title: Role of kinase suppressor of Ras-1 in neuronal survival signaling by extracellular signal-regulated kinase 1/2.
abstract: Scaffolding proteins including kinase suppressor of Ras-1 (KSR1) determine specificity of signaling by extracellular signal-regulated kinase 1/2 (ERK1/2), enabling it to couple diverse extracellular stimuli to various cellular responses. The scaffolding protein(s) that contributes to ERK1/2-mediated neuronal survival has not yet been identified. In cultured rat cortical neurons, BDNF activates ERK1/2 to enhance neuronal survival by suppressing DNA damage- or trophic deprivation-induced apoptosis. Here we report that in this system, BDNF increased KSR1 association with activated ERK1/2, whereas KSR1 knockdown with a short hairpin (sh) RNA reduced BDNF-mediated activation of ERK1/2 and protection against a DNA-damaging drug, camptothecin (CPT). In contrast, BDNF suppression of trophic deprivation-induced apoptosis was unaffected by shKSR1 although blocked by shERK1/2. Also, overexpression of KSR1 enhanced BDNF protection against CPT. Therefore, KSR1 is specifically involved in antigenotoxic activation of ERK1/2 by BDNF. To test whether KSR1 contributes to ERK1/2 activation by other neuroprotective stimuli, we used a cAMP-elevating drug, forskolin. In cortical neurons, ERK1/2 activation by forskolin was protein kinase A (PKA) dependent but TrkB (receptor tyrosine kinase B) independent and was accompanied by the increased association between KSR1 and active ERK1/2. Forskolin suppressed CPT-induced apoptosis in a KSR1 and ERK1/2-dependent manner. Inhibition of PKA abolished forskolin protection, whereas selective PKA activation resulted in an ERK1/2- and KSR1-mediated decrease in apoptosis. Hence, KSR1 is critical for the antiapoptotic activation of ERK1/2 by BDNF or cAMP/PKA signaling. In addition, these novel data indicate that stimulation of cAMP signaling is a candidate neuroprotective strategy to intervene against neurotoxicity of DNA-damaging agents.
authors.affiliation: Kentucky Spinal Cord Injury Research Center, University of Louisville, Louisville, Kentucky 40292, USA.
authors.forename: Erzsebet
authors.initials: E
authors.lastname: Szatmari
authors.forename: Katarzyna B
authors.initials: KB
authors.lastname: Kalita
authors.forename: Giorgi
authors.initials: G
authors.lastname: Kharebava
authors.forename: Michal
authors.initials: M
authors.lastname: Hetman
mesh_terms: D000818:Animals; D002470:Cell Survival / Q000502:physiology; D002478:Cells, Cultured; D019950:Mitogen-Activated Protein Kinase 1 / Q000502:physiology*; D048052:Mitogen-Activated Protein Kinase 3 / Q000502:physiology*; D009474:Neurons / Q000201:enzymology*; D011494:Protein Kinases / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000502:physiology*
chemical_list: D011494:Protein Kinases; C097199:KSR-1 protein kinase; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3