Semaphorin-3A is expressed by tumor cells and alters T-cell signal transduction and function

An important aspect of tumor progression is the ability of cancer cells to escape detection and clearance by the immune system. Recent studies suggest that several tumors express soluble factors interfering with the immune response. Here, we show that semaphorin-3A (Sema-3A), a secreted member of the semaphorin family involved in axonal guidance, organogenesis, and angiogenesis, is highly expressed in several tumor cells. Conditioned media of Sema-3A-transfected COS-7 cells or human recombinant Sema-3A inhibited primary human T-cell proliferation and cytokines production under anti-CD3 plus anti-CD28 stimulating conditions. Sema-3A also inhibited the activation of nonspecific cytotoxic activity in mixed lymphocyte culture (MLC), as measured against K-562 cells. In contrast, suppression of Sema-3A in tumor cells with a small interfering RNA (siRNA) augmented T-cell activation. The inhibitory effect of Sema-3A in T cells is mediated by blockade of Ras/mitogen-activated protein kinase (MAPK) signaling pathway. The presence of Sema-3A increased the activation of the Ras family small GTPase Rap1 and introduction of the dominant-negative mutant of Rap1 (Rap1N17) blunted the immunoinhibitory effects of Sema-3A. These results suggest that Sema-3A inhibits primary T-cell activation and imply that it can contribute to the T-cell dysfunction in the tumor microenvironment. \ua9 2006 by The American Society of Hematology

Cross-talk between vascular endothelial growth factor and semaphorin-3A pathway in the regulation of normal and malignant mesothelial cell proliferation

Vascular endothelial growth factor (VEGF) and semaphorin-3A (Sema-3A) play important roles in the transduction of promitotic and antimitotic signals, respectively. Here, we report that these conflicting signals are integrated via negative feedback between VEGF and Sema-3A pathways in several primary normal, but not malignant, mesothelial cells. Unlike malignant mesothelial (MM) cells, in which VEGF induces cell proliferation, normal mesothelial (NM) cell growth was repressed by VEGF. Although both cell-types expressed an overlapping set of VEGF tyrosine-kinase receptors, only in NM cells VEGF exposure entails a p38 mitogen-activated protein kinase (MAPK)-dependent increased of Sema-3A production. Inhibition of p38 MAPK (by SB202190 and SB203580) or a dominant-negative mutant of Sema-3A receptor plexin-A1 reversed the inhibitory effects of VEGF in NM cells, increasing cyclin D1 synthesis and cell growth. Conversely, sustained activation of p38 MAPK by the p38 MAPK-activating kinases MKK3 and MKK6 or transfection with Sema-3A inhibited VEGF-induced cyclin D1 up-regulation and MM cell proliferation. Therefore, these results delineate a new role of Sema-3A in VEGF function mediated by p38 MAPK and suggest that the abrogation of regulated Sema-3A expression is responsible for VEGF-driven growth of tumor cells

Peptidomimetic Targeting of Cavβ2 Overcomes Dysregulation of the L-Type Calcium Channel Density and Recovers Cardiac Function

Background: L-type calcium channels (LTCCs) play important roles in regulating cardiomyocyte physiology, which is governed by appropriate LTCC trafficking to and density at the cell surface. Factors influencing the expression, half-life, subcellular trafficking, and gating of LTCCs are therefore critically involved in conditions of cardiac physiology and disease. Methods: Yeast 2-hybrid screenings, biochemical and molecular evaluations, protein interaction assays, fluorescence microscopy, structural molecular modeling, and functional studies were used to investigate the molecular mechanisms through which the LTCC Cavβ2 chaperone regulates channel density at the plasma membrane. Results: On the basis of our previous results, we found a direct linear correlation between the total amount of the LTCC pore-forming Cav1.2 and the Akt-dependent phosphorylation status of Cavβ2 both in a mouse model of diabetic cardiac disease and in 6 diabetic and 7 nondiabetic cardiomyopathy patients with aortic stenosis undergoing aortic valve replacement. Mechanistically, we demonstrate that a conformational change in Cavβ2 triggered by Akt phosphorylation increases LTCC density at the cardiac plasma membrane, and thus the inward calcium current, through a complex pathway involving reduction of Cav1.2 retrograde trafficking and protein degradation through the prevention of dynamin-mediated LTCC endocytosis; promotion of Cav1.2 anterograde trafficking by blocking Kir/Gem-dependent sequestration of Cavβ2, thus facilitating the chaperoning of Cav1.2; and promotion of Cav1.2 transcription by the prevention of Kir/Gem-mediated shuttling of Cavβ2 to the nucleus, where it limits the transcription of Cav1.2 through recruitment of the heterochromatin protein 1γ epigenetic repressor to the Cacna1c promoter. On the basis of this mechanism, we developed a novel mimetic peptide that, through targeting of Cavβ2, corrects LTCC life-cycle alterations, facilitating the proper function of cardiac cells. Delivery of mimetic peptide into a mouse model of diabetic cardiac disease associated with LTCC abnormalities restored impaired calcium balance and recovered cardiac function. Conclusions: We have uncovered novel mechanisms modulating LTCC trafficking and life cycle and provide proof of concept for the use of Cavβ2 mimetic peptide as a novel therapeutic tool for the improvement of cardiac conditions correlated with alterations in LTCC levels and function