Missense ‘hotspot’ mutations localized in six p53 codons account for 20% of TP53 mutations in human cancers. Hotspot p53 mutants have lost the tumor suppressive functions of the wildtype protein, but whether and how they may gain additional functions promoting tumorigenesis remain controversial. Here, we generated Trp53^Y217C, a mouse model of the human hotspot mutant TP53^Y220C. DNA damage responses were lost in Trp53^Y217C/Y217C (Trp53^YC/YC) cells, and Trp53^YC/YC fibroblasts exhibited increased chromosome instability compared to Trp53^-/- cells. Furthermore, Trp53^YC/YC male mice died earlier than Trp53^-/- males, with more aggressive thymic lymphomas. This correlated with an increased expression of inflammation-related genes in Trp53^YC/YC thymic cells compared to Trp53^-/- cells. Surprisingly, we recovered only one Trp53^YC/YC female for 22 Trp53^YC/YC males at weaning, a skewed distribution explained by a high frequency of Trp53^YC/YC female embryos with exencephaly and the death of most Trp53^YC/YC female neonates. Strikingly, however, when we treated pregnant females with the anti-inflammatory drug supformin (LCC-12), we observed a fivefold increase in the proportion of viable Trp53^YC/YC weaned females in their progeny. Together, these data suggest that the p53^Y217C mutation not only abrogates wildtype p53 functions but also promotes inflammation, with oncogenic effects in males and teratogenic effects in females.

Stem cell self-renewal often relies on asymmetric fate determination governed by niche signals and/or cell-intrinsic factors but how these regulatory mechanisms cooperate to promote asymmetric fate decision remains poorly understood. In adult Drosophila midgut, asymmetric Notch (N) signaling inhibits intestinal stem cell (ISC) self-renewal by promoting ISC differentiation into enteroblast (EB). We have previously shown that epithelium-derived Bone Morphogenetic Protein (BMP) promotes ISC self-renewal by antagonizing N pathway activity (Tian and Jiang, 2014). Here, we show that loss of BMP signaling results in ectopic N pathway activity even when the N ligand Delta (Dl) is depleted, and that the N inhibitor Numb acts in parallel with BMP signaling to ensure a robust ISC self-renewal program. Although Numb is asymmetrically segregated in about 80% of dividing ISCs, its activity is largely dispensable for ISC fate determination under normal homeostasis. However, Numb becomes crucial for ISC self-renewal when BMP signaling is compromised. Whereas neither Mad RNA interference nor its hypomorphic mutation led to ISC loss, inactivation of Numb in these backgrounds resulted in stem cell loss due to precocious ISC-to-EB differentiation. Furthermore, we find that numb mutations resulted in stem cell loss during midgut regeneration in response to epithelial damage that causes fluctuation in BMP pathway activity, suggesting that the asymmetrical segregation of Numb into the future ISC may provide a fail-save mechanism for ISC self-renewal by offsetting BMP pathway fluctuation, which is important for ISC maintenance in regenerative guts.