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Molecular and Cellular Biology, June 2007, p. 4431-4443, Vol. 27, No. 12
0270-7306/07/$08.00+0     doi:10.1128/MCB.02235-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Characterization of Mammalian Par 6 as a Dual-Location Protein{triangledown}

Erin G. Cline and W. James Nelson*

Departments of Biological Sciences and Molecular and Cellular Physiology, Stanford University, Stanford, California

Received 28 November 2006/ Returned for modification 30 January 2007/ Accepted 27 March 2007

Par 6 acts as a scaffold protein to facilitate atypical protein kinase C-mediated phosphorylation of cytoplasmic protein complexes, leading to epithelial and neuronal cell polarization. In addition to its location in the cytoplasm, Par 6 is localized to the nucleus. However, its organization and potential functions in the nucleus have not been examined. Using an affinity-purified Par 6 antibody and a chimera of Par 6 and green fluorescent protein, we show that Par 6 localizes precisely to nuclear speckles, but not to other nuclear structures, and displays characteristics of speckle proteins. We show that Par 6 colocalizes in the nucleus with Tax, a transcriptional activator of the human T-cell leukemia virus type 1 long terminal repeat, but multiple lines of evidence show that Par 6 is not directly involved in known functions of speckle proteins, including general transcription, splicing, or mRNA transport. Significantly, however, the structure of nuclear speckles is lost when Par 6 levels are reduced by Par 6-specific small interfering RNA. Therefore, we hypothesize that Par 6 in the nucleus acts as a scaffolding protein in nuclear speckle complexes, similar to its role in the cytoplasm.

* Corresponding author. Mailing address: Department of Biological Sciences, The James A. Clark Center, E200B, 318 Campus Drive, Stanford University, Stanford, CA 94305-5430. Phone: (650) 725-7596. Fax: (650) 498-5286. E-mail: wjnelson{at}stanford.edu

{triangledown} Published ahead of print on 9 April 2007.

Molecular and Cellular Biology, June 2007, p. 4431-4443, Vol. 27, No. 12
0270-7306/07/$08.00+0     doi:10.1128/MCB.02235-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



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