Silvia Monestiroli

Inhibitors of histone deacetylases induce tumor-selective apoptosis through activation of the death receptor pathway

Histone deacetylases (HDACs) regulate transcription and specific cellular functions, such as tumor suppression by p53, and are frequently altered in cancer. Inhibitors of HDACs (HDACIs) possess antitumor activity and are well tolerated, supporting the idea that their use might develop as a specific strategy for cancer treatment. The molecular basis for their selective antitumor activity is, however, unknown. We investigated the effects of HDACIs on leukemias expressing the PML-RAR or AML1-ETO oncoproteins, known to initiate leukemogenesis through deregulation of HDACs. Here we report that: (i) HDACIs induce apoptosis of leukemic blasts, although oncogene expression is not sufficient to confer HDACI sensitivity to normal cells; (ii) apoptosis is p53 independent and depends, both in vitro and in vivo, upon activation of the death receptor pathway (TRAIL and Fas signaling pathways); (iii) TRAIL, DR5, FasL and Fas are upregulated by HDACIs in the leukemic cells, but not in normal hematopoietic progenitors. These results show that sensitivity to HDACIs in leukemias is a property of the fully transformed phenotype and depends on activation of a specific death pathway.

Cell-cycle restriction limits DNA damage and maintains self-renewal of leukaemia stem cells.

Rare cells with the properties of stem cells are integral to the development and perpetuation of leukaemias. A defining characteristic of stem cells is their capacity to self-renew, which is markedly extended in leukaemia stem cells. The underlying molecular mechanisms, however, are largely unknown. Here we demonstrate that expression of the cell-cycle inhibitor p21 is indispensable for maintaining self-renewal of leukaemia stem cells. Expression of leukaemia-associated oncogenes in mouse haematopoietic stem cells (HSCs) induces DNA damage and activates a p21-dependent cellular response, which leads to reversible cell-cycle arrest and DNA repair. Activated p21 is critical in preventing excess DNA-damage accumulation and functional exhaustion of leukaemic stem cells. These data unravel the oncogenic potential of p21 and suggest that inhibition of DNA repair mechanisms might function as potent strategy for the eradication of the slowly proliferating leukaemia stem cells.

Impairment of p53 acetylation, stability and function by an oncogenic transcription factor.

Mutations of p53 are remarkably rare in acute promyelocytic leukemias (APLs). Here, we demonstrate that the APL‐associated fusion proteins PML–RAR and PLZF‐RAR directly inhibit p53, allowing leukemic blasts to evade p53‐dependent cancer surveillance pathways. PML–RAR causes deacetylation and degradation of p53, resulting in repression of p53 transcriptional activity, and protection from p53‐dependent responses to genotoxic stress. These phenomena are dependent on the expression of wild‐type PML, acting as a bridge between p53 and PML–RAR. Recruitment of histone deacetylase (HDAC) to p53 and inhibition of p53 activity were abrogated by conditions that either inactivate HDACs or trigger HDAC release from the fusion protein, implicating recruitment of HDAC by PML–RAR as the mechanism underlying p53 inhibition.

Histological and immunohistochemical detection of different Helicobacter species in the gastric mucosa of cats

Detailed histopathological evaluation of the gastric mucosa of Helicobacter-infected cats is complicated by the difficulty of recognizing Helicobacter organisms on hematoxylin and eosin (HE)-stained sections and the ability of multiple Helicobacter species to infect cats. In this study, the presence and localization of different species of Helicobacter in the stomachs of cats was investigated using silver staining and immuno-histochemistry. Five groups containing 5 cats each were established (group 1: urease negative and Helicobacter free; groups 2, 3, 4, and 5: urease positive and infected with Helicobacter heilmannii, unclassified Helicobacter spp., Helicobacter felis, and Helicobacter pylori, respectively). Gastric samples were evaluated by HE and silver staining and by immunohistochemistry with 3 different anti-Helicobacter primary antibodies. Helicobacter were detected by Steiner stain in all infected cats at the mucosal surface, in the lumen of gastric glands, and in the cytoplasm of parietal cells. In silver-stained sections, H. pylori was easily differentiated from H. felis, H. heilmannii, and unclassified Helicobacter spp., which were larger and more tightly coiled. No organisms were seen in uninfected cats. Helicobacter antigen paralleled the distribution of organisms observed in Steiner-stained sections for 2 of the 3 primary antibodies tested. The antisera were not able to discriminate between the different Helicobacter species examined. A small amount of Helicobacter antigen was present in the lamina propria of 3 H. pylori-, 3 H. felis-, and 1 H. heilmannii-infected cat. Minimal mononuclear inflammation was present in uninfected cats and in those infected with unclassified Helicobacter spp. and H. heilmannii cats. In H. felis-infected cats, lymphoid follicular hyperplasia with mild pangastric mononuclear inflammation and eosinophilic infiltrates were present. The H. pylori-infected cats had severe lymphoid follicular hyperplasia and mild to moderate mononuclear inflammation accompanied by the presence of neutrophils and eosinophils. These findings indicate that Steiner staining and immunohistochemistry are useful for detecting Helicobacter infections, particularly when different Helicobacter species can be present. Monoclonal antibodies specific for the different Helicobacter species could be important diagnostic aids. There appear to be differences in the severity of gastritis in cats infected with different Helicobacter species.

Activation of the orphan nuclear receptor RORα induces growth arrest in androgen‐independent DU 145 prostate cancer cells

RORα is a transcription factor which belongs to the family of orphan nuclear receptors. The regulatory functions of this receptor are still poorly understood. However, response elements for RORα are present on the promoter of cell cycle‐related genes suggesting that it might be involved in the control of cell proliferation. In this study, we investigated the expression and the possible function of RORα in a human androgen‐independent prostate cancer cell line (DU 145). The thiazolidinedione‐derivative CGP 52608 has been utilized as the specific ligand and activator of RORα.