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Molecular and Cellular Biology, August 2004, p. 6665-6675, Vol. 24, No. 15
0270-7306/04/$08.00+0     DOI: 10.1128/MCB.24.15.6665-6675.2004

Nucleotide Exchange Factor ECT2 Interacts with the Polarity Protein Complex Par6/Par3/Protein Kinase C{zeta} (PKC{zeta}) and Regulates PKC{zeta} Activity

Xiu-Fen Liu,{dagger} Hiroshi Ishida,{ddagger} Razi Raziuddin,{dagger} and Toru Miki*

Molecular Tumor Biology Section, Basic Research Laboratory, National Cancer Institute, Bethesda, Maryland 20892-4255

Received 25 September 2003/ Returned for modification 21 November 2003/ Accepted 12 May 2004

Regulation of cell polarity is an important biological event that governs diverse cell functions such as localization of embryonic determinants and establishment of tissue and organ architecture. The Rho family GTPases and the polarity complex Par6/Par3/atypical protein kinase C (PKC) play a key role in the signaling pathway, but the molecules that regulate upstream signaling are still not known. Here we identified the guanine nucleotide exchange factor ECT2 as an activator of the polarity complex. ECT2 interacted with Par6 as well as Par3 and PKC{zeta}. Coexpression of Par6 and ECT2 efficiently activated Cdc42 in vivo. Overexpression of ECT2 also stimulated the PKC{zeta} activity, whereas dominant-negative ECT2 inhibited the increase in PKC{zeta} activity stimulated by Par6. ECT2 localization was detected at sites of cell-cell contact as well as in the nucleus of MDCK cells. The expression and localization of ECT2 were regulated by calcium, which is a critical regulator of cell-cell adhesion. Together, these results suggest that ECT2 regulates the polarity complex Par6/Par3/PKC{zeta} and possibly plays a role in epithelial cell polarity.

* Corresponding author. Mailing address: Molecular Tumor Biology Section, Laboratory of Cell Biology, National Cancer Institute, Building 37, Room 2144, 37 Convent Dr., MSC 4255, Bethesda, MD 20892-4255. Phone: (301) 496-2289. Fax: (301) 496-2215. E-mail: toru{at}helix.nih.gov.

{dagger} Present address: Laboratory of Cell Biology, National Cancer Institute, Bethesda, MD 20892-4255.

{ddagger} Present address: Division of Experimental Therapeutics, Walter Reed Army Institute of Research, Silver Spring, MD 20910.

Molecular and Cellular Biology, August 2004, p. 6665-6675, Vol. 24, No. 15
0022-538X/04/$08.00+0     DOI: 10.1128/MCB.24.15.6665-6675.2004




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