Systematic analysis reveals a functional role for STAMBPL1 in the epithelial-mesenchymal transition process across multiple carcinomas.

BACKGROUND: Deubiquitinating enzymes (DUBs) are linked to cancer progression and dissemination, yet less is known about their regulation and impact on epithelial-mesenchymal transition (EMT). METHODS: An integrative translational approach combining systematic computational analyses of The Cancer Genome Atlas cancer cohorts with CRISPR genetics, biochemistry and immunohistochemistry methodologies to identify and assess the role of human DUBs in EMT. RESULTS: We identify a previously undiscovered biological function of STAM-binding protein like 1 (STAMBPL1) deubiquitinase in the EMT process in lung and breast carcinomas. We show that STAMBPL1 expression can be regulated by mutant p53 and that its catalytic activity is required to affect the transcription factor SNAI1. Accordingly, genetic depletion and CRISPR-mediated gene knockout of STAMBPL1 leads to marked recovery of epithelial markers, SNAI1 destabilisation and impaired migratory capacity of cancer cells. Reversely, STAMBPL1 expression reprogrammes cells towards a mesenchymal phenotype. A significant STAMBPL1-SNAI1 co-signature was observed across multiple tumour types. Importantly, STAMBPL1 is highly expressed in metastatic tissues compared to matched primary tumour of the same lung cancer patient and its expression predicts poor prognosis. CONCLUSIONS: Our study provides a novel concept of oncogenic regulation of a DUB and presents a new role and predictive value of STAMBPL1 in the EMT process across multiple carcinomas.

USP10 regulates the stability of the EMT-transcription factor Slug/SNAI2.

Epithelial-to-mesenchymal transition (EMT) is a fundamental mechanism governing the switch of cells from an epithelial to a motile mesenchymal-like state. This transdifferentiation is regulated by key transcription factors, including Slug. The stability and function of Slug can be regulated by multiple mechanisms, including ubiquitin-mediated post-translational modifications. Here, by using a genome wide siRNA screen for human deubiquitinating enzymes (DUBs), we identified USP10 as a deubiquitinase for Slug in cancer cells. USP10 interacts with Slug and mediates its degradation by the proteasome. Importantly, USP10 is concomitantly highly expressed with Slug in cancer biopsies. Genetic knockdown of USP10 leads to suppressed Slug levels with a decreased expression of the mesenchymal marker Vimentin. Further, it reduces the migratory capacity of cancer cells. Reversely, overexpression of USP10 elevates the level of both Slug and Vimentin. Our study identifies USP10 as a regulator of the EMT-transcription factor Slug and cell migration.

SYK Inhibition Induces Apoptosis in Germinal Center-Like B Cells by Modulating the Antiapoptotic Protein Myeloid Cell Leukemia-1, Affecting B-Cell Activation and Antibody Production.

B cells play a major role in the antibody-mediated rejection (AMR) of solid organ transplants, a major public health concern. The germinal center (GC) is involved in the generation of donor-specific antibody-producing plasma cells and memory B cells, which are often poorly controlled by current treatments. Myeloid cell leukemia-1 (Mcl-1), an antiapoptotic member of the B-cell lymphoma-2 family, is essential for maintenance of the GC reaction and B-cell differentiation. During chronic AMR (cAMR), tertiary lymphoid structures resembling GCs appear in the rejected organ, suggesting local lymphoid neogenesis. We report the infiltration of the kidneys with B cells expressing Mcl-1 in patients with cAMR. We modulated GC viability by impairing B-cell receptor signaling, by spleen tyrosine kinase (SYK) inhibition. SYK inhibition lowers viability and Mcl-1 protein levels in Burkitt's lymphoma cell lines. This downregulation of Mcl-1 is coordinated at the transcriptional level, possibly by signal transducer and activator of transcription 3 (STAT3), as shown by (1) the impaired translocation of STAT3 to the nucleus following SYK inhibition, and (2) the lower levels of Mcl-1 transcription upon STAT3 inhibition. Mcl-1 overproduction prevented cells from entering apoptosis following SYK inhibition. In vitro studies with primary tonsillar B cells confirmed that SYK inhibition impaired cell survival and decreased Mcl-1 protein levels. It also impaired B-cell activation and immunoglobulin G secretion by tonsillar B cells. These findings suggest that the SYK-Mcl-1 pathway could be targeted, to improve graft survival by manipulating the humoral immune response.

PHGDH Defines a Metabolic Subtype in Lung Adenocarcinomas with Poor Prognosis.

Molecular signatures are emerging determinants of choice of therapy for lung adenocarcinomas. An evolving therapeutic approach includes targeting metabolic dependencies in cancers. Here, using an integrative approach, we have dissected the metabolic fingerprints of lung adenocarcinomas, and we show that Phosphoglycerate dehydrogenase (PHGDH), the rate-limiting enzyme in serine biosynthesis, is highly expressed in a adenocarcinoma subset with poor prognosis. This subset harbors a gene signature for DNA replication and proliferation. Accordingly, models with high levels of PHGDH display rapid proliferation, migration, and selective channeling of serine-derived carbons to glutathione and pyrimidines, while depletion of PHGDH shows potent and selective toxicity to this subset. Differential PHGDH protein levels were defined by its degradation, and the deubiquitinating enzyme JOSD2 is a regulator of its protein stability. Our study provides evidence that a unique metabolic program is activated in a lung adenocarcinoma subset, described by PHGDH, which confers growth and survival and may have therapeutic implications.

Effect of Mutant p53 Proteins on Glycolysis and Mitochondrial Metabolism.

TP53 is one of the most commonly mutated genes in human cancers. Unlike other tumor suppressors that are frequently deleted or acquire loss-of-function mutations, the majority of TP53 mutations in tumors are missense substitutions, which lead to the expression of full-length mutant proteins that accumulate in cancer cells and may confer unique gain-of-function (GOF) activities to promote tumorigenic events. Recently, mutant p53 proteins have been shown to mediate metabolic changes as a novel GOF to promote tumor development. There is a strong rationale that the GOF activities, including alterations in cellular metabolism, might vary between the different p53 mutants. Accordingly, the effect of different mutant p53 proteins on cancer cell metabolism is largely unknown. In this study, we have metabolically profiled several individual frequently occurring p53 mutants in cancers, focusing on glycolytic and mitochondrial oxidative phosphorylation pathways. Our investigation highlights the diversity of different p53 mutants in terms of their effect on metabolism, which might provide a foundation for the development of more effective targeted pharmacological approaches toward variants of mutant p53.

Subcellular localization of PUMA regulates its pro-apoptotic activity in Burkitt's lymphoma B cells.

The BH3-only protein PUMA (p53-upregulated modulator of apoptosis) is a major regulator of apoptosis. It belongs to the Bcl-2 family of proteins responsible for maintaining mitochondrial outer membrane integrity by controlling the intrinsic (mitochondrial) apoptotic pathway. We describe here a new pathway regulating PUMA activation through the control of its subcellular distribution. Surprisingly, neither PUMA upregulation in normal activated human B lymphocytes nor high levels of PUMA in Burkitt's lymphoma (BL) were associated with cell death. We show that PUMA is localized to the cytosol in these cells. By contrast, various apoptosis-triggering signals were found to promote the translocation of PUMA to the mitochondria in these cells, leading to their death by apoptosis. This apoptosis was associated with the binding of mitochondrial PUMA to anti-apoptotic members of the Bcl-2 family, such as Bcl-2 and Mcl-1. This translocation was caspase-independent but was prevented by inhibiting or knocking down the expression of the MAPK kinase p38. Our data suggest that the accumulation of PUMA in the cytosol may be important for the participation of this protein in apoptosis without the need for prior transcription. This regulatory pathway may be an important feature of differentiation and tumorigenic processes.

Exploiting the potential of autophagy in cisplatin therapy: A new strategy to overcome resistance.

Resistance to cisplatin is a major challenge in the current cancer therapy. In order to explore new therapeutic strategies to cisplatin resistance, we evaluated, in a model of lung cancer (H1299 and H460 cell lines), the nature of the pathways leading to cell death. We observed that H1299 displayed a natural resistance to cisplatin due to an inability to trigger an apoptotic response that correlates with the induction of autophagy. However, pharmacological and genetic approaches showed how autophagy was a mechanism associated to cell death rather than to resistance. Indeed, pro-autophagic stimuli such as mTOR or Akt inhibition mediate cell death in both cell lines to a similar extent. We next evaluated the response to a novel platinum compound, monoplatin, able to promote cell death in an exclusive autophagy-dependent manner. In this case, no differences were observed between both cell lines. Furthermore, in response to monoplatin, two molecular hallmarks of cisplatin response (p53 and MAPKs) were not implicated, indicating the ability of this pro-autophagic compound to overcome cisplatin resistance. In summary, our data highlight how induction of autophagy could be used in cisplatin resistant tumours and an alternative treatment for p53 mutated patient in a synthetic lethally approach.

Mitochondrial hyperfusion promotes NF-κB activation via the mitochondrial E3 ligase MULAN.

Mitochondria are dynamic organelles with a morphology resulting from the balance between two opposing processes: fusion and fission. Little is known about the function of mitochondrial fusion, beside its role in the maintenance of mitochondrial DNA. We report here that enforced mitochondrial hyperfusion, due to the expression of a dominant-negative mutant of Drp1 or of MARCH5, promotes NF-κB activation in a TAK1- and IKK-dependent manner, through the mitochondrial E3 ubiquitin ligase MULAN. The capability of MULAN to activate NF-κB depends on its RING domain and on the E3 ubiquitin ligase TRAF2. Under physiological conditions, stress-induced mitochondrial hyperfusion (SIMH) is also accompanied by NF-κB activation, and the prevention of SIMH or the knockdown of MULAN impairs NF-κB activation. During SIMH, MULAN forms a complex with TRAF2 and modulates its ubiquitylation, signifying that TRAF2 may serve as an ubiquitylated transmitter of NF-κB signaling in this pathway. Our results suggest that mitochondria, through their dynamics, convert stress signals into a cell response leading to NF-κB activation.