Involvement of secreted protein acidic and rich in cysteine (SPARC) downregulation in malignant conversion of aflatoxin B₁-induced rat hepatocellular carcinoma K2 cells

Abstract

  14-3-3 family proteins are involved in various signal transduction pathways. We have previously demonstrated that 14-3-3β/fourteen-three-three beta interactant 1 (FBI1) /specific protein 3 (Sp3) transcription factor/histone deacetylase1 (HDAC1) complex suppresses the mitogen-activated protein kinase phosphatase 1 (MKP-1) gene expression, which negatively regulates the MAP kinase signaling cascade, in aflatoxin B₁ (AFB₁)-induced rat hepatocellular carcinoma (rHCC) K2 cells and finally promotes metastasis and tumorigenicity. In this study, to further elucidate the malignant conversion mechanism of K2 cells, we performed microarray analysis to identify the genes controlled by 14-3-3β/FBI1/Sp3/HDAC1 complex. The data showed that secreted protein, acidic, and rich in cysteine (SPARC) was identified as one of the downregulated target genes. Luciferase reporter assay and chromatin immunoprecipitation (ChIP) analysis revealed that 14-3-3β/FBI1/Sp3/HDAC1 complex bound to GC box in the SPARC promoter region and repressed the transcription. Furthermore, enforced expression of SPARC in K2 cells inhibited colony formation in semi-solid medium. Thus, these results provide the evidence that downregulation of SPARC by the 14-3-3β/FBI1/Sp3/ HDAC1 complex is involved in the malignant conversion of K2 cells.