Organization of functional domains in the docking protein p130Cas

Vinculin-p130Cas interaction is critical for focal adhesion dynamics and mechano-transduction

Adherent cells, when mechanically stressed, show a wide range of responses including large-scale changes in their mechanical behaviour and gene expression pattern. This is in part facilitated by activating the focal adhesion (FA) protein p130Cas through force-induced conformational changes that lead to the phosphorylation by src family kinases. Janostiak et al. [Janostiak et al. Cell Mol Life Sci (2013) DOI 10.1007/s00018-013-1450-x] have reported that the phosphorylation site Y12 on the SH3 domain of p130Cas modulates the binding with vinculin, a prominent mechano-coupling protein in FAs. Tension changes in FAs (due to the anchorage of the SH3 domain and C-terminal) bring about an extension of the substrate domain of p130Cas by unmasking the phosphorylation sites. These observations demonstrate that vinculin is an important modulator of the p130Cas-mediated mechano-transduction pathway in cells. The central aim should be now to test that vinculin is critical for p130Cas incorporation into the focal adhesion complex and for transmitting forces to the p130Cas molecule.

Silencing of p130cas in ovarian carcinoma: a novel mechanism for tumor cell death

BACKGROUND

We investigated the clinical and biological significance of p130cas, an important cell signaling molecule, in ovarian carcinoma.

METHODS

Expression of p130cas in ovarian tumors, as assessed by immunohistochemistry, was associated with tumor characteristics and patient survival. The effects of p130cas gene silencing with small interfering RNAs incorporated into neutral nanoliposomes (siRNA-DOPC), alone and in combination with docetaxel, on in vivo tumor growth and on tumor cell proliferation (proliferating cell nuclear antigen) and apoptosis (terminal deoxynucleotidyl transferase dUTP nick-end labeling) were examined in mice bearing orthotopic taxane-sensitive (HeyA8 and SKOV3ip1) or taxane-resistant (HeyA8-MDR) ovarian tumors (n = 10 per group). To determine the specific mechanisms by which p130cas gene silencing abrogates tumor growth, we measured cell viability (MTT assay), apoptosis (fluorescence-activated cell sorting), autophagy (immunoblotting, fluorescence, and transmission electron microscopy), and cell signaling (immunoblotting) in vitro. All statistical tests were two-sided.

RESULTS

Of 91 ovarian cancer specimens, 70 (76%) had high p130cas expression; and 21 (24%) had low p130cas expression. High p130cas expression was associated with advanced tumor stage (P < .001) and higher residual disease (>1 cm) following primary cytoreduction surgery (P = .007) and inversely associated with overall survival and progression-free survival (median overall survival: high p130cas expression vs low expression, 2.14 vs 9.1 years, difference = 6.96 years, 95% confidence interval = 1.69 to 9.48 years, P < .001; median progression-free survival: high p130cas expression vs low expression, 1.04 vs 2.13 years, difference = 1.09 years, 95% confidence interval = 0.47 to 2.60 years, P = .01). In mice bearing orthotopically implanted HeyA8 or SKOV3ip1 ovarian tumors, treatment with p130cas siRNA-DOPC in combination with docetaxel chemotherapy resulted in the greatest reduction in tumor growth compared with control siRNA therapy (92%-95% reduction in tumor growth; P < .001 for all). Compared with control siRNA therapy, p130cas siRNA-DOPC reduced SKOV3ip1 cell proliferation (31% reduction, P < .001) and increased apoptosis (143% increase, P < .001) in vivo. Increased tumor cell apoptosis may have persisted despite pan-caspase inhibition by the induction of autophagy and related signaling pathways.

CONCLUSIONS

Increased p130cas expression is associated with poor clinical outcome in human ovarian carcinoma, and p130cas gene silencing decreases tumor growth through stimulation of apoptotic and autophagic cell death.

A new signaling paradigm for serotonin: use of Crk-associated substrate in arterial contraction

Crk-associated substrate (CAS), a 130-kDa adaptor protein, was discovered as a tyrosine kinase substrate of Src that was important to cellular motility and actin filament formation. As the tyrosine kinase Src is utilized by the 5-hydroxytryptamine (5-HT)2A receptor in arterial contraction, we tested the hypothesis that CAS was integral to 5-HT2A receptor-mediated vasoconstriction. Rat thoracic aorta was used as a model of the arterial 5-HT2A receptor. Western and immunohistochemistry analyses validated the presence of CAS in the aorta, and tissue bath experiments demonstrated reduction of contraction to 5-HT (13.5 ± 5% control maximum) and the 5-HT2 receptor agonist α-methyl-5-HT (6 ± 2% maximum) by latrunculin B (10−6 mol/l), an actin disruptor. In aorta contracted with 5-HT (10−5 mol/l), tyrosine phosphorylation (Tyr410) of CAS was significantly increased (∼225%), and both contraction and CAS phosphorylation were reduced by the 5-HT2A/2C receptor antagonist ketanserin (3 × 10−8 mol/l). Src is one candidate for 5-HT-stimulated CAS tyrosyl-phosphorylation as 5-HT promoted interaction of Src and CAS in coimmunoprecipitation experiments, and the Src tyrosine kinase inhibitor PP1 (10−5 mol/l) abolished 5-HT-induced tyrosyl-phosphorylation of CAS and reduced 5-HT- and α-methyl-5-HT-induced contraction. Antisense oligodeoxynucleotides delivered to the aorta reduced CAS expression (33% control) and arterial contraction to α-methyl-5-HT (45% of control), independent of changes in myosin light chain phosphorylation. These data are the first to implicate CAS in the signal transduction of 5-HT.

Molecular regulation of osteoclast activity

Osteoclasts are multinucleated cells derived from hematopoietic precursors that are primarily responsible for the degradation of mineralized bone during bone development, homeostasis and repair. In various skeletal disorders such as osteoporosis, hypercalcemia of malignancy, tumor metastases and Paget's disease, bone resorption by osteoclasts exceeds bone formation by osteoblasts leading to decreased bone mass, skeletal fragility and bone fracture. The overall rate of osteoclastic bone resorption is regulated either at the level of differentiation of osteoclasts from their monocytic/macrophage precursor pool or through the regulation of key functional proteins whose specific activities in the mature osteoclast control its attachment, migration and resorption. Thus, reducing osteoclast numbers and/or decreasing the bone resorbing activity of osteoclasts are two common therapeutic approaches for the treatment of hyper-resorptive skeletal diseases. In this review, several of the key functional players involved in the regulation of osteoclast activity will be discussed.

14-3-3 proteins as potential oncogenes

14-3-3 proteins are a family of highly conserved cellular proteins that play key roles in the regulation of central physiological pathways. More than 200 14-3-3 target proteins have been identified, including proteins involved in mitogenic and cell survival signaling, cell cycle control and apoptotic cell death. Importantly, the involvement of 14-3-3 proteins in the regulation of various oncogenes and tumor suppressor genes points to a potential role in human cancer. The present review summarizes current findings implicating a 14-3-3 role in cancer while discussing potential mechanisms and points of action of 14-3-3 during cancer development and progression.

Interaction partners for human ZNF384/CIZ/NMP4--zyxin as a mediator for p130CAS signaling?

Transcription factor ZNF384/CIZ/NMP4 was first cloned in rat as a p130Cas-binding protein and has a role in bone metabolism and spermatogenesis. It is recurrently involved in translocations in acute lymphoblastic leukemia. Translocations t(12;17) and t(12;22) fuse ZNF384 to RNA-binding proteins TAF15 and EWSR1, while a translocation t(12;19) generates an E2A/ZNF384 fusion. We screened for ZNF384 interacting proteins using yeast two-hybrid technology. In contrast to its rat homolog, human ZNF384 does not interact with p130CAS. Zyxin, PCBP1, and vimentin, however, were identified as ZNF384-binding partners. Given the interaction between human zyxin and p130CAS, these results suggest that zyxin indirectly enables the interaction of ZNF384 with p130CAS which is described in rat.

Molecular determinants for interaction of SHEP1 with Cas localize to a highly solvent-protected region in the complex

Protein-protein interactions between SHEP and Cas proteins influence cellular signaling through tyrosine kinases, as well as integrin-mediated signaling, and may be linked to antiestrogen resistance. Data from past studies suggests that association between SHEP and Cas proteins is critical for these cellular effects. In this study, the interacting domains of each protein were co-expressed in bacteria and a soluble stable complex was purified. Deuterium exchange mass spectrometry was used to define regions that are buried when SHEP1 is in complex with Cas. The results reveal four segments in SHEP1 that are highly protected, including a region (residues 619-640) that contains a key residue, tyrosine 635, required for association with Cas. This region is predominately hydrophilic, yet remains protected from solvent in the complex.

Uncoupling Crk signal transduction by Pseudomonas exoenzyme T

Exoenzyme T (ExoT) is a bifunctional type III cytotoxin of Pseudomonas aeruginosa that possesses both Rho GTPase-activating protein and ADP-ribosyltransferase activities. The ADP-ribosyltransferase activity of ExoT stimulated depolymerization of the actin cytoskeleton independent of Rho GTPase-activating protein function, and ExoT was subsequently shown to ADP-ribosylate Crk (CT10 regulator of kinase)-I and Crk-II. Crk proteins are eukaryotic adaptor proteins comprising SH2 and SH3 domains that are components of the integrin signaling pathway leading to Rac1 and Rap1 functions. Mass spectroscopic analysis identified Arg20 as the site of ADP-ribosylation by ExoT. Arg20 is a conserved residue located within the SH2 domain that is required for interactions with upstream signaling molecules such as paxillin and p130cas. Glutathione S-transferase pull-down and far Western assays showed that ADP-ribosylated Crk-I or Crk-I(R20K) failed to bind p130cas or paxillin. This indicates that ADP-ribosylation inhibited the direct interaction of Crk with these focal adhesion proteins. Overexpression of wild-type Crk-I reduced cell rounding by ExoT, whereas expression of dominant-active Rac1 interfered with the ability of ExoT to round cells. Thus, the ADP-ribosylation of Crk uncouples integrin signaling by direct inhibition of the binding of Crk to focal adhesion proteins.

The Serine-rich Domain from Crk-associated Substrate (p130 ) Is a Four-helix Bundle

p130(cas) (Crk-associated substrate) is a docking protein that is involved in assembly of focal adhesions and concomitant cellular signaling. It plays a role in physiological regulation of cell adhesion, migration, survival, and proliferation, as well as in oncogenic transformation. The molecule consists of multiple protein-protein interaction motifs, including a serine-rich region that is positioned between Crk and Src-binding sites. This study reports the first structure of a functional domain of Cas. The solution structure of the serine-rich region has been determined by NMR spectroscopy, demonstrating that this is a stable domain that folds as a four-helix bundle, a protein-interaction motif. The serine-rich region bears strong structural similarity to four-helix bundles found in other adhesion components like focal adhesion kinase, alpha-catenin, or vinculin. Potential sites for phosphorylation and interaction with the 14-3-3 family of cellular regulators are identified in the domain and characterized by site-directed mutagenesis and binding assays. Mapping the degree of amino acid conservation onto the molecular surface reveals a patch of invariant residues near the C terminus of the bundle, which may represent a previously unidentified site for protein interaction.

Molecular basis for regulation of Src by the docking protein p130Cas

The docking protein p130Cas (Cas) becomes tyrosine-phosphorylated in its central substrate domain in response to extracellular stimuli such as integrin-mediated cell adhesion, and transmits signals through interactions with various intracellular signaling molecules such as the adaptor protein Crk. Src-family kinases (SFKs) bind a specific site in the carboxyl-terminal region of Cas and subsequently SFKs phosphorylate progressively the substrate domain in Cas. In this study crystallography, mutagenesis and binding assays were used to understand the molecular basis for Cas interactions with SFKs. Tyrosine phosphorylation regulates binding of Cas to SFKs, and the primary site for this phosphorylation, Y762, has been proposed. A phosphorylated peptide corresponding to Cas residues 759MEDpYDYVHL767 containing the key phosphotyrosine was crystallized in complex with the SH3-SH2 domain of the SFK Lck. The results provide the first structural data for this protein-protein interaction. The motif in Cas 762pYDYV binds to the SH2 domain in a mode that mimics high-affinity ligands, involving dual contacts of Y762 and V765 with conserved residues in SFK SH2 domains. In addition, Y764 is in position to make an electrostatic contact after phosphorylation with a conserved SFK arginine that mediates interactions with other high-affinity SH2 binders. These new molecular data suggest that Cas may regulate activity of Src as a competing ligand to displace intramolecular interactions that occur in SFKs (between the C-terminal tail and the SH2 domain) and restrain and down-regulate the kinase in an inactive form.