Vav1: A Key Player in Agonist-Induced Differentiation of Promyelocytes from Acute Myeloid Leukemia (APL)

Acute promyelocytic leukemia (APL) is the M3 subtype of acute myeloid leukemias, characterized by hyperproliferation of progenitors that are committed to terminal differentiation into granulocytes. Despite recent clinical studies using arsenic trioxide, anthracyclines and anti-CD33 monoclonal antibodies, all-trans retinoic acid (ATRA)-based therapy represents, until today, the standard cure of APL patients. Studies on both APL blasts and APL-derived cell lines have elucidated that the treatment with ATRA promotes the completion of their maturation to neutrophils throughout a complex network that includes the degradation of the PML/RAR-alpha fusion protein and the activation of RAR-alpha-mediated gene transcription. Even if the underlying mechanism by which ATRA interacts with its receptor located on specific DNA sequences is well known, the events mediated by the ATRA target genes, able to elicit the integrated signaling networks that promote maturation of tumoral promyelocytes, are currently studied to identify specific targets for new therapies of APL. Stemming from the above reported consideration, the proposed review will focus on the possible role of the multidomain protein Vav1 as a target molecule in treatment of APL. This proposal arises from evidences demonstrating that, in addition to promote the acquisition of a mature phenotype by normal hematopoietic cells, Vav1 is a crucial molecule in the completion of the differentiation program to neutrophils of APL-derived cells induced by ATRA. Indeed, it was demonstrated that the down-modulation of Vav1 prevents, and the Vav1 over-expression potentiates, the ability of ATRA to induce the acquisition of a mature phenotype by tumoral promyelocytes

Targeting the phosphatidylinositol 3-kinase/Akt/mechanistic target of rapamycin signaling pathway in B-lineage acute lymphoblastic leukemia: An update

Despite considerable progress in treatment protocols, B-lineage acute lymphoblastic leukemia (B-ALL) displays a poor prognosis in about 15–20% of pediatric cases and about 60% of adult patients. In addition, life-long irreversible late effects from chemo- and radiation therapy, including secondary malignancies, are a growing problem for leukemia survivors. Targeted therapy holds promising perspectives for cancer treatment as it may be more effective and have fewer side effects than conventional therapies. The phosphatidylinositol 3-phosphate kinase (PI3K)/Akt/mechanistic target of rapamycin (mTOR) signaling pathway is a key regulatory cascade which controls proliferation, survival and drug-resistance of cancer cells, and it is frequently upregulated in the different subtypes of B-ALL, where it plays important roles in the pathophysiology, maintenance and progression of the disease. Moreover, activation of this signaling cascade portends a poorer prognosis in both pediatric and adult B-ALL patients. Promising preclinical data on PI3K/Akt/mTOR inhibitors have documented their anticancer activity in B-ALL and some of these novel drugs have entered clinical trials as they could lead to a longer event-free survival and reduce therapy-associated toxicity for patients with B-ALL. This review highlights the current status of PI3K/Akt/mTOR inhibitors in B-ALL, with an emphasis on emerging evidence of the superior efficacy of synergistic combinations involving the use of traditional chemotherapeutics or other novel, targeted agents

PLCB2 (phospholipase C, beta 2)

Review on PLCB2 (phospholipase C, beta 2), with data on DNA, on the protein encoded, and where the gene is implicated

Vav1 sustains the in vitro differentiation of normal and tumor precursors to insulin producing cells induced by all-trans retinoic acid (ATRA)

All-trans retinoic acid (ATRA) promotes the development and the function of insulin producing cells and induces partial differentiation of pancreatic tumor cells. A number of evidences clearly indicate that the ATRA mediated signaling may have a substantial role in therapeutic approaches based on restoration of functional beta-cells. Among the proteins up-regulated by ATRA, Vav1 is involved in maturation and function of haematopoietic cells and is essential for retinoids induced differentiation of tumor promyelocytes. The presence of Vav1 in solid tissues, including pancreas, is considered ectopic and no role in the differentiation of human epithelial cells has so far been described. We demonstrated here that Vav1 sustains the maturation to beta-cells of the normal precursors human Biliary Tree Stem/progenitor Cells (hBTSCs) induced by a differentiation medium containing ATRA and that, in the mature normal pancreas, insulin-producing cells express variable levels of Vav1. Using pancreatic ductal adenocarcinoma (PDAC)-derived cells, we also revealed that the ATRA induced up-modulation of Vav1 is essential for the retinoid-induced trans-differentiation of neoplastic cells into insulin producing cells. The results of this study identify Vav1 as crucial molecule in ATRA induced maturation of insulin producing cells and suggest this protein as a marker for new strategies ended to restore functional beta-cells

In triple negative breast tumor cells, PLC-β2 promotes the conversion of CD133high to CD133low phenotype and reduces the CD133-related invasiveness

Beyond its possible relationship with stemness of tumor cells, CD133/prominin is a highly glycosylated trans-membrane protein that correlates with tumor size, metastasis and clinical stage of triple negative breast cancers (TNBC), that represent 20% of all breast tumors and have a particularly worse clinical outcome than other tumor subtypes [1]. The correlation between the levels of CD133 expression and the biology of breast tumor cells was studied in CD133low and CD133high cell subpopulations isolated from MDA-MB-231 cells (ER-, PR-, HER2-). High expression of CD133 characterizes a small percentage of cells with larger adhesion area, lower proliferation rate, higher invasion capability and increased expression of proteins involved in metastasis and drug resistance of breast cancers. PLC-b2 expression, that plays a crucial role in malignancy of breast tumor cells [2, 3], inversely correlates with the levels of CD133 and has a role in inducing the CD133high cells to CD133low cells conversion. The forced up-regulation of PLC-b2 counteracts the invasiveness of CD133high MDAMB- 231, suggesting that, in TNBC, the de-regulation of this PLC isozyme is responsible of the switch from an early to a mature tumoral phenotype also by reducing the expression of CD133. These data might contribute to identify unexplored key steps in TNBC malignancy, to be considered for potential therapeutic strategies

Extracellular human immunodeficiency virus type-1 Tat protein activates phosphatidylinositol 3-kinase in PC12 neuronal cells

We have here investigated the effect of the regulatory Tat protein of the human immunodeficiency virus type 1 (HIV-1) on the PI 3-kinase catalytic activity in PC12 rat pheochromocytoma cells. After as early as 1 min from the beginning of the treatment with recombinant HIV-1 Tat protein, a significant increase in the tyrosine phosphorylation levels of the p85 regulatory subunit of PI 3-kinase was noticed in 48 h serum-starved PC12 cells. Moreover, the addition of Tat to PC12 cells induced a great increase in PI 3-kinase immunoprecipitated with an anti-phosphotyrosine antibody with a peak of activity (19-fold increase with respect to the basal levels) after a 15-min treatment. This increase in PI 3-kinase activity was significantly higher in PC12 cell cultures supplemented with Tat protein than in cultures stimulated by 100 ng/ml nerve growth factor (NGF; 8-fold increase with respect to the basal levels). Further experiments showed that Tat protein was able to specifically activate PI 3-kinase at picomolar concentrations. In fact: (i) maximal activation of PI 3-kinase was observed at concentrations as low as 1 ng/ml and was specifically blocked by anti-Tat neutralizing antibody; (ii) a Tat-dependent activation was also observed in experiments in which PI 3-kinase activity was evaluated in either anti-Tyr(P) or anti-p85 immunoprecipitates; (iii) 100 nM wortmannin completely blocked the Tat-mediated increase in PI 3-kinase activity both in vitro and in vivo. Our data strongly support the concept that extracellular Tat acts as a cell stimulator, inducing intracellular signal transduction in uninfected cells

PLC-βeta2 plays a phenotype dependent role in the malignant potential induced by hypoxia in breast cancer cells

Hypoxia plays a crucial role in malignant progression of solid tumors, including breast cancer, since neoplastic cells adapt to low oxygen availability by modulating the expression of genes involved in survival, proliferation, metabolic reprogramming, stem cell maintenance, EMT, angiogenesis, invasion and metastasis (1). Among the signaling molecules deregulated in breast tumors, the beta2 isoform of the phosphoi- nositide-dependent phospholipase C (PLC-β2) is expressed in the large majority of primary invasive tumors from all histological subtypes in which it strongly correlates with malignancy and with a poor prognosis (2). PLC-β2 is also expressed in breast tumor- derived cells, in which it improves proliferation and motility and sustains invasion capability (3). A decreased PLC-β2 expression is induced by hypoxia in the BT-474 and MCF7 cell lines, that is correlated with the hypoxia-induced modulation of the EMT markers E-cadherin and Vimentin, as well as of the stem cell marker CD133. In contrast, hypoxia induced the increase of PLC-β2 levels in MDA-MB-231 cells, in which it supports the hypoxia-related reorganization of actin cytoskeleton. In all examined cell lines, the prevention of the effects of hypoxia on PLC-β2 also reduced the recovery of HIF-1α, in turn able to exert a phenotype-related role in modulating EMT and expression of CD133 during the cell response to low oxygen. Our data highlighted a peculiar effect of low oxygen availability on PLC-β2 expression in breast tumor cells with different phenotypes and allocate PLC-β2 in the complex and interconnected transcriptional activity induced by hypoxia. Our results also suggest that the forced modulation of PLC-β2 programmed on the basis of the tumor phenotype may prevent malignant progression of breast neoplasia as a consequence of intra-tumoral hypoxia

Correlation between the surface expression of CD133 and the phenotype of breast tumor cells

Originally considered a marker of hematopoietic stem cells, CD133/prominin is a highly glycosylated trans-membrane protein expressed in various tissues, such as breast, in which it seems to regulate ductal branching but not regenerative capacity [1]. CD133 is also expressed in various solid tumors, including breast cancer, in which CD133-positivity seems to identify a restricted subgroup of tumor stem cells [2]. CD133 expression was heterogeneous in different breast carcinomas but, in triple- negative (ER-, PR-, HER2-) invasive ductal breast carcinoma, CD133 correlates with tumor size, metastasis and clinical stage [3]. In order to establish a correlation between the surface recognition of CD133 and the phenotype of tumor cells, the highly invasive breast-derived MDA-MB-231 cells (ER-, PR-, HER2-) were subjected to immunomagnetic separation of CD133+ and CD133- subpopulations, which were analyzed for malignant properties. In comparison to CD133- cells, the expression of CD133 characterizes cells with a larger adhesion area, lower proliferation rate and reduced migration speed. This phenotype correlates with altered expression of malignancy-associated proteins and with a peculiar pattern of PLC, in turn involved in proliferation and motility of breast tumor cells (4-6). This suggests that, in triple negative ductal breast tumor-derived cells, the expression of CD133 characterizes a small subset of cells with a less undifferentiated phenotype. The reduced expression of CD133 at membrane level may constitute a marker of the switch of tumor cells from a less malignant to a mature phenotype since it correlates with the de-regulation of proteins involved in cell proliferation, motility and invasion

Low oxygen availability and malignant evolution of non-invasive breast tumors: potential protective role of all-trans retinoic acid (ATRA)

Reduced oxygen availability plays a crucial role in malignancy of solid tumors, including breast cancer. Even if the presence of hypoxic areas is common in all breast lesions, no data clearly correlate low oxygenation with the acquisition of malignant features by non-invasive cells, particularly by cells from ductal carcinoma in situ (DCIS), the most frequently diagnosed tumor in women in industrialized countries [1]. We demonstrated that 96 hours of culture under moderate hypoxia is sufficient to induce in DCIS-derived cells motility and epithelial-to-mesenchymal transition (EMT) and to enlarge the number of cells expressing the stem cell marker CD133, indicative of their increased malignant potential. Administration of all-trans retinoic acid (ATRA), a well-known anti-leukemic drug with an anti-tumor role in invasive breast tumor cells [2], supports the epithelial phenotype of DCIS-derived cells cultured under hypoxia and reduces the number of CD133 positive cells, abrogating almost completely the effects of poor oxygenation. In DCIS-derived cells, as in leukemic cells, ATRA up-regulates the β2 isoform of PI-PLC (PLC-β2), ectopically expressed in invasive breast tumors in which counteracts the effects of hypoxia on both EMT and CD133 levels [3]. This suggests that the mechanisms triggered by ATRA in non-invasive breast tumor cells cultured under hypoxia may, at least in part, depend on PLC-β2 activity. Overall, we assigned to hypoxia a role in increasing the malignant potential of DCIS-derived cells and identified in ATRA, currently used in treating acute promyelocytic leukemia (APL), an agonist potentially useful in preventing malignant progression of non-invasive breast lesions with hypoxic areas