Insulin-like growth factor I (IGF-I) stimulates proliferation but also increases caspase-3 activity, Annexin-V binding, and DNA-fragmentation in human MG63 osteosarcoma cells: co-activation of pro- and anti-apoptotic pathways by IGF-I.
Insulin-like growth factor-I (IGF-I) was found to promote proliferation, cell survival, and inhibition of apoptosis. But in some instances, IGF-I was found to mildly induce apoptosis, i. e. Fas-mediated apoptosis in human MG63 osteosarcoma cells. In the present study, we intended to further investigate IGF-I dependent pathways leading either to proliferation and cell survival or to cell death. MG63 osteosarcoma cells were treated with serum free medium alone or in combination with IGF-I, a neutralizing antibody against the human IGF-I receptor (alphaIR-3) or non-immune control IgG (1) for two to six days. We investigated cell survival (cell count), proliferation (CD71-FACS), apoptosis (Annexin-V-FACS, Caspase-3 activity, PCD) and anti-apoptosis (112-Ser Bad phosphorylation), and regulation of IGF-I receptor surface expression (IGF-I receptor-FACS). We found that IGF-I treatment (48 h) stimulated cell growth and proliferation, but also mildly induced apoptosis. IGF-I activated specific apoptotic pathways (Caspase-3 activation, Annexin-V binding and DNA degradation), as well as anti-apoptotic signals (Bad phosphorylation at serine 112). alphaIR-3 blocked cell proliferation, strongly induced apoptosis, and inhibited Bad-phosphorylation. Thus, IGF-I treatment overall resulted in increased tumour cell mass, despite a detectable stimulation of apoptosis; in other words proliferation exceeded cell death. If IGF-I was first added on day 0, 2, or 4 of serum free culture, we found decreasing IGF-I specific effects on proliferation and apoptosis. In parallel, we found a down-regulation of IGF-I receptors (FACS) by serum withdrawal, which was partly reversed if IGF-I was added. Therefore receptor number might have an impact on IGF-I function in MG63 cells. In conclusion, co-activation of apoptosis and proliferation by IGF-I might result in higher cell turnover in MG63 osteosarcoma cells. Furthermore, in sarcomas or carcinomas showing clinical association to IGF-I levels and malignancy, IGF-I dependent apoptosis and proliferation could be a significant mechanism of malignant tumour growth.
Raile
K
K
Research Laboratory, Hospital for Children and Adolescents, Faculty of Medicine, University of Leipzig, Leipzig, Germany. klemens.raile@medizin.uni-leipzig.de
Hille
R
R
Laue
S
S
Schulz
A
A
Pfeifer
G
G
Horn
F
F
Kiess
W
W
D017304:Annexin A5 / Q000378:metabolism*; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D001859:Bone Neoplasms; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism*; D002455:Cell Division / Q000187:drug effects*; D045744:Cell Line, Tumor; D053938:DNA Fragmentation / Q000187:drug effects*; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D012516:Osteosarcoma; D011994:Recombinant Proteins / Q000494:pharmacology
D017304:Annexin A5; D011994:Recombinant Proteins; D007334:Insulin-Like Growth Factor I; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases