The Genetics of Susceptibility to Mouse Plasma Cell Tumors

Division Of Basic Sciences - Nci

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Abstract

Cancer susceptibility is a complex genetic trait. Our laboratory has identified and characterized three susceptibility genes: p16, mTOR and MNDA which contribute to the development of mouse plasma cell tumors. We have found that defects in both the coding and regulatory regions of the p16 and mTOR genes are involved in this process. We have generated two genetically engineered mice, for mTOR, which have knocked in the susceptible allele on a resistant background, and have evaluated their phenotypes, in vivo. Mammalian TOR (mTOR) regulates cell growth, proliferation and migration. Because mTOR knock-outs are embryonic lethal, we generated a viable hypomorphic mouse by neo-insertion that partially disrupts mTOR transcription and creates a potential physiologic model of mTORC1/TORC2/mTORC3 inhibition. Homozygous knock-in mice exhibited reductions in body, organ and cell size. Decreases in the total number of T cells, particularly memory cells, and reduced responses to chemokines suggested alterations in T cell homing/homeostasis. TCR-stimulated T cells proliferated less, produced lower cytokine levels and expressed FoxP3. Decreased neutrophil numbers were also observed in the spleen, despite normal development and migration in the bone marrow. However, B cell effects were most pronounced, with a partial block in B cell development in the bone marrow, altered splenic populations, and decreases in proliferation, antibody production and migration to chemokines. In a separate model lacking the neo insertion, we have generated a model to assess decreased mTOR kinase activity as a result of the mutant allele. During the past year, we have studied the function of mTOR allelic variants. Differences have been observed in cell cycle characteristics and DDR proteins which we are currently validating. A series of allelic variants all expressing R to C amino acid changes are being studied for their effects on mTORC1,2,3 signaling. In addition, we have created cell lines with deletions of mTORC1,2 and 3 by CRISPR/Cas9 modification to delete Raptor, Rictor and Meak7, respectively to analyze downstream signaling events. We have now performed transcriptomics, phosphoproteomics and metabolomics and are in the process of integrating these datasets.