Molecular and Functional Differences between Heart mKv1.7 Channel Isoforms

Ion channels are membrane-spanning proteins that allow ions to permeate at high rates. The kinetic characteristics of the channels present in a cell determine the cell signaling profile and therefore cell function in many different physiological processes. We found that Kv1.7 channels from mouse heart muscle have two putative translation initiation start sites that generate two channel isoforms with different functional characteristics, mKv1.7L (489 aa) and a shorter mKv1.7S (457 aa). The electrophysiological analysis of mKv1.7L and mKv1.7S channels revealed that the two channel isoforms have different inactivation kinetics. The channel resulting from the longer protein (L) inactivates faster than the shorter channels (S). Our data supports the hypothesis that mKv1.7L channels inactivate predominantly due to an N-type related mechanism, which is impaired in the mKv1.7S form. Furthermore, only the longer version mKv1.7L is regulated by the cell redox state, whereas the shorter form mKv1.7S is not. Thus, expression starting at each translation initiation site results in significant functional divergence. Our data suggest that the redox modulation of mKv1.7L may occur through a site in the cytoplasmic N-terminal domain that seems to encompass a metal coordination motif resembling those found in many redox-sensitive proteins. The mRNA expression profile and redox modulation of mKv1.7 kinetics identify these channels as molecular entities of potential importance in cellular redox-stress states such as hypoxia

Block of Kv1.7 potassium currents increases glucose-stimulated insulin secretion

Glucose-stimulated insulin secretion (GSIS) relies on repetitive, electrical spiking activity of the beta cell membrane. Cyclic activation of voltage-gated potassium channels (K v ) generates an outward, ‘delayed rectifier’ potassium current, which drives the repolarizing phase of each spike and modulates insulin release. Although several K v channels are expressed in pancreatic islets, their individual contributions to GSIS remain incompletely understood. We take advantage of a naturally occurring cone-snail peptide toxin, Conkunitzin-S1 (Conk-S1), which selectively blocks K v 1.7 channels to provide an intrinsically limited, finely graded control of total beta cell delayed rectifier current and hence of GSIS. Conk-S1 increases GSIS in isolated rat islets, likely by reducing K v 1.7-mediated delayed rectifier currents in beta cells, which yields increases in action potential firing and cytoplasmic free calcium. In rats, Conk-S1 increases glucose-dependent insulin secretion without decreasing basal glucose. Thus, we conclude that K v 1.7 contributes to the membrane-repolarizing current of beta cells during GSIS and that block of this specific component of beta cell K v current offers a potential strategy for enhancing GSIS with minimal risk of hypoglycaemia during metabolic disorders such as Type 2 diabetes

Virus-induced tumor inflammation facilitates effective DC cancer immunotherapy in a Treg-dependent manner in mice

Vaccination using DCs pulsed with tumor lysates or specific tumor-associated peptides has so far yielded limited clinical success for cancer treatment, due mainly to the low immunogenicity of tumor-associated antigens. In this study, we have identified intratumoral virus-induced inflammation as a precondition for effective antitumor DC vaccination in mice. Administration of a tumor-targeted DC vaccine during ongoing virus-induced tumor inflammation, a regimen referred to as oncolysis-assisted DC vaccination (ODC), elicited potent antitumoral CD8+ T cell responses. This potent effect was not replicated by TLR activation outside the context of viral infection. ODC-elicited immune responses mediated marked tumor regression and successful eradication of preestablished lung colonies, an essential prerequisite for potentially treating metastatic cancers. Unexpectedly, depletion of Tregs during ODC did not enhance therapeutic efficacy; rather, it abrogated antitumor cytotoxicity. This phenomenon could be attributed to a compensatory induction of myeloid-derived suppressor cells in Treg-depleted and thus vigorously inflamed tumors, which prevented ODC-mediated immune responses. Consequently, Tregs are not only general suppressors of immune responses, but are essential for the therapeutic success of multimodal and temporally fine-adjusted vaccination strategies. Our results highlight tumor-targeting, replication-competent viruses as attractive tools for eliciting effective antitumor responses upon DC vaccination

Targeting of p53-Transcriptional Dysfunction by Conditionally Replicating Adenovirus Is Not Limited by p53-Homologues

A hallmark of human tumors is the loss of p53 or its transcriptional functions. In this study, we describe the generation of the conditionally replicating adenovirus Adp53sensor for the treatment of p53-dysfunctional tumors. p53-selective attenuation of viral replication was achieved by using p53-dependent expression of the transcriptional repressor Gal4-KRAB that was directed against the adenoviral E1A locus. Adp53sensor shows efficient replication in p53-dysfunctional, but not in p53-active cells. In p53-dysfunctional cells, p53-analogous transcriptional activity by other p53 family members was not sufficient to compromise replication of Adp53sensor. In comparison with a genetically similar, but p53-insensitive virus, Adp53sensor replication was inhibited after systemic infection of p53-wt-mice, but not in p53-ko-mice thus confirming the correct function of the chosen approach. Adp53sensor showed efficient lytic and replicative properties in all investigated cells with p53-dysfunction and successfully inhibited the growth of subcutaneous xenotransplants in vivo. We further demonstrated that intravenous injection of Adp53sensor lead to significantly reduced liver damage compared to the control virus. Together, our data show that Adp53sensor is an oncolytic, p53-selective adenovirus for efficient treatment of p53-dysfunctional tumors with a favorable toxicity profile. Moreover, Adp53sensor provides a strategy that should be applicable to other transcriptionally regulated DNA viruses

Selectivity of Oncolytic Viral Replication Prevents Antiviral Immune Response and Toxicity, but Does Not Improve Antitumoral Immunity

Oncolytic infection elicits antitumoral immunity, but the impact of tumor-selective replication on the balance between antiviral and antitumoral immune responses has not yet been investigated. To address this question, we constructed the highly tumor-selective adenovirus Ad-p53T whose replication in target tumor cells is governed by aberrant telomerase activity and transcriptional p53 dysfunction. Telomerase-dependent or nonselective adenoviruses were constructed as isogenic controls. Following infection of mice with the nonselective adenovirus, viral DNA and mRNA levels correlated with strong stimulation of innate immune response genes and severe liver toxicity, whereas telomerase-/p53-specific replication did not trigger innate immunity and prevented liver damage. Compared to telomerase-dependent or unselective viral replication, telomerase-/p53-specific virotherapy significantly decreased antiviral CD8-specific immune responses and antiviral cytotoxicity in vivo. Consistent with our hypothesis, telomerase-selective replication led to intermediate results in these experiments. Remarkably, all viruses efficiently lysed tumors and induced a therapeutically effective tumor-directed CD8 cytotoxicity. In immunocompetent mice with extended lung metastases burden, treatment of subcutaneous primary tumors with Ad-p53T significantly prolonged survival by inhibition of lung metastases, whereas unselective viral replication resulted in death by liver failure. In summary, the degree of tumor selectivity of viral replication marginally influences antitumoral immune responses, but is a major determinant of antivector immunity and systemic toxicity