The Role and Molecular Mechanism of SLC34A2 in Stemness Maintenance of CD44+CD166+ Lung Cancer Stem Cells (LCSCs) with AT-II cells’ characteristics

Abstract Background Evidence showed some non-small cell lung cancers (NSCLCs) had the type II alveolar epithelium cells’(AT-II cells) characteristics, and AT-II cells were a kind of original stem cells of NSCLCs. But how AT-II cells malignantly transformed into NSCLCs was unclear. Recent evidence indicated SLC34A2 was critical in the development of AT-II cells, and SLC34A2 might be a new gene in the initiation of NSCLCs. However, whether SLC34A2 participated in the malignant transformation of AT-II cells remained unknown. The exact role and mechanism of SLC34A2 in the initiation of NSCLCs needed to be further investigated. Methods The expression of Napi-IIb (encoded by SLC34A2) in the NSCLC cells was compared with that in AT-II cells using immunohistochemistry (IHC). Also coexpression of CD44 and CD166 was detected in these NSCLCs tissues by IHC. Then the CD44 + CD166 + cells were sorted from lung tumor spheres by FACS. They were assessed by sphere, proliferation and tumorgenicity assay. Besides, their expression of surfactants C(SP-C) was stained by IHC. Next, the role and mechanism of SLC34A2 in CD44 + CD166 + lung cancer stem cells were explored by siRNA-mediated SLC34A2 knockdown, related pathway pharmacological inhibition or activation. In vitro findings were furtherly validated in vivo and NSCLCs samples. Results The expression of SLC34A2 was downregulated in NSCLCs cells compared with AT-II cells in clinic samples. Then the CD44 + CD166 + population was identified as CD44 + CD166 + lung cancer stem cells (LCSCs). And LCSCs showed abundant expression of SP-C, the hallmark of AT-II cells. Higher expression of SLC34A2 was found in LCSCs compared to their origin NSCLC cells. Additionally, the expression of SLC34A2 was decreased after LCSCs were differentiated, and the morphology of the differentiated cells from LCSCs was similar to their origin NSCLC cells. Knockdown SLC34A2 made declined abilities of self-renewal, drug-resistance, migration and invasion in vitro as well as tumorigenicity in vivo in LCSCs. And SLC34A2 could maintain stemness of LCSCs via PI3K/AKT/STAT3/Sox2 axis. Besides, the connection between SLC34A2 maintaining stemness of lung cancer stem cells and PI3K/AKT/STAT3/Sox2 axis was also validated in vivo and in clinic samples. Conclusions For the first time, we illustrated the expression of SLC34A2 was downregulated in NSCLCs cells compared with AT-II cells. We discovered the downregulated expression of SLC34A2 performed a vital role in the malignant transformation of AT-II cells into NSCLCs. And SLC34A2 could maintain stemness of CD44 + CD166 + lung cancer stem cells, which were with AT-II cell’s characteristic, via PI3K/AKT/STAT3/Sox2 axis. It had important significance in the revelation of a new mechanism for the initiation of NSCLCs.