High expression of Notch-1 and Jagged-1 mRNA correlates with poor prognosis in breast cancer. Elucidating the cross-talk between Notch and other major breast cancer pathways is necessary to determine which patients may benefit from Notch inhibitors, which agents should be combined with them, and which biomarkers indicate Notch activity in vivo. We explored expression of Notch receptors and ligands in clinical specimens, as well as activity, regulation, and effectors of Notch signaling using cell lines and xenografts. Ductal and lobular carcinomas commonly expressed Notch-1, Notch-4, and Jagged-1 at variable levels. However, in breast cancer cell lines, Notch-induced transcriptional activity did not correlate with Notch receptor levels and was highest in estrogen receptor α–negative (ERα–), Her2/Neu nonoverexpressing cells. In ERα+ cells, estradiol inhibited Notch activity and Notch-1IC nuclear levels and affected Notch-1 cellular distribution. Tamoxifen and raloxifene blocked this effect, reactivating Notch. Notch-1 induced Notch-4. Notch-4 expression in clinical specimens correlated with proliferation (Ki67). In MDA-MB231 (ERα–) cells, Notch-1 knockdown or γ-secretase inhibition decreased cyclins A and B1, causing G2 arrest, p53-independent induction of NOXA, and death. In T47D:A18 (ERα+) cells, the same targets were affected, and Notch inhibition potentiated the effects of tamoxifen. In vivo, γ;-secretase inhibitor treatment arrested the growth of MDA-MB231 tumors and, in combination with tamoxifen, caused regression of T47D:A18 tumors. Our data indicate that combinations of antiestrogens and Notch inhibitors may be effective in ERα+ breast cancers and that Notch signaling is a potential therapeutic target in ERα– breast cancers.

A dramatic increase of chlorophyll (Chl) degradation occurs during senescence of vegetative plant organs and fruit ripening. Although the biochemical pathway of Chl degradation has long been proposed, little is known about its regulatory mechanism. Identification of Chl degradation-disturbed mutants and subsequently isolation of responsible genes would greatly facilitate the elucidation of the regulation of Chl degradation. Here, we describe a nonyellowing mutant of Arabidopsis (Arabidopsis thaliana), nye1-1, in which 50% Chl was retained, compared to less than 10% in the wild type (Columbia-0), at the end of a 6-d dark incubation. Nevertheless, neither photosynthesis-nor senescence-associated process was significantly affected in nye1-1. Characteristically, a significant reduction in pheophorbide a oxygenase activity was detected in nye1-1. However, no detectable accumulation of either chlorophyllide a or pheophorbide a was observed. Reciprocal crossings revealed that the mutant phenotype was caused by a monogenic semidominant nuclear mutation. We have identified AtNYE1 by positional cloning. Dozens of its putative orthologs, predominantly appearing in higher plant species, were identified, some of which have been associated with Chl degradation in a few crop species. Quantitative polymerase chain reaction analysis showed that AtNYE1 was drastically induced by senescence signals. Constitutive overexpression of AtNYE1 could result in either pale-yellow true leaves or even albino seedlings. These results collectively indicate that NYE1 plays an important regulatory role in Chl degradation during senescence by modulating pheophorbide a oxygenase activity.

Development of the DNA gyrase inhibitor, novobiocin, into a selective Hsp90 inhibitor was accomplished through structural modifications to the amide side chain, coumarin ring, and sugar moiety. These species exhibit ~700-fold improved anti-proliferative activity versus the natural product as evaluated by cellular efficacies against breast, colon, prostate, lung, and other cancer cell lines. Utilization of structure–activity relationships established for three novobiocin synthons produced optimized scaffolds, which manifest mid-nanomolar activity against a panel of cancer cell lines and serve as lead compounds that manifest their activities through Hsp90 inhibition.

Cancer stem-like cells (CSC) drive cancer progression and recurrence. Self-renewal expansion of CSC is achieved through symmetric cell division, yet how external stimuli affect intracellular regulatory programs of CSC division modes and stemness remains obscure. Here, we report that the hTERT prostate cancer cells exhibit CSC properties, including a stem cell-associated gene expression signature, long-term tumor-propagating capacity and epithelial-to-mesenchymal transition. In promoting the self-renewal symmetric division of hTERT prostate cancer cells, WNT3a dramatically decreased the ratio of hTERT prostate cancer cells undergoing asymmetric division. Increased WNT/β-catenin signal activation was also detected in hTERT prostate cancer cells. hTERT-mediated CSC properties were at least partially dependent on β-catenin. These findings provide novel cellular and molecular mechanisms for the self-renewal of CSC orchestrated by tumor microenvironmental stimuli and intracellular signals. .