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Key Event Title
|Level of Biological Organization|
Key Event Components
|phosphorylation||transcription factor Sp1||increased|
Key Event Overview
AOPs Including This Key Event
Key Event Description
Specificity protein 1 (Sp1) is a member of the zinc finger transcription factors involved in many biological processes including cell cycle, cell differentiation, cell growth, apoptosis, immune responses, response to DNA damage, and chromatin remodeling. Sp1 can be phosphorylated by many kinases including PKA, PKC-zeta, ERK and CDK. Growth factors such as EGF, FGF2 and VEGF can phosphorylate Sp1 through ERK and MAPK, HGF can activate Sp1 through PI3K, MEK and PKC-zeta, and cyclin A through CDK2 (reviewed by Tan and Khachigian, 2009). There are five confirmed phosphorylation sites on Sp1: Ser59, Ser131, Thr453, Thr579, and Thr739 (Chu and Ferro, 2005). It is thought that changes in Sp1 phosphorylation status alters DNA-binding activity and hence facilitate induction or repression of gene transcription (Li et al., 2004).
How It Is Measured or Detected
DNA binding, promoter activation, and association with other protein factors are the 3 approaches that can be pursued to confirm Sp1 activation (Chu and Ferro, 2005). Altered levels of phosphorylation reportedly result in changed DNA-binding, so examining the phosphorylation status at the known sites (Ser59, Ser131, Thr453, Thr579, and Thr739) using Western blots with phospho-specific antibodies contributes to an understanding of Sp1 acticvation. Electrophoretic mobility shift assay (EMSA) and chromatin immunoprecipitation (ChIP) are DNA binding assays that can be used to assess transcription factor activity, and both have been used to interrogate Sp1 (Hewson et al., 2004). Specificity of Sp1 involvement in transcription of a given gene can be proven by inhibiting Sp1 with mithramycin A or C. This describes a very experimental approach; some protocols for e.g. DNA binding assays can be obtained via https://bio-protocol.org/. However, none of these methods is validated.
Domain of Applicability
Sp1 activation has been reported in mouse, rat and human, and Sp1 is orthologous between these species.
Barbier, D., Garcia-Verdugo, I., Pothlichet, J., Khazen, R., Descamps, D., Rousseau, K., Thornton, D., Si-Tahar, M., Touqui, L., Chignard, M., et al. (2012). Influenza A Induces the Major Secreted Airway Mucin MUC5AC in a Protease–EGFR–Extracellular Regulated Kinase–Sp1–Dependent Pathway. Am. J. Respir. Cell Mol. Biol. 47, 149–157.
Chu, S., and Ferro, T.J. (2005). Sp1: Regulation of gene expression by phosphorylation. Gene 348, 1–11.
Hewson, C.A., Edbrooke, M.R., and Johnston, S.L. (2004). PMA induces the MUC5AC respiratory mucin in human bronchial epithelial cells, via PKC, EGF/TGF-α, Ras/Raf, MEK, ERK and Sp1-dependent mechanisms. J. Mol. Biol. 344, 683-695.
Li, L., He, S., Sun, J.-M., and Davie, J.R. (2004). Gene regulation by Sp1 and Sp3. Biochem. Cell Biol. 82, 460-471.
Perrais, M., Pigny, P., Copin, M.C., Aubert, J.P., and Van Seuningen, I. (2002). Induction of MUC2 and MUC5AC mucins by factors of the epidermal growth factor (EGF) family is mediated by EGF receptor/Ras/Raf/extracellular signal-regulated kinase cascade and Sp1. J. Biol. Chem. 277, 32258-32267.