Expression of a protease-resistant insulin-like growth factor-binding protein-4 inhibits tumour growth in a murine model of breast cancer.
BACKGROUND
Insulin-like growth factor 1 (IGF1) promotes breast cancer and disease progression. Bioavailability of IGF1 is modulated by IGF-binding proteins (IGFBPs). IGFBP4 inhibits IGF1 activity but cleavage by pregnancy-associated plasma protein-A (PAPP-A) protease releases active IGF1.


METHODS
Expression of IGF pathway components and PAPP-A was assessed by western blot or RT-PCR. IGFBP4 (dBP4) resistant to PAPP-A cleavage, but retaining IGF-binding capacity, was used to block IGF activity in vivo. 4T1.2 mouse mammary adenocarcinoma cells transfected with empty vector, vector expressing wild-type IGFBP4 or vector expressing dBP4 were implanted in the mammary fat pad of BALB/c mice and tumour growth was assessed. Tumour angiogenesis and endothelial cell apoptosis were assessed by immunohistochemistry.


RESULTS
4T1.2 cells expressed the IGF1R receptor and IGFBP4. PAPP-A was expressed within mammary tumours but not by 4T1.2 cells. Proliferation and vascular endothelial growth factor (VEGF) production by 4T1.2 cells was increased by IGF1(E3R) (recombinant IGF1 resistant to binding by IGFBPs) but not by wild-type IGF1. IGF1-stimulated microvascular endothelial cell proliferation was blocked by recombinant IGFBP4. 4T1.2 tumours expressing dBP4 grew significantly more slowly than controls or tumours expressing wild-type IGFBP4. Inhibition of tumour growth by dBP4 was accompanied by the increased endothelial cell apoptosis.


CONCLUSIONS
Protease-resistant IGFBP4 blocks IGF activity, tumour growth and angiogenesis.
Ryan
A J
AJ
Molecular and Cellular Therapeutics, Royal College of Surgeons in Ireland, 123 St Stephens Green, Dublin 2, Ireland.
Napoletano
S
S
Fitzpatrick
P A
PA
Currid
C A
CA
O'Sullivan
N C
NC
Harmey
J H
JH
D000230:Adenocarcinoma / Q000378:metabolism / Q000473:pathology; D000818:Animals; D017209:Apoptosis / Q000502:physiology; D048708:Cell Growth Processes / Q000502:physiology; D004195:Disease Models, Animal; D006801:Humans; D018974:Insulin-Like Growth Factor Binding Protein 4 / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000378:metabolism / Q000494:pharmacology; D008325:Mammary Neoplasms, Experimental / Q000098:blood supply / Q000378:metabolism* / Q000473:pathology*; D051379:Mice; D008807:Mice, Inbred BALB C; D009154:Mutation; D009389:Neovascularization, Pathologic / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology; D011266:Pregnancy-Associated Plasma Protein-A / Q000096:biosynthesis / Q000378:metabolism; D017526:Receptor, IGF Type 1 / Q000096:biosynthesis; D011994:Recombinant Proteins / Q000494:pharmacology; D042461:Vascular Endothelial Growth Factor A / Q000096:biosynthesis
D018974:Insulin-Like Growth Factor Binding Protein 4; D011994:Recombinant Proteins; D042461:Vascular Endothelial Growth Factor A; D007334:Insulin-Like Growth Factor I; D017526:Receptor, IGF Type 1; D011266:Pregnancy-Associated Plasma Protein-A