title: 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 overexpressed. 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.
authors.affiliation: Department of Medicine, Division of Digestive Diseases, Emory University School of Medicine, Atlanta, GA 30322, USA.
authors.forename: Mandayam O
authors.initials: MO
authors.lastname: Nandan
authors.forename: Hong S
authors.initials: HS
authors.lastname: Yoon
authors.forename: Weidong
authors.initials: W
authors.lastname: Zhao
authors.forename: Lillian A
authors.initials: LA
authors.lastname: Ouko
authors.forename: Sengthong
authors.initials: S
authors.lastname: Chanchevalap
authors.forename: Vincent W
authors.initials: VW
authors.lastname: Yang
mesh_terms: D000818:Animals; D002455:Cell Division; D002471:Cell Transformation, Neoplastic; D019938:Cyclin D1 / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics; D051766:Early Growth Response Protein 1; D011905:Genes, ras; D017874:Immediate-Early Proteins / Q000235:genetics; D051741:Kruppel-Like Transcription Factors; D048728:MAP Kinase Kinase Kinase 1; D020930:MAP Kinase Kinase Kinases / Q000037:antagonists & inhibitors; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D041681:NIH 3T3 Cells; D034741:RNA, Small Interfering / Q000494:pharmacology; D015398:Signal Transduction; D015534:Trans-Activators / Q000502:physiology*; D014157:Transcription Factors / Q000235:genetics
chemical_list: D004268:DNA-Binding Proteins; D051766:Early Growth Response Protein 1; C486109:Egr1 protein, mouse; D017874:Immediate-Early Proteins; C492214:KLF5 protein, human; C118391:Klf5 protein, mouse; D051741:Kruppel-Like Transcription Factors; D034741:RNA, Small Interfering; D015534:Trans-Activators; D014157:Transcription Factors; D019938:Cyclin D1; D020928:Mitogen-Activated Protein Kinases; D048728:MAP Kinase Kinase Kinase 1; D020930:MAP Kinase Kinase Kinases; C482576:MAP3K1 protein, human; C482578:Map3k1 protein, mouse