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© The Rockefeller University Press, 0021-9525/2001//825 $5.00
The Journal of Cell Biology, Volume 152, Number 4, , 2001 825-834

Rab27a Is Required for Regulated Secretion in Cytotoxic T Lymphocytes

^a Sir William Dunn School of Pathology, University of Oxford, OX1 3RE, United Kingdom
^b Cell and Molecular Biology Division, Division of Biomedical Sciences, Imperial College School of Medicine, London SW7 2AZ, United Kingdom
^c Department of Molecular Cell Biology, University of Birmingham, Birmingham B15 2TT, United Kingdom
Sir William Dunn School of Pathology, South Parks Road, Oxford OX1 3RE, UK.44-1865-27551544-1865-275571

gillian.griffiths{at}path.ox.ac.uk

Rab27a activity is affected in several mouse models of human disease including Griscelli (ashen mice) and Hermansky-Pudlak (gunmetal mice) syndromes. A loss of function mutation occurs in the Rab27a gene in ashen (ash), whereas in gunmetal (gm) Rab27a dysfunction is secondary to a mutation in the subunit of Rab geranylgeranyl transferase, an enzyme required for prenylation and activation of Rabs. We show here that Rab27a is normally expressed in cytotoxic T lymphocytes (CTLs), but absent in ashen homozygotes (ash/ash). Cytotoxicity and secretion assays show that ash/ash CTLs are unable to kill target cells or to secrete granzyme A and hexosaminidase. By immunofluorescence and electron microscopy, we show polarization but no membrane docking of ash/ash lytic granules at the immunological synapse. In gunmetal CTLs, we show underprenylation and redistribution of Rab27a to the cytosol, implying reduced activity. Gunmetal CTLs show a reduced ability to kill target cells but retain the ability to secrete hexosaminidase and granzyme A. However, only some of the granules polarize to the immunological synapse, and many remain dispersed around the periphery of the CTLs. These results demonstrate that Rab27a is required in a final secretory step and that other Rab proteins also affected in gunmetal are likely to be involved in polarization of the granules to the immunological synapse.

Key Words: Rab27a • cytotoxic T lymphocyte • secretory lysosomes • immunological synapse • Arp2/3

© 2001 The Rockefeller University Press

Abbreviations used in this paper: CHS, Chediak-Higashi syndrome; CTL, cytotoxic T lymphocyte; IMDM, Iscove's modified Dulbecco's medium; RGGT, Rab geranylgeranyl transferase; TCR, T cell receptor; WASP, Wiskott-Aldrich syndrome protein.

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