The tumor necrosis factor -related apoptosis-inducing ligand (TRAIL) is a potent inducer of apoptosis in most, but not all, cancer cells. The molecular factors regulating the sensitivity to TRAIL are still incompletely understood. The transcription factor nuclear factor-KB (NF-KB) has been implicated, but its exact role is controversial. We studied different cell lines displaying varying responses to TRAIL and found that TRAIL can activate NF-KB in all our cancer cell lines regardless of their TRAIL sensitivity. Inhibition of NF-KB via adenoviral expression of the IKB-A super-repressor only sensitized the TRAIL-resistant pancreatic cancer cell line Panc-1. Panc-1 cells harbor constitutively activated NF-KB, pointing to a possible role of preactivated NF-KB in protection from TRAIL. Furthermore, we could reduce X-linked inhibitor of apoptosis protein (XIAP) levels in Panc-1 cells by inhibition of constitutively activated NF-KB and sensitize Panc-1 cells to TRAIL by RNA interference against XIAP. These results implicate elevated XIAP levels caused by high basal NF-KB activity in TRAIL resistance and suggest that therapeutic strategies involving TRAIL can be abetted by inhibition of NF-KB and/or XIAP only in tumor cells with constitutively

Insulin-like growth factor-1 within the EPC CM mediates potent acute myocardial repair and chronic remodelling effects post-MI. These findings may provide a rationale for comparative trials of specific growth factors vs. current progenitor cell strategies.

Regulation of sensitivity or resistance for apoptosis by death receptor ligand systems is a key control mechanism in the hematopoietic system. Dysfunctional or deregulated apoptosis can potentially contribute to the development of immune deficiencies, autoimmune diseases, and leukemia. Control of homeostasis starts at the level of hematopoietic stem cells (HSC). To this end, we found that CD34 þ hematopoietic progenitor cells are constitutively resistant to CD95-mediated apoptosis and cannot be sensitized during short-term culture to death receptor-mediated apoptosis by cytokines. Detailed analysis of the death machinery revealed that CD34 þ cells do not express caspase-8a/b, a crucial constituent of the death-inducing signaling complex (DISC) of death receptors. Instead, we found a smaller splice variant termed caspase-8L to be present in HSC. Forced expression of caspase-8L using a recombinant lentiviral vector was able to protect hematopoietic cells from death receptor-induced apoptosis even in the presence of caspase-8a/b. Furthermore, we found that caspase-8L is recruited to the DISC after CD95 triggering, thereby preventing CD95 from connecting to the caspase cascade. These results demonstrate an antiapoptotic function of caspase-8L and suggest a critical role as apoptosis regulator in HSC. Similar to CD34 þ HSC, stem cell-derived leukemic blasts from AML(M0) patients only expressed caspase-8L. Additionally we found, caspase-8L expression in several AML and ALL samples. Thus, caspase-8L expression might explain constitutive resistance to CD95-mediated apoptosis in CD34 þ progenitor cells and might participate in the development of stem cell-derived and other leukemias by providing protection from regulatory apoptosis.

Background-Insulin-like growth factor-1 (IGF-1) is recognized as an important regulator of cardiac structure and cardiomyocyte homeostasis. The prosurvival and antiapoptotic effects of IGF-1 have been investigated in vitro and in rodent models of myocardial infarction (MI). However, the clinical application of IGF-1 has been hampered by dose-dependent side effects both acutely and during chronic administration. We hypothesized that single, low-dose IGF-1 (LD-IGF-1) administered locally and early in the reperfusion phase after acute MI in a large animal model would avoid significant side effects but would have prosurvival effects that would manifest in long-term structural and functional improvement after MI treatment. Methods and Results-Forty-four female Landrace pigs underwent intracoronary administration of LD-IGF-1 or saline 2 hours into the reperfusion phase of acute left anterior descending artery occlusion MI. In the area of infarction, IGF-1 receptor and signaling responses were activated at 30 minutes and cardiomyocyte cell death attenuated at 24 hours after LD-IGF-1 but not saline treatment. Hemodynamic and structural studies using pressure-volume loop, CT, and triphenyltetrazolium chloride analysis 2 months post-MI confirmed a marked reduction in infarct size, attenuation of wall thinning, and augmentation of wall motion in the LD-IGF-1-treated but not in the saline-treated animals. These regional structural benefits were associated with global reductions in left ventricular volumes and significant improvement in left ventricular systolic and diastolic function. Conclusions-One-time LD-IGF-1 effects potent acute myocardial salvage in a preclinical model of left anterior descending artery occlusive MI, extending to long-term benefits in MI size, wall structure, and function and underscoring its potential as an adjunctive therapeutic agent. (Circ Cardiovasc Interv. 2011;4:327-335.)

Monocyte/Macrophages are implicated in initiation of angiogenesis, tissue/organ perfusion and atherosclerosis biology. We recently showed that chemokine receptor CX3CR1 is an essential regulator of monocyte/macrophage derived smooth muscle cell differentiation in the vessel wall after injury. Here we hypothesised the contribution of CX3CR1- CX3CL1 interaction to in vivo neovascularization and studied the functional consequences of genetic and pharmacologic targeting of CX3CR1 in formation, maturation and maintenance of microvascular integrity. Cells functionally deficient in CX3CR1 lacked matrix tunnelling and tubulation capacity in a 3D Matrigel assay. These morphogenic and cytokinetic responses were driven by CX3CL1-CX3CR1 interaction and totally abrogated by a Rho antagonist. To evaluate the role of CX3CR1 system in vivo, Matrigel plugs were implanted in competent CX3CR1+/gfp and functionally deficient CX3CR1gfp/gfp mice. Leaky microvessels (MV) were formed in the Matrigel implanted in CX3CR1gfp/gfp but not in CX3CR1+/gfp mice. In experimental plaque neovascularization immature MV phenotype was observed in CX3CR1gfp/gfp mice, lacking CX3CR1 positive smooth muscle-like cells, extracellular collagen and basement membrane (BM) laminin compared to competent CX3CR1+/gfp mice. This was associated with increased extravasation of platelets into the intima of CX3CR1gfp/gfp but not functionally competent CX3CR1 mice. Pharmacologic targeting using CX3CR1 receptor antagonist in wild type mice resulted in formation of plaque MV with poor BM coverage and a leaky phenotype. Our data indicate a hitherto unrecognised role for functional CX3CR1 in Matrigel and experimental plaque neovascularization in vivo, which may buttress MV collectively in favour of a more stable non-leaky phenotype.

The mitochondrial enzyme manganese superoxide dismutase (MnSOD) has been shown to have two faces with regard to its role in tumor development. On the one side, it is well documented that overexpression of MnSOD slows down cancer cell growth, whereas on the other side MnSOD also has a metastasis-promoting activity. We set out to examine the role of MnSOD in tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis, thought to be a first-line tumor surveillance mechanism and failure to undergo apoptosis might contribute to metastasis formation. We show that overexpression of MnSOD at moderate levels is able to protect cells from TRAIL-induced apoptosis. While caspase-8 activation and Bid cleavage were not affected by MnSOD, we detected a marked decrease in caspase-3 activation pointing to a mitochondrial resistance mechanism. Indeed, we found that MnSOD-overexpressing cells showed reduced cytochrome c and no Smac/DIABLO release into the cytosol. The resulting lack of X-linked inhibitor of apoptosis (XIAP) inhibition by cytosolic Smac/DIABLO most likely caused the TRAIL resistance as RNAi against XIAP-rescued caspase-3 activity and TRAIL sensitivity. Our results show that reactive oxygen species are involved in TRAIL-induced Smac/DIABLO release and in TRAIL-triggered apoptosis. Hence, high levels of MnSOD, which decompose and neutralize these reactive oxygen species, might contribute to metastasis formation by allowing disseminated tumor cells to escape from TRAIL-mediated tumor surveillance. As part of TRAIL regimens, adjuvant treatment with XIAP inhibitors in the form of Smac/DIABLO mimetics or MnSOD inhibitors might be able to break TRAIL resistance of malignant tumor cells.

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