p53 Plays a Role in Mesenchymal Differentiation Programs, in a Cell Fate Dependent Manner

Background: The tumor suppressor p53 is an important regulator that controls various cellular networks, including cell differentiation. Interestingly, some studies suggest that p53 facilitates cell differentiation, whereas others claim that it suppresses differentiation. Therefore, it is critical to evaluate whether this inconsistency represents an authentic differential p53 activity manifested in the various differentiation programs. Methodology/Principal Findings: To clarify this important issue, we conducted a comparative study of several mesenchymal differentiation programs. The effects of p53 knockdown or enhanced activity were analyzed in mouse and human mesenchymal cells, representing various stages of several differentiation programs. We found that p53 downregulated the expression of master differentiation-inducing transcription factors, thereby inhibiting osteogenic, adipogenic and smooth muscle differentiation of multiple mesenchymal cell types. In contrast, p53 is essential for skeletal muscle differentiation and osteogenic re-programming of skeletal muscle committed cells. Conclusions: These comparative studies suggest that, depending on the specific cell type and the specific differentiatio

Mechanism of action for N-substituted benzamide-induced apoptosis

We have analysed the mechanism of action for induction of apoptosis by N-substituted benzamides using declopramide as a lead compound. We show here that declopramide at doses above 250 μM in the mouse 70Z/3 pre-B cell line or in the human promyeolocytic cancer cell line HL60 induced cytochrome c release into the cytosol and caspase-9 activation. The broad spectrum caspase inhibitor zVADfmk and caspase-9 inhibitor zLEDHfmk inhibited apoptosis and improved cell viability when administrated to cells 1 h before exposure to declopramide, whereas the caspase-8 inhibitor zIEDHfmk had less effect. Also, the over expression of Bcl-2 by transfection in 70Z/3 cells inhibited declopramide-induced apoptosis. Prior to the induction of apoptosis, a G2/M cell cycle block was induced by declopramide. The cell cycle block was also observed in the presence of broad spectrum caspase inhibitor zVADfmk and in a transfectant expressing high levels of Bcl-2. Furthermore, while p53 was induced in 70Z/3 cells by declopramide, neither the apoptotic mechanism nor the G2/M cell cycle block were dependent on p53 activation since both effects were also seen in p53 deficient HL60 cells after addition of declopramide

Oral Spore Vaccine Based on Live Attenuated Nontoxinogenic Bacillus anthracis Expressing Recombinant Mutant Protective Antigen

An attenuated nontoxinogenic nonencapsulated Bacillus anthracis spore vaccine expressing high levels of recombinant mutant protective antigen (PA), which upon subcutaneous immunization provided protection against a lethal B. anthracis challenge, was found to have the potential to serve also as an oral vaccine. Guinea pigs immunized per os with the recombinant spore vaccine were primed to B. anthracis vegetative antigens as well as to PA, yet only a fraction of the animals (30% to 50%) mounted a humoral response to all of these antigens. Protective immunity provided by per os immunization correlated with a threshold level of PA neutralizing antibody titers and was long-lasting. Protection conferred by per os immunization was attained when the vaccine was administered in the sporogenic form, which, unlike the vegetative cells, survived passage through the gastrointestinal tract. A comparison of immunization of unirradiated spores with immunization of γ-irradiated spores demonstrated that germination and de novo synthesis of PA were prerequisites for mounting an immune protective response. Oral immunization of guinea pigs with attenuated B. anthracis spores resulted in a characteristic anti-PA immunoglobulin isotype profile (immunoglobulin [G1 IgG1] versus IgG2), as well as induction of specific anti-PA secretory IgA, indicating development of mucosal immunity

Nucleotide sequence of the bovine P53 tumor-suppressor cDNA.

The bovine p53 open reading frame was cloned and characterized using a reverse transcription-polymerase chain reaction amplification (RT-PCR) method. After sequencing, it appeared that this cDNA is able to code for a 386 amino acids protein with high degree of homology with the ovine p53. Furthermore, the homology is not equally distributed along the molecule since the highest divergence is located within the exon 4. The bovine p53 shares 93% and 91% homology with the ovine p53 at the DNA and protein level respectively. © 1995 Informa UK Ltd All rights reserved: reproduction in whole or part not permitted.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Defective apoptosis and B-cell lymphomas in mice with p53 point mutation at Ser 23

Phosphorylation of the p53 tumor suppressor at Ser20 (murine Ser23) has been proposed to be critical for disrupting p53 interaction with its negative regulator, MDM2, and allowing p53 stabilization. To determine the importance of Ser23 for the function of p53 in vivo, we generated a mouse in which the endogenous p53 locus was targeted to replace Ser23 with alanine. We show that, in mouse embryonic fibroblasts generated from Ser23 mutant mice, Ser23 mutation did not dramatically reduce IR-induced p53 protein stabilization or p53-dependent cell cycle arrest. However, in Ser23 mutant thymocytes and in the developing cerebellum, p53 stabilization following IR was decreased and resistance to apoptosis was observed. Homozygous Ser23 mutant animals had a reduced lifespan, but did not develop thymic lymphomas or sarcomas that are characteristic of p53−/− mice. Instead, Ser23 mutant animals died between 1 and 2 years with tumors that were most commonly of B-cell lineage. These data support an important role for Ser20/23 phosphorylation in p53 stabilization, apoptosis and tumor suppression