Insulin-like growth factor-I (IGF-I) and its binding protein IGFBP-4 in human prostatic hyperplastic tissue: gene expression and its cellular localization.

It has been previously reported that 1) type I insulin-like growth factor (IGF) receptors are present in the human prostatic tissue; 2) IGF-I receptors are mainly localized in the epithelial cells; 3) IGF-I is a mitogen for prostatic epithelial cells in culture; and 4) IGF-binding proteins (IGFBPs) are released by these cells in the conditioned medium. To add information on the mechanism of IGF-I action in the human prostate, we studied the expression and cellular localization of mRNA encoding IGF-I and IGFBP-4 in human prostatic hyperplastic (BPH) tissue. Northern analysis of total RNA extracted from BPH tissues with cDNA probes containing the entire coding regions for IGF-I and IGFBP-4 documented the presence of multiple IGF-I mRNA transcripts with lengths of 7.5, 1.7, 1.3, and 1.1 kilobases and a single 2.1-kilobase transcript of IGFBP-4 mRNA. In situ hybridization with the cDNA probes used for Northern analysis and with cRNA probes synthesized from the respective cDNA demonstrated that IGF-I mRNA was only localized in the stromal cells, whereas IGFBP-4 mRNA was predominantly expressed by epithelial cells. In addition, immunoreactive IGF-I was measured in BPH tissue extracts after acidification and reverse phase chromatography. The mean (+/- SD) IGF-I content of six BPH tissues was 28.1 +/- 4.0 ng/g tissue. Our results suggest that in the human prostate, the locally secreted IGF-I exerts its principal biological effects with a paracrine mode of action and demonstrate that IGFBP-4 is mainly expressed by IGF-I target cells.

Sertoli cell proteins in the human seminiferous tubule.

It is well known that rat Sertoli cells in culture secrete both testis-specific proteins, such as inhibin and androgen binding protein (ABP), and proteins which are very similar, if not identical, to serum proteins, such as transferrin (TF), ceruloplasmin, and IGF-I. It is also well known that very few data have been reported about the secretory activity and the hormonal regulation of the Sertoli cell in man, mainly because of the difficulties associated with the isolation of pure cell populations from human tissue. Using histoimmunochemical techniques we tried to localize, with specific antisera, Sertoli cell proteins and, when possible, their receptors in the human testis. The results obtained with our Light Microscopy studies suggest that: (1) human Sertoli cells produce and/or store transferrin (TF), IGF-I, an albumin-like protein and ABP; (2) TF receptors are localized in spermatocytes and early spermatids and are absent in spermatogonia, in the cytoplasm of Sertoli cells and in differentiated spermatids; (3) IGF-I type I receptors are localized in the same germ cells and in the cytoplasm of Sertoli cells. The results obtained with our Electron Microscopy studies suggest that TF and IGF-I are internalized through a receptor mediated endocytosis mechanism both in Sertoli cells (basal compartment) and in germ cells (spermatocytes and early spermatids).

Insulin-like growth factor-I (IGF-I) and IGF-I receptor in human testis: an immunohistochemical study.

Using specific monoclonal antibodies, the authors studied the distribution of insulin growth factor-I (IGF-I) and its receptor in normal human testis by immunostaining techniques. IGF-I was preferentially localized in Sertoli cells. Less evident positivity was found in primary spermatocytes. In the interstitium some Leydig cells were positive for IGF-I. The major positivity for the IGF-I receptor was found in secondary spermatocytes and early spermatids, whereas Sertoli cells were less positive. An intense positivity was found in some Leydig cells.

Immunostaining of transferrin and transferrin receptor in human seminiferous tubules.

Transferrin (TF) and transferrin receptor (TFr) were studied in human testicular biopsy specimens with the use of immunostaining techniques. A polyclonal antibody to human TF (obtained in goat), a murine monoclonal antibody (B3/25) to human TFr, and antisera antigoat IgG and antimouse IgG, both labeled with peroxidase, were used. In seminiferous tubules of subjects with normal spermatogenesis, TF was found mainly in Sertoli cells and, in lesser amounts (probably related to the presence of receptor-TF complexes), in spermatocytes and early spermatids. TFrs were found only in spermatocytes and early spermatids. In patients with spermatogenetic disorders, TF was always found in Sertoli cells, whereas TFrs were found in spermatocytes only when they were present. These results seem to demonstrate that in human seminiferous tubules, Sertoli cells are devoted to the production and/or storage of TF, whereas spermatocytes and early spermatids use TF.