Molecular decoy to the Y-box binding protein-1 suppresses the growth of breast and prostate cancer cells whilst sparing normal cell viability.

The Y-box binding protein-1 (YB-1) is an oncogenic transcription/translation factor that is activated by phosphorylation at S102 whereby it induces the expression of growth promoting genes such as EGFR and HER-2. We recently illustrated by an in vitro kinase assay that a novel peptide to YB-1 was highly phosphorylated by the serine/threonine p90 S6 kinases RSK-1 and RSK-2, and to a lesser degree PKCα and AKT. Herein, we sought to develop this decoy cell permeable peptide (CPP) as a cancer therapeutic. This 9-mer was designed as an interference peptide that would prevent endogenous YB-1(S102) phosphorylation based on molecular docking. In cancer cells, the CPP blocked P-YB-1(S102) and down-regulated both HER-2 and EGFR transcript level and protein expression. Further, the CPP prevented YB-1 from binding to the EGFR promoter in a gel shift assay. Notably, the growth of breast (SUM149, MDA-MB-453, AU565) and prostate (PC3, LNCap) cancer cells was inhibited by ∼90% with the CPP. Further, treatment with this peptide enhanced sensitivity and overcame resistance to trastuzumab in cells expressing amplified HER-2. By contrast, the CPP had no inhibitory effect on the growth of normal immortalized breast epithelial (184htert) cells, primary breast epithelial cells, nor did it inhibit differentiation of hematopoietic progenitors. These data collectively suggest that the CPP is a novel approach to suppressing the growth of cancer cells while sparing normal cells and thereby establishes a proof-of-concept that blocking YB-1 activation is a new course of cancer therapeutics.

Y-box binding protein-1 induces the expression of CD44 and CD49f leading to enhanced self-renewal, mammosphere growth, and drug resistance.

Y-box binding protein-1 (YB-1) is an oncogenic transcription/translation factor expressed in >40% of breast cancers, where it is associated with poor prognosis, disease recurrence, and drug resistance. We questioned whether this may be linked to the ability of YB-1 to induce the expression of genes linked to cancer stem cells such as CD44 and CD49f. Herein, we report that YB-1 binds the CD44 and CD49f promoters to transcriptionally upregulate their expressions. The introduction of wild-type (WT) YB-1 or activated P-YB-1(S102) stimulated the production of CD44 and CD49f in MDA-MB-231 and SUM 149 breast cancer cell lines. YB-1-transfected cells also bound to the CD44 ligand hyaluronan more than the control cells. Similarly, YB-1 was induced in immortalized breast epithelial cells and upregulated CD44. Conversely, silencing YB-1 decreased CD44 expression as well as reporter activity in SUM 149 cells. In mice, expression of YB-1 in the mammary gland induces CD44 and CD49f with associated hyperplasia. Further, activated mutant YB-1(S102D) enhances self-renewal, primary and secondary mammosphere growth, and soft-agar colony growth, which were reversible via loss of CD44 or CD49f. We next addressed the consequence of this system on therapeutic responsiveness. Here, we show that paclitaxel induces P-YB-1(S102) expression, nuclear localization of activated YB-1, and CD44 expression. The overexpression of WT YB-1 promotes mammosphere growth in the presence of paclitaxel. Importantly, targeting YB-1 sensitized the CD44(High)/CD24(Low) cells to paclitaxel. In conclusion, YB-1 promotes cancer cell growth and drug resistance through its induction of CD44 and CD49f.

Transcriptome analysis of the normal human mammary cell commitment and differentiation process.

Mature mammary epithelial cells are generated from undifferentiated precursors through a hierarchical process, but the molecular mechanisms involved, particularly in the human mammary gland, are poorly understood. To address this issue, we isolated highly purified subpopulations of primitive bipotent and committed luminal progenitor cells as well as mature luminal and myoepithelial cells from normal human mammary tissue and compared their transcriptomes obtained using three different methods. Elements unique to each subset of mammary cells were identified, and changes that accompany their differentiation in vivo were shown to be recapitulated in vitro. These include a stage-specific change in NOTCH pathway gene expression during the commitment of bipotent progenitors to the luminal lineage. Functional studies further showed NOTCH3 signaling to be critical for this differentiation event to occur in vitro. Taken together, these findings provide an initial foundation for future delineation of mechanisms that perturb primitive human mammary cell growth and differentiation.

Genomic instability of human mammary epithelial cells overexpressing a truncated form of EMSY.

The EMSY gene encodes a protein that interacts with Brca2 and is amplified in some sporadic cases of human breast cancer. To examine whether overexpression of EMSY would mimic the chromosome instability phenotype that is associated with the loss of Brca2 function, we constructed a lentiviral vector (Lenti-EMSY/GFP) that encodes a truncated form of the Emsy protein, including its Brca2-interacting domain, and green fluorescent protein (GFP) and used it to transduce human telomerase-immortalized human breast epithelial (184-hTert) cells, which have a nearly normal karyotype. At passage 5 after transduction, 39 (26%) of 150 EMSY/GFP-transduced metaphase cells contained at least one structural chromosomal abnormality compared with 19 (13%) of 150 GFP-transduced metaphase cells (P = .003, chi-square test); at passage 10, the corresponding frequencies were 42% and 15%, respectively (P < .001). Mitomycin C also produced a severalfold higher frequency of chromosome breaks in the EMSY/GFP-transduced cells than in the control cells. These results support the hypothesis that EMSY overexpression can play a role in the genesis of human breast cancer.