Effects of extracellular YB-1 protein on cultured cells of human breast cancer

Multifunctional protein YB-1, which takes a part in many DNA/RNA-associated events in cells (transcription, mRNA translation, splicing) is a promising prognostic and predictive marker for various human tumors. Recently it was discovered that protein YB-1 secreted by cells functions as an extracellular mitogen. These results were obtained on kidney mesangial cells and monocytes. Here we studied the effects of extracellular YB-1 on the cell number, migration and gene expression in the populations of three lines of human malignant breast cells (MCF-7, HBL-100, BT-474). We used recombinant full-length protein YB-1, which retained all the functional sites necessary for its various activities, including binding to the receptor Notch-3 (rYB-1). Extracellular rYB-1 increased the number of cells 2- to 3-fold in the tested lines. The wound was made in cell monolayers of HBL-100, MCF-7 and MCF-7/ras. Protein rYB-1 increased the rate of wound healing in MCF-7/ras. Sensitivity to chemotherapeutic agents did not change in the presence of rYB-1 in any of the cell lines studied. We have used expression microarrays to study the effects of rYB-1 on the profile of gene expression in MCF-7 cells and in MCF-7 cells transfected with YB-1-GFP construct. In MCF-7 cells extracellular rYB-1 mainly down-regulated different genes, while in the cells transfected with cDNA of YB-1-GFP the activity of different genes was up-regulated. Our results show that extracellular YB-1 protein and intracellular YB-1 produce diverse changes in the cells of mammary tumors. It is possible that extracellular YB-1 is involved in the regulation of cell proliferation and migration in the metastatic niche.