BACKGROUND

Y-box binding protein-1 is an evolutionary conserved transcription and translation regulating protein that is overexpressed in various human malignancies, including breast cancer. Despite reports of YB-1 and its association with distant spread of breast cancer, the intrinsic mechanism underlying this observation remains elusive. This study investigates the role of YB-1 in mediating metastasis in highly invasive breast cancer cell lines.

METHODS

Silencing the YBX1 gene (which encodes the YB-1 protein) by small interfering RNA (siRNA) was performed in MDA-MB-231 and Hs578T breast cancer cell lines, followed by phenotypic assays including cell migration and invasion assays. Gene expression profiling using Affymetrix GeneChip® Human Transcriptome 2.0 array was subsequently carried out in YB-1 silenced MDA-MB-231 cells. Overexpression and silencing of YBX1 were performed to assess the expression of CORO1C, one of the differentially regulated genes from the transcriptomic analysis. A Gaussia luciferase reporter assay was used to determine if CORO1C is a putative YB-1 downstream target. siRNA-mediated silencing of CORO1C and down-regulation of YBX1 in CORO1C overexpressing MDA-MB-231 cells were performed to evaluate cell migration and invasion.

RESULTS

Downregulation of the YB-1 protein inhibited cell migration and invasion in MDA-MB-231 breast cancer cells. Global gene expression profiling in the YBX1 silenced MDA-MB-231 cells identified differential expression of several genes, including CORO1C (which encodes for an actin binding protein, coronin-1C) as a potential downstream target of YB-1. While knockdown of YBX1 gene decreased CORO1C gene expression, the opposite effects were seen in YB-1 overexpressing cells. Subsequent verification using the reporter assay revealed that CORO1C is an indirect downstream target of YB-1. Silencing of CORO1C by siRNA in MDA-MB-231 cells was also observed to reduce cell migration and invasion. Silencing of YBX1 caused a similar reduction in CORO1C expression, concomitant with a significant decrease in migration in Hs578T cells. In coronin-1C overexpressing MDA-MB-231 cells, increased migration and invasion were abrogated by YB-1 knockdown.

CONCLUSION

It would appear that YB-1 could regulate cell invasion and migration via downregulation of its indirect target coronin-1C. The association between YB-1 and coronin-1C offers a novel approach by which metastasis of breast cancer cells could be targeted and abrogated.