Highlights d Mitochondrial heterogeneity reveals fundamental metabolic properties of HSCs d Lysosomal repression enhances HSC quiescence and potency d Active, but not quiescent, HSCs use glycolysis as their main source of energy d Label-retaining dormant HSCs and low-MMP HSCs exhibit overlapping molecular signatures

p53 is a tumor suppressor protein that prevents oncogenic transformation and maintains genomic stability by blocking proliferation of cells harboring unrepaired or misrepaired DNA. A wide range of genotoxic stresses such as DNA damaging anti-cancer drugs and ionizing radiation promote nuclear accumulation of p53 and trigger its ability to activate or repress a number of downstream target genes involved in various signaling pathways. This cascade leads to the activation of multiple cell cycle checkpoints and subsequent cell cycle arrest, allowing the cells to either repair the DNA or undergo apoptosis, depending on the intensity of DNA damage. In addition, p53 has many transcription-independent functions, including modulatory roles in DNA repair and recombination. This chapter will focus on the role of p53 in regulating or influencing the repair of DNA double-strand breaks that mainly includes homologous recombination repair (HRR) and non-homologous end joining (NHEJ). Through this discussion, we will try to establish that p53 acts as an important linchpin between upstream DNA damage signaling cues and downstream cellular events that include repair, recombination, and apoptosis.

TriplatinNC is a highly positively charged, substitution-inert derivative of the phase II clinical anticancer drug, BBR3464. Such substitution-inert complexes form a distinct subset of polynuclear platinum complexes (PPCs) interacting with DNA and other biomolecules through noncovalent interactions. Rapid cellular entry is facilitated via interaction with cell surface glycosoaminoglycans and is a mechanism unique to PPCs. Nanoscale secondary ion mass spectrometry (nanoSIMS) showed rapid distribution within cytoplasmic and nucleolar compartments, but not the nucleus. In this article, the downstream effects of nucleolar localization are described. In human colon carcinoma cells, HCT116, the production rate of 47S rRNA precursor transcripts was dramatically reduced as an early event after drug treatment. Transcriptional inhibition of rRNA was followed by a robust G1 arrest, and activation of apoptotic proteins caspase-8, -9, and -3 and PARP-1 in a p53-independent manner. Using cell synchronization and flow cytometry, it was determined that cells treated while in G1 arrest immediately, but cells treated in S or G2 successfully complete mitosis. Twenty-four hours after treatment, the majority of cells finally arrest in G1, but nearly one-third contained highly compacted DNA; a distinct biological feature that cannot be associated with mitosis, senescence, or apoptosis. This unique effect mirrored the efficient condensation of tRNA and DNA in cell-free systems. The combination of DNA compaction and apoptosis by TriplatinNC treatment conferred striking activity in platinum-resistant and/or p53 mutant or null cell lines. Taken together, our results support that the biological activity of TriplatinNC reflects reduced metabolic deactivation (substitution-inert compound not reactive to sulfur nucleophiles), high cellular accumulation, and novel consequences of high-affinity noncovalent DNA binding, producing a new profile and a further shift in the structure–activity paradigms for antitumor complexes.

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The signaling cascade induced by the interaction of erythropoietin (EPO) with its receptor (EPO‐R) is a key event of erythropoiesis. We present here data indicating that Fyn, a Src‐family‐kinase, participates in the EPO signaling‐pathway, since Fyn−/− mice exhibit reduced Tyr‐phosphorylation of EPO‐R and decreased STAT5‐activity. The importance of Fyn in erythropoiesis is also supported by the blunted responsiveness of Fyn−/− mice to stress erythropoiesis. Fyn−/− mouse erythroblasts adapt to reactive oxygen species (ROS) by activating the redox‐related‐transcription‐factor Nrf2. However, since Fyn is a physiologic repressor of Nrf2, absence of Fyn resulted in persistent‐activation of Nrf2 and accumulation of nonfunctional proteins. ROS‐induced over‐activation of Jak2‐Akt‐mTOR‐pathway and repression of autophagy with perturbation of lysosomal‐clearance were also noted. Treatment with Rapamycin, a mTOR‐inhibitor and autophagy activator, ameliorates Fyn−/− mouse baseline erythropoiesis and erythropoietic response to oxidative‐stress. These findings identify a novel multimodal action of Fyn in the regulation of normal and stress erythropoiesis.