Figure 4: Over-expression of the MDM2 isoform in p53R172H/R172H tumours promotes mutp53 accumulation and tumorigenesis.
From: Spliced MDM2 isoforms promote mutant p53 accumulation and gain-of-function in tumorigenesis
(a) Increased mRNA levels of the MDM2 isoform similar to human MDM2-B in splenic lymphomas from p53R172H/R172H mice compared with normal spleen tissues as analysed by reverse transcription-PCR. (b) Increased mRNA levels of the MDM2 isoform similar to human MDM2-B in splenic and thymic lymphomas from p53R172H/R172H mice compared with normal spleen and thymus tissues as analysed by Taqman real-time PCR. Data are presented as mean±s.d. P<0.001, Student t-test. Normal spleen: n=8; splenic lymphoma: n=14; normal thymus: n=5; thymic lymphoma: n=10. (c) Increased MDM2 isoform protein levels correlate with mutp53 accumulation in splenic (left) and thymic (right) lymphomas. (d) Schematic model showing the domain structure of mouse MDM2-FL and the MDM2 isoform similar to human MDM2-B which is over-expressed in p53R172H/R172H tumours. TSS: translation starting site. (e) Ectopic expression of the mouse MDM2 isoform (iso MDM2) promoted mutp53 accumulation in H1299-R175H (left), HCT116 p53R248w/− (middle) and p53R172H/R172H MEF (right) cells. Con: Control. Cells were transfected with mouse MDM2 isoform expression vectors, and mutp53 protein levels were measured by western-blot assays at 24 h after transfection. (f) The mouse MDM2 isoform inhibited MDM2-FL-mediated degradation of mutp53 (R175H) in 2KO cells. (g) The mouse MDM2 isoform promoted the growth of HCT116 p53R248w/− xenograft tumours (P=0.01, ANOVA, followed by Student’s t-test) (left panel). This promoting effect was largely abolished in HCT116 p53−/− xenograft tumours (right panel). Tumour volumes are presented as mean±s.d., n=10/group.
