Growth Hormone Effects in Immune Stress: AKT/eNOS Signaling Module in the Cellular Response

Authors: Li, Congjun - Cj; Elsasser, Theodore; Kahl, Stanislaw

Submitted to: Molecular Endocrinology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/25/2009
Publication Date: 3/25/2009
Citation: Li, C., Elsasser, T.H., Kahl, S. 2009. AKT/eNOS Signaling Module Functions as a potential feedback loop in the growth hormone signaling pathway. Journal of Molecular Signaling. 4:1.

Interpretive Summary: After bacterial infection, the activation of the constitutive endothelial nitric-oxide synthase (eNOS) and expression of inducible NOS (iNOS) with subsequent nitric oxide production are among the early cellular responses. On the other hand, Growth hormone can affect the cell’s response to the infection. For example, the GH treatment can increase the eNOS and iNOS activities following an immune challenge. How these two pathways, immune-response and growth hormone, interact to each other (cross-talk) is the subject of this study. We used an established bovine cell line MDBK to investigate the critical control points of growth hormone stimulation, mainly Akt/PKB (Protein Kinase B) and eNOS. Using specific Akt/PKB and eNOS inhibitors and functional proteomic approach, we were able to detect the activities of multiple elements in signal transduction pathways, the downstream targets of Akt/PKB and the changes of those responses by treatment of growth hormone. Combining all the data, we propose that Akt/PKB-eNOS module likely functions not only as a positive affector but also as a negative feed back mediator of GH actions.

Technical Abstract: The activation of the constitutive endothelial nitric-oxide synthase (eNOS) and expression of inducible NOS (iNOS) with subsequent nitric oxide production are among the early cellular responses that follow in a systemic exposure of animals to lipopolysaccharide (LPS). Growth hormone (GH) has been shown to affect several sub-components of the acute phase response in addition to its ability to stimulate growth. The effects of GH treatment on components of the NO generating cascade to account for increases in NO production and protein nitration following an immune challenge indicating the cross-talking between multiple signaling pathways. In the present study we used an established bovine cell line (MDBK) to dissect the critical control points underlying GH-stimulated Akt/PKB and eNOS activity and the roles for Akt/PKB and eNOS signaling pathway in GH-response. Phosphorylation of Akt/PKB and eNOS appeared 15 to 30 min after GH treatment and was maximal at about 75 min; secondary administration of GH had no further effects on the level of phosphorylation of eNOS. Inhibiting the Akt/PKB activity reduced or eliminated the activation (phosphorylation) of eNOS. Using specific Akt/PKB and eNOS inhibitors and functional proteomic approach, we were able to detect the activities of multiple potential signal transduction pathway elements, the downstream targets of Akt/PKB pathway and the modification of those responses by treatment of GH. Combining the data from the in vitro experiments, and the functional proteomic analysis, we propose that Akt/eNOS signaling module may function as a potential feedback loop in GH signal pathway.