Anti-Cd339 monoclonal antibody, clone HMJ1-29

Expression of the Notch ligand JAG1 and Notch pathway activation promote poor prognosis, basal-like breast cancer. We have recently shown that the pseudokinase Tribbles homolog 3 (TRB3) regulates JAG1 expression in this malignancy. TRB3 is a stress and metabolic sensor, and here we show that nutrient deprivation or endoplasmic reticulum stress markedly upregulate TRB3, which serves as a scaffold for the deubiquitinase USP9x. USP9x in turn stimulates JAG1 activity through two mechanisms: (1) through TRB3 deubiquitination and stabilization, and (2) through deubiquitination and activation of Mind Bomb 1, an E3 ligase required for JAG1 ubiquitination-mediated endocytosis and Notch activation. These USP9x activities are confined to the signal-sending cell of a cell pair undergoing Notch signaling. We demonstrate that USP9x is required for TRB3 upregulation and Notch activation in response to cellular stress in basal-like breast cancer cells. These data suggest that TRB3 functions as a sensor of tumor microenvironmental stress and together with USP9x induces the cell survival and tumor-promoting activities of Notch. These findings identify a novel mechanism by which cancer cells survive in their hostile environment and provide potential therapeutic targets in breast cancer.

Notch signaling controls proliferation of multipotent pancreatic progenitor cells (MPCs) and their segregation into bipotent progenitors (BPs) and unipotent pro-acinar cells (PACs). Here, we showed that fast ultradian oscillations of the ligand Dll1 and the transcriptional effector Hes1 were crucial for MPC expansion, and changes in Hes1 oscillation parameters were associated with selective adoption of BP or PAC fate. Conversely, Jag1, a uniformly expressed ligand, restrained MPC growth. However, when its expression later segregated to PACs, Jag1 became critical for the specification of all but the most proximal BPs, and BPs were entirely lost in Jag1; Dll1 double mutants. Anatomically, ductal morphogenesis and organ architecture are minimally perturbed in Jag1 mutants until later stages, when ductal remodeling fails, and signs of acinar-to-ductal met-aplasia appear. Our study thus uncovers that oscillating Notch activity in the developing pancreas, modulated by Jag1, is required to coordinate MPC growth and fate.