Senescence marker protein 30 inhibits tumor growth by reducing HDAC4 expression in non-small cell lung cancer

Background: Senescence marker protein 30 (SMP30), which plays a pivotal role as a suppressor protein in cell proliferation, among other regulatory actions, is a marker of aging that shows decreased expression during senescence. Decreased SMP30 has been identified in several human cancers, but its expression and role in human non-small cell lung cancer (NSCLC) remain unclear. Methods: Using tumor tissue and matched adjacent normal tissue from 341 patients with resected NSCLC, we assessed SMP30 expression using immunohistochemical methods. The relationship between SMP30 expression and clinicopathologic characteristics was investigated by Kaplan-Meier survival analysis and multivariate analysis. Cell viability assay, colony formation assay, EdU incorporation assay and in vivo tumor xenograft models were also performed to investigate NSCLC cell proliferation using A549 and H1299 cell lines. Recombinant lentivirus-meditated in vivo gene overexpression and Western blot were performed to clarify the underlying molecular mechanism of SMP30 inhibiting NSCLC proliferation. Results: SMP30 expression was frequently downregulated in NSCLC tissue, as compared with adjacent non-tumor tissue. Kaplan-Meier survival analyses revealed NSCLC patients with low SMP30 expression had a significantly worse overall survival (OS), with median OS of 18 vs. 67 months in high SMP30 expression group. SMP30 overexpression significantly inhibited A549 and H1299 cell proliferation both in vitro and in tumor xenografts and downregulated the expression of c-Myc and CyclinD1 protein. Moreover, Western blot analyses confirmed that SMP30 overexpression significantly inhibited the histone deacetylase 4 (HDAC4) level in NSCLC cells, and HDAC4 overexpression reversed SMP30-mediated NSCLC repression both in vitro and in vivo. Conclusions: SMP30 inhibited NSCLC proliferation by reducing HDAC4 expression, and SMP30 and HDAC4 may serve as new prognostic biomarkers and future therapeutic targets for NSCLC.