SALL4 correlates with proliferation, metastasis, and poor prognosis in prostate cancer by affecting MAPK pathway

Abstract

Background: The mechanism involved in prostate cancer (PCa) metastasis is still poorly understood, and several oncogenes are known to regulate this process. However, the role of spalt-like transcription factor 4 (SALL4) in PCa metastasis remains unclear.

Methods: We performed RNA-sequencing to compare the mRNA expression profiles of seven localized PCa tissues and six metastatic PCa tissues. SALL4 was then identified and compared in the localized PCa and metastatic PCa. Immunohistochemical studies, qRT-PCR, and Western blot were performed to analyze the expression of SALL4 in PCa patients and cell lines. SALL4 expression and its relevance to clinical traits and prognosis were further explored in the TCGA database and in our 68 clinical samples. Subsequently, we knocked down SALL4 in DU145 and PC3 cells and performed a series of functional assays to explore the effect of SALL4 on PCa progression. Finally, protein levels of SALL4 and core components of the MAPK pathway were measured by Western blot, and cells were treated with PD0325901 to observe proliferation and metastasis.

Results: Significantly higher expression of SALL4 was found in metastatic PCa than in localized PCa. In addition, high SALL4 expression was significantly associated with high pathological T stage, N stage, Gleason score, and poor disease-free survival in TCGA database and in our clinical samples. Functional studies indicated that knockdown of SALL4 in DU145 and PC3 inhibited proliferation, migration, and angiogenesis. Furthermore, the ERK and P38 protein phosphorylation significantly reduced after knockdown of SALL4 in DU145 and PC3, indicating the inactivation of the MAPK signaling pathway. Finally, the proliferation and migration ability of DU145 and PC3 cells were significantly decreased after PD0325901 treatment.

Conclusions: SALL4 predicts unfavorable outcome and is closely associated with PCa progression, suggesting that SALL4 may be a promising prognostic marker and potential therapeutic target for PCa.

Keywords: MAPK pathway; SALL4; metastasis; prostate cancer.