title: Hierarchical scaffolding of an ERK1/2 activation pathway.
abstract: BACKGROUND
  Scaffold proteins modulate cellular signaling by facilitating assembly of specific signaling pathways. However, there is at present little information if and how scaffold proteins functionally interact with each other.
  
  
  RESULTS
  Here, we show that two scaffold proteins, caveolin-1 and IQGAP1, are required for phosphorylation of the actin associated pool of extracellular signal regulated kinase 1 and 2 (ERK1/2) in response to protein kinase C activation. We show by immunofluorescence and proximity ligation assays, that IQGAP1 tethers ERK1/2 to actin filaments. Moreover, siRNA experiments demonstrate that IQGAP1 is required for activation of actin-bound ERK1/2. Caveolin-1 is also necessary for phosphorylation of actin-bound ERK1/2 in response to protein kinase C, but is dispensible for ERK1/2 association with actin. Simultaneous knock down of caveolin-1 and IQGAP1 decreases total phorbol ester-induced ERK1/2 phosphorylation to the same degree as single knock down of either caveolin-1 or IQGAP1, indicating that caveolin-1 and IQGAP1 operate in the same ERK activation pathway. We further show that caveolin-1 knock down, but not IQGAP1 knock down, reduces C-Raf phosphorylation in response to phorbol ester stimulation.
  
  
  CONCLUSIONS
  Based on our data, we suggest that caveolin-1 and IQGAP1 assemble distinct signaling modules, which are then linked in a hierarchical arrangement to generate a functional ERK1/2 activation pathway.
authors.affiliation: Department of Health Sciences, Boston University, Boston, MA 02215, USA. svetter@bu.edu.
authors.forename: Susanne
authors.initials: S
authors.lastname: Vetterkind
authors.forename: Ransom H
authors.initials: RH
authors.lastname: Poythress
authors.forename: Qian Qian
authors.initials: QQ
authors.lastname: Lin
authors.forename: Kathleen G
authors.initials: KG
authors.lastname: Morgan
mesh_terms: D000818:Animals; D051242:Caveolin 1 / Q000378:metabolism*; D002460:Cell Line; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics / Q000378:metabolism; D019908:Proto-Oncogene Proteins c-raf / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics; D051381:Rats; D015398:Signal Transduction; D020703:ras GTPase-Activating Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: C495537:Cav1 protein, rat; D051242:Caveolin 1; C101203:IQ motif containing GTPase activating protein 1; D034741:RNA, Small Interfering; D020703:ras GTPase-Activating Proteins; D011494:Protein Kinases; C097199:KSR-1 protein kinase; C482123:Braf protein, rat; D048493:Proto-Oncogene Proteins B-raf; D019908:Proto-Oncogene Proteins c-raf; D011493:Protein Kinase C; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3