Estrogen receptor regulates insulin-like growth factor-I receptor gene expression in breast tumor cells: involvement of transcription factor Sp1

Abstract

The insulin-like growth factors, IGF-I and IGF-II are a family of mitogenic polypeptides with important roles in growth and differentiation. The biological actions of the IGFs are mediated by the IGF-I receptor (IGF-IR), a cell-surface tyrosine kinase, whose activation by serum IGF-I seems to be a key step in breast cancer initiation. Evidence accumulated indicates that estrogens stimulate the expression and activity of IGF axis components. The aim of our study was to examine the transcriptional mechanisms involved in regulation of IGF-IR gene expression by the estrogen receptor (ER). For this purpose, transient transfections using an IGF-IR promoter-luciferase reporter plasmid were performed in breast cancer-c derived ER-positive MCF-7 cells and isogenic ER-negative C4 cells. To examine the potential involvement of zinc-finger nuclear proteins in the transactivating effect of estrogens, chromatin immunoprecipitation (ChIP) experiments were performed using an Sp1 antibody, along with the Sp1-family-binding inhibitor Mithramycin A. The results obtained indicate that basal IGF-IR promoter activity was 5 . 8-fold higher in MCF-7 than in C4 cells. Estradiol treatment significantly activated the IGF-IR promoter in MCF-7, but not in C4 cells. Furthermore, the estrogen responsive region in the IGF-IR promoter was mapped to a GC-rich sequence located between nucleotides K40 and K188 in the 5 0 flanking region. ChIP experiments revealed that at least part of the estrogen effect on IGF-IR expression was mediated through activation of the Sp1 transcription factor. In summary, our studies demonstrate that IGF-IR gene transcription in breast cancer cells is controlled by interactions between ERa and Sp1. Dysregulated expression of the IGF-IR gene may have pathologic consequences with relevance in breast cancer etiology.

The faah gene is the first direct target of estrogen in the testis: role of histone demethylase LSD1

“…Thus, the latter dose was used in further experiments. Incidentally, it should be noted that concentrations in the high-nM range have been largely used to investigate gene transcriptional regulation by E 2 [23][24][25][26][27] or metabolic effect of this hormone [28]. Moreover, it has been shown that intratesticular concentrations are much higher than serum levels of E 2 [29].…”

Identification of a region in the human IRS2 promoter essential for stress induced transcription depending on SP1, NFI binding and ERK activation in HepG2 cells

“…SP1 has been described as an activator of many genes (Suske 1999). With respect to insulin/IGF1R signaling it has been shown that SP1 is also involved in the regulation of the insulin receptor gene itself (Foti et al 2003) as well as the IGF1R gene (Maor et al 2006). Since there are multiple potential binding sites for SP1 in the IRS2 promoter, Vassen et al (1999), the authors of the first description of the human IRS2 promoter sequence speculated about a major role for SP1 in the transcriptional regulation of the IRS2 gene (Vassen et al 1999).…”

Insulin-like Growth Factor-I Receptor (IGF-IR) Translocates to Nucleus and Autoregulates IGF-IR Gene Expression in Breast Cancer Cells

“…ChIP Assays-ChIP assays were performed as described previously (22,30). Briefly, MCF7 and C4.12.5 cells were crosslinked with 1% formaldehyde at 37°C for 10 min.…”

“…The IGFs and estrogen act in a synergistic fashion in breast epithelial cells (27), and both the MAPK and Akt pathways were shown to mediate the activation of ER␣ by IGF-I (28,29). On the other hand, estrogens regulate IGF-I signaling and the expression of key members of the IGF axis (30). Furthermore, estrogens were shown to induce a physical interaction between ER␣ and IGF-IR, leading to activation and phosphorylation of IGF-IR and downstream signaling molecules (31).…”