Nuclear Import of Serum Response Factor in Airway Smooth Muscle

• Published in: American journal of respiratory cell and molecular biology Vol. 45; no. 3; pp. 453 - 458
• Main Authors: McConville, John F., Fernandes, Darren J., Churchill, Jason, Dewundara, Samantha, Kogut, Paul, Shah, Shardul, Fuchs, Gregory, Kedainis, Dalius, Bellam, Shashi K., Patel, Nina M., McCauley, Joel, Dulin, Nickolai O., Gupta, Mahesh P., Adam, Stephen, Yoneda, Yoshihiro, Camoretti-Mercado, Blanca, Solway, Julian
• Format: Journal Article
• Language: English
• Published: United States American Thoracic Society 01.09.2011
• Subjects: Active Transport, Cell Nucleus; alpha Karyopherins - metabolism; Cell Line; Cell Nucleus - metabolism; Dimerization; Green Fluorescent Proteins - metabolism; Humans; Immunoprecipitation; Microscopy, Fluorescence - methods; Models, Biological; Muscle, Smooth - cytology; Mutation; Protein Binding; Recombinant Fusion Proteins - chemistry; Serum Response Factor - metabolism
• ISSN: 1044-1549; 1535-4989; 1535-4989
• DOI: 10.1165/rcmb.2008-0393OC

We have previously shown that the transcription-promoting activity of serum response factor (SRF) is partially regulated by its extranuclear redistribution. In this study, we examined the cellular mechanisms that facilitate SRF nuclear entry in canine tracheal smooth muscle cells. We used in vitro pull-down assays to determine which karyopherin proteins bound SRF and found that SRF binds KPNA1 and KPNB1 through its nuclear localization sequence. Immunoprecipitation studies also demonstrated direct SRF-KPNA1 interaction in HEK293 cells. Import assays demonstrated that KPNA1 and KPNB1 together were sufficient to mediate rapid nuclear import of SRF-GFP. Our studies also suggest that SRF is able to gain nuclear entry through an auxiliary, nuclear localization sequence-independent mechanism.