The proliferative and antiapoptotic actions of growth hormone and insulin-like growth factor-1 are mediated through distinct signaling pathways in the Pro-B Ba/F3 cell line.
Biological actions of GH can be direct or mediated through insulin-like growth factor I (IGF-I). In the interleukin-3 (IL-3)-dependent Ba/F3 cell line, IGF-I induces cell cycle entry and proliferation. Ba/F3 cells expressing the rat GH receptor (Ba/F3 GHR cells) have been shown to escape from apoptosis and to proliferate under GH stimulation. Using the Ba/F3 GHR cell model, we sought to dissect the signals elicited specifically by IGF-I or GH. In contrast to IGF-I or IL-3, GH is able to maintain cell cycle entry of Ba/F3 GHR cells cultured for 7 days in the absence of serum. The presence of IGF-I messenger RNA was not detected by RT-PCR, and by RIA, IGF-I was not found in culture medium of Ba/F3 GHR cells, unstimulated or stimulated by GH. Moreover, the addition of an anti-IGF-I antibody that blocks IGF-I effects suggests that the actions of GH are not mediated by IGF-I, but appear to be direct. GH or IGF-I stimulation increased expression of cyclins A and D(1) with comparable kinetics, whereas expression of p21(waf1/cip1) seemed delayed in IGF-I-stimulated cells compared with that in GH-stimulated cells. Contrary to GH or IL-3, IGF-I did not induce nuclear factor-kappaB DNA-binding activity in Ba/F3 cells. Inhibition of nuclear factor-kappaB through expression of the mutant IkappaBalpha (A32/36) abrogated the GH-mediated survival signal, but did not result in alterations of the cell cycle in Ba/F3 GHR cells treated with IGF-I. Phosphatidylinositol 3-kinase was required for both survival and proliferative responses to IGF-I. Transfection of a dominant negative form of AKT (AH-AKT) resulted in suppression of IGF-I-mediated cell survival, but not of the antiapoptotic effect of GH in Ba/F3 GHR cells. Thus, GH and IGF-I are able to promote cell survival and proliferation through independent and different pathways in Ba/F3 cells.
Baixeras
E
E
INSERM, U-344, Endocrinologie Moléculaire, Faculté de Médecine Necker, 75730 Paris Cedex 15, France.
Jeay
S
S
Kelly
P A
PA
Postel-Vinay
M C
MC
D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D002417:Cattle; D018797:Cell Cycle Proteins / Q000378:metabolism; D002455:Cell Division / Q000502:physiology; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects / Q000502:physiology; D005799:Genes, Dominant; D013006:Growth Hormone / Q000494:pharmacology / Q000502:physiology*; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology / Q000502:physiology*; D051379:Mice; D009154:Mutation / Q000502:physiology; D016328:NF-kappa B / Q000502:physiology; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000502:physiology; D051057:Proto-Oncogene Proteins c-akt; D015398:Signal Transduction / Q000502:physiology*; D013997:Time Factors
D018797:Cell Cycle Proteins; D013006:Growth Hormone; D007334:Insulin-Like Growth Factor I; D016328:NF-kappa B; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt