title: Polyamine-modulated expression of c-myc plays a critical role in stimulation of normal intestinal epithelial cell proliferation.
abstract: The nuclear protein c-Myc is a transcription factor involved in the control of cell cycle. Our previous studies indicated that cellular polyamines are absolutely required for cell proliferation in crypts of small intestinal mucosa and that polyamines have the ability to stimulate expression of the c-myc gene. The current study went further to determine whether induced nuclear c-Myc plays a role in stimulation of cell proliferation by polyamines in intestinal crypt cells (IEC-6 line). Exposure of normal quiescent cells after 24-h serum deprivation to 5% dialyzed fetal bovine serum (dFBS) increased both cellular polyamines and expression of the c-myc gene. Increased c-Myc protein formed heterodimers with its binding partner, Max, and specifically bound to the Myc/Max binding site, which was associated with an increase in DNA synthesis. Depletion of cellular polyamines by pretreatment with alpha-difluoromethylornithine (DFMO) prevented increases in c-myc expression and DNA synthesis induced by 5% dFBS. c-Myc gene transcription and cell proliferation decreased in polyamine-deficient cells, whereas the natural polyamine spermidine given together with DFMO maintained c-myc gene expression and cell growth at normal levels. Disruption of c-myc expression using specific c-myc antisense oligomers not only inhibited normal cell growth (without DFMO) but also prevented the restoration of cell proliferation by spermidine in polyamine-deficient cells. Ectopic expression of wild-type c-myc by recombinant adenoviral vector containing c-myc cDNA increased cell growth. These results indicate that polyamine-induced nuclear c-Myc interacts with Max, binds to the specific DNA sequence, and plays an important role in stimulation of normal intestinal epithelial cell proliferation.
authors.affiliation: Department of Surgery, University of Maryland School of Medicine, Baltimore, Maryland 21201, USA.
authors.forename: Lan
authors.initials: L
authors.lastname: Liu
authors.forename: Li
authors.initials: L
authors.lastname: Li
authors.forename: Jaladanki N
authors.initials: JN
authors.lastname: Rao
authors.forename: Tongtong
authors.initials: T
authors.lastname: Zou
authors.forename: Huifang M
authors.initials: HM
authors.lastname: Zhang
authors.forename: Dessy
authors.initials: D
authors.lastname: Boneva
authors.forename: Marasa S
authors.initials: MS
authors.lastname: Bernard
authors.forename: Jian-Ying
authors.initials: JY
authors.lastname: Wang
mesh_terms: D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D050976:Basic-Leucine Zipper Transcription Factors; D001798:Blood Proteins / Q000494:pharmacology; D002455:Cell Division / Q000187:drug effects / Q000502:physiology; D004268:DNA-Binding Proteins / Q000378:metabolism; D004847:Epithelial Cells / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D015870:Gene Expression / Q000187:drug effects / Q000502:physiology; D006801:Humans; D007413:Intestinal Mucosa / Q000166:cytology*; D008934:Mitogens / Q000494:pharmacology; D020319:Oligodeoxyribonucleotides, Antisense / Q000494:pharmacology; D011073:Polyamines / Q000378:metabolism* / Q000494:pharmacology; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics* / Q000378:metabolism*; D012333:RNA, Messenger / Q000096:biosynthesis / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects / Q000502:physiology
chemical_list: D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D050976:Basic-Leucine Zipper Transcription Factors; D001798:Blood Proteins; D004268:DNA-Binding Proteins; C499330:MAX protein, human; C489427:MYC protein, human; D008934:Mitogens; C067850:Myc associated factor X; D020319:Oligodeoxyribonucleotides, Antisense; D011073:Polyamines; D016271:Proto-Oncogene Proteins c-myc; D012333:RNA, Messenger; D014157:Transcription Factors