Fig 4.

TβRI nuclear transport requires the L45 loop and Smad2/3. (A) Schematics of the TβRI constructs and their potential of nuclear translocation. ECD, extracellular domain; GS, glycine-serine-rich domain; TM, transmembrane domain. (B) IFA images of TGF-β-treated MDA-MB-231 cells expressing the GFP-fused TβRI constructs indicated in panel A. (C) MDA-MB-231 cells were transfected with HA-tagged wild-type TβRI, the L45(3A) mutant, or the D266A mutant, with the sequences of the L45 loop indicated in panel A. Transfected cells were treated with TGF-β for 0.5 h or left untreated, and the HA-tagged TβRI levels were analyzed in the nuclear fraction and whole-cell lysates by Western blotting. (D) MDA-MB-231/TβRI cells transfected with siRNAs targeting Smad2/3 or control siRNA were treated with TGF-β and subjected to IP, fractionation, and Western blotting as indicated. Abbreviations are the same as in Fig. 2.