SALL4 Promotes Gastric Cancer Progression Through Regulating CD44 Expression

Objective: To explore the functional roles and molecular mechanism of spalt-like transcription factor 4(SALL4) in gastric cancer growth and metastasis and identify its key target genes. To provide evidence for the oncogenic role of SALL4 and offer new molecular target for gastric cancer diagnosis and therapy.Methods: SALL4 expression in poorly differentiated gastric cancer cell line MGC-803 was interfered with SALL4 sh RNA directly or Tet-On inducible SALL4 sh RNA. Real-time PCR and Western blot were used to detect the interference efficiency. Growth curve and cell colony formation assay were used to measure cell proliferation ability. Wound healing assay and Transwell migration assay were used to assess cell motility and migration. The stem cell factors and signaling pathways influenced by SALL4 were investigated by real-time PCR and Western blot. CD44 promoter activity in cells with SALL4 overexpression or knockdown was determined by dual luciferase reporter assay. Chromatin immunoprecipitation assay(Ch IP) was performed to detect the binding of SALL4 to CD44 promoter region. Cell counting assay, cell colony formation assay, wound healing assay, Transwell migration assay and subcutaneous xenograft tumor model were carried out to detect the effects of CD44 rescue on the growth and metastasis of SALL4 knockdown cells.Results: SALL4 expression was efficiently reduced in MGC-803 cells transfected with SALL4 sh RNA or Tet-on inducible SALL4 sh RNA. SALL4 knockdown led to the retarded cell growth and impaired cell metastasis ability. SALL4 knockdown reduced the expression of stem cell factors such as Oct4, Sox2, Nanog, c-Myc, CD44 and the activation of several signaling pathways such as ERK1/2, NF-κB and STAT3 in MGC-803 cells. CD44 promoter activity was reduced in MGC-803 cells transfected with SALL4 sh RNA or si RNA in a dose-dependent manner. SALL4 protein bound to-505 to-305 upstream of the ATG site of CD44 promoter region. Moreover, CD44 rescue could reverse the inhibition of growth and metastasis of SALL4 knockdown cells in vitro and tumor growth in vivo.Conclusions: SALL4 could promote gastric cancer cell proliferation and metastasis in vitro and tumor growth in vivo through transcriptionally activating CD44. The up-regulation of CD44 represents a new mechanism for the oncogenic role of SALL4 in gastric cancer.