Malignant breast tissue contains a rare population of multi-potent cells with the capacity to self-renew; these cells are known as cancer stem-like cells (CSCs) or tumor-initiating cells. Primitive mammary CSCs/progenitor cells can be propagated in culture as floating spherical colonies termed ‘mammospheres'. We show here that the expression of the autophagy protein Beclin 1 is higher in mammospheres established from human breast cancers or breast cancer cell lines (MCF-7 and BT474) than in the parental adherent cells. As a result, autophagic flux is more robust in mammospheres. We observed that basal and starvation-induced autophagy flux is also higher in aldehyde dehydrogenase 1-positive (ALDH1+) population derived from mammospheres than in the bulk population. Beclin 1 is critical for CSC maintenance and tumor development in nude mice, whereas its expression limits the development of tumors not enriched with breast CSCs/progenitor cells. We found that decreased survival in autophagy-deficient cells (MCF-7 Atg7 knockdown cells) during detachment does not contribute to an ultimate deficiency in mammosphere formation. This study demonstrates that a prosurvival autophagic pathway is critical for CSC maintenance, and that Beclin 1 plays a dual role in tumor development.

Synaptic trafficking of AMPA-Rs, controlled by small GTPase Ras signaling, plays a key role in synaptic plasticity. However, how Ras signals synaptic AMPA-R trafficking is unknown. Here we show that low levels of Ras activity stimulate extracellular signal-regulated kinase kinase (MEK)-p42/44 MAPK (extracellular signal-regulated kinase [ERK]) signaling, whereas high levels of Ras activity stimulate additional Pi3 kinase (Pi3K)-protein kinase B (PKB) signaling, each accounting for ∼50% of the potentiation during long-term potentiation (LTP). Spontaneous neural activity stimulates the Ras-MEK-ERK pathway that drives GluR2L into synapses. In the presence of neuromodulator agonists, neural activity also stimulates the Ras-Pi3K-PKB pathway that drives GluR1 into synapses. Neuromodulator release increases with increases of vigilance. Correspondingly, Ras-MEK-ERK activity in sleeping animals is sufficient to deliver GluR2L into synapses, while additional increased Ras-Pi3K-PKB activity in awake animals delivers GluR1 into synapses. Thus, state-dependent Ras signaling, which specifies downstream MEK-ERK and Pi3K-PKB pathways, differentially control GluR2L-and GluR1-dependent synaptic plasticity.[Keywords: Ras; Erk; Pi3 kinase; Src; synaptic plasticity; neuromodulators; behavioral states] Supplemental material is available at http://www.genesdev.org.

Acute glaucoma is a sight-threatening condition characterized by a sudden and substantial rise in intraocular pressure (IOP) and consequent retinal ganglion cell (RGC) death. Angle closure glaucoma, a common cause of glaucoma in Asia that affects tens of millions of people worldwide, often presents acutely with loss of vision, pain, and high IOP. Even when medical and surgical treatment is available, acute angle closure glaucoma can cause permanent and irreversible loss of vision. Toll-like receptor 4 (TLR4) signaling has been previously implicated in the pathogenesis of IOP-induced RGC death, although the underlying mechanisms are largely unknown. In the present study, we used an acute IOP elevation/glaucoma model to investigate the underlying mechanism of RGC death. We found that TLR4 leads to increased caspase-8 expression; this elevation increases IL-1β expression and RGC death via a caspase-1-dependent pathway involving Nod-like receptor family, pyrin domain containing 1 (NLRP1)/NLRP3 inflammasomes and a caspase-1-independent pathway. We show that inhibition of caspase-8 activation significantly attenuates RGC death by down-regulating the activation of NLRP1 and NLRP3, thus demonstrating the pivotal role of caspase-8 in the TLR4-mediated activation of inflammasomes. These findings demonstrate collectively a critical role of caspase-8 in transducing TLR4-mediated IL-1β production and RGC death and highlight signal transduction in a caspase-1-dependent NLRP1/NLRP3 inflammasome pathway and a caspase-1-independent pathway in acute glaucoma. These results provide new insight into the pathogenesis of glaucoma and point to a treatment strategy.retinal ischemia/reperfusion injury | cell apoptosis A cute glaucoma is a significant cause of permanent vision loss and irreversible blindness worldwide (1). It is most common among people of Asian descent, in part due to their having a more crowded anterior chamber (2, 3). With a rapid increase in intraocular pressure (IOP) to levels exceeding retinal perfusion pressure, there is resulting retinal ischemia and retinal ganglion cell (RGC) death. Individuals with angle closure glaucoma are much more likely to lose vision and become blind than those with primary open-angle glaucoma (4). The precise mechanisms by which elevated IOP leads to RGC death are not well understood. Accumulating evidence suggests that overactivated microglia have pivotal roles in triggering neurotoxicity in the CNS, including retinal inflammatory responses (5, 6), by producing proinflammatory factors such as IL-1β. IL-1β production is tightly controlled as part of the innate immune response in the CNS (7).Toll-like receptors (TLRs) and Nod-like receptors (NLRs) are two key pattern recognition receptors (PRRs) in the initiation of the innate immune response (8-10). TLR4 has been shown to have a central role in retinal and CNS ischemia/reperfusion (I/R) injuries (11-13). Neuronal death following ischemic injury activates intense inflammation, which triggers TLR4 signaling. It has been demonstrated that ...

Fragile X syndrome, caused by the loss of FMR1 gene function and loss of fragile X mental retardation protein (FMRP), is the most commonly inherited form of mental retardation. The syndrome is characterized by associative learning deficits, reduced risk of cancer, dendritic spine dysmorphogenesis, and facial dysmorphism. However, the molecular mechanism that links loss of function of FMR1 to the learning disability remains unclear. Here, we report an examination of small GTPase Ras signaling and synaptic AMPA receptor (AMPA-R) trafficking in cultured slices and intact brains of wild-type and FMR1 knock-out mice. In FMR1 knock-out mice, synaptic delivery of GluR1-, but not GluR2L-and GluR4-containing AMPA-Rs is impaired, resulting in a selective loss of GluR1-dependent long-term synaptic potentiation (LTP). Although Ras activity is upregulated, its downstream MEK (extracellular signal-regulated kinase kinase)-ERK (extracellular signal-regulated kinase) signaling appears normal, and phosphoinositide 3-kinase (PI3K)-protein kinase B (PKB; or Akt) signaling is compromised in FMR1 knock-out mice. Enhancing Ras-PI3K-PKB signaling restores synaptic delivery of GluR1-containing AMPA-Rs and normal LTP in FMR1 knock-out mice. These results suggest aberrant Ras signaling as a novel mechanism for fragile X syndrome and indicate manipulating Ras-PI3K-PKB signaling to be a potentially effective approach for treating patients with fragile X syndrome.

Neurofibromatosis type 1 (NF1) is a dominant genetic disorder characterized by multiple benign and malignant nervous system tumors, and by learning defects in 45% of children with NF1 mutations. Studies of neurofibromin, the protein encoded by NF1, have focused on its functions in tumorigenesis and regulation of Ras activity; however, Drosophila NF1 regulates both Ras and cyclic AMP (cAMP) pathways. Expression of a human NF1 transgene rescued cAMP-related phenotypes in NF1 mutant flies (small body size and G protein-stimulated adenylyl cyclase (AC) activity defects), and neuropeptide- and G protein-stimulated AC activity were lower in Nf1-/- as compared to Nf1+/- mouse brains, demonstrating that neurofibromin regulates AC activity in both mammals and flies.

The related small GTPases Ras and Rap1 are important for signaling synaptic AMPA receptor (-R) trafficking during long-term potentiation (LTP) and long-term depression (LTD), respectively. Rap2, which shares 60% identity to Rap1, is present at excitatory synapses, but its functional role is unknown. Here, we report that Rap2 activity, stimulated by NR2A-containing NMDA-R activation, depresses AMPA-R-mediated synaptic transmission via activation of JNK rather than Erk1/2 or p38 MAPK. Moreover, Rap2 controls synaptic removal of AMPA-Rs with long cytoplasmic termini during depotentiation. Thus, Rap2-JNK pathway, which opposes the action of the NR2A-containing NMDA-R-stimulated Ras-ERK1/2 signaling and complements the NR2B-containing NMDA-R-stimulated Rap1-p38 MAPK signaling, channels the specific signaling for depotentiating central synapses.

Purpose: Tumor-initiating cells are resistant to chemotherapy, but how microRNAs play a role in regulating drug resistance of breast tumor-initiating cells (BT-IC) needs to be clarified.Experimental Design: Lentivirus-mediated miR-128 transduction was done in BT-ICs, enriched by mammosphere cultures or CD44 þ CD24 À fluorescence-activated cell sorting. Apoptosis and DNA damage were determined upon treatment with doxorubicin. Expression of miR-128 in breast cancer tissues was examined by in situ hybridization and correlated with breast tumor response to neoadjuvant chemotherapy and patient survival.Results: MiR-128 was significantly reduced in chemoresistant BT-ICs enriched from breast cancer cell lines and primary breast tumors (P < 0.01), accompanied by an overexpression of Bmi-1 and ABCC5, which were identified as targets of miR-128. Ectopic expression of miR-128 reduced the protein levels of Bmi-1 and ABCC5 in BT-ICs, along with decreased cell viability (P < 0.001) and increased apoptosis (P < 0.001) and DNA damage (P < 0.001) in the presence of doxorubicin. Reduced miR-128 expression in breast tumor tissues was associated with chemotherapeutic resistance (P < 0.001) and poor survival of breast cancer patients (P < 0.05; n = 57).Conclusions: Reduction in miR-128 leading to Bmi-1 and ABCC5 overexpression is a stem cell-like feature of BT-ICs, which contributes to chemotherapeutic resistance in breast cancers. Ectopic expression of miR-128 sensitizes BT-ICs to the proapoptotic and DNA-damaging effects of doxorubicin, indicating therapeutic potential. Clin Cancer Res; 17(22); 7105-15. Ó2011 AACR.

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