Biosynthesis of 10 kDa and 7.5 kDa insulin-like growth factor II in a human rhabdomyosarcoma cell line.
In the present study we have analysed the expression of insulin-like growth factor II (IGF-II) in the human rhabdomyosarcoma cell line IN157.IN157 cells express high levels of three IGF-II mRNAs of 6.0 kb, 4.8 kb and 4.2 kb. In contrast, normal skeletal muscle expresses a negligible amount of IGF-II mRNA. Two forms of IGF-II with molecular masses of 7.5 kDa and 10 kDa, corresponding to the mature IGF-II and IGF-II with a C-terminal extension of 21 amino acids (IGF-IIE21), were secreted into the culture medium at amounts of 17 ng/ml (2.3 nM) and 15 ng/ml (1.5 nM), respectively. IN157 cells also produce IGF binding protein-2. The bioactivity of recombinant IGF-IIE21 was compared with human IGF-I and IGF-II. IGF-I, IGF-II and IGF-IIE21 bound with high affinity to human IGF-I receptors (Kd approximately 1 nM), whereas the human IGF-II/mannose 6-phosphate (IGF-II/Man 6-P) receptor bound IGF-II and IGF-IIE21 with Kd values of 0.5 nM and 2 nM, respectively, and IGF-I with about 500 times lower affinity. IGF-II and IGF-IIE21 stimulated DNA synthesis via the IGF-I receptor, whereas the IGF-II/Man 6-P receptor mediated their rapid internalization and inactivation. During culture of IN157 cells about 50% of their IGF-I receptors were occupied by endogenous IGF-II. We conclude that IN157 cells express high levels of bioactive 10 kDa IGF-II and 7.5 kDa IGF-II that may stimulate the proliferation of rhabdomyosarcomas by interaction with IGF-I receptors on the cells.
Nielsen
F C
FC
Department of Clinical Biochemistry, University Hospital, Rigshospitalet, Copenhagen, Denmark.
Haselbacher
G
G
Christiansen
J
J
Lake
M
M
Grønborg
M
M
Gammeltoft
S
S
D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism; D002478:Cells, Cultured; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D018971:Insulin-Like Growth Factor Binding Protein 2; D007335:Insulin-Like Growth Factor II / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D009124:Muscle Proteins / Q000096:biosynthesis / Q000235:genetics; D009132:Muscles / Q000378:metabolism; D009363:Neoplasm Proteins / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D017527:Receptor, IGF Type 2 / Q000378:metabolism; D012208:Rhabdomyosarcoma / Q000378:metabolism*; D014407:Tumor Cells, Cultured
D002352:Carrier Proteins; D018971:Insulin-Like Growth Factor Binding Protein 2; D009124:Muscle Proteins; D009363:Neoplasm Proteins; D017527:Receptor, IGF Type 2; D007335:Insulin-Like Growth Factor II