Stefano Iacovelli

Repression of the Antiapoptotic Molecule Galectin-3 by Homeodomain-Interacting Protein Kinase 2-Activated p53 Is Required for p53-Induced Apoptosis

ABSTRACT Galectin 3 (Gal-3), a member of the β-galactoside binding lectin family, exhibits antiapoptotic functions, and its aberrant expression is involved in various aspects of tumor progression. Here we show that p53-induced apoptosis is associated with transcriptional repression of Gal-3. Previously, it has been reported that phosphorylation of p53 at Ser46 is important for transcription of proapoptotic genes and induction of apoptosis and that homeodomain-interacting protein kinase 2 (HIPK2) is specifically involved in these functions. We show that HIPK2 cooperates with p53 in Gal-3 repression and that this cooperation requires HIPK2 kinase activity. Gene-specific RNA interference demonstrates that HIPK2 is essential for repression of Gal-3 upon induction of p53-dependent apoptosis. Furthermore, expression of a nonrepressible Gal-3 prevents HIPK2- and p53-induced apoptosis. These results reveal a new apoptotic pathway induced by HIPK2-activated p53 and requiring repression of the antiapoptotic factor Gal-3.

ATM is activated by default in mitosis, localizes at centrosomes and monitors mitotic spindle integrity

We previously showed that ATM is responsible for p53 phosphorylation at Ser15 andlocalization at centrosomes during mitosis. When p53 centrosomal localization is preventedby inhibiting polymerization of spindle microtubules, a stabilized form of p53 is transmittedto daughter cells that arrest in the next G1 phase of the cell cycle after exit from mitosis. ATcells are unable to both localize p53 at centrosomes in mitosis and arrest after exposure tomitotic-spindle poisons. Here we show that during mitosis ATM is activated byphosphorylation at Ser1981 and localizes at centosomes. When mitotic spindle is disrupted bynocodazole, ATM is displaced from centrosomes and co-localizes with phospho-Ser15-p53under the form of spots dispersed in the mitotic cytoplasm. After release from nocodazoleblock,as soon as cells exit mitosis, p53 is redirected to the nucleus and its Ser15phosphorylation is substituted by phosphorylation at Ser46. We suggest that ATM is activatedby default at each mitotic onset and phosphorylates p53 at Ser15 so as to keep it inactive atcentrosomes when the spindle is correctly in place or, in case of inactivation of the mitoticspindle, to maintain the memory of a perturbed mitosis.

Purification and Characterization of Adipose-Derived Stem Cells From Patients With Lipoaspirate Transplant

Techniques for medical tissue regeneration require an abundant source of human adult stem cells. There is increasing evidence that adipose stem cells contribute to restoration of tissue vascularization and organ function. The object of our study was to isolate and characterize adult adipose-derived stem cells from patients undergoing on lipoaspirate transplant with the aim to improve tissue regeneration. Adipose-derived stem cells were isolated and purified from the lipoaspirate of 15 patients and characterized for CD markers and the ability to differentiate toward the adipogenic lineage. We found that purified adipose stem cells express high level of CD49d, CD44, CD90, CD105, CD13, and CD71 and these markers of staminality were maintained at high level for at least 3 months and seven passages of in vitro culture. As expected, these cells resulted negative for the endothelial and hematopoietic-specific markers CD31, CD106, CD34, and CD45. Differentiation towards adipogenic lineage demonstrated that purified adipose-derived stem cells are still able to become adipocytes at least 3 months after in vitro culture. The analysis of Akt and MAPK phosphorylation confirmed a modulation of their activity during differentiation. Interestingly, we established for the first time that, among the p53 family members, a strong upregulation of p63 expression occurs in adipocytic differentiation, indicating a role for this transcription factor in adipocytic differentiation. Taken together, these data indicate that purified lipoaspirate-derived stem cells maintain their characteristic of staminality for a long period of in vitro culture, suggesting that they could be applied for cell-based therapy to improve autologous lipoaspirate transplant.

HIPK2 is involved in cell proliferation and its suppression promotes growth arrest independently of DNA damage

Introduction/objectives:  The serine/threonine kinase homeodomain‐interacting protein kinase 2 (HIPK2) is a co‐regulator of an increasing number of transcription factors and cofactors involved in DNA damage response and development. We and others have cloned HIPK2 as an interactor of the p53 oncosuppressor, and have studied the role of this interaction in cell response to stress. Nevertheless, our original cloning of HIPK2 as a p53‐binding protein, was aimed at discovering partners of p53 involved in cell differentiation and development, still controversial p53 functions. To this aim, we used p53 as bait in yeast two‐hybrid screening of a cDNA library from mouse embryo (day 11 postcoitus) when p53 is highly expressed.

Co-targeting of Bcl-2 and mTOR pathway triggers synergistic apoptosis in BH3 mimetics resistant acute lymphoblastic leukemia

Several chemo-resistance mechanisms including the Bcl-2 protein family overexpression and constitutive activation of the PI3K/Akt/mTOR signaling have been documented in acute lymphoblastic leukemia (ALL), encouraging targeted approaches to circumvent this clinical problem. Here we analyzed the activity of the BH3 mimetic ABT-737 in ALL, exploring the synergistic effects with the mTOR inhibitor CCI-779 on ABT-737 resistant cells. We showed that a low Mcl-1/Bcl-2 plus Bcl-xL protein ratio determined ABT-737 responsiveness. ABT-737 exposure further decreased Mcl-1, inducing apoptosis on sensitive models and primary samples, while not affecting resistant cells. Co-inhibition of Bcl-2 and the mTOR pathway resulted cytotoxic on ABT-737 resistant models, by downregulating mTORC1 activity and Mcl-1 in a proteasome-independent manner. Although Mcl-1 seemed to be critical, ectopic modulation did not correlate with apoptosis changes. Importantly, dual targeting proved effective on ABT-737 resistant samples, showing additive/synergistic effects. Together, our results show the efficacy of BH3 mimetics as single agent in the majority of the ALL samples and demonstrate that resistance to ABT-737 mostly correlated with Mcl-1 overexpression. Co-targeting of the Bcl-2 protein family and mTOR pathway enhanced drug-induced cytotoxicity by suppressing Mcl-1, providing a novel therapeutic approach to overcome BH3 mimetics resistance in ALL.

Aberrant Proliferative and Apoptotic Pathways in Acute Lymphoblastic Leukemia (ALL): Molecular Therapies to Overcome Chemo-Resistance

Adult acute lymphoblastic leukemia (ALL) is characterized by a high relapse rate, with the majority of patients developing chemo-resistance and ultimately dying of the disease with a 5-year survival rate of 40% (Faderl et al., 2010). Significant advances, however, have been made in cases carrying the acquired genetic alteration BCR-ABL (ALL-Ph+) targeted by tyrosine-kinase inhibitors (Ottmann & Pfeifer, 2009). Therefore, several studies have recently been carried out to look for additional, therapeutically exploitable, genetic lesions. Aberrant activation of signal transduction pathways (STP) implicated in proliferation and survival mechanisms are generally involved in leukemogenesis and drug resistance (Zhao et al., 2010). Genes in the PI3K/PTEN/AKT/mTOR, RAS/RAF/MEK/ERK, and Jak/STAT pathways are frequently mutated and their expression is often altered in hematopoietic malignancies, including ALL (McCubrey et al., 2011; Steelman et al. 2008). In addition, deregulation of survival mechanisms may confer chemo-resistance to leukemic cells, particularly involving alterations of the Bcl-2 signaling cascade, which may represent one of the most important, potentially druggable, pathways for therapeutic intervention in ALL. Starting from our studies on chemo-resistance in ALL, particularly on multidrug resistance (MDR1) expression and prognostic significance, in this chapter we will illustrate the major pathways aberrantly activated in ALL PI3K/PTEN/AKT/mTOR, RAF/RAS/MEK/ERK, and the Bcl-2 family of proteins with the ultimate goal of summarizing novel targets for