Cell death beyond apoptosis

Flow cytometry in analysis of cell cycle and apoptosis

The capacity for multiparametric measurement of large cell populations rapidly and accurately offered by cytometry has made this methodology indispensable in studies of cell proliferation and cell death. The reviewed cell cycle applications include (1) the univariate analysis of cellular DNA content for identification of G(0/1) versus S versus G(2)/M cells; (2) discrimination between noncycling (G(0); quiescent) and proliferating cells, based on the presence of proliferation-associated proteins; (3) identification of mitotic cells by histone H3 phosphorylation; (4) bivariate analysis of expression of cyclins D, E, A, or B1 versus DNA content; and (5) detection of DNA replicating cells and analysis of cell kinetics from the bivariate distributions of 5-bromo-2'-deoxyuridine (BrdU) incorporation versus DNA content. For the identification of apoptotic cells and discrimination between apoptosis and necrosis, flow cytometry techniques are applied to evaluate for changes in cell morphology, the presence of phosphatidylserine on cell surface, collapse of mitochondrial transmembrane potential, DNA fragmentation, and evidence of caspase activation. Semin Hematol 38:179-193.

Dissecting the pathways to death

This report summarizes recent findings in the field of basic and translational apoptosis research which were presented at the 1st Conference on 'Mechanisms of Cell Death and Disease: Advances in Therapeutic Intervention' organized by the European School of Hematology and the University of Texas MD Anderson Cancer Center, 13-17 May, in Dublin, Ireland, and puts them in the context of the literature. Recent discoveries have significantly advanced the understanding of biochemical and genetic requirements of distinct apoptosis pathways (ie mitochondrial, death-receptor and endoplasmic reticulum-mediated apoptosis) and their dysregulation in disease. Progress has been made especially in the elucidation of the mechanisms of action of the Bcl-2 family members, in detail the formation of channels and their regulation in the mitochondrial membranes, conformational changes in Bax and Bak, and crosstalk of death receptor-triggered apoptosis to the mitochondria by activation of Bax via Bid. In addition, novel insights have been gained about the regulation of caspases and novel caspase signaling pathways, such as activation of caspase-12 by the endoplasmic reticulum stress response. Therapeutic applications of apoptosis manipulation include (1) the inhibition of caspases in acute and chronic neurodegenerative diseases, ie stroke, Alzheimer's or Huntington's disease by drugs and (2) sensitization of cancer cells for drug/radiation-induced apoptosis by modulation of survival signals and viral transfer of apoptosis promoting genes.

Kinases: positive and negative regulators of apoptosis

Cells sense and respond to extracellular factors via receptors on the cell surface that trigger intracellular signaling pathways. The signals received by the receptors on hematopoietic cells often determine if the cell proliferates, survives or undergoes apoptosis. Apoptosis can be induced by almost any cytotoxic stimuli. These stimuli may be an absence of signals arising from cellular receptors, stimulation of specific ligand receptors on the cell surface, chemotherapeutic agents, and ionizing radiation or oxygen radicals, as well as a number of other factors. Cellular kinases and phosphatases participate in signaling cascades that influence this process. We review the ability of the calmodulin-dependent-kinases, I-kappaB kinases, PI3-kinases, Jakkinases, PKC, PKA, and MAP kinase signaling pathways (Erk, Jnk, and p38), to influence the apoptotic process. In addition, we discuss the cross-talk that exists between signaling cascades that are pro-apoptotic and anti-apoptotic.