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Thymosin Beta‐4 Knockdown in IEC‐6 Normal Intestinal Epithelial Cells Induces DNA Re‐replication Via Downregulating Emi1
Author(s) -
Chao TaChung,
Chen KeJay,
Tang MeiChuan,
Chan LiChuan,
Chen PoMin,
Tzeng ChengHwai,
Su Yeu
Publication year - 2014
Publication title -
journal of cellular physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.529
H-Index - 174
eISSN - 1097-4652
pISSN - 0021-9541
DOI - 10.1002/jcp.24609
Subject(s) - biology , microbiology and biotechnology , gene knockdown , cell cycle , dna replication , cancer research , apoptosis , dna , biochemistry
Thymosin β 4 (Tβ 4 ) is a multifunctional protein already used clinically to treat various diseases; however, the promoting effect of this protein on tumor malignancy should not be neglected. Here, we assessed whether Tβ 4 alteration influences normal intestinal epithelial cells because Tβ 4 is deemed a novel target for treating colorectal cancer (CRC). For this purpose, we examined the consequences of shRNA‐mediated knockdown of Tβ 4 in IEC‐6 normal rat small intestinal cells and found that inhibiting Tβ 4 expression significantly suppressed their growth and induced apoptosis in some cells. Flow cytometric analysis further revealed a marked decrease of G0/G1 population but a drastic increase of polyploid ones in these cells. The increase of polyploidy likely resulted from DNA re‐replication because not only the de novo DNA synthesis was greatly increased but also the expression levels of Cdc6 (a replication‐licensing factor), cyclin A, and phosphorylated‐checkpoint kinase 1 were all dramatically elevated. Moreover, marked reductions in both RNA and protein levels of Emi1 (early mitotic inhibitor 1) were also detected in Tβ 4 ‐downregulated IEC‐6 cells which might be accounted by the downregulation of E2F1, a transcription factor capable of inducing Emi1 expression, mediated by glycogen synthase‐3β (GSK‐3β). To our best knowledge, this is the first report showing that inhibiting Tβ 4 expression triggers DNA re‐replication in normal intestinal epithelial cells, suggesting that this G‐actin sequester may play a crucial role in maintaining genome stability in these cells. More importantly, clinical oncologists should take this novel activity into consideration when design CRC therapy based on targeting Tβ 4 . J. Cell. Physiol. 229: 1639–1646, 2014. © 2014 Wiley Periodicals, Inc.