RESUMO
Mutations resulting in decreased activity of p53 tumor suppressor protein promote tumorigenesis. P53 protein levels are tightly regulated through the Ubiquitin Proteasome System (UPS). Several E3 ligases were shown to regulate p53 stability, including MDM2. Here we report that the ubiquitin E3 ligase XIAP (X-linked Inhibitors of Apoptosis) is a direct ligase for p53 and describe a novel approach for modulating the levels of p53 by targeting the XIAP pathway. Using in vivo (live-cell) and in vitro (cell-free reconstituted system) ubiquitylation assays, we show that the XIAP-antagonist ARTS regulates the levels of p53 by promoting the degradation of XIAP. XIAP directly binds and ubiquitylates p53. In apoptotic cells, ARTS inhibits the ubiquitylation of p53 by antagonizing XIAP. XIAP knockout MEFs express higher p53 protein levels compared to wild-type MEFs. Computational screen for small molecules with high affinity to the ARTS-binding site within XIAP identified a small-molecule ARTS-mimetic, B3. This compound stimulates apoptosis in a wide range of cancer cells but not normal PBMC (Peripheral Blood Mononuclear Cells). Like ARTS, the B3 compound binds to XIAP and promotes its degradation via the UPS. B3 binding to XIAP stabilizes p53 by disrupting its interaction with XIAP. These results reveal a novel mechanism by which ARTS and p53 regulate each other through an amplification loop to promote apoptosis. Finally, these data suggest that targeting the ARTS binding pocket in XIAP can be used to increase p53 levels as a new strategy for developing anti-cancer therapeutics.
Assuntos
Apoptose , Proteólise , Proteína Supressora de Tumor p53 , Ubiquitinação , Proteínas Inibidoras de Apoptose Ligadas ao Cromossomo X , Proteínas Inibidoras de Apoptose Ligadas ao Cromossomo X/metabolismo , Proteínas Inibidoras de Apoptose Ligadas ao Cromossomo X/genética , Humanos , Proteína Supressora de Tumor p53/metabolismo , Proteína Supressora de Tumor p53/genética , Apoptose/efeitos dos fármacos , Ubiquitinação/efeitos dos fármacos , Proteólise/efeitos dos fármacos , Animais , Camundongos , Linhagem Celular Tumoral , Ubiquitina-Proteína Ligases/metabolismo , Ubiquitina-Proteína Ligases/genética , Regulação para Cima/efeitos dos fármacos , Ligação ProteicaRESUMO
We examined TikTok user engagement when parents post videos engaging in psychological maltreatment (PM) behaviors towards their children, using the APSAC-endorsed definition of PM. A new TikTok account was created and seeded with PM behavior videos identified previously; similar videos then appeared on the new account's "For You Page" (an algorithmic feed curated by TikTok). Researchers identified 35 creators who had posted at least one PM behavior video, resulting in their full profile being coded (N = 2684 videos) for five engagement metrics, presence of children, and presence of PM behavior. Non-parametric paired comparisons (Mann-Whitney tests) were made within individual creators for: (1) engagement metrics before and after the first PM behavior video, (2) engagement metrics for PM behavior videos versus non-PM videos, (3) engagement metrics for child videos versus non-child videos, and (4) proportion of videos containing children before and after the first PM video. All but one analysis was significant (effect sizes from .28 to .59, average r = .46). We discuss directions for future research, as well as how child welfare and content moderation policy can be updated to change social norms around sharenting.