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.

Atherosclerosis is a chronic inflammatory arterial disease characterized by focal accumulation of lipid and inflammatory cells. It is the number one cause of deaths in the Western world because of its complications of heart attacks and strokes. Statins are effective in only approximately one third of patients, underscoring the urgent need for additional therapies. B cells that accumulate in atherosclerotic lesions and the aortic adventitia of humans and mice are considered to protect against atherosclerosis development. Unexpectedly, we found that selective B cell depletion in apolipoprotein E-deficient (ApoE−/−) mice using a well-characterized mAb to mouse CD20 reduced atherosclerosis development and progression without affecting the hyperlipidemia imposed by a high-fat diet. Adoptive transfer of 5 × 106 or 5 × 107 conventional B2 B cells but not 5 × 106 B1 B cells to a lymphocyte-deficient ApoE−/− Rag-2−/− common cytokine receptor γ-chain–deficient mouse that was fed a high-fat diet augmented atherosclerosis by 72%. Transfer of 5 × 106 B2 B cells to an ApoE−/− mouse deficient only in B cells aggravated atherosclerosis by >300%. Our findings provide compelling evidence for the hitherto unrecognized proatherogenic role of conventional B2 cells. The data indicate that B2 cells can potently promote atherosclerosis development entirely on their own in the total absence of all other lymphocyte populations. Additionally, these B2 cells can also significantly augment atherosclerosis development in the presence of T cells and all other lymphocyte populations. Our findings raise the prospect of B cell depletion as a therapeutic approach to inhibit atherosclerosis development and progression in humans.

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.