The IGF system in neuroblastoma xenografts: focus on IGF-binding protein-6.
With a view to investigating the implication of IGF-binding protein-6 (IGFBP-6) in the growth of neuroblastomas, nude mice were injected with IGFBP-6-expressing or control IGR-N-91 human neuroblastoma cells and the resulting xenografts examined. Expression of IGFBP-3, IGFBP-4 and type 1 and type 2 IGF receptor messengers was similar in control tumours and equal-sized IGFBP-6-expressing tumours that had developed. IGF-II was more strongly expressed in control tumours, and IGFBP-6-expressing tumours contained less IGFBP-2 than controls. In both populations, there was a significant positive correlation between IGF-II and IGFBP-2 expression. In small IGFBP-6-expressing xenografts where tumour development had apparently been arrested, haematoxylin--eosin and TUNEL staining revealed numerous apoptotic cells. In situ hybridization indicated homogeneous distribution of the IGFBP-6 signal in test tumours. In cell culture, IGFBP-6-expressing cells expressed similar amounts of IGFBP-2, IGF-II and N-myc mRNAs as control cells; but media conditioned by IGFBP-6-expressing cells contained less intact IGFBP-2 protein, with no increase in its proteolytic fragment. In media treated with plasminogen, in which IGFBP-2 was proteolysed, IGFBP-6 was increased. With its especially strong affinity for IGF-II and its resistance to proteolysis, IGFBP-6 would act by sequestering IGF-II, hence inhibiting its mitogenic and anti-apoptotic effects. In excess, IGFBP-6 would displace IGF-II from IGFBP-2 whose potentiation of IGF-II action would cease and whose susceptibility to degradation would be increased. This study therefore shows that IGFBP-6 plays a role in neuroblastoma cell growth in vivo and in vitro and that stable overexpression of IGFBP-6 leads to alteration of the initial balance between the IGFBPs.
Grellier
P
P
Institut National de la Santé et de la Recherche Médicale, Unité 515, Hôpital Saint Antoine, 184, rue du Faubourg Saint Antoine, 75571 Paris Cedex 12, France.
Berrebi
D
D
Peuchmaur
M
M
Babajko
S
S
D000818:Animals; D017209:Apoptosis / Q000235:genetics; D002455:Cell Division / Q000235:genetics; D005260:Female; D015870:Gene Expression; D006801:Humans; D017403:In Situ Hybridization / Q000379:methods; D018971:Insulin-Like Growth Factor Binding Protein 2 / Q000235:genetics; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000235:genetics; D018976:Insulin-Like Growth Factor Binding Protein 6 / Q000235:genetics / Q000502:physiology*; D007335:Insulin-Like Growth Factor II / Q000235:genetics; D051379:Mice; D008819:Mice, Nude; D009368:Neoplasm Transplantation; D009447:Neuroblastoma / Q000378:metabolism*; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics; D012333:RNA, Messenger / Q000032:analysis; D013002:Somatomedins / Q000378:metabolism*; D014183:Transplantation, Heterologous
D018971:Insulin-Like Growth Factor Binding Protein 2; D018972:Insulin-Like Growth Factor Binding Protein 3; D018976:Insulin-Like Growth Factor Binding Protein 6; D016271:Proto-Oncogene Proteins c-myc; D012333:RNA, Messenger; D013002:Somatomedins; D007335:Insulin-Like Growth Factor II