PathScan^® Multiplex Western Cocktail II: Phospho-p90RSK, Phospho-p53, Phospho-p38 MAPK and Phospho-S6 Ribosomal Protein Detection Cocktail II #5302

The 90 kDa ribosomal S6 kinases (RSK1-3) are a family of serine/threonine kinases broadly expressed in response to many growth factors, polypeptide hormones and neurotransmitters (1). p90RSK is activated by Erk1 and Erk2 in vitro and in vivo via phosphorylation (2). Several sites, such as Ser380, Thr359 and Ser363, are important for its activation (3).
The p53 tumor suppressor protein plays a major role in cellular response to DNA damage and other genomic aberrations. Activation of p53 can lead to either cell cycle arrest and DNA repair or apoptosis (4). p53 is phosphorylated at multiple sites in vivo and by several different protein kinases in vitro (5,6). DNA damage induces phosphorylation of p53 at Ser15 and Ser20 and leads to reduced interaction of p53 with its negative regulator, oncoprotein MDM2 (7).
p38 MAP kinase controls cellular responses to cytokines and stress (8-11). Like the SAPK/JNK pathway, p38 MAP kinase is activated by a variety of cellular stresses including osmotic shock, inflammatory cytokines, lipopolysaccharides (LPS), UV light and growth factors (8-12). MKK3, MKK6 and SEK activate p38 MAP kinase by phosphorylation at Thr180 and Tyr182.
Growth factors and mitogens induce the activation of p70 S6 kinase, which in turn phosphorylates the S6 ribosomal protein. Phosphorylation of S6 correlates with an increase in translation, particularly of mRNAs with an oligopyrimidine tract in their 5' untranslated regions (13). This group of mRNAs (5'TOP) encodes proteins involved in cell cycle progression and proteins that are part of the translational machinery, such as ribosomal proteins and elongation factors (13,14).