Gene expression and tyrosine kinase activity of insulin receptor in uterine leiomyoma and matched myometrium

Insulin resistance due to lipid-induced signaling defects could be prevented by mahanine

It is well known that free fatty acids (FFAs) play a key role in implementing insulin resistance and type 2 diabetes. Resources of chemical compounds that intervene the derogatory effect of FFAs are indeed very limited. We have isolated mahanine, a carbazole alkaloid, from the leaves of Murraya koenegii that prevented palmitate-induced inhibition of insulin-stimulated phosphorylation of IRbeta, PI3K, PDK1, and Akt in L6 myotubes. This was also reflected in the palmitate-induced inhibition of insulin-stimulated [(3)H] 2-DOG uptake by L6 myotubes, where palmitate adverse effect was significantly blocked by mahanine. Previous reports indicated that one of the major targets of lipid-induced damage in insulin signaling pathway resulting impairment of insulin sensitivity is insulin receptor (IR). Here, we have observed that palmitate significantly increased pPKCepsilon in both cytosol and nuclear region of L6 myotubes in comparison to control. Translocation of pPKCepsilon to the nucleus was associated with the impairment of HMGA1, the architectural transcription factor of IR gene and all these were reversed by mahanine. Palmitate-induced activation of IKK/IkappaBeta/NF-kappaBeta pathway was also attenuated by mahanine. Taken together, mahanine showed encouraging possibility to deal with lipid induced insulin resistance. In order to examine it further, mahanine was administered on nutritionally induced type 2 diabetic golden hamsters; it significantly improved hyperglycemia in all the treated animals. Our results, therefore, suggest that mahanine acts on two important sites of lipid induced insulin resistance (i) impairment of IR gene expression and (ii) activation of NF-kappaBeta pathway, thus, showing promise for its therapeutic choice for type 2 diabetes.

Differential expression of receptor tyrosine kinases (RTKs) and IGF-I pathway activation in human uterine leiomyomas

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-IRbeta and phosphorylated IGF-IRbeta. 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-IRbeta, 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-IRbeta 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.

Insulin receptor tyrosine kinase activity and substrate 1 (IRS-1) expression in human myometrium and leiomyoma

BACKGROUND

Uterine leiomyomas are the commonest tumors of the genital tract. Growth factors seem to be implicated in the development of leiomyoma.

OBJECTIVE

To determine the insulin receptor (IR) tyrosine kinase activity--phosphorylation of exogenous substrate poly(Glu 4: Tyr 1)--and insulin receptor substrate 1 expression in normal myometrium and leiomyoma.

STUDY DESIGN

The study group consisted of 12 women with leiomyoma undergoing routine hysterectomy. Samples of leiomyoma and adjacent normal myometrium were obtained at the time of operation. Plasma membrane fractions were prepared and samples were incubated with and without insulin and incubated with exogenous substrate poly(Glu 4: Tyr 1). IRS-1 expression was studied in the whole lysate via Western blotting using specific antibodies. Data were analyzed using Student's t-test.

RESULTS

The phosphorylation of the exogenous substrate poly(Glu 4: Tyr 1) in myometrium (1.566+/-0.177) and in leiomyoma (1.98+/-0.612) were similar (P=0.774). The IRS-1 levels in myometrium (0.190+/-0.022) and in leiomyoma (0.226+/-0.022) were not different (P=0.184).

CONCLUSIONS

There was no difference in IR tyrosine kinase activity (phosphorylation of exogenous substrate) and IRS-1 expression between normal myometrium and leiomyomata. Other steps in the insulin signaling cascade require further study to investigate the role of insulin receptor in leiomyomata.