Abstract
The loss of intracellular potassium is a pivotal step in the induction of apoptosis but the mechanisms underlying this response are poorly understood. Here we report caspase-dependent stimulation of potassium channels by the Fas receptor in a human Jurkat T cell line. Receptor activation with Fas ligand for 30 min increased the amplitude of voltage-activated potassium currents 2-fold on average. This produces a sustained outward current, approximately 10 pA, at physiological membrane potentials during Fas ligand-induced apoptosis. Both basal and Fas ligand-induced currents were blocked completely by toxins that selectively inhibit Kv1.3 potassium channels. Kv1.3 stimulation required the expression of Fas-associated death domain protein and activation of caspase 8, but did not require activation of caspase 3 or protein synthesis. Furthermore, Kv1.3 stimulation by Fas ligand was prevented by chronic stimulation of protein kinase C with 20 nm phorbol 12-myristate 13-acetate during Fas ligand treatment, which also blocks apoptosis. Thus, Fas ligand increases Kv1.3 channel activity through the same canonical apoptotic signaling cascade that is required for potassium efflux, cell shrinkage, and apoptosis.
Highlights
Programmed cell death, or apoptosis, is an essential process for normal tissue homeostasis and immune system regulation
We show that this increase in potassium channel activity, like several other components of apoptosis, is dependent on Fas receptor activation, recruitment of Fas associated death domain protein (FADD) and caspase 8 activation
Fas ligand increases voltage-activated potassium current before cell shrinkage The voltage-activated potassium conductance of Jurkat T lymphocytes was measured with the conventional whole-cell voltage-clamp technique and normalized to cell capacitance to control for cell size
Summary
Programmed cell death, or apoptosis, is an essential process for normal tissue homeostasis and immune system regulation. Changes in the ionic environment appear to be required for the activation of the apoptotic machinery, such as caspases, nucleases and cytochrome c release [4,8], neither the signaling pathway that triggers potassium efflux after the initiation of apoptosis nor the channels that allow the potassium ions to pass out of the cell have been identified yet. We used Fas ligand-mediated apoptosis of the wellcharacterized human lymphoma Jurkat-T cell line to study the mechanism of potassium efflux and the signaling molecules involved in this important feature of the death pathway. The active effector caspase 3 is a semi-selective protease, which disrupts normal cell function by cleaving key structural proteins and signaling molecules that results in cellular destruction. We show that this increase in potassium channel activity, like several other components of apoptosis, is dependent on Fas receptor activation, recruitment of FADD and caspase 8 activation
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