B-Myb overexpression results in activation and increased Fas/FasL-mediated cytotoxicity of T and NK cells

The human B-myb gene encodes a transcriptional regulator that plays an important role in cell cycle progression, differentiation,and survival. To assess the in vivo role of B-myb, we investigated the phenotype of mouse transgenic lines in which B-Mybexpression in lymphoid tissues was driven by the LCK proximal promoter. Overexpression of B-Myb had no measurable effect onthe subsets of splenic and thymic lymphocytes, but was associated with increased expression of Fas ligand in NK and T cells.B-Myb-overexpressing splenocytes expressed higher IFN-␥ levels and contained higher percentages of cytokine-producing cellsthan wild-type (wt) splenocytes, as detected by Western blot analysis and ELISPOT assays, respectively. Ex vivo-cultured trans-genic thymocytes and splenocytes had decreased survival compared with the corresponding cells from wt mice, possibly dependenton increased expression of Fas ligand. In addition, Fas ligand-dependent cytotoxicity of transgenic T and NK cells was significantlyhigher than that mediated by their wt counterparts. Together, these results indicate that B-Myb overexpression results in T andNK cell activation and increased cytotoxicity. Therefore, in addition to its well-established role in proliferation and differentiation,B-myb also appears to be involved in activation of NK and T cells and in their regulation of Fas/Fas ligand-mediatedcytotoxicit

Myb and ets proteins are candidate regulators of c-kit expression in human hematopoietic cells.

Kit is a tyrosine kinase receptor that plays an important role in human hematopoietic cell growth. The promoter elements that modulate the gene's expression have not been extensively studied. Because of c-kit's acknowledged importance in hematopoiesis, we sought to address this issue in more detail. To perform these studies we analyzed a human c-kit 5' flanking fragment approximately 1 kilobase in length. Deletion constructs showed a region approximately 139 nucleotides upstream from the translation initiation site that was critical for promoter activity. A region containing a potential silencing element was also identified. Sequence analysis indicated several potential Myb- and Ets-binding sites. The functional significance of these sites was explored by showing that both wild-type Myb and Ets-2 protein, but not a DNA binding-deficient Myb mutant protein, bound to distinct 5' flanking fragments that included these sites. Furthermore, binding of recombinant Myb and Ets-2 protein to these fragments could be competed with an excess of double stranded oligodeoxynucleotides containing canonical, but not mutated, Myb- or Ets-binding sites. We also showed that the 5' flanking region of c-kit exhibited promoter activity in nonhematopoietic cells only when the cells were transfected with c-myb or ets-2 expression vectors. Moreover, Myb and Ets-2 coexpression in such cells augmented transactivation of c-kit promoter constructs in comparison to that observed in cells transfected with either construct alone. Promoter constructs lacking various Myb and Ets sites deleted were much less effective in this same system. Finally, Myb and Ets-2 mRNA expression was detected in CD34+, Kit low as well as CD34+, Kit bright cells. In aggregate, these data further define the human c-kit promoter's functional anatomy and suggest that Myb and Ets proteins play an important, perhaps cooperative, role in regulating expression of this critical hematopoietic cell receptor

YAP1 and AR interactions contribute to the switch from androgen-dependent to castration-resistant growth in prostate cancer

The transcriptional co-activator Yes-associated protein 1 (YAP1), a key nuclear effector of the Hippo pathway, is a potent oncogene, and yet, the interaction between YAP1 and androgen receptor (AR) remains unexplored. Here we identify YAP1 as a physiological binding partner and positive regulator of AR in prostate cancer. YAP1 and AR co-localize and interact with each other predominantly within cell nuclei by an androgen-dependent mechanism in a hormone naive and an androgen-independent mechanism in castration-resistant prostate cancer cells. The growth suppressor MST1 kinase modulates androgen-dependent and -independent nuclear YAP1–AR interactions through directly regulating YAP1 nuclear accumulation. Disruption of YAP1 signalling by genetic (RNAi) and pharmacological (Verteporfin) approaches suppresses AR-dependent gene expression and prostate cancer cell growth. These findings indicate that the YAP1–AR axis may have a critical role in prostate cancer progression and serves as a viable drug target