Abstract. The most common therapeutic approach for many cancers is chemotherapy. However, many patients relapse after treatment due to the development of chemoresistance. Recently, targeted therapies represent novel approaches to destroy cancer cells. The PI3K/PTEN/AKT pathway is a key signaling pathway involved in the regulation of cell growth. Dysregulated signaling of this pathway may be associated with activating mutations of PI3K-related genes. Analyses of these mutations reveal that they increase the PI3K signal, stimulate downstream Akt signaling, promote growth factor-independent growth and increase cell invasion and metastasis. In this review, we summarize the PI3K/PTEN/AKT pathway genetic alterations in cancer and their potential clinical applications. IntroductionPhosphatidylinositol 3-kinases (PI3Ks) are lipid kinases that phosphorylate phoshoinositides at the D-3 position of the inositol ring generating second messengers that govern cellular activities and promote various biological properties including proliferation, survival, motility and morphology changes. Members of the PI3K family are grouped into three classes according to sequence homology, substrate preference and tissue distribution (1). In terms of regulating cell division and tumorigenesis, the most important PI3K proteins are those that belong to class IA, the catalytic subunit p110α and its associated regulatory subunit p85. In quiescent cells, the regulatory subunit p85 maintains the p110α catalytic subunit in a lowactivity state. Upon growth factor stimulation, the SH2 domain [Rous-sarcoma (src) oncogene homology-2 domain] of the p85 subunit binds to phosphorylated tyrosine in receptor tyrosine kinases or their substrate adaptor proteins. This binding relieves the inhibition of p110α subunit and mediates recruitment of this subunit to the plasma membrane (2). Activation of p110α leads to the production of phosphatidylinositol 3,4,5-triphosphate (PIP3), which recruits adaptor and effector proteins containing a pleckstrin homology domain (PH domain) to cellular membranes including the protein kinase B (PKB/Akt), phosphoinositide-dependent kinase 1 (PDK-1) (3). Once at the membrane PKB/Akt is phosphorylated at Thr308 and Ser473 by PDK1 and the mTORC2 complex, respectively. Once activated PKB/Akt phosphorylates and actives target proteins involved in many different cellular functions, which span cell cycle progression, cell survival, metabolism, ribosome biogenesis, protein translation, RNA transcription and cell motility (4,5

A growing number of studies have highlighted the role of microRNAs (miRNAs or miRs) in the development and progression of cancer. In particular, the aberrant expression of cancer-related proteins, such as oncogenes and tumor suppressors has been shown to correlate with the modulation of the expression of specific miRNAs. In the present study, we aimed to determine which downregulated miRNAs may be involved in modulating the expression of the oncogenic transcription factor, Yin Yang 1 (YY1). YY1 has been reported to be overexpressed in several malignancies and our previous studies have highlighted the significant correlation between the levels of YY1 and aggressive behavior in non-Hodgkin's lymphoma (NHL). A total of 57 miRNAs that are potentially capable of targeting YY1 was identified through in silico approaches. The search of publicly available NHL datasets, including paired mRNA and miRNA data (GSE23026) highlighted a significant correlation (Pearson's correlation, r>0.5) between the expression levels of YY1 and the expression levels of a limited set of miRNAs, including miR-363, miR-200a, miR-23b, miR-15a and miR-15b. Intriguingly, both hsa-miR-363 and hsa-miR-200a belong to the top 20 miRNAs that were found to be downregulated in Burkitt's lymphoma (BL) tissue compared to normal tissue. Although further validation studies are warranted, the identification of these two miRNAs associated with the upregulation of YY1 in BL may provide further insight into the pathogenesis of this tumor and may contribute to more personalized and targeted treatment approaches for patients with this disease.

The addition of anti-CD20 monoclonal antibody (rituximab) to chemotherapy has significantly improved survival in B-cell lymphoma. However, a substantial number of patients relapse after treatment with rituximab. Understanding of anti-CD20 antibody molecular function may facilitate the development of pharmacologic strategies to overcome resistance. Cell death have been demonstrated to be caused by rituximab binding to CD20 throughout direct and indirect mechanisms. The direct mechanism comprises growth inhibition, induction of apoptosis and sensitization of cells to chemotherapy. While, the indirect mechanisms to Rituximab include complement-dependent cytotoxicity (CDC) and antibody-dependent cellular cytotoxicity (ADCC). However, these mechanisms are still poorly understood. To shed light on this issue, we have analyzed the most significant results showing the role of Rituximab as a signal-inducing antibody and as a chemosensitizing agent through negative regulation of major survival pathways. Mechanisms of resistance to Rituximab are also discussed. Additionally, studies here reported show that, cellular targets are modified after treatment with Rituximab and may become useful for novel therapeutic strategies in the treatment of patients resistant to standard therapy.

Non-Hodgkin lymphomas (NHL) are a heterogeneous group of lymphoproliferative malignancies with variable patterns of behavior and responses to therapy. NHL development and invasion depend on multiple interactions between tumor cells and non-neoplastic cells. Such interactions are usually modulated by several cytokines. Accordingly, it was demonstrated that matrix-metalloproteinase (MMP)-2 and MMP-9 were activated in human lymphoid cell lines by interleukin-6 (IL-6). The activation of these enzymes is associated with tumor invasion and metastasis in human cancers. MMPs are also activated in several cancers by osteopontin (OPN), a secreted glycoprotein that regulates cell adhesion, migration, and survival. However, it is still unclear if MMPs play a role in NHL development and if their activation is determined by OPN and/or IL-6. In the present study, two groups of 78 NHL patients and 95 healthy donors were recruited for the analysis of OPN, MMP-2, MMP-9 and IL-6.Significant higher circulating levels of MMP-2, MMP-9, OPN and IL-6 were observed in NHL patients when compared to healthy donors. Similar data were obtained by analyzing the activity of both MMP-2 and MMP-9. The multivariate regression model indicates that, in both NHL cases and healthy donors, OPN is associated with the increase of MMP-2 and MMP-9 levels independently of IL-6. These data were first confirmed by “in silico” analyses and then by “in vitro” experiments conducted on peripheral blood mononuclear cells randomly selected from both NHL patients and healthy donors.Overall, our data suggest that the activation of MMPs in NHL development is mostly associated with OPN. However, IL-6 may play an important role in the lymphomagenesis through the activation of other molecular pathways. This article is part of a Special Issue entitled: Tumor Microenvironment Regulation of Cancer Cell Survival, Metastasis, Inflammation, and Immune Surveillance edited by Peter Ruvolo and Gregg L. Semenza.

Background: Molecular approaches applied to the study of B-lineage leukemia have made significant contributions in understanding and characterizing the disease. The Kde rearrangement was targeted as clonal marker to characterize Tunisian B-chronic lymphocytic leukemia (B-CLL) and B-acute lymphoblastic leukemia (B-ALL).Objective: We used a multiplex PCR to amplify deletional Kde rearrangements and Southern blot assay with Cκ and Kde probes in seven B-CLL and two B-ALL. Direct sequencing was performed in order to determine the n region.Results: An interesting RSS-Kde biallelic rearrangement was found in one adult male patient with B-ALL, since only Vκ-Kde rearrangement has been reported in adult B-ALL. In B-CLL, one case with two clonal cell proliferations in favor of oligoclonality which is very infrequent in B-CLL was identified and might be associated with bad outcome. These first results need more investigation to establish correlation between molecular characteristic and the poor outcome. Conclusion:The molecular approach was successfully improved and applied for clonality assessment of B-lineage leukemia for a better diagnosis and performing monitoring minimal residual disease.