Defining USP22 Functions During Mammalian Development

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Project Summary Overexpression of the USP22 ubiquitin specific protease is linked to poor patient outcome in multiple types of therapy resistant cancers, leading to its designation as a member of a `death from cancer' gene signature. However, the functions of USP22 in normal cells are not well defined, so it is not clear how this enzyme contributes to cancer formation or progression. USP22 is the catalytic subunit of the deubiquitination module (DUB) within the highly conserved SAGA complex, which regulates multiple steps in the process of gene transcription. In the last funding period, we generated USP22 null mice to further define its functions in vivo, and we discovered a role for USP22 in development of fetal vasculature during development of the placental labyrinth. RNA-seq reveals that TGF-beta and receptor tyrosine kinase (RTK) pathways (e.g. c-Met/HGFR, Errb2, and PDGFR) are down regulated in USP22 mutant placentas. These pathways are essential not only for normal placental development but also for tumorigenesis, and examination of TCGA data reveals that these pathways are up regulated in tumors that overexpress USP22. We hypothesize that USP22 regulates these pathways to control the growth and behavior of normal cells, and that aberrations in USP22 expression contributes to signaling pathway aberrations associated with disease. To test this hypothesis and to define the mechanistic basis of changes in TGF-beta and RTK signaling in Usp22 mutants, we will use mice and cells bearing a conditional null, `floxed' allele or a conditional overexpressing allele of USP22 to 1) Define specific cell lineages in the placenta affected by USP22 loss 2) Define direct molecular targets of USP22 and 3) Determine whether USP22 overexpression is sufficient to drive abnormal TGF-beta1 or RTK signaling in mice. These studies will establish new paradigms for the functions of USP22 in signaling, in development, and in disease. In the longer term, our findings will provide new insights to the etiology of preeclampsia and cancer, and they may provide new avenues for treatment or prevention of these conditions.