Abstract 3449: Development of MRT-2359, an orally bioavailable GSPT1 molecular glue degrader, for the treatment of lung cancers with MYC-induced translational addiction

MYC transcription factors are well-established drivers of human cancers but despite being amongst the most frequently altered oncogenes, no approved therapy targeting MYC-driven tumors has been developed to date. MYC-driven cancers are known to be addicted to protein translation. This addiction creates a dependency on critical components of the translational machinery providing in turn a unique opportunity for therapeutic intervention. We hypothesized that targeting the translation termination factor GSPT1, a key regulator of protein synthesis, would constitute a vulnerability for MYC-driven tumors. Herein we further describe MRT-2359 a potent, selective and orally bioavailable degrader of GSPT1. MRT-2359 was rationally designed using our QuEENTM discovery engine and optimized to achieve a profound and preferential antiproliferative activity in MYC-driven cell lines, such as high N- and L-MYC mRNA expressing non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC) lines. In line with expectations, MRT-2359 activity is dependent on both CRBN and the GSPT1 G-loop degron. We further demonstrate using an inducible system that the sole expression of either N- or L-MYC is sufficient to sensitize initially resistant NSCLC cells to MRT-2359. These studies therefore establish a causal link between N- and L-MYC expression and sensitivity to MRT-2359. Unlike MRT-2359, agents targeting the protein translation initiation machinery or repressing MYC transcription (CDK9 inhibitor) failed to show such differential activity. Mechanistically, RiboSeq and polysome profiling revealed that treatment with MRT-2359 in the N- or L-MYC high cell lines induces ribosome stalling at the stop codon, increased monosomes and decreased polysomes. These changes are indicative of translational repression and were confirmed using puromycilation assays. Proteomics and RNAseq studies finally demonstrated a significant reduction in the total levels of N- or L-MYC leading in turn to the downmodulation of MYC target genes. Despite robust degradation of GSPT1, no marked effect was observed in these assays in low N- or L-MYC lines, confirming the selective activity of MRT-2359 in MYC-driven lung cancers. Last, the anti-tumor activity of MRT-2359 was assessed in >80 lung patient-derived xenografts (PDXs). MRT-2359 demonstrated preferential activity in N- and L-MYC high NSCLC and SCLC PDXs, including numerous instances of tumor regressions, when dosed orally daily or intermittently. Similar levels of anti-tumor activity were also observed in neuroendocrine lung cancer and lymphoma PDXs. Together these results warrant further investigations in the clinic. Oral MRT-2359 is currently in a Phase 1/2 clinical trial in selected cancer patients with MYC-driven NSCLC, SCLC, high grade neuroendocrine cancers and diffuse large B-cell lymphoma (NCT05546268).

Citation Format: Gerald Gavory, Mahmoud Ghandi, Anne-Cecile d’Alessandro, Debora Bonenfant, Maciej Cabanski, Lisa Cantagallo, Agustin Chicas, Qian Chen, Anna Diesslin, Christopher King, Vittoria Massafra, Rajiv Narayan, Arnaud Osmont, Dave Peck, Carolina Perdomo Ortiz, Martin Schillo, Ambika Singh, Ralph Tiedt, Simone Tortoioli, Silvia Buonamici, Filip Janku, Owen Wallace, Bernhard Fasching. Development of MRT-2359, an orally bioavailable GSPT1 molecular glue degrader, for the treatment of lung cancers with MYC-induced translational addiction [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3449.

BRD9 degraders as chemosensitizers in acute leukemia and multiple myeloma

Bromodomain-containing protein 9 (BRD9), an essential component of the SWI/SNF chromatin remodeling complex termed ncBAF, has been established as a therapeutic target in a subset of sarcomas and leukemias. Here, we used novel small molecule inhibitors and degraders along with RNA interference to assess the dependency on BRD9 in the context of diverse hematological malignancies, including acute myeloid leukemia (AML), acute lymphoblastic leukemia (ALL), and multiple myeloma (MM) model systems. Following depletion of BRD9 protein, AML cells undergo terminal differentiation, whereas apoptosis was more prominent in ALL and MM. RNA-seq analysis of acute leukemia and MM cells revealed both unique and common signaling pathways affected by BRD9 degradation, with common pathways including those associated with regulation of inflammation, cell adhesion, DNA repair and cell cycle progression. Degradation of BRD9 potentiated the effects of several chemotherapeutic agents and targeted therapies against AML, ALL, and MM. Our findings support further development of therapeutic targeting of BRD9, alone or combined with other agents, as a novel strategy for acute leukemias and MM.

Abstract 3929: Identification of MRT-2359 a potent, selective and orally bioavailable GSPT1-directed molecular glue degrader (MGD) for the treatment of cancers with Myc-induced translational addiction

Myc transcription factors are well-established drivers of human cancers. However, despite being amongst the most frequently mutated, translocated and overexpressed oncogenes, no therapy targeting the Myc family members directly has been developed to date. To sustain uncontrolled cell proliferation and tumor growth, Myc-driven cancers are known to be addicted to protein translation. This addiction creates a dependency on critical components of the translational machinery providing in turn a unique opportunity for therapeutic intervention. We hypothesized that targeting the translational termination factor GSPT1, a key regulator of protein synthesis, would constitute a vulnerability for Myc-driven tumors. GSPT1 contains a well-defined degron allowing for the recruitment of the E3 ligase cereblon (CRBN) and subsequent proteasomal degradation in the presence of molecular glue degraders. Herein we describe a novel orally bioavailable GSPT1-directed small molecule degrader MRT-2359, which has been rationally designed and optimized to selectively induce apoptosis in translationally addicted cells. MRT-2359 promotes complex formation between CRBN and GSPT1 and potently induces GSPT1 degradation in a CRBN- and degron-dependent manner. The high selectivity of MRT-2359 was subsequently demonstrated by the lack of activity in cells expressing a non-degradable GSPT1 mutant. Although MRT-2359 degrades GSPT1 in all the cell lines tested, profiling in a large panel of cancer lines revealed profound and preferential antiproliferative activity in Myc-driven cell lines, such as high N-Myc expressing non-small cell lung cancer (NSCLC) lines and high L-Myc expressing small cell lung cancer (SCLC) lines. In the Myc-driven cells, degradation of GSPT1 led to translational repression as manifested by a global shift from polysomes to monosomes resulting in the reduction of a subset of proteins as assessed by quantitative proteomics. In particular, N- or L-Myc protein levels decreased and as a consequence the known Myc target genes were downregulated at the mRNA level. Despite the robust degradation of GSPT1, no marked effect was observed in low N-Myc lines, confirming the selective activity of our GSPT1 degrader in Myc-driven lung cancers. Finally, oral administration of MRT-2359 in high N-Myc NSCLC xenografts and PDXs led to complete intratumoral GSPT1 degradation and concomitant decrease in N-Myc protein levels, resulting in tumor regression. In contrast, MRT-2359 had limited or no activity in low N-Myc NSCLC models, further corroborating the selective vulnerability of Myc-driven tumors to GSPT1 degradation. Together these data support the therapeutic potential of GSPT1-directed MGDs in Myc-driven solid tumors addicted to the protein translation machinery and warrant rapid evaluation towards the clinic.

Citation Format: Gerald Gavory, Mahmoud Ghandi, Anne-Cecile d’Alessandro, Debora Bonenfant, Agustin Chicas, Frederic Delobel, Brad Demarco, Alexander Flohr, Christopher King, Anne-Laure Laine, Vittoria Massafra, Rajiv Narayan, Arnaud Osmont, Giorgio Ottaviani, Dave Peck, Sarah Pessa, Nooreen Rubin, Thomas Ryckmans, Martin Schillo, Ambika Singh, Simone Tortoioli, Dominico Vigil, Vladislav Zarayskiy, John Castle, Filip Janku, Owen Wallace, Silvia Buonamici, Bernhard Fasching. Identification of MRT-2359 a potent, selective and orally bioavailable GSPT1-directed molecular glue degrader (MGD) for the treatment of cancers with Myc-induced translational addiction [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3929.

Protein Tyrosine Phosphatase SHP2 Controls Interleukin-8 Expression in Breast Cancer Cells

Treatment of metastasis remains a clinical challenge and the majority of breast cancer-related deaths are the result of drug-resistant metastases. The protein tyrosine phosphatase SHP2 encoded by the proto-oncogene PTPN11 promotes breast cancer progression. Inhibition of SHP2 has been shown to decrease metastases formation in various breast cancer models, but specific downstream effectors of SHP2 remain poorly characterized. Certain cytokines in the metastatic cascade facilitate local invasion and promote metastatic colonization. In this study, we investigated cytokines affected by SHP2 that could be relevant for its pro-tumorigenic properties. We used a cytokine array to investigate differentially released cytokines in the supernatant of SHP2 inhibitor-treated breast cancer cells. Expression of CXCL8 transcripts and protein abundance were assessed in human breast cancer cell lines in which we blocked SHP2 using shRNA constructs or an allosteric inhibitor. The impact of SHP2 inhibition on the phospho-tyrosine-proteome and signaling was determined using mass spectrometry. From previously published RNAseq data (Aceto et al. in Nat. Med. 18:529-37, 2012), we computed transcription factor activities using an integrated system for motif activity response analysis (ISMARA) (Balwierz et al. in Genome Res. 24:869-84, 2014). Finally, using siRNA against ETS1, we investigated whether ETS1 directly influences CXCL8 expression levels. We found that IL-8 is one of the most downregulated cytokines in cell supernatants upon SHP2 blockade, with a twofold decrease in CXCL8 transcripts and a fourfold decrease in IL-8 protein. These effects were also observed in preclinical tumor models. Analysis of the phospho-tyrosine-proteome revealed that several effectors of the mitogen-activated protein kinase (MAPK) pathway are downregulated upon SHP2 inhibition in vitro. MEK1/2 inhibition consistently reduced IL-8 levels in breast cancer cell supernatants. Computational analysis of RNAseq data from SHP2-depleted tumors revealed reduced activity of the transcription factor ETS1, a direct target of ERK and a transcription factor reported to regulate IL-8 expression. Our work reveals that SHP2 mediates breast cancer progression by enhancing the production and secretion of the pro-metastatic cytokine IL-8. We also provide mechanistic insights into the effects of SHP2 inhibition and its downstream repercussions. Overall, these results support a rationale for targeting SHP2 in breast cancer.

Abstract LBA004: Identification of GSPT1-directed molecular glue degrader (MGD) for the treatment of Myc-driven breast cancer

The Myc family of transcription factors is a well-established driver of human cancers. However, despite being amongst the most frequently mutated, translocated and overexpressed oncogenes, no therapy directly targeting the Myc family members has been developed to date. Abnormal activation of Myc results in uncontrolled cell growth that is associated with high translational output and ramp up of the protein translational machinery. This creates a dependency to protein translation and in turn represents a potential therapeutic vulnerability for Myc-driven tumors. Based on these considerations, we hypothesized that targeting the translational termination factor GSPT1, a key player of protein synthesis, may constitute a vulnerability for Myc-driven tumors. Using our proprietary Quantitative and Engineered Elimination of Neosubstrates (QuEENTM) platform we characterized and explored the known G-loop degron in GSPT1 that renders it amenable to cereblon-induced degradation by molecular glue degraders (MGDs). We rationally designed and subsequently screened a proprietary library of cereblon-binding small molecules, including GSPT1-directed MGDs, in human mammary epithelial cells (HMECs) expressing doxycycline-inducible c-Myc. Doxycycline treatment led to sustained c-Myc expression and as a consequence to the induction of key biomarkers of enhanced protein translation, such as phospho 4EBP1 (p4EBP1). We identified MRT-048 as a potent and highly selective GSPT1 degrader and demonstrated its ability to induce cell death in Myc-driven HMEC cells whilst sparing control cells (EC50 0.64 μM vs 30 μM respectively). This confirmed the selective vulnerability of Myc-driven cell growth to GSPT1 degradation. In follow-up studies, we confirmed the correlation between p4EBP1 as biomarker of Myc-activation and sensitivity to MRT-048 in a large panel of breast cancer cell lines. Moreover, MRT-048 treatment of animals xenografted with breast cancer cells induced tumor regression and was associated with complete GSPT1 degradation. Mechanistically, we observed that GSPT1 degradation induced by MRT-048 led to inhibition of genes regulated by Myc and ribosomal stalling at stop codons of several mRNAs. Additionally, polysome profiling of cancer cells treated with MRT-048 was associated with a global reduction of the intensities of the polysome peaks and concomitant increase in the monosome peaks as previously observed in GSPT1 knockdown experiments, suggesting that GSPT1 degradation by our MGD molecules affects both the termination and initiation stages of protein translation. We believe these data support the therapeutic potential of GSPT1-directed MGDs in Myc-driven tumors dependent on protein translation machinery.

Citation Format: Gerald Gavory, Bernhard Fasching, Debora Bonenfant, Amine Sadok, Ambika Singh, Martin Schillo, Vittoria Massafra, Anne-Cecile d’Alessandro, John Castle, Mahmoud Ghandi, Agustin Chicas, Frederic Delobel, Alexander Flohr, Giorgio Ottaviani, Thomas Ryckmans, Anne-Laure Laine, Oliv Eidam, Hannah Wang, Ilona Bernett, Laura Chan, Chiara Gorrini, Theo Roumiliotis, Jyoti Choudhary, Yann-Vai LeBihan, Marc Cabry, Mark Stubbs, Rosemary Burke, Rob Van Montfort, John Caldwell, Rajesh Chopra, Ian Collins, Silvia Buonamici. Identification of GSPT1-directed molecular glue degrader (MGD) for the treatment of Myc-driven breast cancer [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr LBA004.

Therapeutic Assessment of Targeting ASNS Combined with l-Asparaginase Treatment in Solid Tumors and Investigation of Resistance Mechanisms

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 (Cell 2017, 170 (3), 564-576.e16. Cell 2017, 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.

Genome-wide CRISPR screening reveals genetic modifiers of mutant EGFR dependence in human NSCLC

EGFR-mutant NSCLCs frequently respond to EGFR tyrosine kinase inhibitors (TKIs). However, the responses are not durable, and the magnitude of tumor regression is variable, suggesting the existence of genetic modifiers of EGFR dependency. Here, we applied a genome-wide CRISPR-Cas9 screening to identify genetic determinants of EGFR TKI sensitivity and uncovered putative candidates. We show that knockout of RIC8A, essential for G-alpha protein activation, enhanced EGFR TKI-induced cell death. Mechanistically, we demonstrate that RIC8A is a positive regulator of YAP signaling, activation of which rescued the EGFR TKI sensitizing phenotype resulting from RIC8A knockout. We also show that knockout of ARIH2, or other components in the Cullin-5 E3 complex, conferred resistance to EGFR inhibition, in part by promoting nascent protein synthesis through METAP2. Together, these data uncover a spectrum of previously unidentified regulators of EGFR TKI sensitivity in EGFR-mutant human NSCLC, providing insights into the heterogeneity of EGFR TKI treatment responses.

Cancer is caused by cells growing and dividing uncontrollably as a result of mutations in certain genes. Many human lung cancers have a mutation in the gene that makes the protein EGFR. In healthy cells, EGFR allows a cell to respond to chemical signals that encourage healthy growth. In cancer, the altered EGFR is always on, which allows the cell to rapidly grow without any control, resulting in cancer.

One approach to treating these cancers is with drugs that block the activity of mutant EGFR. Although these drugs have been very successful, they do not always succeed in completely treating the cancer. This is because over time the cancer cells can become resistant to the drug and start forming new tumors. One way that this can happen is if random mutations lead to changes in other proteins that make the drug less effective or stop it from accessing the EGFR proteins. However, it is unclear how other proteins in cancer cells affect the response to these EGFR inhibiting drugs.

Now, Zeng et al. have used gene editing to systematically remove every protein from human lung cancer cells grown in the laboratory to see how this affects resistance to EGFR inhibitor treatment. This revealed that a number of different proteins could change how cancer cells responded to the drug. For instance, cells lacking the protein RIC8A were more sensitive to EGFR inhibitors and less likely to develop resistance. This is because loss of RIC8A turns down a key cell survival pathway in cancer cells. Whereas, cancer cells lacking the ARIH2 protein were able to produce more proteins that are needed for cancer cell growth, which resulted in them having increased resistance to EGFR inhibitors.

The proteins identified in this study could be used to develop new drugs that improve the effectiveness of EGFR inhibitors. Understanding how cancer cells respond to EGFR inhibitor treatment could help determine how likely a patient is to develop resistance to these drugs.

Inhibition of DDR1-BCR signalling by nilotinib as a new therapeutic strategy for metastatic colorectal cancer

The clinical management of metastatic colorectal cancer (mCRC) faces major challenges. Here, we show that nilotinib, a clinically approved drug for chronic myeloid leukaemia, strongly inhibits human CRC cell invasion in vitro and reduces their metastatic potential in intrasplenic tumour mouse models. Nilotinib acts by inhibiting the kinase activity of DDR1, a receptor tyrosine kinase for collagens, which we identified as a RAS‐independent inducer of CRC metastasis. Using quantitative phosphoproteomics, we identified BCR as a new DDR1 substrate and demonstrated that nilotinib prevents DDR1‐mediated BCR phosphorylation on Tyr177, which is important for maintaining β‐catenin transcriptional activity necessary for tumour cell invasion. DDR1 kinase inhibition also reduced the invasion of patient‐derived metastatic and circulating CRC cell lines. Collectively, our results indicate that the targeting DDR1 kinase activity with nilotinib may be beneficial for patients with mCRC.

TMEM41B is a novel regulator of autophagy and lipid mobilization

Autophagy maintains cellular homeostasis by targeting damaged organelles, pathogens, or misfolded protein aggregates for lysosomal degradation. The autophagic process is initiated by the formation of autophagosomes, which can selectively enclose cargo via autophagy cargo receptors. A machinery of well-characterized autophagy-related proteins orchestrates the biogenesis of autophagosomes; however, the origin of the required membranes is incompletely understood. Here, we have applied sensitized pooled CRISPR screens and identify the uncharacterized transmembrane protein TMEM41B as a novel regulator of autophagy. In the absence of TMEM41B, autophagosome biogenesis is stalled, LC3 accumulates at WIPI2- and DFCP1-positive isolation membranes, and lysosomal flux of autophagy cargo receptors and intracellular bacteria is impaired. In addition to defective autophagy, TMEM41B knockout cells display significantly enlarged lipid droplets and reduced mobilization and β-oxidation of fatty acids. Immunostaining and interaction proteomics data suggest that TMEM41B localizes to the endoplasmic reticulum (ER). Taken together, we propose that TMEM41B is a novel ER-localized regulator of autophagosome biogenesis and lipid mobilization.

Activation of IGF1R/p110β/AKT/mTOR confers resistance to α-specific PI3K inhibition

Background

The PI3K pathway is hyperactivated in many cancers, including 70 % of breast cancers. Pan- and isoform-specific inhibitors of the PI3K pathway are currently being evaluated in clinical trials. However, the clinical responses to PI3K inhibitors when used as single agents are not as efficient as expected.

Methods

In order to anticipate potential molecular mechanisms of resistance to the p110α isoform-selective inhibitor BYL719, we developed resistant breast cancer cell lines, assessed the concomitant changes in cellular signaling pathways using unbiased phosphotyrosine proteomics and characterized the mechanism of resistance using pharmacological inhibitors.

Results

We found an increase in IGF1R, IRS1/IRS2 and p85 phosphorylation in the resistant lines. Co-immunoprecipitation experiments identified an IGF1R/IRS/p85/p110β complex that causes the activation of AKT/mTOR/S6K and stifles the effects of BYL719. Pharmacological inhibition of members of this complex reduced mTOR/S6K activation and restored sensitivity to BYL719.

Conclusion

Our study demonstrates that the IGF1R/p110β/AKT/mTOR axis confers resistance to BYL719 in PIK3CA mutant breast cancers. This provides a rationale for the combined targeting of p110α with IGF1R or p110β in patients with breast tumors harboring PIK3CA mutations.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-016-0697-1) contains supplementary material, which is available to authorized users.

ANO1/TMEM16A interacts with EGFR and correlates with sensitivity to EGFR-targeting therapy in head and neck cancer

The epidermal growth factor receptor (EGFR) contributes to the pathogenesis of head&neck squamous cell carcinoma (HNSCC). However, only a subset of HNSCC patients benefit from anti-EGFR targeted therapy. By performing an unbiased proteomics screen, we found that the calcium-activated chloride channel ANO1 interacts with EGFR and facilitates EGFR-signaling in HNSCC. Using structural mutants of EGFR and ANO1 we identified the trans/juxtamembrane domain of EGFR to be critical for the interaction with ANO1. Our results show that ANO1 and EGFR form a functional complex that jointly regulates HNSCC cell proliferation. Expression of ANO1 affected EGFR stability, while EGFR-signaling elevated ANO1 protein levels, establishing a functional and regulatory link between ANO1 and EGFR. Co-inhibition of EGFR and ANO1 had an additive effect on HNSCC cell proliferation, suggesting that co-targeting of ANO1 and EGFR could enhance the clinical potential of EGFR-targeted therapy in HNSCC and might circumvent the development of resistance to single agent therapy. HNSCC cell lines with amplification and high expression of ANO1 showed enhanced sensitivity to Gefitinib, suggesting ANO1 overexpression as a predictive marker for the response to EGFR-targeting agents in HNSCC therapy. Taken together, our results introduce ANO1 as a promising target and/or biomarker for EGFR-directed therapy in HNSCC.

CLK2 inhibition ameliorates autistic features associated with SHANK3 deficiency

SH3 and multiple ankyrin repeat domains 3 (SHANK3) haploinsufficiency is causative for the neurological features of Phelan-McDermid syndrome (PMDS), including a high risk of autism spectrum disorder (ASD). We used unbiased, quantitative proteomics to identify changes in the phosphoproteome of Shank3-deficient neurons. Down-regulation of protein kinase B (PKB/Akt)-mammalian target of rapamycin complex 1 (mTORC1) signaling resulted from enhanced phosphorylation and activation of serine/threonine protein phosphatase 2A (PP2A) regulatory subunit, B56β, due to increased steady-state levels of its kinase, Cdc2-like kinase 2 (CLK2). Pharmacological and genetic activation of Akt or inhibition of CLK2 relieved synaptic deficits in Shank3-deficient and PMDS patient-derived neurons. CLK2 inhibition also restored normal sociability in a Shank3-deficient mouse model. Our study thereby provides a novel mechanistic and potentially therapeutic understanding of deregulated signaling downstream of Shank3 deficiency.

Mammary tumor formation and metastasis evoked by a HER2 splice variant

The HER2 gene is amplified and overexpressed in approximately 20% of invasive breast cancers where it is associated with metastasis and poor prognosis. Here, we describe a constitutively active splice variant of HER2 (Delta-HER2) in human mammary epithelial cells that evokes aggressive breast cancer phenotypes. Delta-HER2 overexpression in mammary epithelial cells was sufficient to reduce apoptosis, increase proliferation, and induce expression of mesenchymal markers, features that were associated with greater invasive potential in three-dimensional cultures in vitro and more aggressive tumorigenicity and metastasis in vivo. In contrast, overexpression of wild-type HER2 was insufficient at evoking such effects. Unbiased protein-tyrosine phosphorylation profiling in Delta-HER2-expressing cells revealed increased phosphorylation of several signaling proteins not previously known to be controlled by the HER2 pathway. Furthermore, microarray expression analysis revealed activation of genes known to be highly expressed in ER-negative, high-grade, and metastatic primary breast tumors. Together, our results provide mechanistic insights into the activity of a highly pathogenic splice variant of HER2.

Targeting fibroblast growth factor receptors blocks PI3K/AKT signaling, induces apoptosis, and impairs mammary tumor outgrowth and metastasis

Members of the fibroblast growth factor receptor (FGFR) family have essential roles in normal physiology and in cancer where they control diverse processes. FGFRs have been associated with breast cancer development. Thus, models to study the role of FGFR in breast cancer and their targeting potential are important. We present an in vitro and in vivo analysis of FGFRs in the breast cancer model cell lines 67NR and 4T1. We show that both tumor cell lines coexpress FGFRs and ligands and display autocrine FGFR signaling activity. Fibroblast growth factor receptor substrate 2 (FRS2), a downstream mediator of FGFR, is constitutively tyrosine phosphorylated and multiple signaling pathways are active. Treatment of 67NR and 4T1 cultures with TKI258, an FGFR tyrosine kinase inhibitor (TKI), caused a rapid decrease in FRS2 phosphorylation; decreased the activity of extracellular signal-regulated kinase 1/2 (ERK1/2), AKT, and phospholipase Cgamma; and blocked proliferation of both tumor lines. Furthermore, TKI258 induced 4T1 apoptotic cell death via blockade of the phosphoinositide 3-kinase/AKT pathway. In vivo, one dose of TKI258 rapidly lowered FRS2 phosphorylation and ERK1/2 and AKT activity in mammary tumors. Long-term TKI258 treatment of 4T1 tumor- and 67NR tumor-bearing mice had a significant effect on primary tumor outgrowth and 4T1 tumor-induced lung metastases. A microarray analysis was carried out to identify targets with roles in TKI258 antitumor activity and potential prognostic markers in human breast tumors. Of interest are the downregulated matrix metalloproteases (MMP), in particular MMP9, which is essential for metastatic spread of 4T1 tumors.

Identification of the rapamycin-sensitive phosphorylation sites within the Ser/Thr-rich domain of the yeast Npr1 protein kinase

The Saccharomyces cerevisae nitrogen permease reactivator Npr1 is a hyperphosphorylated protein that belongs to a fungus-specific family of Ser/Thr protein kinases dedicated to the regulation of plasma membrane transporters. Its activity is regulated by the TOR (target of rapamycin) signalling pathway. Inhibition of the TOR proteins by treating yeast cells with the immunosuppressant drug rapamycin promotes rapid dephosphorylation of Npr1. To identify the rapamycin-sensitive phosphorylation sites in yeast Npr1, glutathione-S-transferase (GST)-tagged Npr1 was isolated from untreated or rapamycin-treated cells, and analyzed by mass spectrometry. Here, we report for the first time 22 phosphorylation sites that are clustered in two regions of the N-terminal serine-rich domain. All phosphorylation sites, except two, were found to be rapamycin-sensitive. Some phosphorylation sites are contained in motifs that closely resemble those in mammalian S6K (serines followed by a tyrosine or a phenylalanine) and 4E-BP1 (serines followed by a proline). Other sites, such as serines followed by Ala, Asn, Gln, His, Ile, Leu, or Val, appear to define new motifs. Thus, TOR controls an unusually broad array of phosphorylation sites in Npr1. In addition to phosphorylation by upstream kinases, Npr1 undergoes autophosphorylation that was mapped to three distinct serines in the N-terminal domain of which Ser257 appears to be the main autophosphorylation site. Site-directed mutagenesis confirmed the mass spectral assignments of the autophosphorylation sites and shows that Ser257 is specifically involved in forming an in vitro substrate-binding site.

New advances on the functions of epidermal growth factor receptor and ceramides in skin cell differentiation, disorders and cancers

Recent advances in understanding of the biological functions of the epidermal growth factor and epidermal growth factor receptor (EGF-EGFR) system and ceramide production for the maintenance of skin integrity and barrier function are reported. In particular, the opposite roles of EGFR and ceramide cascades in epithelial keratinocyte proliferation, migration and terminal differentiation are described. Moreover, the functions of ceramides in the epidermal permeability barrier are reviewed. The alterations in EGFR signaling and ceramide metabolism, which might be involved in the etiopathogenesis of diverse skin disorders and cancers, are described. New progress in understanding of skin organization, which might provide the basis for the design of new transcutaneous drug delivery techniques as well as for the development of new therapies of skin disorders and cancers, are reported.

Quantitation of changes in protein phosphorylation: a simple method based on stable isotope labeling and mass spectrometry

Reversible protein phosphorylation plays an important role in many cellular processes. However, a simple and reliable method to measure changes in the extent of phosphorylation is lacking. Here, we present a method to quantitate the changes in phosphorylation occurring in a protein in response to a stimulus. The method consists of three steps: (i) enzymatic digestion in H(2)16O or isotopically enriched H(2)18O to label individual pools of differentially phosphorylated proteins; (ii) affinity selection of phosphopeptides from the combined digests by immobilized metal-affinity chromatography; and (iii) dephosphorylation with alkaline phosphatase to allow for quantitation of changes of phosphorylation by matrix-assisted laser desorption ionization time-of-flight mass spectrometry. We applied this strategy to the analysis of the yeast nitrogen permease reactivator protein kinase involved in the target of rapamycin signaling pathway. Alteration in the extent of phosphorylation at Ser-353 and Ser-357 could be easily assessed and quantitated both in wild-type yeast cells treated with rapamycin and in cells lacking the SIT4 phosphatase responsible for dephosphorylating nitrogen permease reactivator protein. The method described here is simple and allows quantitation of relative changes in the level of phosphorylation in signaling proteins, thus yielding information critical for understanding the regulation of complex protein phosphorylation cascades.

Evaluation of conformational and binding characteristics of various natriuretic peptides and related analogs

The conformational properties of atrial natriuretic factor (ANF), brain natriuretic peptide (BNP), and various analogs and homologs were studied by circular dichroism (CD) spectroscopy in solvent mixtures inducing secondary structures. The CD spectra obtained for rat ANF(99-126), porcine BNP32, and their related analogs indicated that these peptides exhibited mainly a random-coil conformation in pure water. However, the addition of increasing concentrations of 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) gave rise for all peptides to a more ordered secondary structure. The analysis of the far-ultraviolet CD spectra suggested that the peptides exist under two conformational states, beta-turn and beta-sheet, in the presence of 20-60% HFIP/water solutions. Moreover, the characterizations of rANF(99-126) and the analog pBNP1, which combines the cyclic core of bBNP32 with the carboxy- and amino-terminal segments of rANF-(99-126), have been carried out by Fourier transform infrared spectroscopy (FTIR) in 40% HFIP/D2O. The FTIR results indicated that these peptides exist predominantly under a beta-turn and beta-sheet mixed conformation. In addition, the amount of organized secondary structure obtained for human BNP32, bovine aldosterone secretion inhibitory factor, also known as ASIF(69-103) and beta-rANF(92-126), in the presence of a 40% HFIP/phosphate buffer mixture, was similar to that of porcine BNP32, whereas rat BNP32 was found to be more structured. In the same solvent mixture, the CD spectra of Met(O)110-human ANF(99-126) and chicken ANF(99-126) indicated that these peptides possess conformational features different to those of rANF(99-126) and hANF(99-126). Porcine CNP22, C-type natriuretic peptide, and the fragment C-ANF exhibited undefined secondary structure in the presence of 40% HFIP/phosphate buffer. These results suggest that the amino acid residues, not common to the various natriuretic peptides, would be involved in the stabilization of either beta-turn and/or beta-sheet conformations. Moreover, these secondary structures appear as particularly important for the recognition of the ANF-R1A receptor subtype found in bovine adrenal cortex.