Tirofiban induces VEGF production and stimulates migration and proliferation of endothelial cells.

Tirofiban is a fibrinogen receptor antagonist, generated using the tripeptide Arg-Gly-Asp (RGD) as a template. RGD activates integrin receptors and integrin-mediated signals are necessary for normal cells to promote survival and stimulate cell cycle progression. We investigated whether tirofiban activated growth-stimulatory signals in endothelium. For this study human umbilical vein endothelial cells (HUVEC) and human aortic endothelial cells (HAEC) were used. Analysis of cell proliferation, by cell counts, showed that the number of endothelial cells doubled after 72 h of culture in the absence of tirofiban, while they were tripled and even quadrupled, in the presence of increasing doses of the drug. Moreover, tirofiban-stimulated cells had a greater ability to migrate through the transwell filters of Boyden chamber, compared to unstimulated cells. The scratch assay, which mimics cell migration during wound healing, showed that tirofiban stimulated HUVECs to migrate into the leading hedge of the scratch. Western blot showed that tirofiban increased the expression levels of VEGF and the downstream effectors Erk and cyclin D. An inhibitor of VEGFR2 counteracted tirofiban-induced-proliferation, suggesting a role for VEGF in such effect. Our study shows that tirofiban stimulates the migration and proliferation of endothelial cells suggesting that it can promote endothelial repair. Ex vivo cultures of arterial rings confirmed the growth stimulatory effect of tirofiban on endothelium. Thus, the benefits of tirofiban in those with acute coronary syndromes undergoing PTCA may be due to rapid endothelization of damaged vessel, besides antiplatelet effects.

FKBP51 increases the tumour-promoter potential of TGF-beta.

BACKGROUND: FKBP51 (FKBP5 Official Symbol) is a large molecular weight component of the family of FK506 binding proteins (FKBP). In recent years, research studies from our laboratory highlighted functions for FKBP51 in the control of apoptosis and melanoma progression. FKBP51 expression correlated with the invasiveness and aggressiveness of melanoma. Since a role for TGF-ß in the enhanced tumorigenic potential of melanoma cells is widely described, we hypothesized a cooperative effect between FKBP51 and TGF-ß in melanoma progression. METHODS: SAN and A375 melanoma cell lines were utilized for this study. Balb/c IL2γ NOD SCID served to assess the ability to colonize organs and metastasize of different cell lines, which was evaluated by in vivo imaging. Realtime PCR and western blot served for measurement of mRNA and protein expression, respectively. RESULTS: By comparing the metastatic potential of two melanoma cell lines, namely A375 and SAN, we confirmed that an increased capability to colonize murine organs was associated with increased levels of FKBP51. A375 melanoma cell line expressed FKBP51 mRNA levels 30-fold higher in comparison to the SAN mRNA level and appeared more aggressive than SAN melanoma cell line in an experimental metastasis model. In addition, A375 expressed, more abundantly than SAN, the TGF-ß and the pro angiogenic TGF-ß receptor type III (TßRIII) factors. FKBP51 silencing produced a reduction of TGF-ß and TßRIII gene expression in A375 cell line, in accordance with previous studies. We found that the inducing effect of TGF-ß on Sparc and Vimentin expression was impaired in condition of FKBP51 depletion, suggesting that FKBP51 is an important cofactor in the TGF-ß signal. Such a hypothesis was supported by co immunoprecipitation assays, showing that FKBP51 interacted with either Smad2,3 and p300. In normal melanocytes, FKBP51 potentiated the effect of TGF-ß on N-cadherin expression and conferred a mesenchymal-like morphology to such round-shaped cells. CONCLUSIONS: Overall, our findings show that FKBP51 enhances some pro oncogenic functions of TGF-ß, suggesting that FKBP51-overexpression may help melanoma to take advantage of the tumor promoting activities of the cytokine.

Synergy between enzastaurin doxorubicin in inducing melanoma apoptosis.

Melanoma is resistant to most standard chemotherapeutics. We analysed the combined effect of doxorubicin and enzastaurin on cell death of four melanoma cell lines, namely G361, SK-MEL3, A375 and SAN. Enzastaurin IC50 was calculated by measure of growth inhibition with MTS assay and corresponded to 2 µM; the half maximal cytotoxicity of doxorubicin was obtained at 3 µM dose. Evaluation of combination index showed synergism (CI > 1) or additive effect (CI = 1) with all melanoma cell lines, with enzastaurin doses ≥0.6 µM and doxorubicin doses ≥1 µM. Combination of the two drugs resulted in increase in caspase 3 and 8 activation, in comparison with activation by single agents. Caspase 8 activation was impaired by TNFR-1 blocking. Our results show doxorubicin-stimulated production of TNFα, whereas enzastaurin-stimulated TNFR-1 expression on plasma membrane. The effect on TNFR-1 appeared to be mediated by PKCζ inhibition. Taken together, our findings suggest that enzastaurin increases doxorubicin-induced apoptosis of melanoma by a mechanism involving, at least in part, activation of the TNF-α signal.

Toxoplasma gondii Dense Granule Antigen 1 stimulates apoptosis of monocytes through autocrine TGF-ß signaling.

Monocyte/macrophages represent the first line of defense against protozoan parasites. Different mechanisms of monocyte suppression by Toxoplasma gondii that sustain parasite invasion and persistence have been described, including apoptosis. In the present study, we investigated the effect of microbial excretory­secretory polypeptides, namely the microneme protein MIC3 and the dense granule antigen GRA1, on apoptosis of monocytes from patients with congenital toxoplasmosis and healthy individuals. We found that GRA1 but not MIC3 could induce apoptosis of monocytes, observing the effect in samples from both Toxoplasma-infected and uninfected individuals, thus ruling out involvement of mechanisms of apoptosis linked to adaptive immunity or a cellular context related to infection. Selective inhibition of TGF-ß type I receptors reversed GRA1-induced apoptosis, indicating that this apoptosis involved canonical TGF-ß signaling. By using TGF-ß-neutralizing antibodies, we showed that monocyte apoptosis required endogenous TGF-ß and that GRA1 stimulation activated TGF-ß transcription and expression in monocytes but not lymphocytes, suggesting involvement of an autocrine TGF-ß-mediated mechanism in GRA1-induced apoptosis.

FK506 binding proteins as targets in anticancer therapy.

FK506 binding proteins (FKBPs) are the intracellular ligands of FK506 and rapamycin, two natural compounds with powerful and clinically efficient immunosuppressive activity. In recent decades, a relevant role for immunosuppressants as anticancer agents has emerged. Especially, rapamycin and its derivatives are used, with successful results, across a variety of tumors. Of note, rapamycin and FK506 bind to FKBP12, and the resulting complexes interfere with distinct intracellular signaling pathways driven, respectively, by the mammalian target of rapamycin and calcineurin phosphatase. These pathways are related to T-cell activation and growth. Hyperactivation of the mammalian target of rapamycin (mTOR), particularly in cancers that have lost the tumor suppressor gene PTEN, plays an important pathogenetic role in tumor transformation and growth. The signaling pathway involving calcineurin and nuclear factors of activated T-lymphocytes is also involved in the pathogenesis of different cancer types and in tumor metastasis, providing a rationale for use of FK506 in anticancer therapy. Recent studies have focused on FKBPs in apoptosis regulation: Targeting of FKBP12 promotes apoptosis in chronic lymphocytic leukemia, FKBP38 knockdown sensitizes hepatoma cells to apoptosis, and FKBP51 silencing overcomes resistance to apoptosis in acute lymphoblastic leukemia, prostate cancer, melanoma, and glioma. Interestingly, derivatives of FK506 that have the same FKBP12-binding properties as FK506 but lack functional immunosuppressant activity, exert the same apoptotic effect as FK506 in chronic lymphocytic leukemia.These findings suggest that a direct FKBP inhibition represents a further mechanism of immunosuppressants.' anticancer activity. In this review, we focus on the role of FKBP members in apoptosis control and summarize the data on the antitumor effect of selective targeting of FKBP.

The effect of FK506 on transforming growth factor beta signaling and apoptosis in chronic lymphocytic leukemia B cells.

BACKGROUND: Loss of response to transforming growth factor-beta (TGF-beta ) is thought to contribute to the progression of chronic lymphocytic leukemia. Recent findings of over-activation of the TGF-beta signal in FKBP12-knockout mouse prompted us to investigate whether FK506, the canonical ligand of FKBP, can activate the TGF-beta signal in chronic lymphocytic leukemia. DESIGN AND METHODS: We studied 62 chronic lymphocytic leukemia samples from patients with Rai/Binet stage 0 to 4 disease. The TGF-beta signal was investigated by western blotting and flow cytometry. The levels of Bcl2-family members and death-associated-protein kinase were also investigated by western blotting, whereas apoptosis was studied in flow cytometry. Down-modulation of FKBP12 was obtained by gene silencing with short interfering RNA. RESULTS: Twenty-two out of 62 chronic lymphocytic leukemia samples were sensitive to TGF-beta-induced apoptosis. All but two of the responsive samples underwent apoptosis also when cultured with FK506, but not with cyclosporine. Thirteen samples that were not sensitive to TGF-beta were sensitive to FK506. Overall, response to FK506 occurred in 33 samples. FK506 induced Smad2 phosphorylation and nuclear translocation. Accordingly, death-associated-protein kinase, a transcriptional target of Smad, was induced. At the same time, Bcl-2 and Bcl-xL levels decreased whereas the levels of Bim and Bmf increased. A loss of mitochondrial membrane potential preceded caspase activation and cell death. FK506 removed FKBP12 from its binding to the TGF-beta-receptor. FKBP12 release activated the receptor-kinase activity as suggested by the enhanced levels of phospho-Smad found in cells depleted of FKBP12. CONCLUSIONS: Our study shows that most chronic lymphocytic leukemia cells escape the homeostatic control of TGF-beta and that FK506 restores the TGF-beta signal in a proportion of non-responsive samples. We demonstrated that FK506 activates TGF-beta receptor I kinase activity in chronic lymphocytic leukemia, which transduces apoptosis by a mitochondrial-dependent pathway.

Increased CD154 expression in uninfected infants born to HIV-positive mothers exposed to antiretroviral prophylaxis.

Although prevention of mother-to-child HIV transmission by antiretroviral drugs has been shown to be effective, the short- and long-term effects of treatment are not well known. Several reports suggest that antiretroviral drugs act not only by inhibiting viral replication, but also by improving antiviral immunity. In particular, treatment with nucleoside analogs was found to increase CD40 ligand (CD40L; CD154) levels, an inducible molecule expressed on activated T lymphocytes. The present study investigated potential immunostimulatory effects of antiretroviral treatment (ART) in uninfected HIV-exposed infants, receiving either ante- or postnatal therapy to reduce the transmission rate. To this end, we analyzed CD40L expression in unstimulated lymphocytes from peripheral blood samples of uninfected infants vertically exposed to HIV and subjected to ART. The CD45 PanLeucogating strategy was applied in flow cytometry to analyze the lymphocytes of 41 cases and 64 age-matched infants, taken as control. We found increased CD154 expression on both CD4+ and CD8+ lymphocytes in ART-treated infants, compared with the controls. CD154 was apparently functional, because the expression of CD86 on monocytes was enhanced; moreover, inhibition of the CD40-CD40L interaction produced downmodulation of CD86. From these results, we conclude that CD4+ and CD8+ lymphocytes of HIV-exposed noninfected infants, who have been exposed to antiretroviral drugs in fetal and early life, display enhanced CD154 expression and costimulatory activity.

Rapamycin stimulates apoptosis of childhood acute lymphoblastic leukemia cells.

The phosphatidyl-inositol 3 kinase (PI3k)/Akt pathway has been implicated in childhood acute lymphoblastic leukemia (ALL). Because rapamycin suppresses the oncogenic processes sustained by PI3k/Akt, we investigated whether rapamycin affects blast survival. We found that rapamycin induces apoptosis of blasts in 56% of the bone marrow samples analyzed. Using the PI3k inhibitor wortmannin, we show that the PI3k/Akt pathway is involved in blast survival. Moreover, rapamycin increased doxorubicin-induced apoptosis even in nonresponder samples. Anthracyclines activate nuclear factor kappaB (NF-kappaB), and disruption of this signaling pathway increases the efficacy of apoptogenic stimuli. Rapamycin inhibited doxorubicin-induced NF-kappaB in ALL samples. Using a short interfering (si) RNA approach, we demonstrate that FKBP51, a large immunophilin inhibited by rapamycin, is essential for drug-induced NF-kappaB activation in human leukemia. Furthermore, rapamycin did not increase doxorubicin-induced apoptosis when NF-kappaB was overexpressed. In conclusion, rapamycin targets 2 pathways that are crucial for cell survival and chemoresistance of malignant lymphoblasts--PI3k/Akt through the mammalian target of rapamycin and NF-kappaB through FKBP51--suggesting that the drug could be beneficial in the treatment of childhood ALL.

Rapamycin inhibits doxorubicin-induced NF-kappaB/Rel nuclear activity and enhances the apoptosis of melanoma cells.

Inhibition of nuclear factor (NF)-kappaB/Rel can sensitise many tumour cells to death-inducing stimuli, including chemotherapeutic agents, and there are data suggesting that disruption of NF-kappaB may be of therapeutic interest in melanoma. We found that rapamycin sensitised a human melanoma cell line, established from a patient, to the cytolytic effects of doxorubicin. Doxorubicin is a striking NF-kappaB/Rel-inducer, we therefore investigated if rapamycin interfered with the pathway of NF-kappaB/Rel activation, i.e. IkappaBalpha-phosphorylation, -degradation and NF-kappaB/Rel nuclear translocation, and found that the macrolide agent caused a block of IKK kinase activity that was responsible for a reduced nuclear translocation of transcription factors. Western blots for Bcl-2 and c-IAP1 showed increased levels of these anti-apoptotic proteins in cells incubated with doxorubicin, in accordance with NF-kappaB/Rel activation, while rapamycin clearly downmodulated these proteins, in line with its pro-apoptotic ability. The effect of the macrolide on NF-kappa B/Rel induction appeared to be independent of the block in the PI3k/Akt pathway, because it could not be reproduced by the phosphatidyl inositol 3 kinase (PI3k) inhibitor, wortmannin. Recently, the immunophilin, FKBP51, has been shown to be essential for the function of IKK kinase. We found high expression levels of FKBP51 in melanoma cells. Moreover, we confirmed the involvement of this immunophilin in the control of IKK activity. Indeed, IkappaBalpha could not be degraded when FKBP51 was downmodulated by short-interfering RNAs (siRNAs). These findings provide a possible mechanism for the downmodulation of NF-kappaB by rapamycin, since the macrolide agent specifically inhibits FKBP51 isomerase activity. In conclusion, our study demonstrates that rapamycin blocked NF-kappaB/Rel activation independently of PI3k/Akt inhibition suggesting that the macrolide agent could synergise with NF-kappaB-inducing anti-cancer drugs in PTEN-positive tumours.

Activation of NF-kappaB/Rel transcription factors in human primary peripheral blood mononuclear cells by interleukin 7.

Pathways that regulate the activation of NF-kappaB/Rel transcription factors are known to include signaling through a number of cytokine receptors. Interleukin 7 (IL-7), produced by bone marrow and other stromal cells, is a key factor for differentiation and survival in the lymphoid and other compartments. We found that human recombinant IL-7 induced NF-kappaB/Rel activation, analyzed by electrophoretic mobility shift assay (EMSA), in human peripheral blood T lymphocytes from healthy donors. Induced complexes included p65 and p50 NF-kappaB/Rel subunits. These results demonstrate for the first time that IL-7 can participate in signaling leading to NF-kappaB/Rel activation.