Exposure to cellular stress can trigger the p53 tumor suppressor, a sequence-specific transcription factor, to induce cell growth arrest or apoptosis. The choice between these cellular responses is influenced by many factors, including the type of cell and stress, and the action of p53 co-activators. p53 stimulates a wide network of signals that act through two major apoptotic pathways. The extrinsic, death receptor pathway triggers the activation of a caspase cascade, and the intrinsic, mitochondrial pathway shifts the balance in the Bcl-2 family towards the pro-apoptotic members, promoting the formation of the apoptosome, and consequently caspase-mediated apoptosis. The impact of these two apoptotic pathways may be enhanced when they converge through Bid, which is a p53 target. The majority of these apoptotic effects are mediated through the induction of specific apoptotic target genes. However, p53 can also promote apoptosis by a transcription-independent mechanism under certain conditions. Thus, a multitude of mechanisms are employed by p53 to ensure efficient induction of apoptosis in a stage-, tissue- and stress-signal-specific manner. Manipulation of the apoptotic functions of p53 constitutes an attractive target for cancer therapy.

Ectopic lymphoid-like structures (ELS) are often observed in cancer, yet their function is obscure. Although ELSs signify good prognosis in certain malignancies, we found that hepatic ELSs indicate poor prognosis in hepatocellular carcinoma (HCC). We studied an HCC mouse model, displaying abundant ELSs and found that they constitute immunopathological microniches, wherein progenitor malignant hepatocytes appear and thrive in a complex cellular and cytokine milieu until gaining self-sufficiency. Progenitor egression and tumor formation is associated with autocrine production of cytokines previously provided by the niche. ELSs develop upon cooperation between the innate and adaptive immune system which is facilitated by NF-κB activation and abolished by T cell depletion. These aberrant immune foci could be new targets for cancer therapy.

No abstract

contributed equally to this workIn response to environmental stress, the p53 phosphoprotein is stabilized and activated to inhibit cell growth. p53 stability and activity are negatively regulated by the murine double minute (Mdm2) oncoprotein in an autoregulatory feedback loop. The inhibitory effect of Mdm2 on p53 has to be tightly regulated for proper p53 activity. Phosphorylation is an important level of p53 regulation. In response to DNA damage, p53 is phosphorylated at several N-terminal serines. In this study we examined the role of Ser20, a potential phosphorylation site in human p53, in the regulation of p53 stability and function. Substitution of Ser20 by Ala (p53-Ala20) significantly increases the susceptibility of human p53 to negative regulation by Mdm2 in vivo, as measured by apoptosis and transcription activation assays. Mutation of Ser20 to Ala renders p53 less stable and more prone to Mdm2-mediated degradation. While the in vitro binding of p53 to Mdm2 is not increased by the Ala20 mutation, the same mutation results in a markedly enhanced binding in vivo. This is consistent with the conclusion that phosphorylation of Ser20 in vivo attenuates the binding of wild-type p53 to Mdm2. Peptides bearing nonphosphorylated Ser20 or Ala20 compete with p53 for Mdm2 binding, while a similar peptide with phosphorylated Ser20 does not. This implies a critical role for Ser20 in modulating the negative regulation of p53 by Mdm2, probably through phosphorylationdependent inhibition of p53-Mdm2 interaction.

Natural killer cells (NKs) are abundant in the human decidua, regulating trophoblast invasion and angiogenesis. Several diseases of poor placental development are associated with first pregnancies, so we thus looked to characterize differences in decidual NKs (dNKs) in first versus repeated pregnancies. We discovered a population found in repeated pregnancies, which has a unique transcriptome and epigenetic signature, and is characterized by high expression of the receptors NKG2C and LILRB1. We named these cells Pregnancy Trained decidual NK cells (PTdNKs). PTdNKs have open chromatin around the enhancers of IFNG and VEGFA. Activation of PTdNKs led to increased production and secretion of IFN-γ and VEGFα, with the latter supporting vascular sprouting and tumor growth. The precursors of PTdNKs seem to be found in the endometrium. Because repeated pregnancies are associated with improved placentation, we propose that PTdNKs, which are present primarily in repeated pregnancies, might be involved in proper placentation.