Simone Barbero

Caspase-8 association with the focal adhesion complex promotes tumor cell migration and metastasis.

Caspase-8 is a proapoptotic protease that suppresses neuroblastoma metastasis by inducing programmed cell death. Paradoxically, caspase-8 can also promote cell migration among nonapoptotic cells; here, we show that caspase-8 can promote metastasis when apoptosis is compromised. Migration is enhanced by caspase-8 recruitment to the cellular migration machinery following integrin ligation. Caspase-8 catalytic activity is not required for caspase-8-enhanced cell migration; rather, caspase-8 interacts with a multiprotein complex that can include focal adhesion kinase and calpain 2 (CPN2), enhancing cleavage of focal adhesion substrates and cell migration. Caspase-8 association with CPN2/calpastatin disrupts calpastatin-mediated inhibition of CPN2. In vivo, knockdown of either caspase-8 or CPN2 disrupts metastasis among apoptosis-resistant tumors. This unexpected molecular collaboration provides an explanation for the continued or elevated expression of caspase-8 observed in many tumors.

The marine lipopeptide somocystinamide A triggers apoptosis via caspase 8

Screening for novel anticancer drugs in chemical libraries isolated from marine organisms, we identified the lipopeptide somocystinamide A (ScA) as a pluripotent inhibitor of angiogenesis and tumor cell proliferation. The antiproliferative activity was largely attributable to induction of programmed cell death. Sensitivity to ScA was significantly increased among cells expressing caspase 8, whereas siRNA knockdown of caspase 8 increased survival after exposure to ScA. ScA rapidly and efficiently partitioned into liposomes while retaining full antiproliferative activity. Consistent with the induction of apoptosis via the lipid compartment, we noted accumulation and aggregation of ceramide in treated cells and subsequent colocalization with caspase 8. Angiogenic endothelial cells were extremely sensitive to ScA. Picomolar concentrations of ScA disrupted proliferation and endothelial tubule formation in vitro. Systemic treatment of zebrafish or local treatment of the chick chorioallantoic membrane with ScA resulted in dose-dependent inhibition of angiogenesis, whereas topical treatment blocked tumor growth among caspase-8-expressing tumors. Together, the results reveal an unexpected mechanism of action for this unique lipopeptide and suggest future development of this and similar agents as antiangiogenesis and anticancer drugs.

Identification of a Critical Tyrosine Residue in Caspase 8 That Promotes Cell Migration

Caspase 8 is a critical upstream initiator of programmed cell death but, paradoxically, has also been shown to promote cell migration. Here, we show that tyrosine 380 in the linker loop of human caspase 8 is a critical switch determining caspase 8 function. Our studies show that, in addition to its cytosolic distribution, caspase 8 is recruited to lamella of migrating cells. Although the catalytic domain of caspase 8 is sufficient for recruitment and promotion of cell migration, catalytic activity per se is not required. Instead, we find that integrin-mediated adhesion promotes caspase 8 phosphorylation on tyrosine 380. Accordingly, mutation of this site compromises localization to the periphery and the potentiation of cell migration. Mechanistically, this linker region of caspase 8 acts as a Src homology 2 binding site. In particular, tyrosine 380 is critical for interaction with Src homology 2 domains. The results identify a novel mechanism by which caspase 8 is recruited to the lamella of a migrating cell, promoting cell migration independent of its protease activity.

Rab5 Mediates Caspase-8 Promoted Cell Motility and Metastasis

Integrins signaling promotes nonapoptotic functions of caspase-8 via activation of small GTPases from the Rab and Rac families. Integrin ligation promotes Rab5 activity, which mediates subsequent activation of Rac1, cytoskeletal remodeling, and enhanced cell motility.

Paclitaxel promotes a caspase 8-mediated apoptosis through death effector domain association with microtubules

Microtubule-perturbing drugs have become front-line chemotherapeutics, inducing cell-cycle crisis as a major mechanism of action. However, these agents show pleiotropic effects on cells and can induce apoptosis through other means. Paclitaxel, a microtubule-stabilizing agent, induces a caspase-dependent apoptosis, although the precise mechanism(s) remain unclear. Here, we used genetic approaches to evaluate the role of caspase 8 in paclitaxel-mediated apoptosis. We observed that caspase 8-expressing cells are more sensitive to paclitaxel than caspase 8-deficient cells. Mechanistically, caspase 8 was found associated with microtubules, and this interaction increased after paclitaxel treatment. The prodomains death effector domains (DEDs) of caspase 8 were sufficient for interaction with microtubules, but the caspase 8 holoprotein was required for apoptosis. DED-only forms of caspase 8 were found in both primary and tumor cell lines, associating with perinuclear microtubules and the centrosome. Microtubule association, and paclitaxel sensitivity, depends on a critical lysine (K156) within a microtubule-binding motif (KLD) in DED-b of caspase 8. The results show an unexpected pathway of apoptosis mediated by caspase 8.

Caspase-8 as a Regulator of Tumor Cell Motility

The caspases are a family of ubiquitously expressed cysteine proteases best known for their roles in programmed cell death. However, caspases play a number of other roles in vertebrates. In the case of caspase-8, loss of expression is an embryonic lethal phenotype, and caspase-8 plays roles in suppressing cellular necrosis, promoting differentiation and immune signaling, regulating autophagy, and promoting cellular migration. Apoptosis and migration require localization of caspase-8 in the periphery of the cells, where caspase-8 acts as part of distinct biosensory complexes that either promote migration in appropriate cellular microenvironments, or cell death in inappropriate settings. In the cellular periphery, caspase-8 interacts with components of the focal adhesion complex in a tyrosine-kinase dependent manner, promoting both cell migration in vitro and metastasis in vivo. Mechanistically, caspase-8 interacts with components of both focal adhesions and early endosomes, enhancing focal adhesion turnover and promoting rapid integrin recycling to the cell surface. Clinically, this suggests that the expression of caspase-8 may not always be a positive prognostic sign, and that the role of caspase-8 in cancer progression is likely context-dependent.

The Death Effector Domains of Caspase-8 Induce Terminal Differentiation

The differentiation and senescence programs of metazoans play key roles in regulating normal development and preventing aberrant cell proliferation, such as cancer. These programs are intimately associated with both the mitotic and apoptotic pathways. Caspase-8 is an apical apoptotic initiator that has recently been appreciated to coordinate non-apoptotic roles in the cell. Most of these functions are attributed to the catalytic domain, however, the amino-terminal death effector domains (DED)s, which belong to the death domain superfamily of proteins, can also play key roles during development. Here we describe a novel role for caspase-8 DEDs in regulating cell differentiation and senescence. Caspase-8 DEDs accumulate during terminal differentiation and senescence of epithelial, endothelial and myeloid cells; genetic deletion or shRNA suppression of caspase-8 disrupts cell differentiation, while re-expression of DEDs rescues this phenotype. Among caspase-8 deficient neuroblastoma cells, DED expression attenuated tumor growth in vivo and proliferation in vitro via disruption of mitosis and cytokinesis, resulting in upregulation of p53 and induction of differentiation markers. These events occur independent of caspase-8 catalytic activity, but require a critical lysine (K156) in a microtubule-binding motif in the second DED domain. The results demonstrate a new function for the DEDs of caspase-8, and describe an unexpected mechanism that contributes to cell differentiation and senescence.

Src-inducible association of CrkL with procaspase-8 promotes cell migration

Procaspase-8, the zymogen form of the apoptosis-initiator caspase-8, undergoes phosphorylation following integrin-mediated cell attachment to an extracellular matrix substrate. Concordant with cell attachment to fibronectin, a population of procaspase-8 becomes associated with a peripheral insoluble compartment that includes focal complexes and lamellar microfilaments. Phosphorylation of procaspase-8 both impairs its maturation to the proapoptotic form and can promote cell migration. Here we show that the cytoskeletal adaptor protein CrkL promotes caspase-8 recruitment to the peripheral spreading edge of cells, and that the catalytic domain of caspase-8 directly interacts with the SH2 domain of CrkL. We show that the interaction is abolished by shRNA-mediated silencing of Src, in Src-deficient MEFs, and by pharmacologic inhibitors of the kinase. The results provide insight into how tyrosine kinases may act to coordinate the suppression caspase-8 mediated apoptosis, while promoting cell invasion.

Abstract 2241: Serum and plasma IL-17A concentrations in lung cancer patients and controls

Purpose: IL-17A, a cytokine produced by Th17 cells, is reportedly a central regulator of lung tumor growth (Reppert et al., OncoImmunology 1, 2012) and a potential serum biomarker for lung cancer (Xu et al., Biomarkers, 2014). Serum concentrations of IL-17A are too low to measure in most samples (on the order of 0.1 pg/mL) using commercially available ELISAs. In order to overcome this limitation, we developed the S-PLEX™ Human IL-17A ultrasensitive assay which is capable of accurately measuring IL-17A in serum and plasma. We used this assay to measure IL-17A concentrations in serum samples from lung cancer patients and controls. Methods: Serum samples from 59 lung cancer patients and 44 apparently healthy controls (including 14 heavy smokers) were analyzed using S-PLEX technology to determine IL-17A concentrations. In addition, IL-17A concentrations were measured in matched plasma samples from 24 of the controls. S-PLEX is a new ultrasensitive immunoassay format based on MSD9s MULTI-ARRAY® electrochemiluminescence technology. The IL-17A assay requires only 25 μL of serum or plasma per measurement and can be run on the MESO® SECTOR S 600 and MESO QuickPlex® SQ 120 instruments. Results: The S-PLEX Human IL-17A assay was capable of accurately measuring IL-17A concentrations in 125 of the 127 samples tested. The lower limit of detection was 6 fg/mL and the assay range (LLOQ to ULOQ) was from 20 fg/mL to 200,000 fg/mL. Typical intra-plate coefficients of variation (CVs) ranged between 5% and 15%. Control samples run at 3 levels, in multiple replicates over multiple days, produced CVs Conclusion: We have developed a highly specific and sensitive IL-17A assay that is 100 times more sensitive than the current limits of ELISA technology. This assay enables accurate determination of IL-17A concentrations in serum and plasma samples from lung cancer patients and healthy controls. The results from this study do not support the use of IL-17A as an effective serum biomarker for the presence of lung cancer. Citation Format: Animesh Shukla, Sheldon Grove, Simone Barbero, Galina N. Nikolenko, Anu Mathew, Martin K. Stengelin, Eli N. Glezer, Jacob N. Wohlstadter. Serum and plasma IL-17A concentrations in lung cancer patients and controls. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2241.