Cep55 regulation of PI3K/Akt signaling is required for neocortical development and ciliogenesis.

Homozygous nonsense mutations in CEP55 are associated with several congenital malformations that lead to perinatal lethality suggesting that it plays a critical role in regulation of embryonic development. CEP55 has previously been studied as a crucial regulator of cytokinesis, predominantly in transformed cells, and its dysregulation is linked to carcinogenesis. However, its molecular functions during embryonic development in mammals require further investigation. We have generated a Cep55 knockout (Cep55-/-) mouse model which demonstrated preweaning lethality associated with a wide range of neural defects. Focusing our analysis on the neocortex, we show that Cep55-/- embryos exhibited depleted neural stem/progenitor cells in the ventricular zone as a result of significantly increased cellular apoptosis. Mechanistically, we demonstrated that Cep55-loss downregulates the pGsk3ß/ß-Catenin/Myc axis in an Akt-dependent manner. The elevated apoptosis of neural stem/progenitors was recapitulated using Cep55-deficient human cerebral organoids and we could rescue the phenotype by inhibiting active Gsk3ß. Additionally, we show that Cep55-loss leads to a significant reduction of ciliated cells, highlighting a novel role in regulating ciliogenesis. Collectively, our findings demonstrate a critical role of Cep55 during brain development and provide mechanistic insights that may have important implications for genetic syndromes associated with Cep55-loss.

Alpha-B-Crystallin overexpression is sufficient to promote tumorigenesis and metastasis in mice.

BACKGROUND: αB-Crystallin is a heat shock chaperone protein which binds to misfolded proteins to prevent their aggregation. It is overexpressed in a wide-variety of cancers. Previous studies using human cancer cell lines and human xenograft models have suggested potential tumor promoter (oncogene) roles for αB-Crystallin in a wide-spectrum of cancers. METHODS: To determine the causal relationship between CRYAB overexpression and cancer, we generated a Cryab overexpression knock-in mouse model and monitor them for development of spontaneous and carcinogen (DMBA)-induced tumorigenesis. In order to investigate the mechanism of malignancies observed in this model multiple techniques were used such as immunohistochemical characterizations of tumors, bioinformatics analysis of publically available human tumor datasets, and generation of mouse embryonic fibroblasts (MEFs) for in vitro assays (clonogenic survival and migration assays and proteome analysis by mass-spectrometry). RESULTS: This model revealed that constitutive overexpression of Cryab results in the formation of a variety of lethal spontaneous primary and metastatic tumors in mice. In vivo, the overexpression of Cryab correlated with the upregulation of epithelial-to-mesenchymal (EMT) markers, angiogenesis and some oncogenic proteins including Basigin. In vitro, using E1A/Ras transformed MEFs, we observed that the overexpression of Cryab led to the promotion of cell survival via upregulation of Akt signaling and downregulation of pro-apoptotic pathway mediator JNK, with subsequent attenuation of apoptosis as assessed by cleaved caspase-3 and Annexin V staining. CONCLUSIONS: Overall, through the generation and characterization of Cryab overexpression model, we provide evidence supporting the role of αB-Crystallin as an oncogene, where its upregulation is sufficient to induce tumors, promote cell survival and inhibit apoptosis.