Mechanistic target of rapamycin mTOR complex I (mTORC1) integrates various environmental signals to regulate cell growth and metabolism. DEPTOR, also termed DEPDC6, is an endogenous inhibitor of the mTORC1 and mTORC2 activities. The abundance of DEPTOR centrally orchestrates the mTOR signaling network. However, the mechanisms by which the DEPTOR stability is regulated are still elusive. Here, we report that OTU domain-containing ubiquitin aldehyde-binding protein 1 (OTUB1) specifically deubiquitinates DEPTOR by a deubiquitination assay. We found that OTUB1 directly interacted with DEPTOR via its N-terminal domain and deubiquitinated DEPTOR and thereby stabilized DEPTOR in a Cys-91-independent but Asp-88-dependent manner, suggesting that OTUB1 targets DEPTOR for deubiquitination via a deubiquitinase activity independent non-canonical mechanism. The interaction between OTUB1 and DEPTOR was enhanced when the cells were treated with amino acids. Moreover, OTUB1 suppressed amino acid-induced activation of mTORC1 in a DEPTOR-dependent manner and thereby ultimately controlled cellular autophagy, cell proliferation and size. Our findings reveal a mechanism that stabilizes the mTORC1 inhibitor DEPTOR via OTUB1's deubiquitinase activity. Our insights may inform research into various mTOR activity-related diseases, such as cancer, and may contribute to the identification of new diagnostic markers and therapeutic strategies for cancer treatments.

'Don't eat me' signal of CD47 is activated via its interaction with SIRPα protein on myeloid cells, especially phagocytic cells, and prevents malignant cells from anti-tumor immunity in which pyroglutamate modification of CD47 by glutaminyl-peptide cyclotransferase-like protein (isoQC) takes an important part evidenced by our previous report that isoQC is an essential regulator for CD47-SIRPα axis with a strong inhibition on macrophage-mediated phagoctyosis. Therefore, we screened for potential isoQC inhibitors by fluorescence-activated cell sorting assay and identified luteolin as a potent compound that blocked the pyroglutamation of CD47 by isoQC. We further demonstrated that luteolin directly bound to isoQC using pull-down assay and isothermal calorimetric (ITC) assay. In consistency, we showed that luteolin markedly abrogated the cell-surface interaction between CD47 and SIRPα in multiple myeloma H929 cells and consequently promoted the macrophage-mediated phagocytosis. Collectively, our study discovered a promising lead compound targeting isoQC, luteolin, which functions distinctly from current CD47 antibody-based drugs and therefore may potentially overcome the clinical side effects associated with CD47 antibody treatment-induced anemia.

SPOP, a substrate binding adaptor of E3 ubiquitin ligase Cullin3, is frequently mutated in human prostate cancer (PCa). However, whether and how SPOP is regulated at transcriptional level in PCa remain unclear. Here, we report that SPOP is down-regulated in PCa stem-like cells (CSCs) and tissues. Our study reveals that SPOP expression is repressed by TGF-β / SMAD signaling axis in PCa CSCs. SPOP promoter contains SMAD-binding elements (SBEs), which can interact with SMAD3. Moreover, TGF-β signaling inhibitor SB431542 promotes the SPOP expression and abrogates PCa stemness. Clinically, SPOP expression is downregulated in PCa patients, which is significantly related to a poor prognosis and lower survival rate. Thus, our findings uncover a mechanism of how SPOP expression is mediated in PCa CSCs via TGF-β/ SMAD3 signaling.

SCP1 as a nuclear transcriptional regulator acts globally to silence neuronal genes and to affect the dephosphorylation of RNA Pol ll. However, we report the first finding and description of SCP1 as a plasma membrane-localized protein in various cancer cells using EGFP- or other epitope-fused SCP1. Membrane-located SCP1 dephosphorylates AKT at serine 473, leading to the abolishment of serine 473 phosphorylation that results in suppressed angiogenesis and a decreased risk of tumorigenesis. Consistently, we observed increased AKT phosphorylation and angiogenesis followed by enhanced tumorigenesis in Ctdsp1 (which encodes SCP1) gene - knockout mice. Importantly, we discovered that the membrane localization of SCP1 is crucial for impeding angiogenesis and tumor growth, and this localization depends on palmitoylation of a conserved cysteine motif within its NH2 terminus. Thus, our study discovers a novel mechanism underlying SCP1 shuttling between the plasma membrane and nucleus, which constitutes a unique pathway in transducing AKT signaling that is closely linked to angiogenesis and tumorigenesis.