[Abstract unavailable

Amyloid beta (Abeta) 1–42 oligomers accumulate in brains of patients with Mild Cognitive Impairment (MCI) and disrupt synaptic plasticity processes that underlie memory formation. Synaptic binding of Abeta oligomers to several putative receptor proteins is reported to inhibit long-term potentiation, affect membrane trafficking and induce reversible spine loss in neurons, leading to impaired cognitive performance and ultimately to anterograde amnesia in the early stages of Alzheimer's disease (AD). We have identified a receptor not previously associated with AD that mediates the binding of Abeta oligomers to neurons, and describe novel therapeutic antagonists of this receptor capable of blocking Abeta toxic effects on synapses in vitro and cognitive deficits in vivo. Knockdown of sigma-2/PGRMC1 (progesterone receptor membrane component 1) protein expression in vitro using siRNA results in a highly correlated reduction in binding of exogenous Abeta oligomers to neurons of more than 90%. Expression of sigma-2/PGRMC1 is upregulated in vitro by treatment with Abeta oligomers, and is dysregulated in Alzheimer's disease patients' brain compared to age-matched, normal individuals. Specific, high affinity small molecule receptor antagonists and antibodies raised against specific regions on this receptor can displace synthetic Abeta oligomer binding to synaptic puncta in vitro and displace endogenous human AD patient oligomers from brain tissue sections in a dose-dependent manner. These receptor antagonists prevent and reverse the effects of Abeta oligomers on membrane trafficking and synapse loss in vitro and cognitive deficits in AD mouse models. These findings suggest sigma-2/PGRMC1 receptors mediate saturable oligomer binding to synaptic puncta on neurons and that brain penetrant, small molecules can displace endogenous and synthetic oligomers and improve cognitive deficits in AD models. We propose that sigma-2/PGRMC1 is a key mediator of the pathological effects of Abeta oligomers in AD and is a tractable target for small molecule disease-modifying therapeutics.

The focal adhesion kinase (FAK) is a mediator of cellextracellular matrix signaling events and is overexpressed in tumor cells. In order to rapidly down-regulate FAK function in normal and transformed mammary cells, we have used adenoviral gene transduction of the carboxyl-terminal domain of FAK (FAK-CD). Transduction of adenovirus containing FAK-CD in breast cancer cells caused loss of adhesion, degradation of p125FAK , and induced apoptosis. Furthermore, breast tumor cells that were viable without matrix attachment also underwent apoptosis upon interruption of FAK function, demonstrating that FAK is a survival signal in breast tumor cells even in the absence of matrix signaling. In addition, both anchorage-dependent and anchorage-independent apoptotic signaling required Fas-associated death domain and caspase-8, suggesting that a death receptor-mediated apoptotic pathway is involved. Finally, FAK-CD had no effect on adhesion or viability in normal mammary cells, despite the loss of tyrosine phosphorylation of p125 FAK . These results indicate that FAKmediated signaling is required for both cell adhesion and anchorage-independent survival and the disruption of FAK function involves the Fas-associated death domain and caspase-8 apoptotic pathway.As normal epithelial cells become transformed and develop the capacity for invasion and metastasis, they must acquire the property of anchorage-independent growth. This is essential for tumor cells to survive the apoptotic stimuli associated with the loss of adhesion, proteolysis, and migration through their extracellular matrix (ECM) 1 (1, 2). Oncogenic transformation has been shown to suppress apoptosis as a means of enhancing tumor cell survival (3-6). Cells from human tumors have been shown to be more resistant to apoptotic stimuli than normal cells (7). Normal cells undergo apoptosis when they lose ECM adhesion, and this phenomenon has been termed "anoikis" (8, 9). Tumor cells have been thought to be resistant to anoikis, thus allowing them to grow in an anchorage-independent fashion. One of the critical signaling molecules involved in both cell-ECM interactions and anoikis is the focal adhesion kinase (FAK) (10), a tyrosine kinase that localizes to focal adhesions (11,12). Previous studies have shown that FAK is overexpressed in breast, colon, and thyroid cancers (13-17), whereas normal tissues express little detectable FAK. The overexpression of FAK in tumors is likely to affect three functions as follows: motility, adhesion, and survival. FAK is thought to play a role in adhesion-mediated survival because overexpression of a constitutively activated form of FAK in Madin-Darby canine kidney cells has been shown to confer resistance to apoptosis following loss of adherence (10). FAK overexpression in Chinese hamster ovary (CHO) cells caused an increase in migration (18), suggesting that FAK may play a role in motility of CHO cells. Although these experiments were performed in normal cells, they raise the possibility that tumor cells upregulate FAK expression in ord...

Summary Expression of PTEN tumor suppressor is frequently lost in breast cancer in the absence of mutation or promoter methylation through as yet undetermined mechanisms. In this study, we demonstrated that the Rak tyrosine kinase physically interacts with PTEN and phosphorylates PTEN on Tyr 336. The knockdown of Rak enhanced the binding of PTEN to its E3 ligase, NEDD4-1, and promoted PTEN polyubiquitination, leading to PTEN protein degradation. Notably, ectopic expression of Rak effectively suppressed breast cancer cell proliferation, invasion, and colony formation in vitro and tumor growth in vivo. Furthermore, Rak knockdown was sufficient to transform normal mammary epithelial cells. Therefore, Rak acts as a bona fide tumor suppressor gene through the mechanism of regulating PTEN protein stability and function.

No abstract

Summary Hormone signaling is important in a number of disease states, and hormone receptors are effective therapeutic targets. PGRMC1 (progesterone receptor membrane component 1) is a member of a multi-protein complex that binds to progesterone and other steroids, as well as pharmaceutical compounds. In spite of its name, PGRMC1 shares homology with cytochrome b5-related proteins rather than hormone receptors, and heme binding is the sole biochemical activity of PGRMC1. PGRMC1 and its homologues regulate cholesterol synthesis by activating the P450 protein Cyp51/lanosterol demethylase, and the cholesterol synthetic pathway is an important target in cardiovascular disease and in treating infections. PGRMC1 binding partners include multiple P450 proteins, PAIR-BP1, Insig, and an uncharacterized hormone/drug-binding protein. PGRMC1 is induced in a spectrum of cancers, where it promotes cell survival and damage resistance, and PGRMC1 is also expressed in the nervous system and tissues involved in drug metabolism, cholesterol synthesis and hormone synthesis and turnover. One of the appealing features of PGRMC1 and its associated protein complex is its affinity for steroids and drugs. Together with its biological role in promoting tumor survival, PGRMC1 is an attractive target for therapeutic intervention in cancer and related malignancies.

Tumorigenesis requires the concerted action of multiple pathways, including pathways that stimulate proliferation and increase metabolism. Progesterone receptor membrane component 1 (Pgrmc1) is related to cytochrome b 5 , binds to heme, and is associated with DNA damage resistance and apoptotic suppression. Pgrmc1 is induced by carcinogens, including dioxin, and is up-regulated in multiple types of cancer. In the present study, we found that Pgrmc1 increased in vivo tumor growth, anchorage-independent growth, and migration. Pgrmc1 also promoted proliferation in the absence of serum in A549 non-small cell lung cancer cells but enhanced proliferation regardless of serum concentration in MDA-MB-468 breast cancer cells. Pgrmc1 promotes cholesterol synthesis and binds to Insig (insulininduced gene), Scap (sterol regulatory element binding protein cleavage activating protein), and P450 proteins, but Pgrmc1 did not affect cholesterol synthesis in lung cancer cells. Pgrmc1 is also associated with progesterone signaling and plasminogen activator inhibitor (PAI1) RNA binding protein, but neither progesterone activity nor PAI1 transcript levels were altered in Pgrmc1-knockdown lung cancer cells. Pgrmc1 homologues bind to aryl ligands identified in an in silico screen, and we have found that a Pgrmc1 ligand induced cell death in a Pgrmc1-specific manner in multiple breast and lung tumor cell lines. Our data support a role for Pgrmc1 in promoting cancer-associated phenotypes and provide a therapeutic approach for targeting Pgrmc1 with a small molecule in lung and breast cancer.

Focal adhesion kinase (FAK) is a nonreceptor protein tyrosine kinase that plays a key role in maintaining focal adhesion function and cell survival and is implicated in cell migration, adhesion, and cell cycle control (9,13,18,20,33,44). Overexpression of FAK is a common event in numerous tumor systems, including breast, colon, and thyroid carcinomas (2,24,32,41), and occurs at early stages of tumorigenesis, before a tumor has developed the capacity for invasion and metastasis (2). Importantly, FAK has been shown to be one of the critical factors protecting cells from apoptosis, but the exact mechanism is unknown (8,9,12,19,37,43). Attenuation of FAK expression by antisense oligonucleotides led to apoptosis in tumor cells (42), and the treatment of cells with anti-FAK antibody (18, 26) or overexpression of the focal adhesion targeting (FAT) domain of FAK led to cell rounding, detachment, and apoptosis (19,21,40). We have created a model system for the attenuation of FAK function by adenoviral gene transduction of the carboxy-terminal domain of FAK (FAK-CD) and have demonstrated a loss of adhesion and apoptosis in breast cancer cells with this treatment (43). Both anchoragedependent and anchorage-independent apoptotic signaling required Fas-associated death domain protein (FADD) and caspase 8, suggesting an important role for FAK in inhibiting death receptor-related apoptosis (43). This finding provided additional evidence that a death receptor-mediated apoptotic pathway or death receptor-related death domain proteins are involved in the apoptotic process triggered by the expression of FAK-CD.The loss of adhesion and induction of apoptosis upon attenuation of FAK function by the expression of FAK-CD is similar to the phenomenon of anoikis (7-9). Intriguingly, there is evidence for the involvement of death receptor-related, death domain-containing proteins in anoikis (7, 35), whereby the silencer of death domain (SODD) and dominant-negative FADD efficiently inhibited anoikis in Madin-Darby canine kidney (MDCK) cells and in a number of untransformed epithelial cell lines. In these studies, it was also shown that cell matrix detachment activated caspase 8. However, the linkage of the signaling pathways to the death receptors remains unknown.RIP is a serine/threonine kinase that contains a death domain (17, 38) and is named for its association with the death receptor complex. RIP interacts with the death domains of cell surface receptors of the tumor necrosis factor (TNF) superfamily and death domain adaptor proteins (3,5,17) and plays an indispensable role in 39). Recently, it was shown that TNF alpha-mediated activation of NF-B depends on the association of RIP and FAK (11). TNF-induced NF-B DNA binding activity and activation of IB kinases were markedly impaired in FAK Ϫ/Ϫ cells (11). However, it has been well established that RIP has a dual function and is capable of either inducing apoptosis or activating cellular survival signals (14,17,23,27,38,39). Similarly, it has been proposed that RIP is one of the switch...