HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Attias, Z Articles by Vaisman, N Search for Related Content PubMed PubMed Citation Articles by Attias, Z Articles by Vaisman, N

Department of Human Molecular Genetics and Biochemistry, Sackler School of Medicine, Tel Aviv University, Tel Aviv 69978, Israel
¹ Unit on Clinical Nutrition, Tel Aviv Sourasky Medical Center, Tel Aviv, Israel

(Requests for offprints should be addressed to H Werner; Email: hwerner{at}post.tau.ac.il)

The insulin-like growth factor-I receptor (IGF-IR) has an important role in colorectal cancer development and progression. IGF-IR displays a potent anti-apoptotic activity and is overexpressed in primary tumors and colon cancer-derived cell lines. Folic acid, a member of the vitamin B family, is a chemopreventive agent whose deficiency has been linked to an enhanced colon cancer risk. The present study was aimed at testing the hypothesis that part of the modulatory effect of folic acid on malignant transformation may be attributed to its ability to regulate IGF-IR gene expression. Regulation of IGF-IR gene expression by folic acid was assessed using western blots, RT-PCR, transient transfections and chromatin immunoprecipitation assays. Activation of the IGF-IR signaling pathway was evaluated by measuring phosphorylation of ERK, and apoptosis was assayed using poly (ADP-ribose) polymerase cleavage and annexin V-FITC staining. Results obtained showed that folic acid induced a dose-dependent decrease in IGF-IR protein and mRNA levels in the HCT116 +/+ colon cancer cell line. This effect was associated with a significant reduction in IGF-IR promoter activity. Similar effects were elicited by the folic acid metabolites dihydrofolic acid and tetrahydrofolic acid. In addition, folic acid abrogated the IGF-I-stimulated phosphorylation of the downstream signaling molecule ERK1/2 and exhibited a pro-apoptotic activity. Moreover, folic acid induced a significant decrease in Sp1 binding to the IGF-IR promoter region. Finally, folic acid had no effect in wild-type p53-depleted HCT116 –/– and Caco-2 cells. In conclusion, the mechanism of action of folic acid involves regulation of IGF-IR gene expression. The ability of folic acid to downregulate the IGF-I signal transduction pathway may allow the micronutrient to function as a chemopreventive agent. Folic acid deficiency, on the other hand, may lead to increased IGF-IR gene expression, with ensuing pathological activation by endocrine and/or autocrine/paracrine IGF-I.