Epidermal growth factor receptor and notch pathways participate in the tumor suppressor function of gamma-secretase

Gamma-secretase, a unique aspartyl protease, is required for the regulated intramembrane proteolysis of Notch and APP, pathways that are implicated, respectively, in the pathogenesis of cancer and Alzheimer disease. However, the mechanism whereby reduction of gamma-secretase causes tumors such as squamous cell carcinoma (SCC) remains poorly understood. Here, we demonstrate that gamma-secretase functions in epithelia as a tumor suppressor in an enzyme activity-dependent manner. Notch signaling is down-regulated and epidermal growth factor receptor (EGFR) is activated in SCC caused by genetic reduction of gamma-secretase. Moreover, the level of EGFR is inversely correlated with the level of gamma-secretase in fibroblasts, suggesting that the up-regulation of EGFR stimulates hyperproliferation in epithelia of mice with genetic reduction of gamma-secretase. Supporting this notion is our finding that the proliferative response of fibroblasts lacking gamma-secretase activity is more sensitive when challenged by either EGF or an inhibitor of EGFR as ompared with wild type cells. Interestingly, the up-regulation of EGFR is independent of Notch signaling, suggesting that the EGFR pathway functions in parallel with Notch in the tumorigenesis of SCC. Collectively, our results establish a novel mechanism linking the EGFR pathway to the tumor suppressor role of gamma-secretase and that mice with genetic reduction of gamma-secretase represent an excellent rodent model for clarifying pathogenesis of SCC and for testing therapeutic strategy to ameliorate this type of human cancer.     

Nonredundant role of Bax and Bak in Bid-mediated apoptosis

Animal models suggest that Bax and Bak play an essential role in the implementation of apoptosis and as a result can hinder tumorigenesis. We analyzed the expression of these proteins in 50 human glioblastoma multiforme (GBM) tumors. We found that all the tumors expressed Bak, while three did not express Bax. In vitro, Bax-deficient GBM (BdGBM) exhibited an important resistance to various apoptogenic stimuli (e.g., UV, staurosporine, and doxorubicin) compared to the Bax-expressing GBM (BeGBM). Using an antisense strategy, we generated Bak(-) BeGBM and Bak(-) BdGBM, which enabled us to show that the remaining sensitivity of the BdGBM to apoptosis was due to the overexpression of Bak. Bax/Bak single or double deficiency had no influence on either the clonogenicity or the growth of tumors in Swiss nude mice. Of note, Bak(-) BeGBM cells were resistant to apoptosis induced by caspase 8 (C8) but not to that induced by granzyme B (GrB). Cells lacking both Bax and Bak (i.e., Bak(-) BdGBM) were completely resistant to all stimuli including the microinjection of C8 and GrB. We show that GrB-cleaved Bid and C8-cleaved Bid differ in size and utilize preferentially Bax and Bak, respectively, to promote cytochrome c release from mitochondria. Our results suggest that Bax deficiency is compensated by an increase of the expression of Bak in GBM and show, for the first time in human cancer, that the double Bax and Bak deficiency severely impairs the apoptotic program.     

Ten polymorphic microsatellite loci isolated from the alpine caddisfly Allogamus uncatus Brauer (Trichoptera: Limnephilidae)

Here we report the development of 10 microsatellite loci for the alpine caddisfly, Allogamus uncatus. Polymorphism as detected in 24 individuals ranged from three to 17 alleles per locus, and observed heterozygosity ranged from 0.087 to 0.864. These primers will enable research on the genetic population structure of this species, the extent of gene flow among alpine permanent and temporary streams, and the genetic consequences of extinction/recolonization events.     

Characterization of cryobiological responses in TF-1 cells using interrupted freezing procedures

Cryopreservation currently is the only method for long-term preservation of cellular viability and function for uses in cellular therapies. Characterizing the cryobiological response of a cell type is essential in the approach to designing and optimizing cryopreservation protocols. For cells used in therapies, there is significant interest in designing cryopreservation protocols that do not rely on dimethyl sulfoxide (Me₂SO) as a cryoprotectant, since this cryoprotectant has been shown to have adverse effects on hematopoietic stem cell (HSC) transplant patients. This study characterized the cryobiological responses of the human erythroleukemic stem cell line TF-1, as a model for HSC. We measured the osmotic parameters of TF-1 cells, including the osmotically-inactive fraction, temperature-dependent membrane hydraulic conductivity and the membrane permeability to 1 M Me₂SO. A two-step freezing procedure (interrupted rapid cooling with hold time) and a graded freezing procedure (interrupted slow cooling without hold time) were used to characterize TF-1 cell recovery during various phases of the cooling process. One outcome of these experiments was high recovery of TF-1 cells cryopreserved in the absence of traditional cryoprotectants. The results of this study of the cryobiology of TF-1 cells will be critical for future understanding of the cryobiology of HSC, and to the design of cryopreservation protocols with specific design criteria for applications in cellular therapies.     

Soluble M1 protein of Streptococcus pyogenes triggers potent T cell activation

Streptococcus pyogenes of the M1 serotype is commonly associated with large outbreaks of invasive streptococcal infections and development of streptococcal toxic shock syndrome (STSS). The pathogenesis behind these infections is believed to involve bacterial superantigens that induce potent inflammatory responses, but the reason why strains of the M1 serotype are over-represented in STSS is still not understood. In the present investigation, we show that a highly purified soluble form of the M1 protein from S. pyogenes , which lacks the membrane-spanning region, is a potent inducer of T cell proliferation and release of Th1 type cytokines. M1 protein-evoked T cell proliferation was HLA class II-dependent but not MHC-restricted, did not require intracellular processing and was Vβ-restricted. Extensive mass spectrometry studies indicated that there were no other detectable proteins in the preparation. Taken together, our data demonstrate that soluble M1 protein is a novel streptococcal superantigen, which likely contributes to the excessive T cell activation and hyperinflammatory response seen in severe invasive streptococcal infections.     

Mycorrhiza Symbiosis Increases the Surface for Sunlight Capture in Medicago truncatula for Better Photosynthetic Production

Arbuscular mycorrhizal (AM) fungi play a prominent role in plant nutrition by supplying mineral nutrients, particularly inorganic phosphate (P_i), and also constitute an important carbon sink. AM stimulates plant growth and development, but the underlying mechanisms are not well understood. In this study, Medicago truncatula plants were grown with Rhizophagus irregularis BEG141 inoculum (AM), mock inoculum (control) or with P_i fertilization. We hypothesized that AM stimulates plant growth through either modifications of leaf anatomy or photosynthetic activity per leaf area. We investigated whether these effects are shared with P_i fertilization, and also assessed the relationship between levels of AM colonization and these effects. We found that increased P_i supply by either mycorrhization or fertilization led to improved shoot growth associated with increased nitrogen uptake and carbon assimilation. Both mycorrhized and P_i-fertilized plants had more and longer branches with larger and thicker leaves than the control plants, resulting in an increased photosynthetically active area. AM-specific effects were earlier appearance of the first growth axes and increased number of chloroplasts per cell section, since they were not induced by P_i fertilization. Photosynthetic activity per leaf area remained the same regardless of type of treatment. In conclusion, the increase in growth of mycorrhized and P_i-fertilized Medicago truncatula plants is linked to an increase in the surface for sunlight capture, hence increasing their photosynthetic production, rather than to an increase in the photosynthetic activity per leaf area.     

Synthesis and evaluation of 4-(1-aminoalkyl)-N-(4-pyridyl)cyclohexanecarboxamides as Rho kinase inhibitors and neurite outgrowth promoters

The influence of stereochemistry and alkyl side chain length on the bioactivity of the Rho kinase inhibitor Y-27632 [(+)-1, R=Me] was examined by the synthesis of (+)- and (-)-1, and two alkyl chain analogs (+)- and (-)-2 (R=n-propyl) and (-)-3 (R=n-octyl) as well as their evaluation in enzymatic and neurite outgrowth assays.     

Specificity and reactive loop length requirements for crmA inhibition of serine proteases

The viral serpin, crmA, is distinguished by its small size and ability to inhibit both serine and cysteine proteases utilizing a reactive loop shorter than most other serpins. Here, we characterize the mechanism of crmA inhibition of serine proteases and probe the reactive loop length requirements for inhibition with two crmA reactive loop variants. P1 Arg crmA inhibited the trypsin-like proteases, thrombin, and factor Xa, with moderate efficiencies (approximately 10(2)-10(4) M(-1)sec(-1)), near equimolar inhibition stoichiometries, and formation of SDS-stable complexes which were resistant to dissociation (k(diss) approximately 10(-7) sec(-1)), consistent with a serpin-type inhibition mechanism. Trypsin was not inhibited, but efficiently cleaved the variant crmA as a substrate (k(cat)/K(M) of approximately 10(6) M(-1) sec(-1)). N-terminal sequencing confirmed that the P1 Arg-P1'Cys bond was the site of cleavage. Altering the placement of the Arg in a double mutant P1 Gly-P1'Arg crmA resulted in minimal ability to inhibit any of the trypsin family proteases. This variant was cleaved by the proteases approximately 10-fold less efficiently than P1 Arg crmA. Surprisingly, pancreatic elastase was rapidly inhibited by wild-type and P1 Arg crmAs (10(5)-10(6) M(-1)sec(-1)), although with elevated inhibition stoichiometries and higher rates of complex dissociation. N-terminal sequencing showed that elastase attacked the P1'Cys-P2'Ala bond, indicating that crmA can inhibit proteases using a reactive loop length similar to that used by other serpins, but with variations in this inhibition arising from different effective P2 residues. These results indicate that crmA inhibits serine proteases by the established serpin conformational trapping mechanism, but is unusual in inhibiting through either of two adjacent reactive sites.