title: Cellular stress-induced up-regulation of FMRP promotes cell survival by modulating PI3K-Akt phosphorylation cascades.
abstract: BACKGROUND
  Fragile X syndrome (FXS), the most commonly inherited mental retardation and single gene cause of autistic spectrum disorder, occurs when the Fmr1 gene is mutated. The product of Fmr1, fragile X linked mental retardation protein (FMRP) is widely expressed in HeLa cells, however the roles of FMRP within HeLa cells were not elucidated, yet. Interacting with a diverse range of mRNAs related to cellular survival regulatory signals, understanding the functions of FMRP in cellular context would provide better insights into the role of this interesting protein in FXS. Using HeLa cells treated with etoposide as a model, we tried to determine whether FMRP could play a role in cell survival.
  
  
  METHODS
  Apoptotic cell death was induced by etoposide treatment on Hela cells. After we transiently modulated FMRP expression (silencing or enhancing) by using molecular biotechnological methods such as small hairpin RNA virus-induced knock down and overexpression using transfection with FMRP expression vectors, cellular viability was measured using propidium iodide staining, TUNEL staining, and FACS analysis along with the level of activation of PI3K-Akt pathway by Western blot. Expression level of FMRP and apoptotic regulator BcL-xL was analyzed by Western blot, RT-PCR and immunocytochemistry.
  
  
  RESULTS
  An increased FMRP expression was measured in etoposide-treated HeLa cells, which was induced by PI3K-Akt activation. Without FMRP expression, cellular defence mechanism via PI3K-Akt-Bcl-xL was weakened and resulted in an augmented cell death by etoposide. In addition, FMRP over-expression lead to the activation of PI3K-Akt signalling pathway as well as increased FMRP and BcL-xL expression, which culminates with the increased cell survival in etoposide-treated HeLa cells.
  
  
  CONCLUSIONS
  Taken together, these results suggest that FMRP expression is an essential part of cellular survival mechanisms through the modulation of PI3K, Akt, and Bcl-xL signal pathways.
authors.affiliation: Department of Pharmacology, College of Pharmacy and Research Institute of Pharmaceutical Sciences, Seoul National University, Seoul, Korea.
authors.forename: Se Jin
authors.initials: SJ
authors.lastname: Jeon
authors.forename: Jung Eun
authors.initials: JE
authors.lastname: Seo
authors.forename: Sung-Il
authors.initials: SI
authors.lastname: Yang
authors.forename: Ji Woong
authors.initials: JW
authors.lastname: Choi
authors.forename: David
authors.initials: D
authors.lastname: Wells
authors.forename: Chan Young
authors.initials: CY
authors.lastname: Shin
authors.forename: Kwang Ho
authors.initials: KH
authors.lastname: Ko
mesh_terms: D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology; D002470:Cell Survival / Q000187:drug effects / Q000235:genetics; D005047:Etoposide / Q000494:pharmacology; D051860:Fragile X Messenger Ribonucleoprotein 1 / Q000096:biosynthesis* / Q000235:genetics; D005600:Fragile X Syndrome / Q000235:genetics / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D013312:Stress, Physiological; D015854:Up-Regulation; D051020:bcl-X Protein / Q000235:genetics / Q000378:metabolism
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D005047:Etoposide; D051860:Fragile X Messenger Ribonucleoprotein 1; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D051020:bcl-X Protein; C494811:BCL2L1 protein, human; C497683:FMR1 protein, human