Open AccessOsteopontin activates the diabetes-associated potassium channel TALK-1 in pancreatic β-cells
Author(s) -
Matthew Dickerson,
Nicholas C. Vierra,
Sarah C. Milian,
Prasanna K. Dadi,
David A. Jacobson
Publication year - 2017
Publication title -
plos one
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.99
H-Index - 332
ISSN - 1932-6203
DOI - 10.1371/journal.pone.0175069
Subject(s) - intracellular , hek 293 cells , microbiology and biotechnology , potassium channel , biology , islet , ion channel , cell culture , endocrinology , insulin , genetics , receptor
Glucose-stimulated insulin secretion (GSIS) relies on β-cell Ca 2+ influx, which is modulated by the two-pore-domain K + (K2P) channel, TALK-1. A gain-of-function polymorphism in KCNK16 , the gene encoding TALK-1, increases risk for developing type-2 diabetes. While TALK-1 serves an important role in modulating GSIS, the regulatory mechanism(s) that control β-cell TALK-1 channels are unknown. Therefore, we employed a membrane-specific yeast two-hybrid (MYTH) assay to identify TALK-1-interacting proteins in human islets, which will assist in determining signaling modalities that modulate TALK-1 function. Twenty-one proteins from a human islet cDNA library interacted with TALK-1. Some of these interactions increased TALK-1 activity, including intracellular osteopontin (iOPN). Intracellular OPN is highly expressed in β-cells and is upregulated under pre-diabetic conditions to help maintain normal β-cell function; however, the functional role of iOPN in β-cells is poorly understood. We found that iOPN colocalized with TALK-1 in pancreatic sections and coimmunoprecipitated with human islet TALK-1 channels. As human β-cells express two K + channel-forming variants of TALK-1, regulation of these TALK-1 variants by iOPN was assessed. At physiological voltages iOPN activated TALK-1 transcript variant 3 channels but not TALK-1 transcript variant 2 channels. Activation of TALK-1 channels by iOPN also hyperpolarized resting membrane potential ( V m ) in HEK293 cells and in primary mouse β-cells. Intracellular OPN was also knocked down in β-cells to test its effect on β-cell TALK-1 channel activity. Reducing β-cell iOPN significantly decreased TALK-1 K + currents and increased glucose-stimulated Ca 2+ influx. Importantly, iOPN did not affect the function of other K2P channels or alter Ca 2+ influx into TALK-1 deficient β-cells. These results reveal the first protein interactions with the TALK-1 channel and found that an interaction with iOPN increased β-cell TALK-1 K + currents. The TALK-1/iOPN complex caused V m hyperpolarization and reduced β-cell glucose-stimulated Ca 2+ influx, which is predicted to inhibit GSIS.