Enhanced Activation of an Amino-Terminally Truncated Isoform of Voltage-Gated Proton Channel HVCN1 Enriched in Malignant B cells

Abstract

epithelium prone to infection and in intestine leads to obstruction. Patients homozygous for F508del, have a tremendous variation in the severity of disease. Recent Genome-wide association studies indicate that this variation is due to presence of modifier genes, with SLC6A14 as the top modifier (Sun et.al.,2012). SLC6A14 is a Naþ/Cl-dependent cationic/neutral amino-acid transporter on the surface of lung and colonic epithelium. As both transporters are expressed apically, we hypothesized that SLC6A14 would modify the fluid secretory capacity of the epithelium. So in collaboration with TCP, we generated a SLC6A14 knock-out mouse. We can measure in-vivo fluid secretion in mice, using an intestinal closed-loop assay. SLC6A14 knock-out mice exhibited a decrease in cAMP stimulated fluid secretion mediated via CFTR relative to Wt control. To explore the mechanism by which this modification occurs, we utilized a BHK heterologous expression system, overexpressing CFTR and SLC6A14. Interestingly, the functional interaction can be recapitulated in this system, suggesting that it not tissue-type dependent. Preliminary biochemical and anion-flux studies support the hypothesis that SLC6A14 does not affect the processing or stability of Wt or F508del-CFTR proteins rather it augments the activity of these channel proteins once localized to the cell surface. Future studies will focus on understanding if this augmentation is related to modification of CFTR's phosphorylation dependent gating. These results show a positive impact of SLC6A14 on CFTR channel function and fluid secretion, providing an alternative drug target for CF patients. 96-PlatEnhanced Activation of an Amino-Terminally Truncated Isoform of Voltage-Gated Proton Channel HVCN1 Enriched in Malignant B cells

Identification of an HV1 voltage‐gated proton channel in insects

“…Lately, a transcriptional isoform of the human H V 1 has been found, which exhibits slightly different biophysical properties. This isoform is almost undetectable in healthy B cells, although it is strongly upregulated in chronic lymphocytic leukemia B cells .…”

“…Furthermore, H V 1 triggers the light emitting process in dinoflagellates . In humans, it is necessary during the respiratory burst of phagocytes , is involved in the maturation of human sperm , is upregulated in breast and colorectal cancer , supports pH homeostasis in airway epithelia , and plays a pivotal role in several other processes of the immune system . Until today, we have a limited knowledge about tissues and species where H V 1 resides, as well as its function.…”

Hv1 Proton Channels in Dinoflagellates: Not Just for Bioluminescence?

“…In humans, H V 1 appears in three alternatively spliced forms that result in two different protein sequences, designated short and long (Hondares et al. ). The short protein results from splicing out the first intron (i.e.…”

The intimate and controversial relationship between voltage‐gated proton channels and the phagocyte NADPH oxidase

“…Knowing the HVCN1 gene makes proteomic screening possible. Such screens have provided evidence correlating H V 1 expression and B‐cell malignancies , cystic fibrosis , and Crohn's (inflammatory bowel) disease in humans, hyperoxia‐induced lung injury in mice , and vitiligo in chickens .…”

“…Progress on H V 1 was quite rapid, and will be summarized only briefly here because of its limited relevance to our main topic. In rapid succession, it was discovered that H V 1 is a dimer both in heterologous expression systems and in situ in phagocytes , although each protomer has a separate conduction pathway , and the monomer functions almost normally but with faster opening kinetics ; the dimer was found to open cooperatively ; a knockout mouse was produced and found to appear grossly normal but with distinct deficiencies ; a ‘signature sequence’ of amino acids was identified as RxWRxxR in the S4 helix that has enabled the discovery of several new H V 1 ; the phosphorylation site responsible for enhanced gating was identified as Thr 29 on the intracellular N terminus ; and the selectivity mechanism was elucidated in which Asp–Arg interaction is crucial . A crystal structure of the closed mouse H V 1 has been reported , but the open state structure relies on homology models and EPR measurements .…”