Analysis of procoagulant phosphatidylserine-exposing platelets by imaging flow cytometry.

Background: Upon platelet activation, a subpopulation of procoagulant platelets is formed, characterized by the exposure of the anionic aminophospholipid phosphatidylserine (PS) on the surface membrane.

Objective: To evaluate procoagulant PS-exposing platelets by imaging flow cytometry.

Methods: Platelet ultrastructure was examined by transmission electron microscopy, and a comprehensive analysis of procoagulant platelets was performed using imaging flow cytometry; platelets were fluorescently labeled for the markers glycoprotein (GP)IX, activated integrin αIIbβ3, CD62P, and PS exposure.

Tyrosine kinase receptor EGFR regulates the switch in cancer cells between cell survival and cell death induced by autophagy in hypoxia.

Autophagy is an intracellular lysosomal degradation pathway where its primary function is to allow cells to survive under stressful conditions. Autophagy is, however, a double-edge sword that can either promote cell survival or cell death. In cancer, hypoxic regions contribute to poor prognosis due to the ability of cancer cells to adapt to hypoxia in part through autophagy.

Palmitoylation supports the association of tetraspanin CD63 with CD9 and integrin alphaIIbbeta3 in activated platelets.

CD63 and CD9 are members of the tetraspanin superfamily of integral membrane proteins that function as organizers of multi-molecular signaling complexes involved in cell morphology, motility and proliferation. Tetraspanin complexes cluster dynamically in unique cholesterol-rich tetraspanin-enriched microdomains (TEMs). In resting platelets, CD63 is located in the membranes of lysosomes and dense granules.

Hypoxia induces autophagic cell death in apoptosis-competent cells through a mechanism involving BNIP3.

Hypoxia (lack of oxygen) is a physiological stress often associated with solid tumors. Hypoxia correlates with poor prognosis since hypoxic regions within tumors are considered apoptosisresistant. Autophagy (cellular "self digestion") has been associated with hypoxia during cardiac ischemia and metabolic stress as a survival mechanism.

Mitochondrial electron-transport-chain inhibitors of complexes I and II induce autophagic cell death mediated by reactive oxygen species.

Autophagy is a self-digestion process important for cell survival during starvation. It has also been described as a form of programmed cell death. Mitochondria are important regulators of autophagy-induced cell death and damaged mitochondria are often degraded by autophagosomes.

Platelet tetraspanin complexes and their association with lipid rafts.

Tetraspanins are a superfamily of integral membrane proteins that facilitate the organization of membrane and intracellular signaling molecules into dynamic signaling microdomains, tetraspanin-enriched microdomains (TEMs). Four tetraspanin family members have been identified in platelets: CD9, CD151 and TSSC6, which are constitutively associated with alphaIIbbeta3, and CD63, which is present on granule membranes in resting platelets and associates with alphaIIbbeta3-CD9 following platelet activation. CD63 and CD9 associate with a type II phosphatidylinositol 4-kinase, PI4K55, in both resting and activated platelets.

CD63 modulates spreading and tyrosine phosphorylation of platelets on immobilized fibrinogen.

CD63 is a member of the tetraspanin superfamily of integral membrane proteins. Present on a variety of cells, tetraspanins can form lateral associations with integrins and may act as 'organizers' of multimolecular networks that modulate integrinmediated signaling, cell morphology, motility and migration. In resting platelets, CD63 is present on the membranes of dense granules and lysosomes but relocates to the plasma membrane following platelet activation and exocytosis where it associates with the platelet integrin alphaIIBbeta3-CD9 complex and with the actin cytoskeleton in an alphaIIBbeta 3-dependent manner.

BNIP3 plays a role in hypoxic cell death in human epithelial cells that is inhibited by growth factors EGF and IGF.

Hypoxic regions within solid tumors are often resistant to chemotherapy and radiation. BNIP3 (Bcl-2/E1B 19 kDa interacting protein) is a proapoptotic member of the Bcl-2 family that is expressed in hypoxic regions of tumors. During hypoxia, BNIP3 expression is increased in many cell types and upon forced overexpression BNIP3 induces cell death.