Follistatin-like protein 1 (FSTL1) plays a critical role in lung organogenesis, but is downregulated during lung cancer development and progression. The prognostic significance and functional consequences of FSTL1 downregulation in lung cancer are unclear. Here, reduced levels of FSTL1 were detected in various tumors compared with normal tissues and were associated with poor clinical outcome in patients with non-small cell lung cancer, particularly those with lung adenocarcinoma. FSTL1 expression negatively correlated with the metastatic potential of lung cancer cells. Antibody-based neutralization of extracellular FSTL1 increased cellular migration/invasion while addition of recombinant FSTL1 protein diminished the metastatic capacity of lung cancer cells in vitro and in vivo. Notably, treatment with FSTL1 effectively prevented the metastatic progression of lung cancer cells in an orthotopic animal model. Mechanistically, FSTL1 directly bound to the proform of secreted phosphoprotein 1 (SPP1)/osteopontin, restraining proteolytic activation of SPP1, which led to inactivation of integrin/CD44-associated signaling and rearrangement of the actin cytoskeleton. Combined low expression of FSTL1 and high expression of SPP1 predicted a poorer prognosis for patients with lung cancer. This study highlights the novel interaction between FSTL1 and SPP1 and new opportunities to effectively target SPP1-driven metastatic cancers characterized by FSTL1 downregulation.Significance: These findings describe the novel interaction between FSTL1 and SPP1 and its role in the metastatic progression of lung adenocarcinoma.
Drug resistance remains a serious issue of clinical importance and is a consequence of cancer stemness. In this study, we showed that the level of Aldolase A (ALDOA) expression is significantly associated with the IC50 value of chemotherapy drugs in lung cancer. Our data revealed that ALDOA overexpression resulted in a significant increase of lung tumor spheres. The use of ingenuity pathway analysis (IPA) resulted in the identification of POU5F1 (Oct4) as the leading transcription factor of ALDOA. We observed high expression of ALDOA, Oct4 and stemness markers in collected spheroid cells. DUSP4 and TRAF4 were confirmed as major downstream targets of the ALDOA-Oct4 axis. Knockdown of these molecules significantly decreased the stemness ability of cells. In addition, we investigated whether miR-145 targets the 3′-UTR of Oct4 and is regulated by ALDOA due to the involvement of ALDOA in glycolysis and metabolic reprogramming. Furthermore, we constructed several mutant forms of ALDOA that disrupted its enzymatic activity and showed that they still induced significant in vitro sphere formation and in vivo tumorigenicity. These results demonstrated that ALDOA-mediated spheroid formation is independent of its enzymatic activity. In the clinical component, we also showed that the combination of ALDOA and TRAF4 or DUSP4 is positively correlated with poor overall survival in a xenograft model and cancer patients through immunohistochemical analyses. The results of our study revealed novel functional roles of ALDOA in inducing cancer stemness via the inhibition of miR-145 expression and the activation of Oct4 transcription. These findings offer new therapeutic strategies for modulation of lung cancer stemness to enhance chemotherapeutic responses in lung cancer patients.
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