title: MXD3 regulation of DAOY cell proliferation dictated by time course of activation.
abstract: BACKGROUND
  MXD3 is a basic-helix-loop-helix-leucine-zipper transcription factor involved in cellular proliferation. In previous studies we demonstrated that knock-down of MXD3 in the human medulloblastoma cell line DAOY resulted in decreased proliferation. Surprisingly, overexpression of MXD3 in DAOY cells also decreased proliferation and increased cell death, suggesting that persistent expression of MXD3 triggers an apoptotic response, perhaps as a fail-safe mechanism. To investigate this apparent paradox in detail we developed a tamoxifen inducible system to analyze the temporal effects of MXD3 in the proliferation and transcriptional response of DAOY cells upon acute induction compared with long-term expression of MXD3.
  
  
  RESULTS
  We find that acute induction of MXD3 initially promotes cell cycle progression as assessed by a transient increase in bromodeoxyuridine incorporation. However, persistent induction of MXD3 ultimately results in decreased proliferation based on cell counts. Finally, with microarray expression profiling and gene ontology analysis we identify several major pathways enriched in response to acute (immune response, apoptosis, cell cycle) versus persistent (cell adhesion) MXD3 activation.
  
  
  CONCLUSIONS
  In this study, we demonstrate that acute MXD3 activation results in a transient increase in cell proliferation while persistent activation of MXD3 eventually results in an overall decrease in cell number, suggesting that the time course of MXD3 expression dictates the cellular outcome. Microarray expression profiling and gene ontology analysis indicate that MXD3 regulates distinct genes and pathways upon acute induction compared with persistent expression, suggesting that the cellular outcome is specified by changes in MXD3 transcriptional program in a time-dependent manner.
authors: Tin
authors: T
authors: Ngo
authors: Gustavo A
authors: GA
authors: Barisone
authors: Kit S
authors: KS
authors: Lam
authors: Department of Pharmacology, UC Davis School of Medicine, 451 Health Sciences Drive, 3503 GBSF, Davis, CA 95616, USA. ediaz@ucdavis.edu.
authors: Elva
authors: E
authors: Dίaz
mesh_terms: D017209:Apoptosis; D001921:Brain / Q000378:metabolism / Q000473:pathology; D001932:Brain Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008527:Medulloblastoma / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D021381:Protein Transport; D012097:Repressor Proteins / Q000235:genetics* / Q000378:metabolism; D015854:Up-Regulation
chemical_list: C543450:MXD3 protein, human; D012097:Repressor Proteins