Marjo de Graauw

Annexin A1 regulates TGF-β signaling and promotes metastasis formation of basal-like breast cancer cells

Annexin A1 (AnxA1) is a candidate regulator of the epithelial- to mesenchymal (EMT)-like phenotypic switch, a pivotal event in breast cancer progression. We show here that AnxA1 expression is associated with a highly invasive basal-like breast cancer subtype both in a panel of human breast cancer cell lines as in breast cancer patients and that AnxA1 is functionally related to breast cancer progression. AnxA1 knockdown in invasive basal-like breast cancer cells reduced the number of spontaneous lung metastasis, whereas additional expression of AnxA1 enhanced metastatic spread. AnxA1 promotes metastasis formation by enhancing TGFβ/Smad signaling and actin reorganization, which facilitates an EMT-like switch, thereby allowing efficient cell migration and invasion of metastatic breast cancer cells.

Heat shock protein 27 is the major differentially phosphorylated protein involved in renal epithelial cellular stress response and controls focal adhesion organization and apoptosis.

We used two-dimensional difference gel electrophoresis to determine early changes in the stress-response pathways that precede focal adhesion disorganization linked to the onset of apoptosis of renal epithelial cells. Treatment of LLC-PK1 cells with the model nephrotoxicant 1,2-(dichlorovinyl)-l-cysteine (DCVC) resulted in a >1.5-fold up- and down-regulation of 14 and 9 proteins, respectively, preceding the onset of apoptosis. Proteins included those involved in metabolism, i.e. aconitase and pyruvate dehydrogenase, and those related to stress responses and cytoskeletal reorganization, i.e. cofilin, Hsp27, and α-b-crystallin. The most prominent changes were found for Hsp27, which was related to a pI shift in association with an altered phosphorylation status of serine residue 82. Although both p38 and JNK were activated by DCVC, only inhibition of p38 with SB203580 reduced Hsp27 phosphorylation, which was associated with accelerated reorganization of focal adhesions, cell detachment, and apoptosis. In contrast, inhibition of JNK with SP600125 maintained cell adhesion as well as protection against apoptosis. Active JNK co-localized at focal adhesions after DCVC treatment in a FAK-dependent manner. Inhibition of active JNK localization at focal adhesions did not prevent DCVC-induced phosphorylation of Hsp27. Overexpression of a phosphorylation-defective mutant Hsp27 acted as a dominant negative and accelerated the DCVC-induced changes in the focal adhesions as well as the onset of apoptosis. Our data fit a model whereby early p38 activation results in a rapid phosphorylation of Hsp27, a requirement for proper maintenance of cell adhesion, thus suppressing renal epithelial cell apoptosis.

Annexin A2 phosphorylation mediates cell scattering and branching morphogenesis via cofilin Activation.

ABSTRACT Dynamic remodeling of the actin cytoskeleton is required for cell spreading, motility, and migration and can be regulated by tyrosine kinase activity. Phosphotyrosine proteomic screening revealed phosphorylation of the lipid-, calcium-, and actin-binding protein annexin A2 (AnxA2) at Tyr23 as a major event preceding ts-v-Src kinase-induced cell scattering. Expression of the phospho-mimicking mutant Y23E-AnxA2 itself was sufficient to induce actin reorganization and cell scattering in MDCK cells. While Y23E-AnxA2, but not Y23A-AnxA2, enhanced Src- or hepatocyte growth factor (HGF)-induced cell scattering, short hairpin RNA-mediated knockdown of AnxA2 inhibited both v-Src- and HGF-induced cell scattering. Three-dimensional branching morphogenesis was induced in wild-type-AnxA2-expressing cells only in the presence of HGF, while Y23E-AnxA2 induced HGF-independent branching morphogenesis. Knockdown of AnxA2 prevented lumen formation during cystogenesis. The Y23E-AnxA2-induced scattering was associated with dephosphorylation/activation of the actin-severing protein cofilin. Likewise, inactive S3E-cofilin and constitutively active LIM kinase, a direct upstream kinase of cofilin, inhibited Y23E-AnxA2-induced scattering. Together, our studies indicate an essential role for AnxA2 phosphorylation in regulating cofilin-dependent actin cytoskeletal dynamics in the context of cell scattering and branching morphogenesis.

Diclofenac inhibits tumor necrosis factor-α-induced nuclear factor-κB activation causing synergistic hepatocyte apoptosis.

Drug‐induced liver injury (DILI) is an important clinical problem. It involves crosstalk between drug toxicity and the immune system, but the exact mechanism at the cellular hepatocyte level is not well understood. Here we studied the mechanism of crosstalk in hepatocyte apoptosis caused by diclofenac and the proinflammatory cytokine tumor necrosis factor α (TNF‐α). HepG2 cells were treated with diclofenac followed by TNF‐α challenge and subsequent evaluation of necrosis and apoptosis. Diclofenac caused a mild apoptosis of HepG2 cells, which was strongly potentiated by TNF‐α. A focused apoptosis machinery short interference RNA (siRNA) library screen identified that this TNF‐α‐mediated enhancement involved activation of caspase‐3 through a caspase‐8/Bid/APAF1 pathway. Diclofenac itself induced sustained activation of c‐Jun N‐terminal kinase (JNK) and inhibition of JNK decreased both diclofenac and diclofenac/TNF‐α‐induced apoptosis. Live cell imaging of GFPp65/RelA showed that diclofenac dampened the TNF‐α‐mediated nuclear factor kappaB (NF‐κB) translocation oscillation in association with reduced NF‐κB transcriptional activity. This was associated with inhibition by diclofenac of the TNF‐α‐induced phosphorylation of the inhibitor of NF‐κB alpha (IκBα). Finally, inhibition of IκB kinase β (IKKβ) with BMS‐345541 as well as stable lentiviral short hairpin RNA (shRNA)‐based knockdown of p65/RelA sensitized hepatocytes towards diclofenac/TNF‐α‐induced cytotoxicity. Conclusion: Together, our data suggest a model whereby diclofenac‐mediated stress signaling suppresses TNF‐α‐induced survival signaling routes and sensitizes cells to apoptosis. (HEPATOLOGY 2011;)

TNF-α-mediated NF-κB survival signaling impairment by cisplatin enhances JNK activation allowing synergistic apoptosis of renal proximal tubular cells

Cisplatin-induced nephrotoxicity is an important limiting factor for cisplatin use. Tumor necrosis factor-α (TNF-α) is known to contribute to cisplatin-induced nephrotoxicity by inducing an inflammatory process aggravating the primary injury, thereby resulting in acute kidney injury (AKI). The present study investigates the pathways synergistically activated by cisplatin and TNF-α responsible for TNF-α-enhanced cisplatin-induced renal cell injury. To do so, immortalized renal proximal tubular epithelial cells (IM-PTECs) were co-treated with TNF-α and cisplatin. Under these conditions, cisplatin induced dose-dependent apoptosis in IM-PTECs, which was significantly enhanced by TNF-α. Transcriptomic analysis revealed that cisplatin inhibited the typical TNF-α response and cisplatin/TNF-α treatment up-regulated cell death pathways while it down-regulated survival pathways compared to cisplatin alone. In concordance, the gene expression levels of kidney injury markers combined with activation of specific inflammatory mediators were enhanced by cisplatin/TNF-α treatment, resembling the in vivo cisplatin-induced nephrotoxicity response. Furthermore, combined cisplatin/TNF-α treatment inhibited NF-κB nuclear translocation and NF-κB-mediated gene transcription leading to enhanced and prolonged JNK and c-Jun phosphorylation. JNK sustained activation further inhibited NF-κB signaling via a feedback loop mechanism. This led to an alteration in the transcription of the NF-κB-induced anti-apoptotic genes c-IAP2, Bcl-XL, Bruce and Bcl2 and pro-apoptotic genes Bfk and Xaf1 and consequently to sensitization of the IM-PTECs toward cisplatin/TNF-α-induced toxicity. In conclusion, our findings support a model whereby renal cells exposed to both cisplatin and TNF-α switch into a more pro-apoptotic and inflammatory program by altering their NF-κB/JNK/c-Jun balance.

Drug-Induced Endoplasmic Reticulum and Oxidative Stress Responses Independently Sensitize Toward TNFα-Mediated Hepatotoxicity

Drug-induced liver injury (DILI) is an important clinical problem. Here, we used a genomics approach to in detail investigate the hypothesis that critical drug-induced toxicity pathways act in synergy with the pro-inflammatory cytokine tumor necrosis factor α (TNFα) to cause cell death of liver HepG2 cells. Transcriptomics of the cell injury stress response pathways initiated by two hepatoxicants, diclofenac and carbamazepine, revealed the endoplasmic reticulum (ER) stress/translational initiation signaling and nuclear factor-erythroid 2 (NF-E2)-related factor 2 (Nrf2) antioxidant signaling as two major affected pathways, which was similar to that observed for the majority of ∼80 DILI compounds in primary human hepatocytes. Compounds displaying weak or no TNFα synergism, namely ketoconazole, nefazodone, and methotrexate, failed to synchronously induce both pathways. The ER stress induced was primarily related to protein kinase R-like ER kinase (PERK) and activating transcription factor 4 (ATF4) activation and subsequent expression of C/EBP homologous protein (CHOP), which was all independent of TNFα signaling. Identical ATF4 dependent transcriptional programs were observed in primary human hepatocytes as well as primary precision-cut human liver slices. Targeted RNA interference studies revealed that whereas ER stress signaling through inositol-requiring enzyme 1α (IRE1α) and activating transcription factor 6 (ATF6) acted cytoprotective, activation of the ER stress protein kinase PERK and subsequent expression of CHOP was pivotal for the onset of drug/TNFα-induced apoptosis. Whereas inhibition of the Nrf2-dependent adaptive oxidative stress response enhanced the drug/TNFα cytotoxicity, Nrf2 signaling did not affect CHOP expression. Both hepatotoxic drugs enhanced expression of the translational initiation factor EIF4A1, which was essential for CHOP expression and drug/TNFα-mediated cell killing. Our data support a model in which enhanced drug-induced translation initiates PERK-mediated CHOP signaling in an EIF4A1 dependent manner, thereby sensitizing toward caspase-8-dependent TNFα-induced apoptosis.

Tumor cell migration screen identifies SRPK1 as breast cancer metastasis determinant

Tumor cell migration is a key process for cancer cell dissemination and metastasis that is controlled by signal-mediated cytoskeletal and cell matrix adhesion remodeling. Using a phagokinetic track assay with migratory H1299 cells, we performed an siRNA screen of almost 1,500 genes encoding kinases/phosphatases and adhesome- and migration-related proteins to identify genes that affect tumor cell migration speed and persistence. Thirty candidate genes that altered cell migration were validated in live tumor cell migration assays. Eight were associated with metastasis-free survival in breast cancer patients, with integrin β3-binding protein (ITGB3BP), MAP3K8, NIMA-related kinase (NEK2), and SHC-transforming protein 1 (SHC1) being the most predictive. Examination of genes that modulate migration indicated that SRPK1, encoding the splicing factor kinase SRSF protein kinase 1, is relevant to breast cancer outcomes, as it was highly expressed in basal breast cancer. Furthermore, high SRPK1 expression correlated with poor breast cancer disease outcome and preferential metastasis to the lungs and brain. In 2 independent murine models of breast tumor metastasis, stable shRNA-based SRPK1 knockdown suppressed metastasis to distant organs, including lung, liver, and spleen, and inhibited focal adhesion reorganization. Our study provides comprehensive information on the molecular determinants of tumor cell migration and suggests that SRPK1 has potential as a drug target for limiting breast cancer metastasis.

cAMP signalling protects proximal tubular epithelial cells from cisplatin-induced apoptosis via activation of Epac

Nephrotoxicity is the principal dose‐limiting factor for cisplatin chemotherapy and is primarily associated with proximal tubular epithelial cells, including disruption of cell adhesions and induction of apoptosis. Cell adhesion and survival is regulated by, amongst other factors, the small GTPase Rap and its activator, the exchange protein directly activated by cAMP (Epac). Epac is particularly enriched in renal tubule epithelium. This study investigates the cytoprotective effects of cAMP–Epac–Rap signalling in a model of cisplatin‐induced renal cell injury.

The nuclear factor κB family member RelB facilitates apoptosis of renal epithelial cells caused by cisplatin/tumor necrosis factor α synergy by suppressing an epithelial to mesenchymal transition-like phenotypic switch.

Cis-diamminedichloroplatinum(II) (cisplatin)–induced renal proximal tubular apoptosis is known to be preceded by actin cytoskeleton reorganization, in conjunction with disruption of cell-matrix and cell-cell adhesion. In the present study, we show that the proinflammatory cytokine tumor necrosis factor α (TNF-α) aggravated these cisplatin-induced F-actin and cell adhesion changes, which was associated with enhanced cisplatin-induced apoptosis of immortalized proximal tubular epithelial cells. TNF-α–induced RelB expression and lentiviral small hairpin RNA (shRNA)-mediated knockdown of RelB, but not other nuclear factor κB members, abrogated the synergistic apoptosis observed with cisplatin/TNF-α treatment to the level of cisplatin-induced apoptosis. This protective effect was associated with increased stress fiber formation, cell-matrix, and cell-cell adhesion in the shRNARelB (shRelB) cells during cisplatin/TNF-α treatment, mimicking an epithelial-to-mesenchymal phenotypic switch. Indeed, gene array analysis revealed that knockdown of RelB was associated with upregulation of several actin regulatory genes, including Snai2 and the Rho GTPase proteins Rhophilin and Rho guanine nucleotide exchange factor 3 (ARHGEF3). Pharmacological inhibition of Rho kinase signaling re-established the synergistic apoptosis induced by combined cisplatin/TNF-α treatment of shRelB cells. In conclusion, our study shows for the first time that RelB is required for the cisplatin/TNF-α–induced cytoskeletal reorganization and apoptosis in renal cells by controlling a Rho kinase–dependent signaling network.

Elucidation of Signaling Pathways from Large-Scale Phosphoproteomic Data Using Protein Interaction Networks

Phosphoproteomic experiments typically identify sites within a protein that are differentially phosphorylated between two or more cell states. However, the interpretation of these data is hampered by the lack of methods that can translate site-specific information into global maps of active proteins and signaling networks, especially as the phosphoproteome is often undersampled. Here, we describe PHOTON, a method for interpreting phosphorylation data within their signaling context, as captured by protein-protein interaction networks, to identify active proteins and pathways and pinpoint functional phosphosites. We apply PHOTON to interpret existing and novel phosphoproteomic datasets related to epidermal growth factor and insulin responses. PHOTON substantially outperforms the widely used cutoff approach, providing highly reproducible predictions that are more in line with current biological knowledge. Altogether, PHOTON overcomes the fundamental challenge of delineating signaling pathways from large-scale phosphoproteomic data, thereby enabling translation of environmental cues to downstream cellular responses.