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Growth hormone induces tyrosine phosphorylation of annexin I in rat osteosarcoma cells
J P Salles1, J C Netelenbos, M C Slootweg
1Research Institute for Endocrinology, Reproduction, and Metabolism, Free University Hospital, Amsterdam, The Netherlands.
Abstract:
GH induces phosphorylation of a number of cellular proteins, of which several have now been identified, such as mitogen-activated protein kinase, insulin receptor substrate-1, and members of the JAK kinase and STAT families of proteins. However, other phosphorylated proteins remain unidentified. Growth factors and cytokines, including epidermal growth factor, insulin, pp60v-scr, and angiotensin II, induce a rapid phosphorylation of annexin I, a 35-kDa member of the annexin family of Ca2+ and phospholipid-binding proteins. The osteoblast-like rat osteosarcoma cell-line UMR-106.01, in which GH acts as a mitogen via a high affinity GH receptor, was used as a model for GH-induced protein phosphorylation. It is demonstrated by immunoblotting and immunoprecipitation techniques that GH induces the phosphorylation of annexin I on tyrosine residues. This phosphorylation is dose and time dependent. Induction of annexin I phosphorylation is delayed compared with that of JAK2. These results identify annexin I as a protein that becomes tyrosine phosphorylated under the influence of GH and show that phosphorylation of annexin I is a general phenomenon that follows activation of a cell by hormones or cytokines.
Insights
Growth hormone (GH) triggers the phosphorylation of annexin I on tyrosine residues in rat osteosarcoma cells. This finding identifies annexin I as a key protein in GH signaling pathways.
Area of Science:
- Cellular Biology
- Molecular Endocrinology
- Signal Transduction
Background:
- Growth hormone (GH) activates intracellular signaling pathways, leading to the phosphorylation of various cellular proteins.
- While some GH-induced phosphoproteins are identified (e.g., MAPK, IRS-1, JAK/STAT), others remain unknown.
- Annexin I, a calcium and phospholipid-binding protein, is known to be phosphorylated by other growth factors and cytokines.
Purpose of the Study:
- To investigate whether GH induces the phosphorylation of annexin I in a specific cellular model.
- To characterize the nature and kinetics of GH-induced annexin I phosphorylation.
Main Methods:
- Utilized the UMR-106.01 rat osteosarcoma cell line, a model for GH-induced mitogenesis.
- Employed immunoblotting and immunoprecipitation techniques to detect and analyze protein phosphorylation.
Main Results:
- GH was demonstrated to induce the tyrosine phosphorylation of annexin I in UMR-106.01 cells.
- Annexin I phosphorylation by GH was shown to be both dose- and time-dependent.
- The onset of annexin I phosphorylation was observed to be delayed relative to JAK2 phosphorylation.
Conclusions:
- Annexin I is identified as a novel substrate for tyrosine phosphorylation mediated by growth hormone.
- GH-induced annexin I phosphorylation is a significant cellular event, highlighting its role in GH signaling.
- This phosphorylation phenomenon appears to be a general response to cellular activation by hormones and cytokines.