Abelson virus transformation prevents TRAIL expression by inhibiting FoxO3a and NF-kappaB

In-depth mapping of DNA-PKcs signaling uncovers noncanonical features of its kinase specificity

DNA-PKcs is a DNA damage sensor kinase with established roles in DNA double-strand break repair via nonhomologous end joining. Recent studies have revealed additional roles of DNA-PKcs in the regulation of transcription, translation, and DNA replication. However, the substrates through which DNA-PKcs regulates these processes remain largely undefined. Here, we utilized quantitative phosphoproteomics to generate a high coverage map of DNA-PKcs signaling in response to ionizing radiation and mapped its interplay with the ATM kinase. Beyond the detection of the canonical S/T-Q phosphorylation motif, we uncovered a noncanonical mode of DNA-PKcs signaling targeting S/T-ψ-D/E motifs. Sequence and structural analyses of the DNA-PKcs substrate recognition pocket revealed unique features compared to closely related phosphatidylinositol 3-kinase-related kinases that may explain its broader substrate preference. These findings expand the repertoire of DNA-PKcs and ATM substrates while establishing a novel preferential phosphorylation motif for DNA-PKcs.

FOXO3a-interacting proteins' involvement in cancer: a review

Due to its role in apoptosis, differentiation, cell cycle arrest, and DNA damage repair in stress responses (oxidative stress, hypoxia, chemotherapeutic drugs, and UV irradiation or radiotherapy), FOXO3a is considered a key tumor suppressor that determines radiotherapeutic and chemotherapeutic responses in cancer cells. Mutations in the FOXO3a gene are rare, even in cancer cells. Post-translational regulations are the main mechanisms for inactivating FOXO3a. The subcellular localization, stability, transcriptional activity, and DNA binding affinity for FOXO3a can be modulated via various post-translational modifications, including phosphorylation, acetylation, and interactions with other transcriptional factors or regulators. This review summarizes how proteins that interact with FOXO3a engage in cancer progression.

IN-DEPTH MAPPING OF DNA-PKcs SIGNALING UNCOVERS CONSERVED FEATURES OF ITS KINASE SPECIFICITY

DNA-PKcs is a DNA damage sensor kinase with established roles in DNA double-strand break repair via non-homologous end joining. Recent studies have revealed additional roles of DNA-PKcs in the regulation of transcription, translation and DNA replication. However, the substrates through which DNA-PKcs regulates these processes remain largely undefined. Here we utilized quantitative phosphoproteomics to generate a high coverage map of DNA-PKcs signaling in response to ionizing radiation and mapped its interplay with the ATM kinase. Beyond the detection of the canonical S/T-Q phosphorylation motif, we uncovered a non-canonical mode of DNA-PKcs signaling targeting S/T-ψ-D/E motifs. Cross-species analysis in mouse pre-B and human HCT116 cell lines revealed splicing factors and transcriptional regulators phosphorylated at this novel motif, several of which contain SAP domains. These findings expand the list of DNA-PKcs and ATM substrates and establish a novel preferential phosphorylation motif for DNA-PKcs that connects it to proteins involved in nucleotide processes and interactions.

Radiofrequency EMF irradiation effects on pre-B lymphocytes undergoing somatic recombination

Intense electromagnetic fields (EMFs) induce DNA double stranded breaks (DSBs) in exposed lymphocytes.We study developing pre-B lymphocytes following V(D)J recombination at their Immunoglobulin light chain loci (IgL). Recombination physiologically induces DNA DSBs, and we tested if low doses of EMF irradiation affect this developmental stage. Recombining pre-B cells, were exposed for 48 h to low intensity EMFs (maximal radiative power density flux S of 9.5 µW/cm² and electric field intensity 3 V/m) from waves of frequencies ranging from 720 to 1224 MHz. Irradiated pre-B cells show decreased levels of recombination, reduction which is dependent upon the power dose and most remarkably upon the frequency of the applied EMF. Although 50% recombination reduction cannot be obtained even for an S of 9.5 µW/cm² in cells irradiated at 720 MHz, such an effect is reached in cells exposed to only 0.45 µW/cm² power with 950 and 1000 MHz waves. A maximal four-fold recombination reduction was measured in cells exposed to 1000 MHz waves with S from 0.2 to 4.5 µW/cm² displaying normal levels of γH2AX phosphorylated histone. Our findings show that developing B cells exposure to low intensity EMFs can affect the levels of production and diversity of their antibodies repertoire.

HTLV-1 Tax-mediated inhibition of FOXO3a activity is critical for the persistence of terminally differentiated CD4+ T cells

The mechanisms involved in the persistence of activated CD4+ T lymphocytes following primary human T leukemia/lymphoma virus type 1 (HTLV-1) infection remain unclear. Here, we demonstrate that the HTLV-1 Tax oncoprotein modulates phosphorylation and transcriptional activity of the FOXO3a transcription factor, via upstream activation of the AKT pathway. De novo HTLV-1 infection of CD4+ T cells or direct lentiviral-mediated introduction of Tax led to AKT activation and AKT-dependent inactivation of FOXO3a, via phosphorylation of residues Ser253 and Thr32. Inhibition of FOXO3a signalling led to the long-term survival of a population of highly activated, terminally differentiated CD4+Tax+CD27negCCR7neg T cells that maintained the capacity to disseminate infectious HTLV-1. CD4+ T cell persistence was reversed by chemical inhibition of AKT activity, lentiviral-mediated expression of a dominant-negative form of FOXO3a or by specific small interfering RNA (siRNA)-mediated silencing of FOXO3a. Overall this study provides new mechanistic insight into the strategies used by HTLV-1 to increase long-term maintenance of Tax+CD4+ T lymphocytes during the early stages of HTLV-1 pathogenesis.

FoxO3a and disease progression

The Forkhead box O (FoxO) family has recently been highlighted as an important transcriptional regulator of crucial proteins associated with the many diverse functions of cells. So far, FoxO1, FoxO3a, FoxO4 and FoxO6 proteins have been identified in humans. Although each FoxO family member has its own role, unlike the other FoxO families, FoxO3a has been extensively studied because of its rather unique and pivotal regulation of cell proliferation, apoptosis, metabolism, stress management and longevity. FoxO3a alteration is closely linked to the progression of several types of cancers, fibrosis and other types of diseases. In this review, we will examine the function of FoxO3a in disease progression and also explore FoxO3a’s regulatory mechanisms. We will also discuss FoxO3a as a potential target for the treatment of several types of disease.

PPARγ and Oxidative Stress: Con(β) Catenating NRF2 and FOXO

Peroxisome-proliferator activator receptor γ (PPARγ) is a nuclear receptor of central importance in energy homeostasis and inflammation. Recent experimental pieces of evidence demonstrate that PPARγ is implicated in the oxidative stress response, an imbalance between antithetic prooxidation and antioxidation forces that may lead the cell to apoptotic or necrotic death. In this delicate and intricate game of equilibrium, PPARγ stands out as a central player devoted to the quenching and containment of the damage and to foster cell survival. However, PPARγ does not act alone: indeed the nuclear receptor is at the point of interconnection of various pathways, such as the nuclear factor erythroid 2-related factor 2 (NRF2), Wnt/β-catenin, and forkhead box proteins O (FOXO) pathways. Here we reviewed the role of PPARγ in response to oxidative stress and its interaction with other signaling pathways implicated in this process, an interaction that emerged as a potential new therapeutic target for several oxidative-related diseases.

Applications of post-translational modifications of FoxO family proteins in biological functions

The functions of the FoxO family proteins, in particular their transcriptional activities, are modulated by post-translational modifications (PTMs), including phosphorylation, acetylation, ubiquitination, methylation and glycosylation. These PTMs occur in response to different cellular stresses, which in turn regulate the subcellular localization of FoxO family proteins, as well as their half-life, DNA binding, transcriptional activity and ability to interact with other cellular proteins. In this review, we summarize the role of PTMs of FoxO family proteins in linking their biological and functional relevance with various diseases.