¹Department of Medicine, University of Sydney at Nepean Hospital, Penrith, New South Wales, Australia

Correspondence: Professor JS Wiley, Department of Medicine, University of Sydney, Level 5 Spurrett Building, Nepean Hospital, Penrith, NSW 2750, Australia. E-mail:wileyj@medicine.usyd.edu.au

Received 19 June 2006; Accepted 10 July 2006; Published online 28 November 2006.

Abstract

Phospholipase D (PLD) is a ubiquitous enzyme that can be activated by extracellular adenosine 5'-triphosphate (ATP) or phorbol 12-myristate 13-acetate (PMA) in B-lymphocytes from subjects with chronic lymphocytic leukaemia (CLL). In this study, ATP- but not PMA-induced PLD stimulation in CLL B-lymphocytes was abolished in the presence of an anti-P2X₇ receptor monoclonal antibody, as well as in B-lymphocytes from CLL subjects homozygous for the Glu⁴⁹⁶ to Ala loss-of-function P2X₇ polymorphism. Rottlerin, an inhibitor of novel protein kinase C (PKC) isoforms, but not GF 109203X, an inhibitor of conventional PKC isoforms, impaired the ATP-stimulated PLD activity in CLL B-lymphocytes. In contrast, both inhibitors impaired PLD activity stimulated by PMA, a known mediator of PKC activation. The inhibition of P2X₇-stimulated PLD activity by rottlerin was attributed to a target downstream of P2X₇ activation, as the ATP-mediated ⁸⁶Rb⁺ efflux from CLL B-lymphocytes was not altered in the presence of rottlerin. Our results indicate a possible role for novel PKC isoforms in the regulation of P2X₇-mediated PLD activity.