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Activation of a serine/threonine kinase signaling pathway by transforming growth factor type beta
Abstract:
Transforming growth factor type beta (TGF-beta) is a multifunctional factor that regulates proliferation and differentiation of many cell types. TGF-beta mediates its effects by binding to and activating cell surface receptors that possess serine/threonine kinase activity. However, the intracellular signaling pathways through which TGF-beta receptors act remain largely unknown. Here we show that TGF-beta activates a 78-kDa protein (p78) serine/threonine kinase as evidenced by an in-gel kinase assay. Ligand-induced activation of the kinase was near-maximal 5 min after TGF-beta addition to the cells and occurred exclusively on serine and threonine residues. This kinase is distinct from TGF-beta receptor type II, as well as several cytoplasmic serine/threonine kinases of similar size, including protein kinase C, Raf, mitogen-activated protein kinase kinase kinase, and ribosomal S6 kinase. Indeed, these kinases can be separated almost completely from p78 kinase by immunoprecipitation with specific antibodies. Furthermore, using different cell lines, we demonstrate that p78 kinase is activated only in cells for which TGF-beta can act as a growth inhibitory factor. These data raise the interesting possibility that protein serine/threonine kinases contribute to the intracellular relay of biological signals originating from receptor serine/threonine kinases such as the TGF-beta receptors.
Insights
Transforming growth factor-beta (TGF-beta) activates a novel 78-kDa protein kinase (p78) in cells. This kinase is involved in TGF-beta
Area of Science:
- Cell Biology
- Molecular Signaling
- Biochemistry
Background:
- Transforming growth factor-beta (TGF-beta) is a key regulator of cell proliferation and differentiation.
- TGF-beta exerts its effects through cell surface receptors with serine/threonine kinase activity.
- The intracellular signaling pathways downstream of TGF-beta receptors are not fully understood.
Purpose of the Study:
- To identify and characterize intracellular signaling molecules activated by TGF-beta.
- To investigate the role of protein kinases in mediating TGF-beta's biological effects.
Main Methods:
- Utilized in-gel kinase assays to detect kinase activity.
- Employed immunoprecipitation with specific antibodies to differentiate kinases.
- Tested kinase activation across various cell lines with differing TGF-beta responses.
Main Results:
- Identified and characterized a novel 78-kDa protein (p78) serine/threonine kinase activated by TGF-beta.
- Kinase activation was rapid (near-maximal at 5 min) and occurred on serine and threonine residues.
- The p78 kinase is distinct from known kinases like protein kinase C and Raf, and its activation correlated with TGF-beta's growth inhibitory effects.
Conclusions:
- TGF-beta activates a specific p78 serine/threonine kinase, suggesting its involvement in TGF-beta signaling.
- This finding provides a potential link between receptor serine/threonine kinases and intracellular signaling cascades.
- Protein serine/threonine kinases may play a crucial role in relaying signals from TGF-beta receptors.