ResultsA TAT-SNX9 peptide specifically blocks pSMAD3 nuclear import and profibrotic TGF-β signaling. We previously determined that SNX9 has an obligate role in mediating profibrotic TGF-β signaling dependent upon SMAD3 (24). In order to investigate colony formation, and cell migration; and (b) fibrotic changes associated with the bleomycin (BLM) and adenoviral models of lung fibrosis. Moreover, a 3-amino acid point mutant of the TAT-SNX9 peptide unable to bind pSMAD3 was ineffective in analogous in vitro and in vivo assays. Lysates from AKR-2B cells untreated (-) or stimulated (+) for 45 minutes with 5 ng/ml TGF-β were incubated with GST beads or the indicated fusion proteins immobilized on GST beads. Bound proteins were eluted and assessed by Western blot analysis for pSMAD3 or pSMAD2. Cell lysate reflects signal obtained from 10 μg total protein; the slower migrating band in the pSMAD3 lane is a nonspecific protein (right, representative of 3 separate experiments). (B) AKR-2B cells were transduced for 90 minutes with the indicated concentration of TAT peptide. Following washing and 1 hour TGF-β (5 ng/ml) treatment, nuclear fractions were isolated and assessed by Western blot analysis for pSMAD2, pSMAD3, or histone deacetylase 1 (HDAC) (left, representative of 3 separate experiments). Quantitation of nuclear pSMADs was performed with ImageJ software (NIH) and represents the mean ± SEM of 3 experiments (right). (C) Left panels: AKR-2B cells were incubated with vehicle (top panels) or transduced (bottom panels) as in B with TAT-SH3 or TAT-LC (1.8 μM). Following treatment with or without TGF-β (5 ng/ml) for 1 hour, immunofluorescence for SMAD3 or the HA-tagged TAT peptide was performed as described in Methods and nuclei were stained with DAPI. Upper and lower panels show 2 distinct microscopic fields for each condition. Original magnification in C: ×100. Right: quantitation of nuclear SMAD3 from 30 cells in each of 3 experiments. *P < 0.05; **P < 0.005; ***P < 0.0005, 1-way ANOVA followed by Dunnett's multiple comparisons test.
The Journal of Clinical Investigation
R E S E A R C H A R T I C L E2 5 4 3 jci.orgVolume 127 Number 7 July 2017 sion of this fragment could act in trans as a dominant inhibitor of pSMAD3 nuclear uptake. To address this issue, constructs were prepared expressing either the SNX9 SH3 or LC domains fused to the cell-penetrating TAT peptide from HIV (39). Subsequent to TAT peptide transduction, cultures were treated with TGF-β and nuclear accumulation of pSMAD2 or pSMAD3 determined. As shown in Figure 1B and Supplemental Figure 2, while the TAT-SH3 peptide inhibited nuclear import of pSMAD3 in a dose-dependent manner and increased cytoplasmic pSMAD3, it had no effect on pSMAD2. Furthermore, consistent with the inability of the LC domain to bind receptorregulated SMADs (R-SMADs) ( Figure 1A), it was similarly ineffective in modulating nuclear translocation ( Figure 1B). These biochemical findings were independently confirmed using immunofluorescence ( Figure 1C and Supplemental Figure 3). While t...