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RAS–MAPK signalling is fundamental for cell proliferation and is altered in most human cancers1–3. However, our mechanistic understanding of how RAS signals through RAF is still incomplete. Although studies revealed snapshots for autoinhibited and active RAF–MEK1–14-3-3 complexes4, the intermediate steps that lead to RAF activation remain unclear. The MRAS–SHOC2–PP1C holophosphatase dephosphorylates RAF at serine 259, resulting in the partial displacement of 14-3-3 and RAF–RAS association3,5,6. MRAS, SHOC2 and PP1C are mutated in rasopathies—developmental syndromes caused by aberrant MAPK pathway activation6–14—and SHOC2 itself has emerged as potential target in receptor tyrosine kinase (RTK)–RAS-driven tumours15–18. Despite its importance, structural understanding of the SHOC2 holophosphatase is lacking. Here we determine, using X-ray crystallography, the structure of the MRAS–SHOC2–PP1C complex. SHOC2 bridges PP1C and MRAS through its concave surface and enables reciprocal interactions between all three subunits. Biophysical characterization indicates a cooperative assembly driven by the MRAS GTP-bound active state, an observation that is extendible to other RAS isoforms. Our findings support the concept of a RAS-driven and multi-molecular model for RAF activation in which individual RAS–GTP molecules recruit RAF–14-3-3 and SHOC2–PP1C to produce downstream pathway activation. Importantly, we find that rasopathy and cancer mutations reside at protein–protein interfaces within the holophosphatase, resulting in enhanced affinities and function. Collectively, our findings shed light on a fundamental mechanism of RAS biology and on mechanisms of clinically observed enhanced RAS–MAPK signalling, therefore providing the structural basis for therapeutic interventions.

[Image: see text] Asparagine deprivation by l-asparaginase (L-ASNase) is an effective therapeutic strategy in acute lymphoblastic leukemia, with resistance occurring due to upregulation of ASNS, the only human enzyme synthetizing asparagine (Annu. Rev. Biochem.2006, 75 (1), 629–654). l-Asparaginase efficacy in solid tumors is limited by dose-related toxicities (OncoTargets and Therapy 2017, pp 1413–1422). Large-scale loss of function genetic in vitro screens identified ASNS as a cancer dependency in several solid malignancies (Cell2017, 170 (3), 564–576.e16. Cell2017, 170 (3), 577–592.e10). Here we evaluate the therapeutic potential of targeting ASNS in melanoma cells. While we confirm in vitro dependency on ASNS silencing, this is largely dispensable for in vivo tumor growth, even in the face of asparagine deprivation, prompting us to characterize such a resistance mechanism to devise novel therapeutic strategies. Using ex vivo quantitative proteome and transcriptome profiling, we characterize the compensatory mechanism elicited by ASNS knockout melanoma cells allowing their survival. Mechanistically, a genome-wide CRISPR screen revealed that such a resistance mechanism is elicited by a dual axis: GCN2-ATF4 aimed at restoring amino acid levels and MAPK-BCLXL to promote survival. Importantly, pharmacological inhibition of such nodes synergizes with l-asparaginase-mediated asparagine deprivation in ASNS deficient cells suggesting novel potential therapeutic combinations in melanoma.

Transcription factor networks shape the gene expression programs responsible for normal cell identity and pathogenic state. Using Core Regulatory Circuitry analysis (CRC), we identify PAX8 as a candidate oncogene in Renal Cell Carcinoma (RCC) cells. Validation of large-scale functional genomic screens confirms that PAX8 silencing leads to decreased proliferation of RCC cell lines. Epigenomic analyses of PAX8-dependent cistrome demonstrate that PAX8 largely occupies active enhancer elements controlling genes involved in various metabolic pathways. We selected the ferroxidase Ceruloplasmin (CP) as an exemplary gene to dissect PAX8 molecular functions. PAX8 recruits histone acetylation activity at bound enhancers looping onto the CP promoter. Importantly, CP expression correlates with sensitivity to PAX8 silencing and identifies a subset of RCC cases with poor survival. Our data identifies PAX8 as a candidate oncogene in RCC and provides a potential biomarker to monitor its activity., Transcription factors are critical regulators of cell identity. Here, the authors use computational and functional genomic approaches to show an oncogenic role of PAX8 in renal cancer. Mechanistic dissection of PAX8 functions reveal its role in activating genes associated with metabolic pathways.

Here, Tordella et. al identified senescence regulators relevant to cancer by screening an shRNA library targeting genes deleted in hepatocellular carcinoma (HCC). They show that knockdown of the SWI/SNF component ARID1B prevents oncogene-induced senescence and cooperates with RAS to induce liver tumors, and their results provide new insights into the mechanisms by which epigenetic regulators can affect tumor progression.

SummaryCell polarity plays a key role in the development of the central nervous system (CNS). Interestingly, disruption of cell polarity is seen in many cancers. ASPP2 is a haplo-insufficient tumor suppressor and an activator of the p53 family. In this study, we show that ASPP2 controls the polarity and proliferation of neural progenitors in vivo, leading to the formation of neuroblastic rosettes that resemble primitive neuroepithelial tumors. Consistent with its role in cell polarity, ASPP2 influences interkinetic nuclear migration and lamination during CNS development. Mechanistically, ASPP2 maintains the integrity of tight/adherens junctions. ASPP2 binds Par-3 and controls its apical/junctional localization without affecting its expression or Par-3/aPKCλ binding. The junctional localization of ASPP2 and Par-3 is interdependent, suggesting that they are prime targets for each other. These results identify ASPP2 as a regulator of Par-3, which plays a key role in controlling cell proliferation, polarity, and tissue organization during CNS development.

Squamous cell carcinoma (SCC) is highly malignant and refractory to therapy. The majority of existing mouse SCC models involve multiple gene mutations. Very few mouse models of spontaneous SCC have been generated by a single gene deletion. Here we report a haploinsufficient SCC mouse model in which exon 3 of the Tp53BP2 gene (a p53 binding protein) was deleted in one allele in a BALB/c genetic background. Tp53BP2 encodes ASPP2 (ankyrin repeats, SH3 domain and protein rich region containing protein 2). Keratinocyte differentiation induces ASPP2 and its expression is inversely correlated with p63 protein in vitro and in vivo. Up-regulation of p63 expression is required for ASPP2(Δexon3/+) BALB/c mice to develop SCC, as heterozygosity of p63 but not p53 prevents them from developing it. Mechanistically, ASPP2 inhibits ΔNp63 expression through its ability to bind IκB and enhance nuclear Rel/A p65, a component of the NF-κB transcription complex, which mediates the repression of p63. Reduced ASPP2 expression associates with tumor metastasis and increased p63 expression in human head and neck SCCs. This study identifies ASPP2 as a tumor suppressor that suppresses SCC via inflammatory signaling through NF-κB-mediated repression of p63.

The skin is the site where two of the most common types of epithelial cancer, basal cell carcinoma (BCC) and squamous cell carcinoma (SCC), arise. In this work, we have investigated how ASPP2, a member of a family of proteins that interact with the p53 family, can affect skin tumourigenesis. ASPP2 is expressed in the squamous epithelia of various organs, localising exclusively in the upper and most differentiated layers. We show here that Balb/c ASPP2-null and heterozygous mice develop spontaneous SCCs. To investigate how the absence of ASPP2 from the epithelial compartment could lead to tumour formation, we analysed ASPP2’s relationship with pathways involved in the normal homeostasis of the epithelium, such as p63 and Notch. ΔNp63 is the main p63 isoform expressed in the adult epidermis, and its function is to drive the proliferation of the basal keratinocytes. Aberrant or misplaced activation of ΔNp63 in the epithelium is a known initiating cause for SCC. Consistent with this, ΔNp63 was found to be highly expressed in tumours derived from ASPP2-deficient mice. Our results indicate that ASPP2 is important in limiting ΔNp63 expression in the differentiated epithelium, preventing cell proliferation in the upper layers of the skin. This is achieved by antagonising ΔNp63 transcript and protein expression, resulting in a mutually exclusive expression pattern during differentiation of keratinocytes, as well as in epithelial cancer. ASPP2 expression was found reduced or lost in human SCC cell lines and during head and neck cancer progression, reflecting what was observed in ASPP2-deficient mice. Overall, our results indicate a possible mechanism by which p63 expression can be regulated in the skin, and provide a new model for the spontaneous formation of SCC in vivo. Additionally, we found that ASPP2 can cooperate with and enhance the activity of skin pro-differentiation pathways, such as Notch. In contrast to p63, ASPP2 and Notch1 are co-expressed in the differentiated layers of the squamous epithelium. Moreover, ASPP2 can interact with components of Notch nuclear transcriptional machinery, and it is shuttled into the nuclear compartment upon activation of Notch pathway. This recruitment results in modulation of Notch transcriptional activity on specific target genes with a differential pattern of binding sites, providing new insights into the understanding of Notch transcriptional regulation.

The adaptor protein p140Cap/SNIP is a novel Src-binding protein that regulates Src activation through C-terminal Src kinase (Csk). Here, by gain and loss of function approaches in breast and colon cancer cells, we report that p140Cap immobilizes E-cadherin at the cell membrane and inhibits EGFR and Erk1/2 signalling, blocking scatter and proliferation of cancer cells. p140Cap-dependent regulation of E-cadherin/EGFR cross-talk and cell motility is due to the inhibition of Src kinase. However, rescue of Src activity is not sufficient to restore Erk1/2 phosphorylation and proliferation. Indeed, p140Cap also impairs Erk1/2 phosphorylation by affecting Ras activity, downstream to the EGFR. In conclusion, p140Cap stabilizes adherens junctions and inhibits EGFR and Ras signalling through the dual control of both Src and Ras activities, thus affecting crucial cancer properties such as invasion and growth. Interestingly, p140Cap expression is lost in more aggressive human breast cancers, showing an inverse correlation with EGFR expression. Therefore, p140Cap mechanistically behaves as a tumour suppressor that inhibits signalling pathways leading to aggressive phenotypes.

We recently identified p140Cap as a novel adaptor protein, expressed in epithelial‐rich tissues and phosphorylated upon cell matrix adhesion and growth factor treatment. Here, we characterise p140Cap as a novel Src‐binding protein, which regulates Src activation via C‐terminal Src kinase (Csk). p140Cap silencing increases cell spreading, migration rate and Src kinase activity. Accordingly, increased expression of p140Cap activates Csk, leading to inhibition of Src and downstream signalling as well as of cell motility and invasion. Moreover, cell proliferation and ‘ in vivo ’ breast cancer cell growth are strongly impaired by high levels of p140Cap, providing the first evidence that p140Cap is a novel negative regulator of tumour growth.