Methylation-regulated tumor suppressor gene HOXB4 inhibits human lung adenocarcinoma A549 cell invasion and metastasis through the RAP1 signaling pathway.

Background: Homeobox B4 (HOXB4), which belongs to the homeobox (HOX) family, possesses transcription factor activity and plays a crucial role in stem cell self-renewal and tumorigenesis. However, its role in the development and progression of lung adenocarcinoma (LUAD) remains unclear. Therefore, in current study, we investigated the biological role of HOXB4 in LUAD. Methods: We determined the relationships between HOXB4 and LUAD using numerous databases and analysis tools, including TIMER2, The Cancer Genome Atlas (TCGA), Gene Expression Omnibus (GEO), UALCAN, MethMarkerDB, and Sangerbox. Furthermore, LUAD cell lines overexpressing HOXB4 protein were constructed to investigate its effects on LUAD cell functions. Finally, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) were used to enrich the HOXB4-related pathway. We also determined the effects of HOXB4 overexpression on the transcription of RAP1 signaling pathway-related genes, as well as the expression of epithelial-mesenchymal transition (EMT)-related proteins in LUAD cells. Results: Compared with its expression in normal lung tissues, HOXB4 expression was significantly reduced, while its DNA methylation was increased in LUAD tissues. HOXB4 DNA methylation played an essential role in the process of LUAD genesis, and was associated with LUAD prognosis and diagnosis. Functionally, in vitro experiments revealed that overexpression of HOXB4 significantly inhibited the proliferation, invasion, and migration of LUAD cells, and promoted apoptosis and cell cycle arrest. In addition, GO and KEGG revealed enrichment in RNA polymerase II transcription factor activity and the RAP1 signaling pathway, and HOXB4 overexpression inhibited progressions of the RAP1 signaling pathway and the EMT. Conclusions: HOXB4 may inhibit the development of LUAD. In this process, hypermethylation of HOXB4 predicted early-stage LUAD and was associated with a poorer prognosis. Furthermore, HOXB4 regulated the EMT in LUAD cells through the RAP1 pathway, which in turn affected LUAD metastasis and invasion.