Ca2+-induced apoptosis through calcineurin dephosphorylation of BAD.
ABSTRACT The Ca2+-activated protein phosphatase calcineurin induces apoptosis, but the mechanism is unknown. Calcineurin was found to dephosphorylate BAD, a pro-apoptotic member of the Bcl-2 family, thus enhancing BAD heterodimerization with Bcl-xL and promoting apoptosis. The Ca2+-induced dephosphorylation of BAD correlated with its dissociation from 14-3-3 in the cytosol and translocation to mitochondria where Bcl-xL resides. In hippocampal neurons, L-glutamate, an inducer of Ca2+ influx and calcineurin activation, triggered mitochondrial targeting of BAD and apoptosis, which were both suppressible by coexpression of a dominant-inhibitory mutant of calcineurin or pharmacological inhibitors of this phosphatase. Thus, a Ca2+-inducible mechanism for apoptosis induction operates by regulating BAD phosphorylation and localization in cells.
SourceAvailable from: Antonella Maffei[Show abstract] [Hide abstract]
ABSTRACT: Human islet β-cells exploit an autocrine dopamine mediated inhibitory circuit to regulate insulin secretion. β-cells also express the dopamine active transporter (DAT) and the large neutral amino acid transporter heterodimer enabling them to import circulating dopamine (DA) or its biosynthetic precursor, L-3,4-dihydroxyphenylalanine (L-DOPA). The capacity to import DA or L-DOPA from the extracellular space possibly indicates that DA may be an endocrine signal as well. In humans, a mixed meal stimulus is accompanied by contemporary serum excursions of incretins, DA and L-DOPA, suggesting that DA may act as an anti-incretin as postulated by the foregut hypothesis proposed to explain the early effects of bariatric surgery on type 2 diabetes. In this report, we take a translational step backwards and characterize the kinetics of plasma DA and incretin production following a mixed meal challenge in a rat model and study the integration of incretin and DA signaling at the biochemical level in a rodent β-cell line and islets. We found that there are similar excursions of incretins and DA in rats, as those reported in humans, following a mixed meal challenge and that DA counters incretin enhanced Glucose stimulated insulin secretion (GSIS) and intracellular signaling at multiple points from dampening calcium fluxes to inhibiting proliferation as well as apoptosis. Our data suggest that DA is an important regulator of insulin secretion and may represent one axis of a gut level circuit of Glucose and β-cell mass homeostasis.Molecular Endocrinology 03/2015; DOI:10.1210/me.2014-1273 · 4.20 Impact Factor
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ABSTRACT: The members of the Bcl-2 family of proteins are crucial regulators of apoptosis. In order to determine cell fate, these proteins must be targeted to distinct intracellular membranes, including the mitochondrial outer membrane (MOM), the membrane of the endoplasmic reticulum (ER) and its associated nuclear envelope. The targeting sequences and mechanisms that mediate the specificity of these proteins for a particular cellular membrane remain poorly defined. Several Bcl-2 family members have been reported to be tail-anchored via their predicted hydrophobic COOH-terminal transmembrane domains (TMDs). Tail-anchoring imposes a posttranslational mechanism of membrane insertion on the already folded protein, suggesting that the transient binding of cytosolic chaperone proteins to the hydrophobic TMD may be an important regulatory event in the targeting process. The TMD of certain family members is initially concealed and only becomes available for targeting and membrane insertion in response to apoptotic stimuli. These proteins either undergo a conformational change, posttranslational modification or a combination of these events enabling them to translocate to sites at which they are functional. Some Bcl-2 family members lack a TMD, but nevertheless localize to the MOM or the ER membrane during apoptosis where they execute their functions. In this review, we will focus on the intracellular targeting of Bcl-2 family members and the mechanisms by which they translocate to their sites of action. Furthermore, we will discuss the posttranslational modifications which regulate these events.Biochimica et Biophysica Acta (BBA) - Molecular Cell Research 03/2004; 1644(2-3):95-105. DOI:10.1016/S0167-4889(03)00176-9 · 5.30 Impact Factor
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ABSTRACT: INTRODUCTION Breast cancer is the most significant worldwide health problem in women >35-40 years of age. In addition, breast cancer accounts for ~1.35 million new cases and >450,000 cancer-related mortalities annually worldwide . Despite improved early detection, treatment options, and survival, the morbidity and mortality continue to increase, and numerous patients with invasive breast cancer develop metastatic diseases. Thus, there is an urgent requirement to search for and identify novel biomarkers to predict tumor recurrence and metastasis and to develop more novel treatment strategies to effectively control aggressive breast cancers . An important feature of the signal transduction pathway in cancer is reversible serine/threonine phosphorylation of proteins and any aberrant activity in the kinases or phosphatases can disturb the phosphorylation/dephosphorylation cycle leading to uncontrolled proliferation. Therefore, identification of key signaling molecules (kinases and phosphatases) responsible for neoplastic development can have potential clinical relevance allowing for diagnosis, early detection and intervention . Calcineurin (CN) is a Ca 2+ and calmodulin dependent serine/threonine protein phosphatase . CN is a heterodimer with a 61 kDa catalytic A subunit (CnA) and a 19 kDa regulatory B subunit (CnB). The B subunit has four Ca 2+ binding sites and has generally been thought of as only regulating CnA . ABSTRACT Background: Calcineurin (CN) is a Ca