LIM Homeodomain Transcription Factor Isl-1 Enhances Follicle Stimulating Hormone-β and Luteinizing Hormone-β Gene Expression and Mediates the Activation of Leptin on Gonadotropin Synthesis

Abstract

The Lin-11, Isl-1, and Mec-3 (LIM) homeodomain transcription factor Isl-1 has been reported to be involved in pituitary development in the early stages of mouse embryogenesis. Our recent studies have shown that Isl-1 is mainly located in the pituitary gonadotropes throughout pituitary development and persists to adulthood. We still do not know the physiological functions of Isl-1 expression and its related mechanisms in the pituitary gland. The aim of the present study was to examine the hypothesis that Isl-1 is involved in regulating pituitary gonadotropin hormone (FSH/LH) production by activating FSHβ and LHβ gene expressions. We have shown that Isl-1 activates FSHβ and LHβ subunit promoters and endogenous gene transcription in LβT2 cells. In addition, Isl-1 overexpression significantly increased FSH synthesis and secretion but not LH. The actions of Isl-1 were not observed when the homeodomain or LIM1 domains are mutated. This demonstrates that Isl-1 induction of FSHβ and LHβ is by both direct and indirect binding of Isl-1 to DNA sequences. Furthermore, Isl-1 expressional level was up-regulated in LβT2 cells after exposure to GnRH, activin, and leptin. However, RNA interference-induced knockdown of Isl-1 significantly reduced the effect of leptin but did not obviously influence the stimulating effects of GnRH and activin on LH and FSH production. In conclusion, the results demonstrate that the LIM-homeodomain transcription factor Isl-1 functions to increase FSHβ/LHβ gene transcription, and mediates the effects of leptin on gonadotropin synthesis.

LIM-homeodomain Transcription Factor Isl-1 Mediates the Effect of Leptin on Insulin Secretion in Mice

“…To study the effect of the global serum leptin on Isl-1 expression, adult male mice were randomly divided into the high fat diet (HFD), the regular grain diet control, and fasted mice (n Ն 6 for each group) as previous reported (27,28), the HFD and control groups were fed 24 h, and the fasted group was starved for 24 h. The procedures for blood and tissue collections were similar to our previous report (29).…”

“…The ChIP experiment was performed as our report (29). Input and immunoprecipitated DNA were amplified by PCR using primers listed in Table 1.…”

“…The methods of the vector transfection and luciferase activity detection were performed as our report (29).…”

“…Common PCR-Real-time PCR and common PCR were performed as described previously (29). All RNA extractions were treated with RNase-free DNase 1 (Promega) for 1 h at 37 ºC.…”

“…Immunofluorescence-The immunofluorescence of pancreas sections and NIT cells was performed using methods described earlier (29). Antibodies against OBRa, OBRb, and Isl-1 were from R&D Systems, and anti-insulin antibody was from Invitrogen.…”