A CC-SAM, for Coiled Coil-Sterile α Motif, Domain Targets the Scaffold KSR-1 to Specific Sites in the Plasma Membrane.

1Department of Molecular Biology, Cell Biology and Biochemistry, Brown University, Providence, RI 02903, USA.
Science Signaling (Impact Factor: 7.65). 12/2012; 5(255):ra94. DOI: 10.1126/scisignal.2003289
Source: PubMed

ABSTRACT Kinase suppressor of Ras-1 (KSR-1) is an essential scaffolding protein that coordinates the assembly of the mitogen-activated protein kinase (MAPK) module, consisting of the MAPK kinase kinase Raf, the MAPK kinase MEK (mitogen-activated or extracellular signal-regulated protein kinase kinase), and the MAPK ERK (extracellular signal-regulated kinase) to facilitate activation of MEK and thus ERK. Although KSR-1 is targeted to the cell membrane in part by its atypical C1 domain, which binds to phospholipids, other domains may be involved. We identified another domain in KSR-1 that we termed CC-SAM, which is composed of a coiled coil (CC) and a sterile α motif (SAM). The CC-SAM domain targeted KSR-1 to specific signaling sites at the plasma membrane in growth factor-treated cells, and it bound directly to various micelles and bicelles in vitro, indicating that the CC-SAM functioned as a membrane-binding module. By combining nuclear magnetic resonance spectroscopy and experiments in cultured cells, we found that membrane binding was mediated by helix α3 of the CC motif and that mutating residues in α3 abolished targeting of KSR-1 to the plasma membrane. Thus, in addition to the atypical C1 domain, the CC-SAM domain is required to target KSR-1 to the plasma membrane.

1 Follower
  • [Show abstract] [Hide abstract]
    ABSTRACT: Store-operated calcium (Ca(2+)) entry (SOCE) is a vital Ca(2+) signaling pathway in nonexcitable as well as electrically excitable cells, regulating countless physiological and pathophysiological pathways. Stromal interaction molecules (STIMs) are the principal regulating molecules of SOCE, sensing changes in sarco-/endoplasmic reticulum (S/ER) luminal Ca(2+) levels and directly interacting with the Orai channel subunits to orchestrate the opening of Ca(2+) release-activated Ca(2+) (CRAC) channels. Recent atomic resolution structures on human STIM1 and STIM2 have illuminated critical mechanisms of STIM function in SOCE; further, the first high-resolution structure of the Drosophila melanogaster Orai channel has revealed vital data on the atomic composition of the CRAC channel pore and the assembly of individual Orai subunits. This chapter focuses on the mechanistic information garnered from these high-resolution structures and the supporting biophysical, biochemical, and live cell work that has enhanced our understanding of the relationship between STIM and Orai structural features and CRAC channel function.
    Current Topics in Membranes 01/2013; 71:59-93. DOI:10.1016/B978-0-12-407870-3.00003-2 · 1.77 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The molecular scaffold Kinase Suppressor of Ras 1 (KSR1) regulates the activation of the Raf/MEK/ERK signal transduction pathway. KSR1 disruption in mouse embryo fibroblasts (MEFs) abrogates growth factor-induced ERK activation, H-Ras(V12)-induced replicative senescence, and H-Ras(V12)-induced transformation. Caveolin-1 has been primarily described as a major component of the coating structure of caveolae, which can serve as a lipid binding adaptor protein and coordinates the assembly of Ras, Raf, MEK, and ERK. In this study, we show that KSR1 interacts with caveolin-1 and is responsible for MEK and ERK redistribution to caveolin-1 rich fractions. The interaction between KSR1 and caveolin-1 is essential for optimal activation of ERK, as a KSR1 mutant unable to interact with caveolin-1 does not efficiently mediate growth factor-induced ERK activation at the early stages of pathway activation. Furthermore, abolishing the KSR1-caveolin-1 interaction increases growth factor demands to promote H-Ras(V12)-induced proliferation and has adverse effects on H-Ras(V12)-induced cellular senescence and transformation. These data show that caveolin-1 is necessary for optimal KSR1-dependent ERK activation by growth factors and oncogenic Ras.
    Molecular and Cellular Biology 07/2014; 34(18). DOI:10.1128/MCB.01633-13 · 5.04 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The kinase suppressor of Ras 2 (KSR2) is a scaffold protein for the extracellular signal-regulated protein kinase (ERK) signaling pathway. KSR2 mediates germline mpk-1 (Caenorhabditis elegans ERK) phosphorylation in C. elegans and has been implicated the regulation of meiosis. KSR2-/- mice exhibit metabolic abnormalities and are reproductively impaired. The role of KSR2 in meiosis and fertility in mice has yet to be elucidated. Here, we describe a novel truncated KSR2 mRNA identified in mouse testes (T-KSR2). Further analysis demonstrates T-KSR2 is specific to mouse testes and mature sperm cells. The detection of T-KSR2 may enhance our understanding of mechanisms controlling spermatogenesis and fertility.
    04/2014; 4. DOI:10.1016/j.fob.2014.04.004