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A more recent version of this article appeared on October 1, 2007
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Submitted on October 19, 2006
Revised on July 9, 2007
Accepted on July 11, 2007
Receptor Controls Basolateral Delivery
*Thoracic Diseases Research Unit, Department of Biochemistry and Molecular Biology and Mayo Clinic Cancer Center, Mayo Clinic College of Medicine, Rochester, MN 55905;
Department of Neurobiochemistry, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel
Monitoring Editor: Keith Mostov
TGF
receptors stimulate diverse signaling processes that control a wide range of biological responses. In polarized epithelia, the TGF
type II receptor (T2R) is localized at the basolateral membranes. Sequential cytoplasmic truncations resulted in receptor missorting to apical surfaces and indicated an essential targeting element(s) near the receptors C-terminus. Point mutations in the full-length receptor confirmed this prediction and a unique basolateral-targeting region was elucidated between residues 529 and 538 (LTAxxVAxxR) which was distinct, but colocalized within a clinically significant signaling domain essential for TGF
-dependent activation of the Smad2/3 cascade. Transfer of a terminal 84 amino acids fragment, containing the LTAxxVAxxR element, to the apically-sorted influenza HA protein was dominant and directed basolateral HA expression. While delivery to the basolateral surfaces was direct and independent of any detectable transient apical localization, fluorescence recovery after photobleaching demonstrated similar mobility for the wild-type receptor and a missorted mutant lacking the targeting motif. This latter finding excludes the possibility that the domain acts as a cell membrane retention signal and supports the hypothesis that T2R sorting occurs from an intracellular compartment.