1. Background
2. Objectives
3. Methods
3.1. Plasmid Construction
3.2. Cell Culture
3.3. DNA Transfection
3.4. Western Blotting
3.5. Cytoplasmic and Nuclear Fractionation
3.6. Co-immunoprecipitation
3.7. Juglone and PiB Treatments
3.8. Wnt3a and XAV939 Treatments
3.9. Statistical Analysis
4. Results
4.1. Characterization of Pin1 Expression and Localization in Pulmonary Fibrosis Cells
Structural and expression analysis of Pin1 in pulmonary fibrosis (PF) cells. A, schematic representation of the Pin1 protein, showing its WW domain at the N-terminal and peptidyl-prolyl cis/trans isomerase (PPIase) domain at the C-terminal end. This structural organization is essential for Pin1's function in the post-translational modification of proteins. B, comparative analysis of endogenous Pin1 expression in various cell lines. Western blotting was performed using a Pin1 antibody on AEII cells, MRC-5 cells, SH-SY5Y cells, HEK 293T cells, THLE2 cells, and HepG2 cells (lanes 1 - 6). GAPDH served as the loading control. Densitometric quantification from three independent experiments is presented in the lower panel as a column chart, showing relative expression values (100, 218, 321, 165, 187, and 287) with mean ± standard deviation (SD). All increases were statistically significant (P < 0.01) compared to the control. C, comparative Pin1 expression in human lung fibroblast cells versus cancer cells. Western blotting was performed using a Pin1 antibody on AEII cells, A549, and H1299 cancer cell lines (lanes 1 - 3). D, subcellular localization of Pin1 in MRC-5 cells. Cytoplasmic and nuclear fractions of mock or wild-type Pin1 (Pin1 WT) transfected MRC-5 cells were prepared. Total (panels 1 - 3), cytoplasmic (lanes 4 - 6), and nuclear (lanes 7 - 9) fractions were visualized using specific antibodies against Pin1. GAPDH was used as the cytoplasmic marker and H3 as the nuclear fraction marker. (** P < 0.01)
4.2. Pin1 and Latent Membrane Protein 1 Cooperatively Enhance Wnt/β-Catenin Signaling
Pin1 and latent membrane protein 1 (LMP1) modulation of Wnt/β-catenin signaling in MRC-5 cells: A, Pin1 overexpression enhances Wnt/β-catenin signaling. MRC-5 cells were mock-transfected or transfected with 4 µg wild-type Pin1 (Pin1 WT). Seventy-two hours post-transfection, cells were lysed for analysis. Densitometric quantification showed that Pin1 WT increased β-catenin (218%), Cyclin D1 (227%), and Axin2 (258%) relative to mock (100%, P < 0.01). B, Pin1 knockdown reduces β-catenin signaling (lane 1: Untreated MRC-5 cells; lane 2: Control siRNAs and 4 µg of Pin1 WT; lane 3: Pin1-specific siRNAs; lane 4: The Pin1 WT overexpression with Pin1-specific siRNAs). Quantification showed Pin1 at 222% with WT, suppressed to 21% with siRNA, and restored to 135% with WT+siRNA. β-catenin rose to 245%, dropped to 43%, and recovered to 152%. Cyclin D1 increased to 186%, decreased to 54%, and restored to 201%. Axin2 surged to 321%, reduced to 51%, and partially restored to 125%. All changes were statistically significant (P < 0.05 to P < 0.001). C, LMP1 expression modulates Wnt/β-catenin signaling. MRC-5 cells were mock-transfected or transfected with 4 µg LMP1. Cells were lysed 72 hours post-transfection. Quantification confirmed that LMP1 significantly increased Pin1 (281%), β-catenin (278%), cyclin D1 (267%), and Axin2 (298%) relative to mock (100%, P < 0.01). Negative (-) and positive (+) signs: The negative (-) sign indicates the absence of a specific treatment (e.g., no siRNA or overexpression), while the positive (+) sign indicates the presence of the respective treatment (e.g., Pin1 WT or siRNA). Primary antibodies: Pin1 (Abcam, #ab53361), β-catenin (cell signaling technology, #8480), cyclin D1 (Abcam, #ab16663), Axin2 (cell signaling technology, #2151), and GAPDH (loading control, cell signaling technology, #5174). Relative levels of Pin1, β-catenin, cyclin D1, and Axin2 were quantified using ImageJ 1.46 (data represent mean values from three separate experiments; * P < 0.05, ** P < 0.01, and *** P < 0.001).
4.3. Pin1 Synergizes with Wnt3a and Latent Membrane Protein 1 to Modulate the Wnt/β-Catenin Pathway in Pulmonary Fibrosis
Effects of Wnt signaling modulators on Pin1 and β-catenin signaling: A, effects of Wnt3a and Pin1 overexpression on β-catenin components. Cells were treated under four conditions: Untreated control (lane 1), Wnt3a treatment (50 ng/mL) (lane 2), wild-type Pin1 (Pin1 WT, lane 3), and Pin1 WT overexpression with Wnt3a treatment (lane 4). Densitometric analysis showed that β-catenin increased from 100% in control to 236% (P < 0.001) with Wnt3a, 241% (P < 0.001) with Pin1 WT, and 392% (P < 0.001) with Wnt3a + Pin1 WT. Cyclin D1 rose to 256% (P < 0.001), 264% (P < 0.01), and 401% (P < 0.01), while Axin2 reached 231% (P < 0.001), 251% (P < 0.01), and 295% (P < 0.01), respectively. B, effects of XAV939 and Pin1 overexpression on β-catenin signaling components. Cells were treated under four conditions: Untreated control (lane 1), XAV939 treatment (20 µM) (lane 2), Pin1 WT overexpression (lane 3), and Pin1 WT overexpression with XAV939 treatment (lane 4). Quantitative densitometry revealed that β-catenin decreased to 34% (P < 0.001) with XAV939, increased to 253% (P < 0.01) with Pin1 WT, and was partly restored to 67% (P < 0.05) with XAV939+Pin1 WT. Cyclin D1 fell to 52% (P < 0.01), rose to 248% (P < 0.001), and was restored to 78% (P < 0.01). Axin2 decreased to 28% (P < 0.01), increased to 236% (P < 0.01), and was restored to 89% (P < 0.05). C, effects of latent membrane protein 1 (LMP1) and Pin1 knockdown on Wnt/β-catenin signaling in MRC-5 cells. Lane 1 represents mock-transfected cells, lane 2 shows cells transfected with LMP1 and treated with control siRNAs, and lane 3 depicts cells transfected with LMP1 and treated with Pin1-specific siRNAs. Densitometric quantification confirmed that LMP1 significantly increased β-catenin to 244% (P < 0.01), cyclin D1 to 250% (P < 0.01), and Axin2 to 280% (P < 0.01). Silencing Pin1 in the presence of LMP1 reduced β-catenin to 121% (P < 0.05), cyclin D1 to 131% (P < 0.05), and Axin2 to 143% (P < 0.05). D, co-immunoprecipitation (Co-IP) analysis showing interaction between Pin1 and β-catenin pathway proteins. Lanes 1 and 2 represent input samples, lanes 3 and 4 show Co-IP using a Pin1 antibody, and lanes 5 and 6 represent Co-IP using IgG as the control. Antibodies used were Pin1 (Abcam, #ab53361), β-catenin (cell signaling technology, #8480), cyclin D1 (Abcam, #ab16663), Axin2 (cell signaling technology, #2151), and GAPDH (loading control, cell signaling technology, #5174). Relative levels of Pin1, β-catenin, cyclin D1, and Axin2 were quantified using ImageJ 1.46r (data is shown as the mean values from three separate experiments. Statistical significance was determined by Student's t-test; significance levels are * P < 0.05, ** P < 0.01, and *** P < 0.001 compared to the corresponding controls; ‘+’ and ‘−’ the presence or absence of specific treatments such as Wnt3a, XAV939, Pin1 WT overexpression, LMP1, or siRNA, as described in each panel).
4.4. Therapeutic Potential of Pin1 Inhibitors in Modulating the Wnt/β-Catenin Cascade in Pulmonary Fibrosis
Effects of Pin1 inhibitors on Wnt/β-catenin pathway: A, effects of Juglone on Wnt/β-catenin signaling components. MRC-5 cells were treated under four conditions: Untreated control (lane 1), Juglone treatment (20 µM, lane 2), wild-type Pin1 (Pin1 WT) overexpression (lane 3), and Pin1 WT overexpression combined with Juglone treatment (lane 4). Juglone, as a Pin1 inhibitor, primarily reduces Pin1 activity rather than its protein levels. Therefore, the presence of Pin1 protein in lane 2 does not indicate the absence of inhibition but reflects that the inhibitor does not decrease total protein levels. Densitometric quantification (lower panel) confirmed significant reductions of β-catenin, cyclin D1, and Axin2 upon Juglone treatment compared to Pin1 WT (P < 0.05 - 0.01). B, effects of PiB on Wnt/β-catenin cascade components. MRC-5 cells were treated under similar conditions as in (A): Untreated control (lane 1), PiB treatment (20 µM, lane 2), Pin1 WT overexpression (lane 3), and Pin1 WT overexpression with PiB treatment (lane 4). Similar to Juglone, PiB inhibits Pin1 activity without significantly reducing total Pin1 protein levels. Quantitative analysis (lower panel) showed that PiB markedly suppressed Pin1-induced increases in β-catenin, cyclin D1, and Axin2 (P < 0.05 - 0.001). C, effects of latent membrane protein 1 (LMP1), Juglone, and PiB on Wnt/β-catenin signaling. Lane 1 shows cells transfected with LMP1 alone, lane 2 depicts cells transfected with LMP1 and treated with Juglone (20 µM), and lane 3 represents cells transfected with LMP1 and treated with PiB (20 µM). The LMP1 alone enhances Wnt/β-catenin signaling, while co-treatment with Pin1 inhibitors reduces pathway activation, demonstrating the ability of Juglone and PiB to attenuate LMP1-mediated enhancement of the signaling cascade. Densitometry (lower panel) demonstrated that both Juglone and PiB significantly reduced LMP1-induced upregulation of β-catenin, cyclin D1, and Axin2 [P < 0.05; ‘+’ the inclusion of a specific treatment (e.g., Juglone, PiB, Pin1 WT, LMP1), ‘−’ its absence, in all panels] (* P < 0.05, ** P < 0.01, and *** P < 0.001).
4.5. Proposed Model: Regulation of the Wnt/β-Catenin Pathway by Pin1 and Its Modulators
Schematic representation of Pin1 modulation in the Wnt/β-catenin pathway and its regulation by Epstein-Barr virus (EBV)-latent membrane protein 1 (LMP1), inhibitors, and implications in pulmonary fibrosis (PF): A schematic diagram illustrating the regulatory effects of Pin1 on the Wnt/β-catenin signaling pathway. Arrowheads indicate activation or promotion of signaling, while bar-ended arrows represent inhibition. Pin1 overexpression (Pin1 box) activates the Wnt/β-catenin pathway, leading to increased levels of β-catenin and its downstream targets cyclin D1 and Axin2. The EBV-LMP1 (EBV LMP1 oval) enhances Pin1 expression, further promoting the pathway. Inhibition of the Wnt pathway is represented by XAV939 (bar-ended arrow), which suppresses β-catenin stabilization. Juglone and PiB (bar-ended arrows) inhibit Pin1 activity, reducing pathway activation.



![Effects of Pin1 inhibitors on Wnt/β-catenin pathway: A, effects of Juglone on Wnt/β-catenin signaling components. MRC-5 cells were treated under four conditions: Untreated control (lane 1), Juglone treatment (20 µM, lane 2), wild-type Pin1 (Pin1 WT) overexpression (lane 3), and Pin1 WT overexpression combined with Juglone treatment (lane 4). Juglone, as a Pin1 inhibitor, primarily reduces Pin1 activity rather than its protein levels. Therefore, the presence of Pin1 protein in lane 2 does not indicate the absence of inhibition but reflects that the inhibitor does not decrease total protein levels. Densitometric quantification (lower panel) confirmed significant reductions of β-catenin, cyclin D1, and Axin2 upon Juglone treatment compared to Pin1 WT (P < 0.05 - 0.01). B, effects of PiB on Wnt/β-catenin cascade components. MRC-5 cells were treated under similar conditions as in (A): Untreated control (lane 1), PiB treatment (20 µM, lane 2), Pin1 WT overexpression (lane 3), and Pin1 WT overexpression with PiB treatment (lane 4). Similar to Juglone, PiB inhibits Pin1 activity without significantly reducing total Pin1 protein levels. Quantitative analysis (lower panel) showed that PiB markedly suppressed Pin1-induced increases in β-catenin, cyclin D1, and Axin2 (P < 0.05 - 0.001). C, effects of latent membrane protein 1 (LMP1), Juglone, and PiB on Wnt/β-catenin signaling. Lane 1 shows cells transfected with LMP1 alone, lane 2 depicts cells transfected with LMP1 and treated with Juglone (20 µM), and lane 3 represents cells transfected with LMP1 and treated with PiB (20 µM). The LMP1 alone enhances Wnt/β-catenin signaling, while co-treatment with Pin1 inhibitors reduces pathway activation, demonstrating the ability of Juglone and PiB to attenuate LMP1-mediated enhancement of the signaling cascade. Densitometry (lower panel) demonstrated that both Juglone and PiB significantly reduced LMP1-induced upregulation of β-catenin, cyclin D1, and Axin2 [P < 0.05; ‘+’ the inclusion of a specific treatment (e.g., Juglone, PiB, Pin1 WT, LMP1), ‘−’ its absence, in all panels] (* P < 0.05, ** P < 0.01, and *** P < 0.001). Effects of Pin1 inhibitors on Wnt/β-catenin pathway: A, effects of Juglone on Wnt/β-catenin signaling components. MRC-5 cells were treated under four conditions: Untreated control (lane 1), Juglone treatment (20 µM, lane 2), wild-type Pin1 (Pin1 WT) overexpression (lane 3), and Pin1 WT overexpression combined with Juglone treatment (lane 4). Juglone, as a Pin1 inhibitor, primarily reduces Pin1 activity rather than its protein levels. Therefore, the presence of Pin1 protein in lane 2 does not indicate the absence of inhibition but reflects that the inhibitor does not decrease total protein levels. Densitometric quantification (lower panel) confirmed significant reductions of β-catenin, cyclin D1, and Axin2 upon Juglone treatment compared to Pin1 WT (P < 0.05 - 0.01). B, effects of PiB on Wnt/β-catenin cascade components. MRC-5 cells were treated under similar conditions as in (A): Untreated control (lane 1), PiB treatment (20 µM, lane 2), Pin1 WT overexpression (lane 3), and Pin1 WT overexpression with PiB treatment (lane 4). Similar to Juglone, PiB inhibits Pin1 activity without significantly reducing total Pin1 protein levels. Quantitative analysis (lower panel) showed that PiB markedly suppressed Pin1-induced increases in β-catenin, cyclin D1, and Axin2 (P < 0.05 - 0.001). C, effects of latent membrane protein 1 (LMP1), Juglone, and PiB on Wnt/β-catenin signaling. Lane 1 shows cells transfected with LMP1 alone, lane 2 depicts cells transfected with LMP1 and treated with Juglone (20 µM), and lane 3 represents cells transfected with LMP1 and treated with PiB (20 µM). The LMP1 alone enhances Wnt/β-catenin signaling, while co-treatment with Pin1 inhibitors reduces pathway activation, demonstrating the ability of Juglone and PiB to attenuate LMP1-mediated enhancement of the signaling cascade. Densitometry (lower panel) demonstrated that both Juglone and PiB significantly reduced LMP1-induced upregulation of β-catenin, cyclin D1, and Axin2 [P < 0.05; ‘+’ the inclusion of a specific treatment (e.g., Juglone, PiB, Pin1 WT, LMP1), ‘−’ its absence, in all panels] (* P < 0.05, ** P < 0.01, and *** P < 0.001).](https://brieflands.com/journals/ijpr/articles/160860/figures/ijpr-24-1-160860-i004-preview.webp)
