Activation of Janus kinase/signal transducer and activator of transcription 3 pathway by growth hormone-releasing hormone

Abstract

Growth hormone-releasing hormone (GHRH) can act as a potent growth factor in various cancers. The mitogenic activity of this neuropeptide is exerted through binding to the pituitary type receptors (GHRH-R) or their splice variants (SV). In the present work, we studied whether this hormone can activate the JAK2/STAT3 pathway which plays a crucial role in cancer cell proliferation and is also linked to carcinogenesis. We transfected HeLa human cervical cancer cells, which are not sensitive to GHRH analogs with the pGHRH-R. Transfected cells responded to the GHRH or its antagonist with an increase or a decrease in proliferation, respectively. These results were confirmed by the expression of proliferating cell nuclear antigen. We then showed that these effects are linked to the activation of the JAK2/STAT3 pathway. Our work demonstrates the activation of JAK/STAT3 pathway by GHRH and sheds further light to the mechanisms of the antitumorogenic action of GHRH antagonists.

Fig. 1

Western blot analysis of the expression of a GHRH in T47D human breast and HeLa human cervical cancer cells, b GHRH-R in T47D human breast and HeLa human cervical cancer cells, and c GHRH-R in HeLa human cervical cancer before and after the transfection with pcDNA3-GHRHR vector. Protein levels were normalized to β-actin signal

Fig. 2

a Effect of 1 μM GHRH (1–29)NH₂ and 1 μM GHRH antagonist JMR-132 on the proliferation rate (upper panel) and the expression of PCNA (lower panel) in the HeLa cervical carcinoma cells. NS Not significant. PCNA protein levels were normalized to β-actin signal. The results are representative of two independent experiments. b Effect of 1 μM GHRH (1–29)NH₂ and 1 μM GHRH antagonist JMR-132 on the proliferation rate (upper panel) and the expression of PCNA (lower panel) in the HeLa cells transfected with pcDNA3-GHRH-R vector. *P < 0.05 versus control, **P < 0.01 versus control. PCNA protein levels were normalized to β-actin signal. The results are representative of two independent experiments

Fig. 3

Activation of STAT3 in HeLa cells (a) and in HeLa-pcDNA3-GHRH-R cells (b) by 1 μΜ GHRH after 0, 5, or 10 min, and after 24 h. Protein levels were normalized to STAT3 signal (loading control). The figure is representative of two independent experiments

Fig. 4

Activation of JAK2 in HeLa cells (a) and in HeLa-pcDNA3-GHRH-R cells (b) by 1 μΜ GHRH after 0, 5, or 10 min, and after 24 h. Protein levels were normalized to JAK2 signal (loading control). The figure is representative of two independent experiments