title: Brain-derived neurotrophic factor-, epidermal growth factor-, or A-Raf-induced growth of HaCaT keratinocytes requires extracellular signal-regulated kinase.
abstract: The epidermal growth factor (EGF) receptor plays an important role in epithelial cells by controlling cell proliferation and survival. Keratinocytes also express another class of receptor tyrosine kinases, the neurotrophin receptors. To analyze the biological role of the neurotrophin brain-derived neurotrophic factor (BDNF) in keratinocytes, we expressed the BDNF receptor TrkB in immortalized human HaCaT keratinocytes. Stimulation of HaCaT-TrkB cells with BDNF induced DNA synthesis and increased mitochondrial reduction capacities, both indications of proliferating cells. An analysis of the signal transduction cascade revealed that the activated TrkB receptor effectively utilized components of the EGF receptor signaling pathway to control cell proliferation. Mitogenic signaling induced by BDNF or EGF was completely abrogated by the MAP kinase kinase inhibitor PD-98059, whereas inhibition of phosphatidylinositol 3-kinase by wortmannin only delayed the proliferative response. The importance of the extracellular signal-regulated kinase signaling pathway for growth of HaCaT keratinocytes was further demonstrated with HaCaT cells engineered to express an inducible A-Raf-estrogen receptor fusion protein (DeltaA-Raf:ER). Despite differences in the amplitude and duration of extracellular signal-regulated kinase activation, HaCaT cells expressing DeltaA-Raf:ER proliferated after activation of mutant A-Raf protein kinase. Proliferation was completely inhibited by PD-98059. Proliferation of HaCaT cells induced by EGF, BDNF, or DeltaA-Raf:ER was also accompanied by biosynthesis of the transcription factors Egr-1 and c-Jun, suggesting that these proteins may be part of the mitogenic signaling cascade.
authors.affiliation: Dept. of Medical Biochemistry and Molecular Biology, Bldg. 44, Univ. of Saarland Medical Center, D-66421 Homburg, Germany.
authors.forename: Oliver G
authors.initials: OG
authors.lastname: Rössler
authors.forename: Gerald
authors.initials: G
authors.lastname: Thiel
mesh_terms: D019208:Brain-Derived Neurotrophic Factor / Q000494:pharmacology*; D002455:Cell Division / Q000187:drug effects / Q000502:physiology; D002461:Cell Line, Transformed; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000235:genetics; D051766:Early Growth Response Protein 1; D004789:Enzyme Activation / Q000502:physiology; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D066246:ErbB Receptors / Q000378:metabolism; D006801:Humans; D017874:Immediate-Early Proteins / Q000096:biosynthesis / Q000235:genetics; D015603:Keratinocytes / Q000166:cytology* / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D048491:Proto-Oncogene Proteins A-raf; D051057:Proto-Oncogene Proteins c-akt; D016755:Proto-Oncogene Proteins c-jun / Q000096:biosynthesis / Q000235:genetics; D019908:Proto-Oncogene Proteins c-raf / Q000235:genetics / Q000494:pharmacology*; D020813:Receptor, trkB / Q000378:metabolism; D011960:Receptors, Estrogen / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000494:pharmacology; D014157:Transcription Factors / Q000096:biosynthesis / Q000235:genetics; D015533:Transcriptional Activation / Q000187:drug effects
chemical_list: D019208:Brain-Derived Neurotrophic Factor; D004268:DNA-Binding Proteins; C497325:EGR1 protein, human; D051766:Early Growth Response Protein 1; D017874:Immediate-Early Proteins; D011518:Proto-Oncogene Proteins; D016755:Proto-Oncogene Proteins c-jun; D011960:Receptors, Estrogen; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; D004815:Epidermal Growth Factor; D066246:ErbB Receptors; D020813:Receptor, trkB; D017346:Protein Serine-Threonine Kinases; D048491:Proto-Oncogene Proteins A-raf; D051057:Proto-Oncogene Proteins c-akt; D019908:Proto-Oncogene Proteins c-raf; D020928:Mitogen-Activated Protein Kinases