ABSTRACT
The insulin-like growth factor (IGF) system plays an important role in mammary gland biology as well as in the etiology of breast cancer. The IGF-I receptor (IGF-IR), which mediates the biological actions of IGF-I and IGF-II, has emerged in recent years as a promising therapeutic target. The IGF and estrogen signaling pathways act in a synergistic manner in breast epithelial cells. The present study was aimed at investigating 1) the putative translocation of IGF-IR and the related insulin receptor (IR) to the nucleus in breast cancer cells, 2) the impact of IGF-IR and IR levels on IGF-IR biosynthesis in estrogen receptor (ER)-positive and ER-depleted breast cancer cells, and 3) the potential transcription factor role of IGF-IR in the specific context of IGF-IR gene regulation. We describe here a novel mechanism of autoregulation of IGF-IR gene expression by cellular IGF-IR, which is seemingly dependent on ER status. Regulation of the IGF-IR gene by IGF-IR protein is mediated at the level of transcription, as demonstrated by 1) binding assays (DNA affinity chromatography and ChIP) showing specific IGF-IR binding to IGF-IR promoter DNA and 2) transient transfection assays showing transactivation of the IGF-IR promoter by exogenous IGF-IR. The IR is also capable of translocating to the nucleus and binding the IGF-IR promoter in ER-depleted, but not in ER-positive, cells. However, transcription factors IGF-IR and IR display diametrically opposite activities in the context of IGF-IR gene regulation. Thus, whereas IGF-IR stimulated IGF-IR gene expression, IR inhibited IGF-IR promoter activity. In summary, we have identified a novel mechanism of IGF-IR gene autoregulation in breast cancer cells. The clinical implications of these findings and, in particular, the impact of IGF-IR/IR nuclear localization on targeted therapy require further investigation.
Subject(s)
Breast Neoplasms/metabolism , Cell Nucleus/metabolism , Gene Expression Regulation, Neoplastic , Neoplasm Proteins/biosynthesis , Promoter Regions, Genetic , Receptor, IGF Type 1/biosynthesis , Transcription, Genetic , Active Transport, Cell Nucleus/genetics , Breast Neoplasms/genetics , Cell Line, Tumor , Cell Nucleus/genetics , Female , Humans , Insulin-Like Growth Factor I/genetics , Insulin-Like Growth Factor I/metabolism , Insulin-Like Growth Factor II/genetics , Insulin-Like Growth Factor II/metabolism , Neoplasm Proteins/genetics , Receptor, IGF Type 1/genetics , Receptor, Insulin/genetics , Receptor, Insulin/metabolismABSTRACT
OBJECTIVE: To compare the effect of two different techniques of testicular fixation on testicular function. DESIGN: Experimental study. SETTING: Surgical animal laboratory at an academic medical center. PATIENT(S): Sixteen mature golden hamsters underwent classic transfixation orchiopexy and true dartos pouch orchiopexy. INTERVENTION(S): Classic transfixation orchiopexy (CTO) involved transfixation of the testicular wall at two different points and fixation of the dartos fascia. True dartos pouch orchiopexy (TDPO) involved creating a window in the dartos fascia, passage of the testicle, and closure of the window from both sides of the testicle. MAIN OUTCOME MEASURE(S): Flow cytometric separation of testicular cells into haploid, diploid, and tetraploid fractions for histogram analysis. RESULT(S): A significant decrease in testicular weight was observed in 6 out of 16 animals undergoing CTO. Diploid cells comprised the main cell fraction, and almost no haploid or tetraploid cells were observed, while in the 16 animals undergoing TDPO no change from the control pattern was observed. CONCLUSION(S): This experimental work supports our clinical impression that TDPO should replace CTO as the method of choice for the treatment of an undescended testicle in children.
