The transcriptional factor YY1 upregulates the novel invasion suppressor HLJ1 expression and inhibits cancer cell invasion.

By using microarray and an invasion/metastasis lung cell line model, we identified the DnaJ-like heat shock protein 40, HLJ1, and found that the expression of HLJ1 correlates negatively with cancer cell invasion ability. Overexpression of HLJ1 can suppress cancer cell invasion in vitro. We further characterize the putative promoter region and investigate the transcriptional regulations of human HLJ1. A serial deletion of the 1.2 kb at the 5'-flanking region of the human HLJ1 gene was subcloned into a vector containing reporter gene and transfected into human lung adenocarcinoma cell line CL1-0, followed by luciferase activity assay. The results indicated that the region from -232 to +176 could drive the basal transcriptional activity of the HLJ1 gene. Sequence analysis of the HLJ1 gene promoter region showed absence of a TATA box, but identified an inverted CCAAT box and four YY1 transcriptional factor-binding sites, which may be important in the regulation of HLJ1 expression. Co-transfection of the YY1 and HLJ1 basal promoter regions, site-directed mutagenesis, and electrophoretic mobility shift assay confirmed that YY1 could upregulate HLJ1 basal promoter activity. Furthermore, we also demonstrated that overexpression of YY1 in CL1-0 cells can increase HLJ1 expression and reduce cell invasive capability. The reduction of cancer cell invasive ability is, at least in part, through upregulation of E-cadherin expression. The increase in HLJ1 and E-cadherin expression, as well as the suppression of invasion ability, can be reversed specifically by HLJ1 siRNA.