Biomedical subjects

Cristian Bellodi

Publications and source records attributed to Cristian Bellodi.

7 recordsLinked to original sources

PubMed2006

A cytoplasmic PML mutant inhibits p53 function.

The promyelocytic leukaemia gene (Pml) is a tumor suppressor identified in acute promyelocytic leukaemia (APL), where it is fused to RAR alpha gene as a result of the chromosomal translocation t(15;17). Pml encodes both nuclear and cytoplasmic isoforms. While nuclear PML has been intensively investigated, cytoplasmic PML proteins are less characterized. PML nuclear isoforms (nPML) are the essential components of subnuclear structures referred to as PML nuclear bodies (PML-NB). In response to cellular insults such as DNA damage and oncogenic activation, nPML modulates p53 activity through CBP-mediated acetylation and activates its pro-apoptotic and growth suppressive functions. Two missense mutations resulting in truncated PML cytoplasmic proteins (Mut PML) have been identified in aggressive APL cases. Here we report that cytoplasmic PML is able to induce the relocation of nPML to the cytoplasm, thus reducing the number of PML-NBs. Remarkably, Mut PML inhibits p53 transcriptional, growth suppressive, and apoptotic functions, thus suggesting that cytoplasmic expression of PML has an impact on survival through inhibition of nuclear PML. Overall our findings shed new light on the role of PML cytoplasmic proteins in the regulation of p53.

Apoptosis↗

PubMed2006

Cytoplasmic function of mutant promyelocytic leukemia (PML) and PML-retinoic acid receptor-alpha.

The promyelocytic leukemia (PML) tumor suppressor of acute promyelocytic leukemia (APL) regulates major apoptotic and growth-suppressive pathways. In APL, PML is involved in a chromosomal translocation generating the PML-retinoic acid receptor-alpha (RARalpha) fusion protein. Two missense mutations in the remaining PML alleles have been identified, which give rise to a truncated cytoplasmic PML protein (Mut PML). APL patients carrying these mutations display resistance to retinoic acid (RA) and very poor prognosis. Here we show that Mut PML associates with the cytoplasmic regions we refer to as PML-cytoplasmic bodies (PML-CBs). Mut PML interacts with PML-RARalpha in PML-CB and potentiates PML-RARalpha-mediated inhibition of RA-dependent transcription. Remarkably, Mut PML stabilizes PML-RARalpha and inhibits differentiation induced by pharmacological doses of RA. A mutant form of PML-RARalpha that accumulates in the cytoplasm inhibits RA-dependent transcription and differentiation, thus suggesting that cytoplasmic localization of PML-RARalpha may contribute to transformation. Finally, we show that the bcr3 PML-RARalpha form is predominantly cytoplasmic and accumulates in PML-CBs. Taken together, these findings reveal novel insights into the molecular mechanisms contributing to APL.

Animals↗

PubMed2005

Genetic polymorphisms of Fas (CD95) and Fas ligand (CD178) influence the rise in CD4+ T cell count after antiretroviral therapy in drug-naïve HIV-positive patients.

Fas and Fas ligand (FasL) are the main genes that control cell death in the immune system. Indeed, they are crucial for the regulation of T lymphocyte homeostasis because they can influence cell proliferation. A strong debate exists on the importance of Fas/FasL system during HIV infection, which is characterized by the loss of CD4+ T cells directly, or indirectly, caused by the virus. To investigate whether the genetic background of the host plays a role in the immunoreconstitution, we studied the influence of different Fas and FasL polymorphisms on CD4+ T lymphocyte count and plasma viral load following initiation of highly active antiretroviral therapy (HAART) in drug-naïve HIV+ patients. We studied 131 individuals, who were compared to 136 healthy donors. Statistical analysis was performed by using Chi2 test, Fischer's Exact Test, and analysis for repeated measurements. The group of HIV+ patients had an unexpected lower frequency of FasLnt169 polymorphism (delT allele) than healthy controls (p = 0.039). We then observed no significant differences in the immune reconstitution, in terms of CD4+ T cell increase, when the influence of single alleles of the gene Fas or FasL was considered. However, the combination of some polymorphisms of Fas or FasL significantly influenced CD4+ T cell production and viral load decrease, showing that these genes can play a role in the immunoreconstitution triggered by antiretroviral therapy.

Adult↗

PubMed2005

MOZ-TIF2 inhibits transcription by nuclear receptors and p53 by impairment of CBP function.

Chromosomal rearrangements associated with acute myeloid leukemia (AML) include fusions of the genes encoding the acetyltransferase MOZ or MORF with genes encoding the nuclear receptor coactivator TIF2, p300, or CBP. Here we show that MOZ-TIF2 acts as a dominant inhibitor of the transcriptional activities of CBP-dependent activators such as nuclear receptors and p53. The dominant negative property of MOZ-TIF2 requires the CBP-binding domain (activation domain 1 [AD1]), and coimmunoprecipitation and fluorescent resonance energy transfer experiments show that MOZ-TIF2 interacts with CBP directly in vivo. The CBP-binding domain is also required for the ability of MOZ-TIF2 to extend the proliferative potential of murine bone marrow lineage-negative cells in vitro. We show that MOZ-TIF2 displays an aberrant nuclear distribution and that cells expressing this protein have reduced levels of cellular CBP, leading to depletion of CBP from PML bodies. In summary, our results indicate that disruption of the normal function of CBP and CBP-dependent activators is an important feature of MOZ-TIF2 action in AML.

Acetyltransferases↗

PubMed2004

Balanced regulation of mRNA production for Fas and Fas ligand in lymphocytes from centenarians: how the immune system starts its second century.

BACKGROUND: The functionality of the immune system during aging is crucial for protection against the most common age-related diseases. Apoptosis plays a central role in the senescence of the immune system, as evidenced by the increased plasma membrane expression of a key molecule like Fas protein. We analyzed the mRNA levels of different forms of Fas (total [tFas] and membrane [mFas]) and of its ligand (FasL) in peripheral blood lymphocytes from centenarians, the best example of successful aging, who were compared with young and middle-aged donors. METHODS AND RESULTS: Using real-time polymerase chain reaction, we quantified mRNA for different forms of Fas and for FasL. In resting lymphocytes, mRNA for tFas, but not for mFas, significantly increases with age, whereas FasL mRNA significantly decreases. In vitro production of Fas/FasL mRNA after different stimuli was similar in cells from the 3 groups. Even if the percentage of Fas+ cells was higher than in the other groups, peripheral blood lymphocytes from centenarians had normal Fas-induced apoptosis, as revealed by flow cytometry. By ELISA, we observed that cells from centenarians showed normal in vitro production of the soluble form of Fas (sFas) and that plasma levels of such molecule were significantly higher in centenarians than in the other groups. CONCLUSIONS: Lymphocytes from centenarians are able to balance the production of proapoptotic (mFas and FasL) and antiapoptotic (sFas) molecules, whose proportions are likely crucial for the well-preserved immune functionality at the extreme limits of human life.

Adult↗

PubMed2003

MDR1 C3435T genetic polymorphism does not influence the response to antiretroviral therapy in drug-naive HIV-positive patients.

P-glycoprotein, a membrane-localized protein transporter, codified by the MDR1 gene, influences the response to pharmacological treatments, including antiretroviral drugs. MDR1 polymorphism C3435T is correlated with the functionality of the protein. We investigated the influence of this polymorphism in the reconstitution of the peripheral CD4 T cell pool in 149 drug-naive HIV-positive patients starting highly active antiretroviral therapy. The MDR1 C3435Tpolymorphism did not influence response to therapy, suggesting no disadvantages for individuals with a different genotype.

CD4 Lymphocyte Count↗

PubMed2003

Development of real time PCR assays for the quantification of Fas and FasL mRNA levels in lymphocytes: studies on centenarians.

Apoptosis plays a central role in the homeostasis of the immune system. During aging, there is an altered regulation of pivotal molecules that are responsible for the regulation of this type of cell death, such as those of the Fas/FasL system. Understanding the regulation of these genes can help to clarify, at least in part, the age-related changes that occur in immune cells. We have developed an original real time PCR assay for quantification of mRNA for Fas and FasL, and have studied a group of young donors, middle aged subjects and centenarians. We have found that the production of Fas mRNA is greatly increased in resting lymphocytes from centenarians; such an increase follows an age-related trend. On the contrary, the production of mRNA for the molecule, which is the natural ligand of Fas, i.e. FasL, is consistently reduced. Our preliminary results suggest that during aging a subtle balance in the production of molecules that cause apoptosis could exist, and that, in order to avoid an excessive death of immune cells, a still unknown mechanism could compensate the increase of Fas with the reduction of FasL.

Aged↗