Insulin-like growth factor receptors in normal and tumorous adult human adrenocortical glands

Abstract

We have identified and characterized insulin-like growth factor (IGF)-I and IGF-II/mannose-6-phosphate (IGF-II/M6P) receptors in normal adult human adrenocortical tissue. Furthermore, we investigated the IGF-I receptor concentration and binding characteristics in benign and carcinomatous adrenocortical tumors. Membrane preparations of 14 normal adrenocortical glands showed a mean specific 125I-IGF-I binding (SB) of 5.0 +/- 0.5% and a competition by unlabeled ligands which is characteristic of the IGF-I receptor. The Scatchard analysis revealed a single class of high affinity binding sites with a dissociation constant (Kd) of 0.16 +/- 0.03 nmol/l, and a receptor concentration (RC) of 19.2 +/- 2.5 nmol/kg protein. Affinity cross-linking experiments with normal and tumorous adrenocortical tissue displayed a band at an apparent molecular mass of 135 kDa, corresponding to the size of the normal alpha-subunit of the IGF-I receptor. In agreement, 125I-IGF-II binding to normal adult human adrenocortical membranes was characteristic for the IGF-II/M6P receptor, and the Scatchard analysis revealed the presence of a single class of high affinity binding sites (SB 7.5 +/- 0.5%, RC 1137 +/- 265 nmol/kg protein, Kd 2.20 +/- 0.46 nmol/l, n = 6). The identity of the IGF-II/M6P receptor in adrenocortical tissue was further confirmed by Western blotting showing a specific band at 220 kDa. When 125I-IGF-I binding in adrenocortical hyperplasias (SB 4.1 +/- 0.4%, RC 19.6 +/- 2.0 nmol/kg protein, Kd 0.19 +/- 0.04 nmol/l, n = 4) and adenomas (SB 4.0 +/- 1.1%, RC 17.5 +/- 3.1 nmol/kg protein, Kd 0.21 +/- 0.04 nmol/l, n = 4) was compared with the 125I-IGF-I binding in normal adrenocortical tissue, similar IGF-I receptor concentration and binding kinetics were found. In contrast, three out of four hormonally active adrenocortical carcinomas showed a strongly elevated specific 125I-IGF-I binding with a 3- to 4-fold increase in IGF-I receptor concentration, as compared with normal adrenocortical tissue. This resulted in a significantly higher mean specific binding and receptor concentration in adrenocortical carcinomas, while the binding kinetics and the size of the alpha-subunit of the IGF-I receptor remained unaltered (n = 4, SB 13.8 +/- 4.2%, RC 72.2 +/- 21.3 nmol/kg protein, Kd 0.17 +/- 0.02 nmol/l). In summary, we show that intact IGF-I and IGF-II receptors are present in normal adult human adrenocortical tissue. While the abundance of the IGF-I receptor in adrenocortical hyperplasias and adenomas was similar to normal tissue, a strong overexpression of the intact IGF-I receptor was found in three out of four adrenocortical carcinomas.

Autocrine role of IGF-II in proliferation of human adrenocortical carcinoma NCI H295R cell line

“…Here we show that the IGF-II (and not the IGF-I) gene is strongly expressed in H295R cells as in malignant human adrenocortical tumors (Ilvesmäki et al 1993, Gicquel et al 1994. We also show that IGF-II mRNAs are efficiently translated, with accumulation of IGF-II protein in culture media during cell proliferation, partly as precursor forms, as we previously showed in frozen adrenocortical carcinomas (Boulle et al 1998 (Weber et al 1997) but the expression of the IGF-II M6P receptor in adrenocortical tumors has only been studied at the mRNA level; RT-PCR has been used to show that the gene is expressed both in normal and tumorous adrenals (Ilvesmäki et al 1993).…”

“…IGF-II mRNA is efficiently translated and malignant tumors contain large amounts of IGF-II protein, partly as precursor forms (Boulle et al 1998). IGF-I and IGF-II receptors are present in adrenal tissues and overexpression of the type 1 IGF receptor has been shown in adrenocortical carcinomas (Kamio et al 1991, Ilvesmäki et al 1993, Backlin et al 1995, Weber et al 1997. These previous studies all used frozen tumor tissues and give strong evidence for a role for IGF-II in adrenocortical tumor proliferation.…”

“…The tumors with these abnormalities exhibit strong overexpression of the IGF-II gene (Ilvesmäki et al 1993, Gicquel et al 1994 and large amounts of IGF-II protein (Boulle et al 1998). The type 1 IGF receptor (Weber et al 1997) and the IGF-binding protein-2 (IGFBP-2) (Boulle et al 1998) are also specifically overproduced in malignant adrenocortical tumors. These findings strongly implicate the IGF system in adrenocortical tumor progression.…”

Increased Expression of Insulin-Like Growth Factor I and/or Its Receptor in Gastrinomas Is Associated with Low Curability, Increased Growth, and Development of Metastases

“…Specifically, IGF-I and IGF-IR were detected in 80% to 100% and 92% of undifferentiated/poorly differentiated thyroid tumors (39), respectively; 67% to 100% and 50% to 100% of follicular thyroid cancers (39,40,43); 39% to 100% and 42-95% of papillary thyroid cancers (39,40,43); 80-100% and 50% of medullary thyroid cancer (46); 57% and 71% of pheochromocytomas (38); and 90% and 75% to 94% of adrenocortical cancers (38,41 Our results show that gastrinomas from different patients show a wide variation in the expression with IGF-I and IGF-IR mRNA levels. In follicular and papillary thyroid cancer, IGF-I and IGF-IR levels increases were reported of 2-to 7-fold, in adrenal cortical cancers IGF-IR was increased 3-to 5-fold (38), whereas in pancreatic cancer they were increased by 32-and 4.4-fold, respectively (34). Furthermore, our study showed a high significance (r = 0.66, P < 0.0001) between the level of expression of IGF-I and IGF-IR in a given gastrinoma.…”

Molecular genetics of adrenocortical tumours, from familial to sporadic diseases

“…receptors has been shown in ACC (69 (71). In ACC, only the maternal H19 allele is expressed, so expression of this gene is abolished in most ACCs displaying paternal isodisomy (62).…”