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Molecular and Cellular Biology, April 2006, p. 2595-2614, Vol. 26, No. 7
0270-7306/06/$08.00+0     doi:10.1128/MCB.26.7.2595-2614.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Rab22a Regulates the Sorting of Transferrin to Recycling Endosomes{ddagger}

Javier G. Magadán,1,2 M. Alejandro Barbieri,2,{dagger} Rosana Mesa,1 Philip D. Stahl,2 and Luis S. Mayorga1*

Laboratorio de Biología Celular y Molecular, Instituto de Histología y Embriología (IHEM-CONICET), Facultad de Ciencias Médicas, Universidad Nacional de Cuyo, 5500 Mendoza, Argentina,1 Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, Missouri 631102

Received 8 August 2005/ Returned for modification 1 September 2005/ Accepted 13 January 2006

Rab22a is a member of the Rab family of small GTPases that localizes in the endocytic pathway. In CHO cells, expression of canine Rab22a (cRab22a) causes a dramatic enlargement of early endocytic compartments. We wondered whether transferrin recycling is altered in these cells. Expression of the wild-type protein and a GTP hydrolysis-deficient mutant led to the redistribution of transferrin receptor to large cRab22a-positive structures in the periphery of the cell and to a significant decrease in the plasma membrane receptor. Kinetic analysis of transferrin uptake indicates that internalization and early recycling were not affected by cRab22a expression. However, recycling from large cRab22a-positive compartments was strongly inhibited. A similar effect on transferrin transport was observed when human but not canine Rab22a was expressed in HeLa cells. After internalization for short periods of time (5 to 8 min) or at a reduced temperature (16°C), transferrin localized with endogenous Rab22a in small vesicles that did not tubulate with brefeldin A, suggesting that the endogenous protein is present in early/sorting endosomes. Rab22a depletion by small interfering RNA disorganized the perinuclear recycling center and strongly inhibited transferrin recycling. We speculate that Rab22a controls the transport of the transferrin receptor from sorting to recycling endosomes.

* Corresponding author. Mailing address: Instituto de Histología y Embriología (IHEM-CONICET), Casilla de Correo 56, 5500 Mendoza, Argentina. Phone: 54-261-4494143. Fax: 54-261-4494117. E-mail: lmayorga{at}fcm.uncu.edu.ar.

{ddagger} Supplemental material for this article may be found at http://mcb.asm.org/.

{dagger} Present address: Department of Biological Sciences, Florida International University, University Park, Miami, FL 33199.

Molecular and Cellular Biology, April 2006, p. 2595-2614, Vol. 26, No. 7
0022-538X/06/$08.00+0     doi:10.1128/MCB.26.7.2595-2614.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.





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