Identification and characterization of insulin-like growth factor (IGF)-binding protein expression and secretion by adult human adrenocortical cells: differential regulation by IGFs and adrenocorticotropin

Abstract

In previous studies we have shown that IGF-II stimulates basal as well as ACTH-induced cortisol secretion from adult human adrenocortical cells more potently than IGF-I, and that both IGFs predominantly stimulate androgen biosynthesis. The steroidogenic effect of IGF-I and IGF-II is mediated through interaction with the IGF-I receptor, and modified by locally produced IGF-binding proteins (IGFBPs). In the present study, we identified and characterized IGFBP synthesis in normal adult human adrenocortical cells in primary culture, and investigated the effect of ACTH and recombinant human IGF-I and -II on the regulation of IGFBP expression and secretion.Using RT-PCR, we identified the mRNA of all six high-affinity IGFBPs, in both adrenocortical tissue and monolayer cell cultures of adrenocortical cells. Using Western ligand and immunoblotting and two-dimensional Western ligand blotting we confirmed the secretion of IGFBP-1, -2, -3, -4 and -5 by adrenocortical cells in primary culture.The quantification of IGFBPs indicated that IGFBP-3 accounts for almost half the binding activity in conditioned medium of unstimulated cells (47%), followed by IGFBP-4 (20%), IGFBP-5 (15%), IGFBP-2 (12%) and IGFBP-1 (6%). After treatment with ACTH, the abundance of IGFBP-1 was upregulated significantly 2·6-fold, while IGFBP-3 was induced only slightly (1·3-fold). IGFBP-2, -4 and -5 remained unchanged. In contrast, IGF-I and -II (6·5 nM) predominantly induced the abundance of IGFBP-5 (2-and 1·6-fold respectively) and IGFBP-3 (2-and 1·7-fold respectively), while IGFBP-1, -2 and -4 were unaltered. The induction of IGFBP-1 and -5 by ACTH and IGFs, respectively, was paralleled by an increase in the amount of IGFBP-1 and -5 mRNA in these cells.In conclusion, all six high-affinity IGFBPs are expressed in the adult human adrenal gland, and the presence of at least five high-affinity IGFBPs has been demonstrated in conditioned medium of adult human adrenocortical cells. Furthermore, the expression and secretion of IGFBP-1 is upregulated by ACTH, whereas IGFBP-5 is induced by IGF-I and -II. Together with earlier findings, these results suggest that IGFBPs play an important modulatory role in the regulation of the differentiated adrenocortical function.

The Insulin and IGF-I Pathway in Endocrine Glands Carcinogenesis

“…In contrast, three out of four hormonally active ACCs showed strongly elevated specific IGF-I binding with a 3-4-fold increase in IGF-IR concentration, as compared with normal adrenocortical tissue [194]. H295R cells overexpress also IGFBP-2 [195], which accounts for only 12% of the IGFBP activity in normal adrenocortical cells, but seems to play a specific role in the progression of ACCs by modulating IGF-II activity [196]. In support of the hypothesis of a tumor-growth-promoting effect of IGFBP-2 is the observation that Y-1 mouse adrenocortical tumor cells overexpressing IGFBP-2 show increased tumorigenic potential and cell proliferation [197].…”

“…Treatment of adult human adrenocortical cells with ACTH predominantly stimulated the abundance of IGFBP-1 and to a lesser extent that of IGFBP-3, while IGF-I and IGF-II selectively induced the accumulation of IGFBP-3 and IGFBP-5 in the medium [205, 206]. Quantification of the specific bands by γ counting revealed that IGFBP-3 accounts for more than half of the detected IGFBP activity, followed by IGFBP-1 with 20% and IGFBP-4 with approximately 10% [196]. …”

Role of the Insulin-like Growth Factor System in Adrenocortical Growth Control and Carcinogenesis

“…In adult human adrenocortical cells, both IGFs stimulate basal and ACTH-induced steroid biosynthesis by upregulating steroidogenic key enzymes and ACTH-receptor expression [5, 23 ± 24]. In analogy to the finding in fetal I time and dose -dependent stimulation of steroidbiosynthesis by IGF-I and -II [3,9 -11,12,85 -88,23,90,91] I predominant stimulation of androgen -secretion more potently by IGF-II than by IGF-I [4,6,8,23] I Stimulation of IGFBP -3, -4 and -5 expression and secretion by IGF-I and -II [6][7][8] I Differential modulation of IGF-induced steroidbiosynthesis by IGFBP-1 [89]…”

Insulin‐like growth factor binding protein 2 (IGFBP‐2) separates hypertrophic and hyperplastic effects of growth hormone (GH)/IGF‐I excess on adrenocortical cells in vivo

“…Development and function of the adrenal glands are markedly influenced by components of the IGF system (11)(12)(13)(14)(15). Besides IGF-I and -II, IGF-I receptors (IGF-IR), and IGF-II/mannose 6-phosphate receptors (IGF-II/ M6PR) (16,17), messenger RNA expression for all six high-affinity IGF binding proteins (IGFBPs) has been detected in fetal (18) and adult human adrenocortical tissue (18,19). Conditioned media of adrenal cells from various species were found to contain several IGFBPs (19 -22).…”