Different modes of regulated cell death (RCD) can be initiated by distinct molecular machineries and their morphological manifestations can be diffi cult to discriminate. Moreover, cells responding to stress often activate an adaptive response centered around autophagy, and whether such a response is cytoprotective or cytotoxic cannot be predicted based on morphological parameters only. Molecular defi nitions are therefore important to understand various RCD subroutines from a mechanistic perspective. In vitro, various forms of RCD including apoptosis and autophagic cell death can be easily discriminated from each other with assays that involve chemical or pharmacological interventions targeting key components of either pathway. Here, we detail a straightforward method to discriminate apoptosis from autophagic cell death by fl ow cytometry, based on the broad-spectrum caspase inhibitor Z-VAD-fmk and the genetic inhibition of ATG5.

Programmed Cell Death

In metazoans, cyclin-dependent kinase 7 (CDK7) has essential roles in both the cell-division cycle and transcription, as a CDK-activating kinase (CAK) and as a component of the general transcription factor TFIIH, respectively. Controversy over its double duty has been resolved, but questions remain. First, how does CDK7 achieve the dual substrate specificity necessary to perform both roles? Second, is there a deeper connection implied by the dichotomy of CDK7 function, for example similar mechanisms controlling cell division and gene expression, and/or actual coordination of the two processes? Enzymological studies have revealed solutions to the unusual substrate recognition problem, and there is evidence that the distinct functions of CDK7 can be regulated independently. Finally, despite divergence in their wiring, the CAK-CDK networks of budding yeast, fission yeast and metazoans all link transcriptional regulation with operation of the cell-cycle machinery. This connection might help to ensure that mRNAs encoding effectors of cell division are expressed at the right time in the cycle.

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Secrets of a double agent: CDK7 in cell-cycle control and transcription

Chk1 suppresses a caspase-2 apoptotic response to dna damage that bypasses p53, bcl-2 and caspase-3

Mass Spectrometric Mapping of Linker Histone H1 Variants Reveals Multiple Acetylations, Methylations, and Phosphorylation as Well as Differences between Cell Culture and Tissue

Polo-like kinases (PLKs) are a group of highly conserved serine/threonine protein kinases that play a key role in processes such as cell division and checkpoint regulation of mitosis. About 80% of human tumors, of various origins, express high levels of PLK transcripts. However, PLK mRNA is mostly absent in surrounding healthy tissues. Overexpression of PLK is associated with a poor prognosis in several tumor types and a lower overall survival rate. The overexpression of PLKs in human tumors, but not in healthy nondividing cells, makes them an attractive, selective target for cancer drug development. PLK inhibitors interfere with different stages of mitosis, such as centrosome maturation, spindle formation, chromosome separation, and cytokinesis. They induce mitotic chaos and severely perturb cell cycle progression, eventually leading to cancer cell death. Several PLK inhibitors are in development and are undergoing evaluations as potential cancer treatments. This review includes an overview of PLK inhibitors in early clinical development (i.e., BI 2536, BI 6727, GSK461364, ON 019190.Na, and HMN-214) and in advanced preclinical development (i.e., ZK-thiazolidinone, NMS-1, CYC-800, DAP-81, and LC-445). If proof of principle is confirmed in large studies, PLK inhibitors will offer a new targeted antitumor therapy for cancer patients.

Polo-Like Kinase (PLK) Inhibitors in Preclinical and Early Clinical Development in Oncology

Drosophila researchers met in sunny San Diego for the 49th annual meeting of The Genetics Society of America. It was cold outside and even colder inside. Like last year, ‘Mitosis, Meiosis and Cell Division’ was no longer a session. Instead, we searched out and covered talks and posters in ‘Cell Division and Growth Control’, ‘Gametogenesis’, ‘Cytoskeleton and Cell Biology’ and ‘Genome and Chromosome Structure’. We split up for maximal coverage and re-grouped later for the Workshop on Cell Cycle and Checkpoints. We apologize in advance for the brevity or omission of some reports.

Cell cycle regulation.

Ionizing radiation (IR) can induce apoptosis via p53, which is the most commonly mutated gene in human cancers Loss of p53, however, can render cancer cells refractory to therapeutic effects of IR Alternate p53-independent pathways exist but are not as well understood as p53-dependent apoptosis Studies of how IR induces p53-independent cell death could benefit from the existence of a genetically tractable model In Drosophila melanogaster, IR induces apoptosis in the imaginal discs of larvae, typically assayed at 4–6 hr after exposure to a LD50 dose In mutants of Drosophila Chk2 or p53 homologs, apoptosis is severely diminished in these assays, leading to the widely held belief that IR-induced apoptosis depends on these genes in Drosophila In this article, we show that IR-induced apoptosis still occurs in the imaginal discs of chk2 and p53 mutant larvae, albeit with a delay We demonstrate that this phenomenon is a true apoptotic response because it requires caspase activity and the chromosomal locus that encodes the pro-apoptotic genes reaper, hid, and grim We also show that Chk2- and p53-independent apoptosis is IR dose-dependent and is therefore probably triggered by a DNA damage signal We conclude that Drosophila has Chk2- and p53-independent pathways to activate caspases and induce apoptosis in response to IR This work establishes Drosophila as a model for p53-independent apoptosis, which is of potential therapeutic importance for inducing cell death in p53-deficient cancer cells

https://www.pnas.org/content/pnas/103/26/9952.full.pdf

Anita Wichmann

Papers

Cell cycle regulation.

Ionizing radiation induces caspase-dependent but Chk2- and p53-independent cell death in Drosophila melanogaster

Modulation of ionizing radiation-induced apoptosis by bantam microRNA in Drosophila.

E2F1 and E2F2 have opposite effects on radiation-induced p53-independent apoptosis in Drosophila.