LDB2 is a novel diagnostic and prognostic biomarker and inhibits bladder cancer metastasis by activating p38 MAPK/ERK1/2/JNK signaling pathway.

LIM domain binding protein 2 (LDB2), a transcriptional co-regulator of the LIM protein family, is reported to be downregulated in various tumors. However, its role in bladder cancer (BLCA) remains undefined. This study analyzed the molecular mechanism of LDB2 in inhibiting the metastasis of bladder cancer and its diagnostic and prognostic value in BLCA. We integrated The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) datasets with enrichment analysis to evaluate the expression, diagnostic potential, and prognostic significance of LDB2 in BLCA. Immunohistochemistry (IHC) was performed to assess LDB2 expression in normal and metastatic tissues and its correlation with clinical stage and prognosis. Functional assays, including clonogenic and Transwell assays, were conducted in LDB2 knockdown and overexpression cell lines to examine its role in proliferation, migration, and invasion. Gene expression was assessed at both mRNA and protein levels using qPCR and Western blot. Additionally, CIBERSORT analysis was performed to explore the correlation between LDB2 expression and immune cell infiltration in BLCA. LDB2 expression was significantly lower in metastatic bladder cancer tissues compared with normal bladder tissues (all p < 0.001). Its expression was positively correlated with early clinical stage and favorable prognosis (all p < 0.05), Moreover, LDB2 showed strong diagnostic performance in distinguishing tumor from normal tissues, with AUC values of 0.91 (95% CI 0.86-0.96) in the TCGA cohort and 0.96 (95% CI 0.88-1.00) in the GSE37815 dataset. Furthermore, in vitro assays demonstrated that LDB2 knockdown significantly promoted invasion, metastasis, and colony formation in bladder cancer cells, whereas its overexpression suppressed these malignant behaviors. Mechanistic studies revealed that LDB2 knockdown markedly reduced the phosphorylation of key MAPK pathway components, including p38 MAPK, ERK1/2, and JNK, whereas LDB2 overexpression enhanced their phosphorylation. Immune infiltration analysis indicated that elevated LDB2 expression was associated with increased immune cell infiltration, particularly showing significant correlations with macrophages and mast cells. LDB2 may serve as a novel diagnostic biomarker and tumor suppressor by inhibiting proliferation, invasion, and metastasis via activation of the p38 MAPK/ERK1/2/JNK pathway and modulating the tumor immune microenvironment.