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HIV-1 Nef Expression Inhibits the Activity of a Ca²⁺-Dependent K⁺ Channel Involved in the Control of the Resting Potential in CEM Lymphocytes

Olga Zegarra-Moran^1,2,*, Andrea Rasola^1,, Michela Rugolo, Anna M. Porcelli, Bernard Rossi and Luis J. V. Galietta^*

^* Laboratorio di Genetica Molecolare, Istituto Giannina Gaslini, Genova, Italy; Unité de Recherches en Immunologie Cellulaire et Moléculaire, Institut National de la Santé et de la Recherche Médicale, Unit 364, Nice, France; and Laboratorio di Biochimica, Dipartimento di Biologia, Università di Bologna, Bologna, Italy

The HIV-1 Nef protein plays an important role in the development of the pathology associated with AIDS. Despite various studies that have dealt with different aspects of Nef function, the complete mechanism by which it alters the physiology of infected cells remains to be established. Nef can associate with cell membranes, therefore supporting the hypothesis that it might interact with membrane proteins as ionic channels and modify their electrical properties. By using the patch-clamp technique, we found that Nef expression determines a 25-mV depolarization of lymphoblastoid CEM cells. Both charybdotoxin (CTX) and the membrane-permeable Ca²⁺ chelator BAPTA/AM depolarized the membrane of native cells without modifying that of Nef-transfected cells. These data suggested that the resting potential in native CEM cells is settled by a CTX- and Ca²⁺-sensitive K⁺ channel (K_Ca,CTX), whose activity is absent in Nef-expressing cells. This was confirmed by direct measurements of whole-cell K_Ca,CTX currents. Single-channel recordings on excised patches showed that a K_Ca,CTX channel of 35 pS with a half-activation near 400 nM Ca²⁺ was present in both native and Nef-transfected cells. The measurements of free intracellular Ca²⁺ were not different in the two cell lines, but Nef-transfected cells displayed an increased Ca²⁺ content in ionomycin-sensitive stores. Taken together, these results indicate that Nef expression alters the resting membrane potential of the T lymphocyte cell line by inhibiting a K_Ca,CTX channel, possibly by intervening in the regulation of intracellular Ca²⁺ homeostasis.

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