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Logo of nihpaAbout Author manuscriptsSubmit a manuscriptNIH Public Access; Author Manuscript; Accepted for publication in peer reviewed journal;
Oncogene. Author manuscript; available in PMC Jan 25, 2006.
Published in final edited form as:
PMCID: PMC1351030
NIHMSID: NIHMS2404

Krüppel-like factor 5 mediates the transforming activity of oncogenic H-Ras

Abstract

Previous studies indicate that Krüppel-like factor 5 (KLF5), also known as intestinal-enriched Krüppel-like factor (IKLF), is a positive regulator of cell proliferation and gives rise to a transformed phenotype when over-expressed. Here we demonstrate that levels of KLF5 transcript and protein are significantly elevated in oncogenic H-Ras-transformed NIH3T3 cells. These cells display an accelerated rate of proliferation in both serum-containing and serum-deprived media and form anchorage-independent colonies in soft agar assays. H-Ras-transformed cells also contain elevated mitogen-activated protein kinase (MAPK) activity. When treated with inhibitors of MEK (MAPK kinase), H-Ras-transformed cells lose their growth advantage and no longer form colonies. Significantly, levels of KLF5 transcript and protein are substantially reduced in H-Ras-transformed cells treated with MEK inhibitors. Moreover, inhibition of KLF5 expression in H-Ras-transformed cells with KLF5-specific small interfering RNA (siRNA) leads to a decreased rate of proliferation and a significant reduction in colony formation. H-Ras-transformed cells also contain elevated levels of Egr1 that are diminished by MEK inhibitors. Inhibition of Egr1 by siRNA results in a reduced level of KLF5, indicating that Egr1 mediates the inductive action of MAPK on KLF5. Lastly, KLF5 activates expression of cyclin D1. These findings indicate that the increased expression of KLF5 in H-Ras-transformed cells is secondary to increased MAPK activity from H-Ras overexpression and that the elevated level of KLF5 is in part responsible for the proproliferative and transforming activities of oncogenic H-Ras.

Keywords: IKLF, transformation, mitogen-activated protein kinase, Egr1, cyclin D1, proliferation, small interfering RNA, anchorage-independent growth
Abbreviations: DMEM, Dulbecco’s modified Eagle’s medium, ERK, extra-cellular signal-regulated kinase, FBS, fetal bovine serum, GAPDH, glyceraldehydes-3-phosphate dehydrogenase, GKLF, gut-enriched Krüppel-like factor, IKLF, intestinal Krüppel-like factor, KLF, Krüppel-like factor, MAPK, mitogen-activated protein kinase, MEK, MAPK/ERK kinase, PBS, phosphate-buffered saline, PI, propidium iodide, PMA, phorbol-12-myristate-13-acetate, RT—PCR, reverse transcription—polymerase chain reaction, siRNA, small interfering RNA
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