title: The K-Ras 4A isoform promotes apoptosis but does not affect either lifespan or spontaneous tumor incidence in aging mice.
abstract: Ras proteins function as molecular switches in signal transduction pathways, and, here, we examined the effects of the K-ras4A and 4B splice variants on cell function by comparing wild-type embryonic stem (ES) cells with K-ras(tmDelta4A/tmDelta4A) (exon 4A knock-out) ES cells which express K-ras4B only and K-ras(-/-) (exons 1-3 knock-out) ES cells which express neither splice variant, and intestinal epithelium from wild-type and K-ras(tmDelta4A/tmDelta4A) mice. RT-qPCR analysis found that K-ras4B expression was reduced in K-ras(tmDelta4A/tmDelta4A) ES cells but unaffected in small intestine. K-Ras deficiency did not affect ES cell growth, and K-Ras4A deficiency did not affect intestinal epithelial proliferation. K-ras(tmDelta4A/tmDelta4A) and K-ras(-/-) ES cells showed a reduced capacity for differentiation following LIF withdrawal, and K-ras(-/-) cells were least differentiated. K-Ras4A deficiency inhibited etoposide-induced apoptosis in ES cells and intestinal epithelial cells. However, K-ras(tmDelta4A/tmDelta4A) ES cells were more resistant to etoposide-induced apoptosis than K-ras(-/-) cells. The results indicate that (1) K-Ras4A promotes apoptosis while K-Ras4B inhibits it, and (2) K-Ras4B, and possibly K-Ras4A, promotes differentiation. The findings raise the possibility that alteration of the K-Ras4A/4B isoform ratio modulates tumorigenesis by differentially affecting stem cell survival and/or differentiation. However, K-Ras4A deficiency did not affect life expectancy or spontaneous overall tumor incidence in aging mice.
authors.affiliation: Sir Alastair Currie Cancer Research UK Laboratories, Molecular Medicine Centre, The University of Edinburgh, Western General Hospital, Crewe Road, Edinburgh EH4 2XU, UK.
authors.forename: Sarah J
authors.initials: SJ
authors.lastname: Plowman
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Arends
authors.forename: David G
authors.initials: DG
authors.lastname: Brownstein
authors.forename: Feijun
authors.initials: F
authors.lastname: Luo
authors.forename: Paul S
authors.initials: PS
authors.lastname: Devenney
authors.forename: Lorraine
authors.initials: L
authors.lastname: Rose
authors.forename: Ann-Marie
authors.initials: AM
authors.lastname: Ritchie
authors.forename: Rachel L
authors.initials: RL
authors.lastname: Berry
authors.forename: David J
authors.initials: DJ
authors.lastname: Harrison
authors.forename: Martin L
authors.initials: ML
authors.lastname: Hooper
authors.forename: Charles E
authors.initials: CE
authors.lastname: Patek
mesh_terms: D000375:Aging / Q000502:physiology*; D000818:Animals; D017209:Apoptosis; D002454:Cell Differentiation; D049109:Cell Proliferation; D004847:Epithelial Cells / Q000502:physiology; D011905:Genes, ras / Q000502:physiology*; D015994:Incidence; D007421:Intestine, Small / Q000378:metabolism / Q000473:pathology; D008136:Longevity / Q000502:physiology*; D051379:Mice; D018345:Mice, Knockout; D009374:Neoplasms, Experimental / Q000209:etiology*; D020033:Protein Isoforms; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013234:Stem Cells / Q000378:metabolism / Q000473:pathology
chemical_list: D020033:Protein Isoforms