SODD Promotes Lung Cancer Tumorigenesis by Activating the PDK1/AKT and RAF/MEK/ERK Signaling

Background: The Bcl2-associated athanogene4 (BAG4/SODD) protein could be identified as a tumor marker for several malignancies and plays a major role in the occurrence, development, and drug resistance of tumors. However, the role of Silencer of death domains (SODD) in lung carcinogenesis is still elusive.

Objective: To illuminate the effect of SODD on the proliferation, migration, invasion, and apoptosis of lung cancer cells and tumor growth in vivo and explore the corresponding mechanism.

Methods: The expression of SODD in tumor and normal tissues was determined and compared via western blot. SODD gene knockout lung cancer cells (H1299 cells) were established through a CRISPR/Cas9 gene deleting system, and a transient SODD overexpression of H1299 cells was also constructed. Then, cell proliferation and invasion were assessed through colony formation and cell counting kit-8 assays, transwell migration assays, and wound healing assays. Cell drug sensitivity is also analyzed by Cell Counting Kit-8 assay. The flow cytometer was used to perform cell circle and apoptosis analysis. The interaction of SODD and RAF-1 was confirmed by co-immunoprecipitation, and the phosphorylated level of Phosphatidylinositol 3-kinase (PI3K), Serine/threonine-protein kinase (AKT), Rapidly accelerated fibrosarcoma (RAF)-1,and extracellular signal regulated kinase (ERK) in cells was examined by western blot to evaluate the activation of PI3K/PDK1/AKT and RAF/MEK/ERK pathways. In vivo, Xenograft tumor assay of SODD knockout H1299 cells was used to evaluate further the role of SODD on the proliferation of H1299 cells.

Results: SODD binds to RAF-1 and is over-expressed in lung tissues, and promotes the proliferation, migration, invasion, and drug sensitivity of H1299 cells. The reduced cells in the S phase and increased cells arrested in the G2/M phase were found in SODD knockout H1299 cells, and more cells got apoptosis. The expression of 3-phosphoinositide-dependent protein kinase 1(PDK1) protein in SODD knockout H1299 cells decreases distinctively, and the phosphorylated level of AKT, RAF-1, and ERK-1 kinase in SODD knockout H1299 cells is also less than that in normal H1299 cells. In contrast, SODD overexpression significantly increases the phosphorylation of AKT. In vivo, SODD promotes the tumorigenicity of H1299 cells in nude mice.

Conclusions: SODD is overexpressed in lung tissues and plays a considerable role in the development and progression of lung cancer by regulating the PI3K/PDK1/AKT and RAF/MEK/ERK pathways.