STAT3 upregulation in pituitary somatotroph adenomas induces growth hormone hypersecretion
Cuiqi Zhou, … , Kolja Wawrowsky, Shlomo Melmed
Cuiqi Zhou, … , Kolja Wawrowsky, Shlomo Melmed
Published March 16, 2015
Citation Information: J Clin Invest. 2015;125(4):1692-1702. https://doi.org/10.1172/JCI78173.
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Research Article Endocrinology

STAT3 upregulation in pituitary somatotroph adenomas induces growth hormone hypersecretion

Abstract

Pituitary somatotroph adenomas result in dysregulated growth hormone (GH) hypersecretion and acromegaly; however, regulatory mechanisms that promote GH hypersecretion remain elusive. Here, we provide evidence that STAT3 directly induces somatotroph tumor cell GH. Evaluation of pituitary tumors revealed that STAT3 expression was enhanced in human GH-secreting adenomas compared with that in nonsecreting pituitary tumors. Moreover, STAT3 and GH expression were concordant in a somatotroph adenoma tissue array. Promoter and expression analysis in a GH-secreting rat cell line (GH3) revealed that STAT3 specifically binds the Gh promoter and induces transcription. Stable expression of STAT3 in GH3 cells induced expression of endogenous GH, and expression of a constitutively active STAT3 further enhanced GH production. Conversely, expression of dominant-negative STAT3 abrogated GH expression. In primary human somatotroph adenoma-derived cell cultures, STAT3 suppression with the specific inhibitor S3I-201 attenuated GH transcription and reduced GH secretion in the majority of derivative cultures. In addition, S3I-201 attenuated somatotroph tumor growth and GH secretion in a rat xenograft model. GH induced STAT3 phosphorylation and nuclear translocation, indicating a positive feedback loop between STAT3 and GH in somatotroph tumor cells. Together, these results indicate that adenoma GH hypersecretion is the result of STAT3-dependent GH induction, which in turn promotes STAT3 expression, and suggest STAT3 as a potential therapeutic target for pituitary somatotroph adenomas.

Authors

Cuiqi Zhou, Yonghui Jiao, Renzhi Wang, Song-Guang Ren, Kolja Wawrowsky, Shlomo Melmed

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Figure 2

STAT3 binds the rat Gh promoter and activates Gh transcription.

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STAT3 binds the rat Gh promoter and activates Gh transcription. (A) Repr...
(A) Representation of potential STAT-binding motifs on the rat Gh promoter and 3 primer pairs designed for ChIP. (B) STAT3 binds the Gh promoter, as assessed by ChIP. Normalized inputs of GH3 chromatin DNA were pulled down by STAT3 or negative IgG antibodies. The DNA template was amplified by PCR using primer pairs 1–3. Quantitative ChIP results are shown. Ratios of the “ChIP band” to the “input band” were calculated, and IgG controls were normalized to 1. ChIP experiments and PCR reactions were repeated twice, and quantification is presented as mean ± SEM. (C) STAT3 activates Gh transcription, as assessed by a dual-luciferase reporter assay. Equal amounts of STAT3 or pIRES2-ZsGreen1 (ZsGreen) stable cells (5 × 105 cells per well) were transfected with the rat Gh promoter –4,192/+167, –1,752/+167, or pGL4.10 control, and luciferase activity was measured. (D) STAT3 inhibitor S3I-201 suppresses Gh transcription. GH3 cells were transfected with rat Gh promoter –4,192/+167, –1,752/+167, or pGL4.10 control and treated with increasing amounts of S3I-201. Transcriptional activities of rat Gh promoter –4,192/+167 and –1,752/+167 were both normalized to pGL4.10 controls. Ten ng pGL4.74 (hRluc/TK) plasmid was cotransfected to normalize transfection efficiency. Experiments were repeated 3 times. C and D show representative experiments, and cells were transfected or treated in triplicate wells. Results are presented as mean ± SEM. Student’s t test, *P < 0.01.