The K-Ras 4A isoform promotes apoptosis but does not affect either lifespan or spontaneous tumor incidence in aging mice.
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.
Plowman
Sarah J
SJ
Sir Alastair Currie Cancer Research UK Laboratories, Molecular Medicine Centre, The University of Edinburgh, Western General Hospital, Crewe Road, Edinburgh EH4 2XU, UK.
Arends
Mark J
MJ
Brownstein
David G
DG
Luo
Feijun
F
Devenney
Paul S
PS
Rose
Lorraine
L
Ritchie
Ann-Marie
AM
Berry
Rachel L
RL
Harrison
David J
DJ
Hooper
Martin L
ML
Patek
Charles E
CE
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
D020033:Protein Isoforms