XIAP reverses various functional activities of FRNK in endothelial cells

Antiatherogenic Effect of Resveratrol Attributed to Decreased Expression of ICAM-1 (Intercellular Adhesion Molecule-1)

Objective- Increasing evidence shows that resveratrol has antiatherogenic effects, but its underlying mechanisms are unknown. Thus, we evaluated the molecular mechanisms underlying the antiatherogenic effect of resveratrol. Approach and Results- Using the previously established mouse atherosclerosis model of partial ligation of the left carotid artery, we evaluated the role of resveratrol in antiatherosclerosis. We attempted to determine the mechanisms associated with focal adhesions using vascular endothelial cells. The results showed that resveratrol stimulated focal adhesion kinase cleavage via resveratrol-increased expression of lactoferrin in endothelial cells. Furthermore, we found that an N-terminal focal adhesion kinase fragment cleaved by resveratrol contained the FERM (band 4.1, ezrin, radixin, and moesin)-kinase domain. Furthermore, resveratrol inhibited lipopolysaccharide-stimulated adhesion of THP-1 human monocytes by decreased expression of ICAM-1 (intercellular adhesion molecule-1). A decreased ICAM-1 level was also observed in the left carotid artery of mice treated with resveratrol. To understand the relationship between resveratrol-induced antiinflammation and focal adhesion disruption, endothelial cells were transfected with FERM-kinase. Ectopically expressed FERM-kinase, the resveratrol-cleaved focal adhesion kinase fragment, was found in the nuclear fraction and inhibited the transcription level of icam-1 via the Nrf2 (nuclear factor erythroid 2-related factor 2)-antioxidant response element complex. Finally, ectopically expressed FERM-kinase blocked tumor necrosis factor-α- or IL- (interleukin) stimulated monocytic binding to endothelial cells. Conclusions- Our results show that resveratrol inhibits the expression of ICAM-1 via transcriptional regulation of the FERM-kinase and Nrf2 interaction, thereby blocking monocyte adhesion. These suppressive effects on the inflammatory mechanism suggest that resveratrol delayed the onset of atherosclerosis.

Regulation of Focal Adhesion Kinase through a Direct Interaction with an Endogenous Inhibitor

Focal adhesion kinase (FAK) plays a key role in integrin and growth factor signaling pathways. FAK-related non-kinase (FRNK) is an endogenous inhibitor of FAK that shares its primary structure with the C-terminal third of FAK. FAK S910 phosphorylation is known to regulate FAK protein-protein interactions, but the role of the equivalent site on FRNK (S217) is unknown. Here we determined that S217 is highly phosphorylated by ERK in cultured rat aortic smooth muscle cells. Blocking phosphorylation by mutation (S217A) greatly increased FRNK inhibitory potency, resulting in strong inhibition of FAK autophosphorylation at Y397 and induction of smooth muscle cell apoptosis. FRNK has been proposed to compete for FAK anchoring sites in focal adhesions, but we did not detect displacement of FAK by WT-FRNK or superinhibitory S217A-FRNK. Instead, we found FRNK interacted directly with FAK, and this interaction is markedly strengthened for the superinhibitory S217A-FRNK. The results suggest that FRNK limits growth and survival signaling pathways by binding directly to FAK in an inhibitory complex, and this inhibition is relieved by phosphorylation of FRNK at S217.

Mitsugumin 53 (MG53) ligase ubiquitinates focal adhesion kinase during skeletal myogenesis

The striated muscle-specific mitsugumin 53 (MG53) is a novel E3 ligase that induces the ubiquitination of insulin receptor substrate 1 (IRS-1) during skeletal myogenesis, negatively regulating insulin-like growth factor and insulin signaling. Here we show that focal adhesion kinase (FAK) is the second target of MG53 during skeletal myogenesis. The FAK protein level gradually decreased, whereas its mRNA level was constant during myogenesis in C2C12 cells and MyoD-overexpressing mouse embryonic fibroblasts. The FAK protein was associated with the E2 enzyme UBE2H and the E3 enzyme MG53 in endogenous and exogenous immunoprecipitation experiments. FAK ubiquitination and degradation was induced by MG53 overexpression in myoblasts but abolished by MG53 or UBE2H knockdown in myotubes. Because RING-disrupted MG53 mutants (C14A and ΔR) did not induce FAK ubiquitination and degradation, the RING domain was determined to be required for MG53-induced FAK ubiquitination. Taken together, these data indicate that MG53 induces FAK ubiquitination with the aid of UBE2H during skeletal myogenesis.

FERM domain promotes resveratrol-induced apoptosis in endothelial cells via inhibition of NO production

Focal adhesion kinase (FAK) consists of an N-terminal band 4.1; ezrin, radixin, moesin (FERM) domain; tyrosine kinase domain; and C-terminal FA targeting domain. Here we show that ectopically expressed FERM is largely located in the cytosolic fraction under quiescent conditions. We further found that this ectopically expressed FERM domain aggravates endothelial cell apoptosis triggered by 100 μM resveratrol, whereas FERM had no effect on apoptosis induced by TNF-α. We determined that resveratrol at low doses (<20 μM) promotes phosphorylation (S1177) of eNOS via an AMPK-dependent pathway. The presence of the FERM domain blocked this resveratrol-stimulated eNOS phosphorylation and NO production. Thus, the pro-apoptotic activity of cytosolic FERM domain is at least partially mediated by down-regulation of NO, a critical cell survival factor. Consistently, we found that the apoptosis induced by cytosolic FERM in the presence of resveratrol was reversed by an NO donor, SNAP. In conclusion, FERM located in the cytosolic fraction plays a pivotal role in aggravating cell apoptosis through diminishing NO production.

IAPs on the move: role of inhibitors of apoptosis proteins in cell migration

Inhibitors of Apoptosis Proteins (IAPs) are a class of highly conserved proteins predominantly known for the regulation of caspases and immune signaling. However, recent evidence suggests a crucial role for these molecules in the regulation of tumor cell shape and migration by controlling MAPK, NF-κB and Rho GTPases. IAPs directly control Rho GTPases, thus regulating cell shape and migration. For instance, XIAP and cIAP1 function as the direct E3 ubiquitin ligases of Rac1 and target it for proteasomal degradation. IAPs are differentially expressed in tumor cells and have been targeted by several cancer therapeutic drugs that are currently in clinical trials. Here, we summarize the current knowledge on the role of IAPs in the regulation of cell migration and discuss the possible implications of these observations in regulating tumor cell metastases.

Regulation of cell migration, invasion and metastasis by IAP proteins and their antagonists

Inhibitor of apoptosis (IAP) proteins are a family comprised of a total of eight mammalian members that were initially described to act as endogenous inhibitors of caspases. In addition, extensive evidence has been accumulated over the last years showing that IAP proteins can regulate various signal transduction pathways, thereby exerting non-apoptotic functions beyond the inhibition of apoptosis. For example, IAP proteins have been implied in the control of cell motility, migration, invasion and metastasis. However, currently the question is controversially discussed whether or not they positively or negatively control these processes. As small-molecule inhibitors of IAP proteins have entered the stage of clinical evaluation as experimental cancer therapeutics, a better understanding of their various cellular effects will be critical for their rational use in the treatment of human diseases.

Inhibitor of Apoptosis Proteins: Promising Targets for Cancer Therapy

Cancer is a disease in which normal physiological processes are imbalanced, leading to tumour formation, metastasis and eventually death. Recent biological advances have led to the advent of targeted therapies to complement traditional chemotherapy and radiotherapy. However, a major problem still facing modern medicine is resistance to therapies, whether targeted or traditional. Therefore, to increase the survival rates of cancer patients, it is critical that we continue to identify molecular targets for therapeutic intervention. The Inhibitor of Apoptosis (IAP) proteins act downstream of a broad range of stimuli, such as cytokines and extracellular matrix interactions, to regulate cell survival, proliferation and migration. These processes are dysregulated during tumourigenesis and are critical to the metastatic spread of the disease. IAPs are commonly upregulated in cancer and have therefore become the focus of much research as both biomarkers and therapeutic targets. Here we discuss the roles that IAPs may play in cancer, and the potential benefits and pitfalls that targeting IAPs could have in the clinic.