling pathway triggered by IGF-II is uncoupled between the IGF-IIR and Gi-2 alpha in quiescent cells and that PDGF and EGF restore the IGF-IIR-Gi-2 coupling. This study also indicates that low concentrations of IGF-I reduce the pertussis toxin substrate activity of Gi-2 alpha in primed-competent cells in a time course slower than that of IGF-II, but not at all in quiescent cells. However, both of these cells had similar Kd values and numbers of IGF-I binding sites. Therefore, the IGF-I signaling pathway may also be uncoupled between the IGF-IR and Gi-2 alpha in quiescent cells and restored by PDGF and EGF. In BALB/c 3T3 cells transfected with temperature-sensitive Kirsten sarcoma virus bearing the v-Ki-ras gene (ts cells), a 40-kDa pertussis toxin substrate was also identified as Gi-2 alpha. In nonpermissive ts cells, IGF-II was without effect on the pertussis toxin substrate activity of Gi-2 alpha or on calcium influx.(ABSTRACT TRUNCATED AT 400 WORDS)
Okamoto
T
T
Fourth Department of Internal Medicine, University of Tokyo School of Medicine, Japan.
Asano
T
T
Harada
S
S
Ogata
E
E
Nishimoto
I
I
D000818:Animals; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism / Q000502:physiology; D002478:Cells, Cultured; D007335:Insulin-Like Growth Factor II / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D015689:Oncogene Protein p21(ras) / Q000378:metabolism*; D037342:Pertussis Toxin; D015398:Signal Transduction; D013696:Temperature; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D010566:Virulence Factors, Bordetella; D007335:Insulin-Like Growth Factor II; D037342:Pertussis Toxin; D015689:Oncogene Protein p21(ras); D002118:Calcium