Wilms tumor is a common embryonic tumor in childhood. Two Wilms tumor-suppressor genes, WT1 and WT2, are located on chromosome 11p, WT2 at 11p15.5 close to the IGF-II gene, which is highly expressed in some Wilms tumors. We established Wilms tumor cell lines to investigate the regulation of tumor cell growth by IGF-II. We demonstrated that Wilms tumor cells produce more IGF-II than normal kidney cells. Both types I and II IGF receptors reside on these cells. In serum-free culture medium, tumor cell growth is reversibly inhibited by suramin via interfering with IGF-II binding. Wilms tumor cell growth is also arrested by IGF binding protein-3, capturing the continuously produced IGF-II, and by alpha IR-3, a type I IGF receptor-blocking antibody. Thus, we demonstrated the whole loop of elevated synthesis, secretion, receptor binding, and autocrine growth stimulation of IGF-II through type I IGF receptor in Wilms tumor cell cultures. We concluded that IGF-II plays a crucial role in the regulation of growth of this embryonic tumor. Overproduction of IGF-II by the tumor cell is the limiting step for Wilms tumor growth, supporting its important role as an embryonic growth factor.

The concentration of mRNA of insulin-like growth factor-II is (IGF-II) much elevated in some embryonic tumours such as Wilms tumour (nephroblastoma). In order to prove whether or not IGF-II is produced by the tumour tissue, IGF-II was extracted from freshly frozen tissue of Wilms tumour and hepatoblastoma. Normal adjacent tissue of kidney and liver was used as a control. The total IGF-II in Wilms tumour was 548.4 +/- 77.4 ng/g (n = 7) compared to 112.8 +/- 38.2 ng/g (n = 5) in kidney. In two hepatoblastomas, it was 96.1 +/- 22.8 ng/g compared to 30.1 +/- 14.2 ng/g in normal liver. Small pieces of fresh primary tissue of several Wilms tumours were successfully transplanted into immunodeficient nude mice. In serum of tumour-bearing mice IGF-II was elevated compared to normal mice. Liver weight of tumour bearing mice was higher than that of control mice (2.29 +/- 0.4 g and 2.02 +/- 0.06 g; P < 0.005). This was also found for kidney weight (0.58 +/- 0.01 g vs. 0.51 +/- 0.01 g in controls, P < 0.001). In contrast, serum glucose (9.73 +/- 0.29 mmol/l compared to 11.80 +/- 0.42 mmol/l in controls, P < 0.0005) was decreased. However, there was no significant difference in nose-tail length of tumour-bearing compared to control mice. These results demonstrate that besides the highly increased IGF-II-mRNA, the synthesis of the peptide IGF-II and its release into circulation are also elevated in Wilms tumour transplanted into nude mice.(ABSTRACT TRUNCATED AT 250 WORDS)

Insulin-like growth factor-II (IGF-II) is thought to play a critical role in the development of embryonic tumors such as Wilms' tumor. However, despite highly elevated IGF-II mRNA levels in tumors, IGF-II is not elevated in the serum of patients with Wilms' tumors. Recently high molecular weight forms of IGF-II ('big'-or pro-IGF-II) have been found to be produced by some tumors. In order to prove whether or not high molecular weight forms of IGF-II are produced by Wilms' tumor cells and secreted into the culture medium, we established Wilms' tumor cell lines. After column chromatography of the culture medium, IGF-II and pro-IGF-II concentrations were measured. For pro-IGF-II measurement we established a pro-IGF-II RIA using a rabbit polyclonal antiserum directed against amino acids 7-21 (E 7-21 ) of the E-domain of pro-IGF-II. Gel electrophoresis and Western blotting with anti-IGF-II antibodies revealed a band at 7.5 kDa corresponding to fully processed IGF-II and bands between 10 and 20 kDa. Using pro-IGF-II antiserum, bands between 10 and 25 kDa were detected. We conclude that in vitro cultured Wilms' tumor cells produce and release various forms of 'big IGF-II' with molecular masses between 10 and 25 kDa. It remains uncertain whether these high molecular weight forms of IGF-II represent normal precursors of IGF-II or incorrectly processed IGF-II.