Differential Expression of Receptor Tyrosine Kinases (RTKs) and IGF-I Pathway Activation in Human Uterine Leiomyomas

Abstract

Uterine leiomyomas (fibroids) are benign tumors that are prevalent in women of reproductive age. Research suggests that activated receptor tyrosine kinases (RTKs) play an important role in the enhanced proliferation observed in fibroids. In this study, a phospho-RTK array technique was used to detect RTK activity in leiomyomas compared with myometrial tissue. We found that fifteen out of seventeen RTKs evaluated in this study were highly expressed (P < 0.02-0.03) in the leiomyomas, and included the IGF-I/IGF-IR, EGF/EGFR, FGF/FGF-R, HGF/HGF-R, and PDGF/PDGF-R gene families. Due to the higher protein levels of IGF-IR observed in leiomyomas by us in earlier studies, we decided to focus on the activation of the IGF-IR, its downstream effectors, and MAPKp44/42 to confirm our earlier findings; and validate the significance of the increased IGF-IR phosphorylation observed by RTK array analysis in this study. We used immunolocalization, western blot, or immunoprecipitation studies and confirmed that leiomyomas overexpressed IGF-IRβ and phosphorylated IGF-IRβ. Additionally, we showed that the downstream effectors, Shc, Grb2, and MAPKp44/42 (P < 0.02-0.001) were also overexpressed and involved in IGF-IR signaling in these tumors, while IRS-I, PI3K, and AKT were not. In vitro studies showed that IGF-I (100 ng/mL) increased the proliferation of uterine leiomyoma cells (UtLM) (P < 0.0001), and that phosphorylated IGF-IRβ, Shc, and MAPKp44/42 were also overexpressed in IGF-I-treated UtLM cells (P < 0.05), similar to the tissue findings. A neutralizing antibody against the IGF-IRβ blocked these effects. These data indicate that overexpression of RTKs and, in particular, activation of the IGF-IR signaling pathway through Shc/Grb2/MAPK are important in mediating uterine leiomyoma growth. These data may provide new anti-tumor targets for noninvasive treatment of fibroids.

All-trans-retinoic acid mediates changes in PI3K and retinoic acid signaling proteins of leiomyomas

“…It regulates fundamental cellular functions, including transcription, translation, proliferation, growth, and survival (14,15). Recently, we, as well as other groups, presented evidence on the involvement of the PI3K/Akt signaling in leiomyoma development by demonstrating differential changes related to PI3K/Akt signaling proteins in leiomyomas compared with myometrial cells (16)(17)(18). Other investigators have shown that the PI3K/Akt pathway plays an important role in RA signaling for certain cell types, such as SH-SY5Y human neuroblastoma cells and HL-60 cells (19,20).…”

Increased expression of tuberin in human uterine leiomyoma

“…We proceeded to examine the activity of the p42/44 MAPK pathway (25)(26)(27), which is critical in the regulation of SMC proliferation and migration (28,29). Our results showed that leiomyoma tissues have significantly lower levels of phospho-MAPK than in myometrium tissues, but total MAPK levels were similar in both tissues (Fig.…”

Involvement of FKHR (FOXO1) transcription factor in human uterus leiomyoma growth

“…Recent publications from our laboratory have shown that abundant expression and activation of Akt protein can be induced in the rat uterus by administration of E 2 (1), and the expression and activation of Akt can be detected in the leiomyoma and adjacent myometrium of human uteri (2,3). The level of Akt in leiomyomatous uteri changed in parallel with the expression of estrogen (E) and P receptors, cyclin D1 and the antiapoptotic Bcl-2 protein (2)(3)(4)(5). One of the most important substrates of Akt/protein kinase B are FOXO proteins.…”