TGF­ß1 induces CREB1­mediated miR­1290 upregulation to antagonize lung fibrosis via Napsin A.

The pathologic mechanisms of pulmonary fibrosis (PF), one of the most common chronic pulmonary diseases, remain unclear. Napsin A is an aspartic proteinase that has been regarded as a hallmark of pulmonary adenocarcinoma. The present study aimed to investigate the specific function and molecular mechanisms of Napsin A in PF from the perspective of microRNA (miRNA or miR) regulation. In the present study, it was found that miR­1290 downregulated the expression of Napsin A by binding to its 3'­UTR. Cell viability was examined by MTT assay. The protein levels of α­smooth muscle actin (α­SMA), Collagen I and Napsin A were examined by western blot analysis. The predicted targeting of Napsin A by miR­1290 was validated by luciferase reporter assay. The protein content of α­SMA was examined by immunofluorescence staining. miR­1290 was found to be upregulated in blood samples from patients with PF and in TGF­ß1­stimulated A549 cells. miR­1290 was found to directly target Napsin A. miR­1290 overexpression also significantly promoted A549 cell proliferation and increased the protein levels of markers of fibrosis. Napsin A knockdown exerted effects on A549 cell proliferation and TGF­ß1­induced fibrosis that were similar to those induced by miR­1290 overexpression; more importantly, Napsin A knockdown significantly reversed the effects of miR­1290 inhibition, indicating that miR­1290 promotes TGF­ß1­induced fibrosis by targeting Napsin A. Moreover, TGF­ß1­induced CAMP responsive element binding protein 1 (CREB1) overexpression promoted the transcription of miR­1290 in A549 cells. On the whole, the findings of the present study demonstrate that TGF­ß1­induced CREB1 overexpression induces the significant upregulation of miR­1290 expression, thus aggravating TGF­ß1­induced fibrotic changes in A549 cells via the miR­1290 downstream target, Napsin A.