Consequences of Shb and c-Abl interactions for cell death in response to various stress stimuli.
ABSTRACT The adaptor protein Shb has previously been shown to regulate apoptosis in response to cytokines and inhibitors of angiogenesis although the mechanisms governing these effects have remained obscure. We currently demonstrate interactions between Shb and c-Abl and that Shb regulates c-Abl kinase activity. The data suggest that c-Abl binds to tyrosine phosphorylated Shb via a concerted effort involving both the c-Abl SH3 and SH2 domains. The biological significance of the Shb/c-Abl interaction was presently tested in overexpression experiments and was found to promote hydrogen peroxide-induced cell death. We also show by Shb knockdown experiments that Shb regulates c-Abl activity and modulates cell death in response to the genotoxic agent cisplatin and the endoplasmic reticulum stress-inducer tunicamycin. The findings are in agreement with the notion of Shb playing a pivotal role in modulating c-Abl pro-apoptotic signaling in response to various stress stimuli.
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ABSTRACT: Cisplatin continues to be one of the cornerstone drugs in modern chemotherapy thus playing an important role among cytotoxic agents in the treatment of epithelial malignancies. Cisplatin damages, indiscriminately, cancerous and normal tissue. Its severe side effects arise from induction of apoptosis in various cell types in normal tissue in treated patients especially in peripheral nerves, renal tubules, bone marrow and gastrointestinal tract. Apoptosis may arise from the modulation of a number of signaling pathways by cisplatin including the mitochondrial pathway, the DNA damage signaling, stress-related signals, the ERK pathway and others. Patented platform technologies have been used for the liposomal encapsulation of cisplatin (Lipoplatin™) into tumor targeted 110-nm in diameter nanoparticles. Based on the molecular mechanisms of cisplatin including active import / export across the cell membrane, signaling pathway modulation and DNA damage an attempt is made to speculate on the molecular mechanisms of Lipoplatin™. The advantage of Lipoplatin™ over cisplatin is suggested to result from the ability of Lipoplatin™ to target primary tumors and metastases using the permeability of the vasculature of the growing tumor for its preferential extravasation and to cause a greater damage to tumor tissue compared to normal tissue as demonstrated in human studies. The nanoparticles are then avidly taken up by the tumors either via phagocytosis or by direct fusion with the cell membrane. The two mechanisms result to an overall 10 to 400-fold higher intracellular uptake of total platinum in tumor cells compared to cells in normal tissue in human studies. Animal studies shown here suggest that genes wrapped up in Lipoplatin™ shells target not only the tumors after systemic delivery but also their vasculature and result in the expression of a functional gene product after crossing the cell membrane barrier. It is being inferred that Lipoplatin™ is endowed with the properties of cisplatin plus the ability of its nanoparticles to target and kill endothelial cells of tumor vasculature suggesting that this drug has two properties, that of a chemotherapy drug and that of an antiangiogenesis agent, combined together. Lipoplatin™ is finishing successfully two non-inferiority phase III clinical trials as first line treatment against non-small cell lung cancer (NSCLC) and has received the orphan drug designation by EMEA against pancreatic cancer.Cancer therapy 01/2007; 5:349-376.
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ABSTRACT: The Src homology-2 domain protein B (Shb) is an adapter protein operating downstream of several tyrosine kinase receptors and consequently Shb regulates various cellular responses. Absence of Shb was recently shown to reduce hematopoietic stem cell proliferation through activation of focal adhesion kinase (FAK) and thus we sought to investigate Shb's role in the progression of leukemia.Journal of hematology & oncology. 06/2014; 7(1):45.
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ABSTRACT: The widely expressed adaptor protein Shb has previously been reported to contribute to T cell function due to its association with the T cell receptor and furthermore, several of Shb's known interaction partners are established regulators of blood cell development and function. In addition, Shb deficient embryonic stem cells displayed reduced blood cell colony formation upon differentiation in vitro. The aim of the current study was therefore to explore hematopoietic stem and progenitor cell function in the Shb knockout mouse. Shb deficient bone marrow contained reduced relative numbers of long-term hematopoietic stem cells (LT-HSCs) that exhibited lower proliferation rates. Despite this, Shb knockout LT-HSCs responded promptly by entering the cell cycle in response to genotoxic stress by 5-fluorouracil treatment. In competitive LT-HSC transplantations, Shb null cells initially engrafted as well as the wild-type cells but provided less myeloid expansion over time. Moreover, Shb knockout bone marrow cells exhibited elevated basal activities of focal adhesion kinase/Rac1/p21-activated kinase signaling and reduced responsiveness to Stem Cell Factor stimulation. Consequently, treatment with a focal adhesion kinase inhibitor increased Shb knockout LT-HSC proliferation. The altered signaling characteristics thus provide a plausible mechanistic explanation for the changes in LT-HSC proliferation since these signaling intermediates have all been shown to participate in LT-HSC cell cycle control. In summary, the loss of Shb dependent signaling in bone marrow cells, resulting in elevated focal adhesion kinase activity and reduced proliferative responses in LT-HSCs under steady state hematopoiesis, confers a disadvantage to the maintenance of LT-HSCs over time.Experimental Cell Research 03/2013; · 3.56 Impact Factor