Suppression of polyamine catabolism by activated Ki‐ras in human colon cancer cells

Abstract

An activated Ki-ras was expressed in the human colon adenocarcinoma cell line Caco-2 to study the effects of Ki-ras oncogene on polyamine metabolism during gastrointestinal tumorigenesis. Multiple clones selected for expression of the mutant Ki-ras transgene displayed a suppression of transcription of a key catabolic enzyme in polyamine catabolism spermidine/spermine N1-acetyltransferase (SSAT). Gene expression analysis, with cDNA microarrays, showed that Ki-ras transfected clones had decreased levels of expression, compared to mock transfected cells, of peroxisome proliferator-activated receptor gamma (PPARgamma), a member of the nuclear hormone receptor family and an important regulator of cell proliferation and differentiation. The activated Ki-ras suppressed SSAT expression by a mechanism involving the PPARgamma response element (PPRE) located at +48 bp relative to the transcription start site of the SSAT gene. Transient expression of the PPARgamma protein in Ki-ras expressing Caco-2 clones, or treatment with the PPARgamma ligand ciglitazone, led to an increase in the SSAT promoter activity. A MEK1/2 inhibitor PD98059 induced transcription of both PPARgamma and SSAT genes in the activated Ki-ras clones, suggesting that the mitogen-activated protein kinases (MAPKs) were involved in the regulation of SSAT expression by PPARgamma. We concluded that mutated Ki-ras suppressed SSAT via a transcriptional mechanism involving the PPARgamma signaling pathway.

Kallikrein 6 is a mediator of K-RAS-dependent migration of colon carcinoma cells

“…Caco2 cells were stably transfected to constitutively express mutant K-RAS (Ignatenko et al, 2004a). RT-PCR and subsequent RFLP analysis confirmed that two Caco2 clones, Caco/Kras6 and Caco/KRAS26, express the K-RAS G12V mutation (Ignatenko et al, 2004a). Microarray analysis was performed on these Caco/K-RAS clones and several changes in gene expression were observed compared to mock transfected Caco/Neo cells.…”

“…Caco2 cells are highly differentiated colon cancer cells that express wild-type K-RAS (Shahrzad et al, 2005;Turck et al, 2005). Caco2 cells were stably transfected to constitutively express mutant K-RAS (Ignatenko et al, 2004a). RT-PCR and subsequent RFLP analysis confirmed that two Caco2 clones, Caco/Kras6 and Caco/KRAS26, express the K-RAS G12V mutation (Ignatenko et al, 2004a).…”

“…RT-PCR analysis of codon 12 of the K-RAS gene was performed as previously described (Ignatenko et al, 2004a).…”

Polyamines and cancer: old molecules, new understanding

“…ODC transcription is regulated by androgens in mammalian and human prostate cancer cells 38 . Inappropriate MYC expression due to chromosomal translocation is the cancers 36 . The KRAS-dependent signalling pathway regulates SSAT transcription through a mechanism involving peroxisome-proliferator-activated receptor-γ (PPARγ), a putative tumour suppressor.…”

“…PPARγ positively regulates the transcription of SSAT through a PPAR response element (PPRE) in the SSAT promoter 37 . KRAS suppresses SSAT transcription by inhibiting PPARγ expression and subsequent binding to the SSAT promoter 36 . So, polyamine synthesis and catabolism are both regulated by signalling pathways that are influenced by oncogenes and tumour- Cell-culture studies indicate that wild-type APC suppresses transcription of MYC, which is an activator of ornithine decarboxylase (ODC) transcription.…”