HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Shenker, B. J. Articles by Boesze-Battaglia, K. Search for Related Content PubMed PubMed Citation Articles by Shenker, B. J. Articles by Boesze-Battaglia, K.

A Novel Mode of Action for a Microbial-Derived Immunotoxin: The Cytolethal Distending Toxin Subunit B Exhibits Phosphatidylinositol 3,4,5-Triphosphate Phosphatase Activity¹

Bruce J. Shenker^2,*, Mensur Dlaki, Lisa P. Walker^*, Dave Besack^*, Eileen Jaffe^¶, Ed LaBelle and Kathleen Boesze-Battaglia

^* Department of Pathology and Department of Biochemistry, University of Pennsylvania School of Dental Medicine, Philadelphia, PA 19104; Department of Microbiology, Montana State University, Bozeman, MT 59717; University of Pennsylvania School of Veterinary Medicine, Philadelphia, PA 19104; and ^¶ Fox Chase Cancer Center, Philadelphia, PA 19111

The Actinobacillus actinomycetemcomitans cytolethal distending toxin (Cdt) is a potent immunotoxin that induces G₂ arrest in human lymphocytes. We now show that the CdtB subunit exhibits phosphatidylinositol (PI)-3,4,5-triphosphate phosphatase activity. Breakdown product analysis indicates that CdtB hydrolyzes PI-3,4,5-P₃ to PI-3,4-P₂ and therefore functions in a manner similar to phosphatidylinositol 5-phosphatases. Conserved amino acids critical to catalysis in this family of enzymes were mutated in the cdtB gene. The mutant proteins exhibit reduced phosphatase activity along with decreased ability to induce G₂ arrest. Consistent with this activity, Cdt induces time-dependent reduction of PI-3,4,5-P₃ in Jurkat cells. Lymphoid cells with defects in SHIP1 and/or ptase and tensin homolog deleted on chromosome 10 (PTEN) (such as Jurkat, CEM, Molt) and, concomitantly, elevated PI-3,4,5-P₃ levels were more sensitive to the toxin than HUT78 cells which contain functional levels of both enzymes and low levels of PI-3,4,5-P₃. Finally, reduction of Jurkat cell PI-3,4,5-P₃ synthesis using the PI3K inhibitors, wortmannin and LY290004, protects cells from toxin-induced cell cycle arrest. Collectively, these studies show that the CdtB not only exhibits PI-3,4,5-P₃ phosphatase activity, but also that toxicity in lymphocytes is related to this activity.

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ This work was supported by U.S. Public Health Service Grants DE06014 and DE014191.

² Address correspondence and reprint requests to Dr. Bruce J. Shenker, Department of Pathology, University of Pennsylvania School of Dental Medicine, 240 South 40th Street, Philadelphia, PA 19104-6030. E-mail address: shenker{at}pobox.upenn.edu

³ Abbreviations used in this paper: Cdt, cytolethal distending toxin; PI, phosphatidylinositol; RT, room temperature; PTEN, ptase and tensin homolog deleted on chromosome 10.

This article has been cited by other articles:

				S. J. Harris, R. V. Parry, J. Westwick, and S. G. Ward Phosphoinositide Lipid Phosphatases: Natural Regulators of Phosphoinositide 3-Kinase Signaling in T Lymphocytes J. Biol. Chem., February 1, 2008; 283(5): 2465 - 2469. [Abstract] [Full Text] [PDF]