Polyamine-modulated expression of c-myc plays a critical role in stimulation of normal intestinal epithelial cell proliferation

• Published in: American Journal of Physiology: Cell Physiology 2005-01, Vol.288 (1), p.C89-C99
• Main Authors: Liu, Lan, Li, Li, Rao, Jaladanki N, Zou, Tongtong, Zhang, Huifang M, Boneva, Dessy, Bernard, Marasa S, Wang, Jian-Ying
• Format: Article
• Language: English
• Subjects: Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; Basic-Leucine Zipper Transcription Factors; Blood Proteins - pharmacology; Cell Division - drug effects; Cell Division - physiology; DNA-Binding Proteins - metabolism; Epithelial Cells - cytology; Epithelial Cells - drug effects; Epithelial Cells - physiology; Gene Expression - drug effects; Gene Expression - physiology; Humans; Intestinal Mucosa - cytology; Mitogens - pharmacology; Oligodeoxyribonucleotides, Antisense - pharmacology; Polyamines - metabolism; Polyamines - pharmacology; Proto-Oncogene Proteins c-myc - genetics; Proto-Oncogene Proteins c-myc - metabolism; RNA, Messenger - biosynthesis; RNA, Messenger - metabolism; Transcription Factors - metabolism; Transcription, Genetic - drug effects; Transcription, Genetic - physiology
• ISSN: 0363-6143; 1522-1563
• DOI: 10.1152/ajpcell.00326.2004

Departments of 1 Surgery and 2 Pathology, University of Maryland School of Medicine, and 3 Baltimore Veterans Affairs Medical Center, Baltimore, Maryland 21201 Submitted 8 July 2004 ; accepted in final form 1 September 2004 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 -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. ornithine decarboxylase; -difluoromethylornithine; growth arrest; gene expression; intestinal epithelium Address for reprint requests and other correspondence: J.-Y. Wang, Dept. of Surgery, Baltimore Veterans Affairs Medical Center, 10 North Greene St., Baltimore, MD 21201 (E-mail: jwang{at}smail.umaryland.edu )