p66SHC promotes apoptosis and antagonizes mitogenic signaling in T cells

Potential New Therapies "ROS-Based" in CLL: An Innovative Paradigm in the Induction of Tumor Cell Apoptosis

Chronic lymphocytic leukemia, in spite of recent advancements, is still an incurable disease; the majority of patients eventually acquire resistance to treatment through relapses. In all subtypes of chronic lymphocytic leukemia, the disruption of normal B-cell homeostasis is thought to be mostly caused by the absence of apoptosis. Consequently, apoptosis induction is crucial to the management of this illness. Damaged biological components can accumulate as a result of the oxidation of intracellular lipids, proteins, and DNA by reactive oxygen species. It is possible that cancer cells are more susceptible to apoptosis because of their increased production of reactive oxygen species. An excess of reactive oxygen species can lead to oxidative stress, which can harm biological elements like DNA and trigger apoptotic pathways that cause planned cell death. In order to upset the balance of oxidative stress in cells, recent therapeutic treatments in chronic lymphocytic leukemia have focused on either producing reactive oxygen species or inhibiting it. Examples include targets created in the field of nanomedicine, natural extracts and nutraceuticals, tailored therapy using biomarkers, and metabolic targets. Current developments in the complex connection between apoptosis, particularly ferroptosis and its involvement in epigenomics and alterations, have created a new paradigm.

P66Shc Mediates SUMO2-induced Endothelial Dysfunction

Sumoylation is a post-translational modification that can regulate different physiological functions. Increased sumoylation, specifically conjugation of SUMO2/3 (small ubiquitin like modifier 2/3), is detrimental to vascular health. However, the molecular mechanism mediating this effect is poorly understood. Here, we demonstrate that SUMO2 modifies p66Shc, which impairs endothelial function. Using multiple approaches, we show that p66Shc is a direct target of SUMO2. Mass spectrometry identified that SUMO2 modified lysine-81 in the unique collagen homology-2 domain of p66Shc. SUMO2ylation of p66Shc increased phosphorylation at serine-36, causing it to translocate to the mitochondria. Notably, sumoylation-deficient p66Shc (p66ShcK81R) was resistant to SUMO2-induced p66ShcS36 phosphorylation and mitochondrial translocation. Ingenuity pathway analysis showed that majority of effects of p66Shc SUMO2ylation were mediated via p66ShcK81. Finally, p66ShcK81R knockin mice were resistant to SUMO2-induced endothelial dysfunction. Collectively, our work uncovers a posttranslational modification of redox protein p66Shc and identifies SUMO2-p66Shc signaling as a regulator of vascular endothelial function.

p66Shc deficiency in CLL cells enhances PD-L1 expression and suppresses immune synapse formation

Introduction: Escape from immunosurveillance is a hallmark of chronic lymphocytic leukemia (CLL) cells. In the protective niche of lymphoid organs, leukemic cells suppress the ability of T lymphocytes to form the immune synapse (IS), thereby hampering T-cell mediated anti-tumoral activities. By binding its cognate receptor PD-1 at the surface of T lymphocytes, the inhibitory ligand PD-L1, which is overexpressed in CLL cells, mediates the T-cell suppressive activities of CLL cells. However, the molecular mechanism underlying PD-L1 overexpression in CLL cells remains unknown. We have previously reported a defective expression of the pro-apoptotic and pro-oxidant adaptor p66Shc in CLL cells, which is causally related to an impairment in intracellular reactive oxygen species (ROS) production and to the activation of the ROS-sensitive transcription factor NF-κB. The fact that PD-L1 expression is regulated by NF-κB suggests a mechanistic relationship between p66Shc deficiency and PD-L1 overexpression in CLL cells. Methods: 62 treatment-naive CLL patients and 43 healthy donors were included in this study. PD-L1 and p66Shc expression was quantified in B cells by flow cytometry and qRT-PCR. IS architecture and local signaling was assessed by flow cytometry and confocal microscopy. CD8+ cell killing activity was assessed by flow cytometry. Results: Here we show that residual p66Shc expression in leukemic cells isolated both from CLL patients and from the CLL mouse model Eμ-TCL1 inversely correlated with PD-L1 expression. We also show that the PD-L1 increase prevented leukemic cells from forming ISs with T lymphocytes. Reconstitution of p66Shc, but not of a ROS-defective mutant, in both CLL cells and the CLL-derived cell line MEC-1, enhanced intracellular ROS and decreased PD-L1 expression. Similar results were obtained following treatment of CLL cells with H2O2 as exogenous source of ROS, that normalized PD-L1 expression and recovered IS formation. Discussion: Our data provide direct evidence that the p66Shc-deficiency-related ROS depletion in CLL cells concurs to enhance PD-L1 expression and provides a mechanistic basis for the suppression of T cell-mediated anti-tumoral functions in the immunosuppressive lymphoid niche.

Deletion of p66Shc Dysregulates ERK and STAT3 Activity in Mouse Embryonic Stem Cells, Enhancing Their Naive-Like Self-Renewal in the Presence of Leukemia Inhibitory Factor

The ShcA adapter protein is necessary for early embryonic development. The role of ShcA in development is primarily attributed to its 52 and 46 kDa isoforms that transduce receptor tyrosine kinase signaling through the extracellular signal regulated kinase (ERK). During embryogenesis, ERK acts as the primary signaling effector, driving fate acquisition and germ layer specification. P66Shc, the largest of the ShcA isoforms, has been observed to antagonize ERK in several contexts; however, its role during embryonic development remains poorly understood. We hypothesized that p66Shc could act as a negative regulator of ERK activity during embryonic development, antagonizing early lineage commitment. To explore the role of p66Shc in stem cell self-renewal and differentiation, we created a p66Shc knockout murine embryonic stem cell (mESC) line. Deletion of p66Shc enhanced basal ERK activity, but surprisingly, instead of inducing mESC differentiation, loss of p66Shc enhanced the expression of core and naive pluripotency markers. Using pharmacologic inhibitors to interrogate potential signaling mechanisms, we discovered that p66Shc deletion permits the self-renewal of naive mESCs in the absence of conventional growth factors, by increasing their responsiveness to leukemia inhibitory factor (LIF). We discovered that loss of p66Shc enhanced not only increased ERK phosphorylation but also increased phosphorylation of Signal transducer and activator of transcription in mESCs, which may be acting to stabilize their naive-like identity, desensitizing them to ERK-mediated differentiation cues. These findings identify p66Shc as a regulator of both LIF-mediated ESC pluripotency and of signaling cascades that initiate postimplantation embryonic development and ESC commitment.

p66Shc in Cardiovascular Pathology

p66Shc is a widely expressed protein that governs a variety of cardiovascular pathologies by generating, and exacerbating, pro-apoptotic ROS signals. Here, we review p66Shc’s connections to reactive oxygen species, expression, localization, and discuss p66Shc signaling and mitochondrial functions. Emphasis is placed on recent p66Shc mitochondrial function discoveries including structure/function relationships, ROS identity and regulation, mechanistic insights, and how p66Shc-cyt c interactions can influence p66Shc mitochondrial function. Based on recent findings, a new p66Shc mitochondrial function model is also put forth wherein p66Shc acts as a rheostat that can promote or antagonize apoptosis. A discussion of how the revised p66Shc model fits previous findings in p66Shc-mediated cardiovascular pathology follows.

Hematopoietic and Nonhematopoietic p66Shc Differentially Regulates Stem Cell Traffic and Vascular Response to Ischemia in Diabetes

Aims: Peripheral artery disease (PAD) is a severe complication of diabetes, characterized by defective traffic of hematopoietic stem/progenitor cells (HSPCs). We examined the hematopoietic versus nonhematopoietic role of p66Shc in regulating HSPC traffic and blood flow recovery after ischemia in diabetic mice. Results: Using streptozotocin-induced diabetes, chimeric mice with green fluorescent protein (GFP)⁺ bone marrow (BM), and the hind limb ischemia model, we found that the physiologic mobilization and homing of HSPCs were abolished by diabetes, along with impaired vascular recovery. Hematopoietic deletion of p66Shc, obtained by transplanting p66Shc^-/- BM cells into wild-type (Wt) recipients, but not nonhematopoietic deletion, constrained hyperglycemia-induced myelopoiesis, rescued postischemic HSPC mobilization, and improved blood flow recovery in diabetic mice. In Wt diabetic mice transplanted with BM cells from GFP⁺p66Shc^-/- mice, the amount of HSPCs homed to ischemic muscles was greater than in mice transplanted with GFP⁺p66Shc^+/+ cells, with recruited cells displaying higher expression of adhesion molecules and Vegf. In 40 patients with diabetes, p66Shc gene expression in mononuclear cells was correlated with myelopoiesis and elevated in the presence of PAD. In 13 patients with diabetes and PAD, p66Shc expression in HSPC-mobilized peripheral blood cells was inversely correlated with VEGF expression. Innovation: For the first time, we dissect the role of hematopoietic versus nonhematopoietic p66Shc in regulating HSPC traffic and ischemic responses. Conclusion: Hematopoietic deletion of p66Shc was sufficient to rescue HSPC mobilization and homing in diabetes after ischemia and improved blood flow recovery. Inhibiting p66Shc in blood cells may be a novel strategy to counter PAD in diabetes. Antioxid. Redox Signal. 36, 593-607. Clinical Trial No.: NCT02790957.

Unraveling and Targeting Myocardial Regeneration Deficit in Diabetes

Cardiomyopathy is a common complication in diabetic patients. Ventricular dysfunction without coronary atherosclerosis and hypertension is driven by hyperglycemia, hyperinsulinemia and impaired insulin signaling. Cardiomyocyte death, hypertrophy, fibrosis, and cell signaling defects underlie cardiomyopathy. Notably, detrimental effects of the diabetic milieu are not limited to cardiomyocytes and vascular cells. The diabetic heart acquires a senescent phenotype and also suffers from altered cellular homeostasis and the insufficient replacement of dying cells. Chronic inflammation, oxidative stress, and metabolic dysregulation damage the population of endogenous cardiac stem cells, which contribute to myocardial cell turnover and repair after injury. Therefore, deficient myocardial repair and the progressive senescence and dysfunction of stem cells in the diabetic heart can represent potential therapeutic targets. While our knowledge of the effects of diabetes on stem cells is growing, several strategies to preserve, activate or restore cardiac stem cell compartments await to be tested in diabetic cardiomyopathy.

Progression Risk Score Estimation Based on Immunostaining Data in Oral Cancer Using Unsupervised Hierarchical Clustering Analysis: A Retrospective Study in Taiwan

This study aimed to investigate whether the progression risk score (PRS) developed from cytoplasmic immunohistochemistry (IHC) biomarkers is available and applicable for assessing risk and prognosis in oral cancer patients. Participants in this retrospective case-control study were diagnosed between 2012 and 2014 and subsequently underwent surgical intervention. The specimens from surgery were stained by IHC for 16 cytoplasmic target markers. We evaluated the results of IHC staining, clinical and pathological features, progression-free survival (PFS), and overall survival (OS) of 102 oral cancer patients using a novel estimation approach with unsupervised hierarchical clustering analysis. Patients were stratified into high-risk (52) and low-risk (50) groups, according to their PRS; a metric consisting of cytoplasmic PLK1, PhosphoMet, SGK2, and SHC1 expression. Moreover, PRS could be extended for use in the Cox proportional hazard regression model to estimate survival outcomes with associated clinical parameters. Our study findings revealed that the high-risk patients had a significantly increased risk in cancer progression compared with low-risk patients (hazard ratio (HR) = 2.20, 95% confidence interval (CI) = 1.10-2.42, p = 0.026). After considering the influences of demographics, risk behaviors, and tumor characteristics, risk estimation with PRS provided distinct PFS groups for patients with oral cancer (p = 0.017, p = 0.019, and p = 0.020). Our findings support that PRS could serve as an ideal biomarker for clinical use in risk stratification and progression assessment in oral cancer.

Epidermal growth factor receptor and integrins meet redox signaling through P66shc and Rac1

This review examines the concerted role of Epidermal Growth Factor Receptor (EGFR) and integrins in regulating Reactive oxygen species (ROS) production through different signaling pathways. ROS as such are not always deleterious to the cells but they also act as signaling molecules, that regulates numerous indespensible physiological fuctions of life. Many adaptor proteins, particularly Shc and Grb2, are involved in mediating the downstream signaling pathways stimulated by EGFR and integrins. Integrin-induced activation of EGFR and subsequent tyrosine phosphorylation of a class of acceptor sites on EGFR leads to alignment and tyrosine phosphorylation of Shc, PLCγ, the p85 subunit of PI-3 K, and Cbl, followed by activation of the downstream targets Erk and Akt/PKB. Functional interactions between these receptors result in the activation of Rac1 via these adaptor proteins, thereby leading to Reactive Oxygen Species. Both GF and integrin activation can produce oxidants independently, however synergistically there is increased ROS generation, suggesting a mutual cooperation between integrins and GFRs for redox signalling. The ROS produced further promotes feed-forward stimulation of redox signaling events such as MAPK activation and gene expression. This relationship has not been reviewed previously. The literature presented here can have multiple implications, ranging from looking at synergistic effects of integrin and EGFR mediated signaling mechanisms of different proteins to possible therapeutic interventions operated by these two receptors. Furthermore, such mutual redox regulation of crosstalk between EGFR and integrins not only add to the established models of pathological oxidative stress, but also can impart new avenues and opportunities for targeted antioxidant based therapeutics.

Src homolog and collagen homolog1 isoforms in acute and chronic liver injuries

Src homolog and collagen homolog (SHC) proteins are adaptor proteins bound to cell surface receptors that play an important role in signal transduction and related diseases. As an important member of the SHC protein family, SHC1 regulates cell proliferation and apoptosis, reactive oxygen species (ROS) production, and oxidative stress. Three isomeric proteins namely, p46shc, p52shc, and p66shc, are produced from the same SHC1 gene locus. All the three proteins are found in the liver, and are widely expressed in various hepatic cells. SHC1 has been proven to be associated with acute and chronic liver injuries of different etiologies, and plays important roles in liver fibrosis and hepatocellular carcinoma (HCC). Therefore, this review summarizes recent studies that discuss and explore the role of SHC1 in the occurrence and progression of liver diseases. We also provide a theoretical basis for future studies.

p66ShcA potentiates the cytotoxic response of triple-negative breast cancers to PARP inhibitors

Triple-negative breast cancers (TNBCs) lack effective targeted therapies, and cytotoxic chemotherapies remain the standard of care for this subtype. Owing to their increased genomic instability, poly (ADP-ribose) polymerase (PARP) inhibitors (PARPi) are being tested against TNBCs. In particular, clinical trials are now interrogating the efficacy of PARPi combined with chemotherapies. Intriguingly, while response rates are low, cohort of patients do respond to PARPi in combination with chemotherapies. Moreover, recent studies suggest that an increase in levels of ROS may sensitize cells to PARPi. This represents a therapeutic opportunity, as several chemotherapies, including doxorubicin, function in part by producing ROS. We previously demonstrated that the p66ShcA adaptor protein is variably expressed in TNBCs. We now show that, in response to therapy-induced stress, p66ShcA stimulated ROS production, which, in turn, potentiated the synergy of PARPi in combination with doxorubicin in TNBCs. This p66ShcA-induced sensitivity relied on the accumulation of oxidative damage in TNBCs, rather than genomic instability, to potentiate cell death. These findings suggest that increasing the expression of p66ShcA protein levels in TNBCs represents a rational approach to bolster the synergy between PARPi and doxorubicin.

Structure-functional implications of longevity protein p66Shc in health and disease

ShcA (Src homologous- collagen homologue), family of adapter proteins, consists of three isoforms which integrate and transduce external stimuli to different signaling networks. ShcA family consists of p46Shc, p52Shc and p66Shc isoforms, characterized by having multiple protein-lipid and protein-protein interaction domains implying their functional diversity. Among the three isoforms p66Shc is structurally different containing an additional CH2 domain which attributes to its dual functionality in cell growth, mediating both cell proliferation and apoptosis. Besides, p66Shc is also involved in different biological processes including reactive oxygen species (ROS) production, cell migration, ageing, cytoskeletal reorganization and cell adhesion. Moreover, the interplay between p66Shc and ROS is implicated in the pathology of various dreadful diseases. Accordingly, here we discuss the recent structural aspects of all ShcA adaptor proteins but are highlighting the case of p66Shc as model isoform. Furthermore, this review insights the role of p66Shc in progression of chronic age-related diseases like neuro diseases, metabolic disorders (non-alcoholic fatty liver, obesity, diabetes, cardiovascular diseases, vascular endothelial dysfunction) and cancer in relation to ROS. We finally conclude that p66Shc might act as a valuable biomarker for the prognosis of these diseases and could be used as a potential therapeutic target.

P66Shc: A Pleiotropic Regulator of B Cell Trafficking and a Gatekeeper in Chronic Lymphocytic Leukemia

Neoplastic B cells from chronic lymphocytic leukemia patients (CLL) have a profound deficiency in the expression of p66Shc, an adaptor protein with pro-apoptotic and pro-oxidant activities. This defect results in leukemic B cell resistance to apoptosis and additionally impinges on the balance between chemokine receptors that control B cell homing to secondary lymphoid organs and the sphingosine phosphate receptor S1PR1 that controls their egress therefrom, thereby favoring leukemic B cell accumulation in the pro-survival lymphoid niche. Ablation of the gene encoding p66Shc in the Eµ-TCL1 mouse model of human CLL enhances leukemogenesis and promotes leukemic cell invasiveness in both nodal and extranodal organs, providing in vivo evidence of the pathogenic role of the p66Shc defect in CLL pathogenesis. Here we present an overview of the functions of p66Shc in B lymphocytes, with a specific focus on the multiple mechanisms exploited by p66Shc to control B cell trafficking and the abnormalities in this process caused by p66Shc deficiency in CLL.

Regulation of Selective B Cell Autophagy by the Pro-oxidant Adaptor p66SHC

p66SHC is a pro-oxidant member of the SHC family of protein adaptors that acts as a negative regulator of cell survival. In lymphocytes p66SHC exploits both its adaptor and its reactive oxygen species (ROS)-elevating function to antagonize mitogenic and survival signaling and promote apoptosis. As a result, p66SHC deficiency leads to the abnormal expansion of peripheral T and B cells and lupus-like autoimmunity. Additionally, a defect in p66SHC expression is a hallmark of B cell chronic lymphocytic leukemia, where it contributes to the accumulation of long-lived neoplastic cells. We have recently provided evidence that p66SHC exerts a further layer of control on B cell homeostasis by acting as a new mitochondrial LC3-II receptor to promote the autophagic demise of dysfunctional mitochondria. Here we discuss this finding in the context of the autophagic control of B cell homeostasis, development, and differentiation in health and disease.

The Shc protein Rai enhances T-cell survival under hypoxia

Hypoxia occurs in physiological and pathological conditions. T cells experience hypoxia in pathological and physiological conditions as well as in lymphoid organs. Indeed, hypoxia-inducible factor 1α (HIF-1α) affects T cell survival and functions. Rai, an Shc family protein member, exerts pro-survival effects in hypoxic neuroblastoma cells. Since Rai is also expressed in T cells, we here investigated its role in hypoxic T cells. In this work, hypoxia differently affected cell survival, proapoptotic, and metabolic programs in T cells, depending upon Rai expression. By using Jurkat cells stably expressing Rai and splenocytes from Rai^-/- mice, we demonstrated that Rai promotes T cell survival and affects cell metabolism under hypoxia. Upon exposure to hypoxia, Jurkat T cells expressing Rai show (a) higher HIF-1α protein levels; (b) a decreased cell death and increased Akt/extracellular-signal-regulated kinase phosphorylation; (c) a decreased expression of proapoptotic markers, including caspase activities and poly(ADP-ribose) polymerase cleavage; (d) an increased glucose and lactate metabolism; (e) an increased activation of nuclear factor-kB pathway. The opposite effects were observed in hypoxic splenocytes from Rai^-/- mice. Thus, Rai plays an important role in hypoxic signaling and may be relevant in the protection of T cells against hypoxia.

Myricetin prevents thapsigargin-induced CDK5-P66Shc signalosome mediated pancreatic β-cell dysfunction

Chronic endoplasmic reticulum (ER) stress has deleterious effects on pancreatic β-cell function and survival in type 2 diabetes (T2D). Cyclin-dependent kinase 5 (CDK5) plays a critical role in β-cell failure under diabetic milieu conditions. However, little information is available on CDK5's ability to impair the function of β-cells via a chemical ER stress inducer thapsigargin. Myricetin, a natural flavonoid, has therapeutic potential for the treatment of type 2 diabetes mellitus. Therefore, we examined the effect of CDK5 on thapsigargin-induced β-cell apoptosis, and explored the relationship between myricetin and CDK5. Exposure of beta cells with thapsigargin, induced a Src-mediated redox signaling (VAV2-Rac1-NOX) formation and CDK5 activation. Activated CDK5 induced antiapoptotic protein myeloid cell leukemia sequence 1 (Mcl-1) degradation which was associated with p66Shc serine 36 phosphorylation, causing beta cell apoptosis via mitochondrial dysfunction. Exposure of beta cells to myricetin resulted in an acute inhibition of Src-mediated redox signaling (VAV2-Rac1-NOX) formation and CDK5 activation. Myricetin inhibited CDK5 activation by directly binding to its ATP-binding pocket. Treatment with myricetin also enhanced the stability of Mcl-1 after thapsigargin treatment. Inhibition of CDK5 with myricetin or roscovitine, a CDK5 inhibitor attenuates thapsigargin induced p66Shc serine 36 phosphorylation and also reduced mitochondrial dysfunction by decreasing mitochondrial ROS and caspase-3 activation. In addition, myricetin was observed to enhance PDX-1 and insulin mRNA expression and potentiate glucose stimulated insulin secretion (GSIS). Taken together, these findings indicate that thapsigargin-induced early molecular events lead to CDK5-p66Shc signalosome contributes to thapsigargin-induced pancreatic β-cell dysfunction. Myricetin blocked thapsigargin induced CDK5-p66Shc signalosome formation and prevented pancreatic beta cell dysfunction. In this study, we demonstrated for the first time that thapsigargin initiated CDK5-p66Shc signalosome mediates the pancreatic beta cell dysfunction and myricetin protects the pancreatic beta cells through the inhibition of CDK5-p66Shc signalosome.

p66Shc deficiency in the Eμ-TCL1 mouse model of chronic lymphocytic leukemia enhances leukemogenesis by altering the chemokine receptor landscape

The Shc family adaptor p66Shc acts as a negative regulator of proliferative and survival signals triggered by the B-cell receptor and, by enhancing the production of reactive oxygen species, promotes oxidative stress-dependent apoptosis. Additionally, p66Shc controls the expression and function of chemokine receptors that regulate lymphocyte traffic. Chronic lymphocytic leukemia cells have a p66Shc expression defect which contributes to their extended survival and correlates with poor prognosis. We analyzed the impact of p66Shc ablation on disease severity and progression in the Eμ-TCL1 mouse model of chronic lymphocytic leukemia. We showed that Eμ-TCL1/p66Shc^-/- mice developed an aggressive disease that had an earlier onset, occurred at a higher incidence and led to earlier death compared to that in Eμ-TCL1 mice. Eμ-TCL1/p66Shc^-/- mice displayed substantial leukemic cell accumulation in both nodal and extranodal sites. The target organ selectivity correlated with upregulation of chemokine receptors whose ligands are expressed therein. This also applied to chronic lymphocytic leukemia cells, where chemokine receptor expression and extent of organ infiltration were found to correlate inversely with these cells' level of p66Shc expression. p66Shc expression declined with disease progression in Eμ-TCL1 mice and could be restored by treatment with the Bruton tyrosine kinase inhibitor ibrutinib. Our results highlight p66Shc deficiency as an important factor in the progression and severity of chronic lymphocytic leukemia and underscore p66Shc expression as a relevant therapeutic target.

Modulation of Obesity and Insulin Resistance by the Redox Enzyme and Adaptor Protein p66Shc

Initially reported as a longevity-related protein, the 66 kDa isoform of the mammalian Shc1 locus has been implicated in several metabolic pathways, being able to act both as an adaptor protein and as a redox enzyme capable of generating reactive oxygen species (ROS) when it localizes to the mitochondrion. Ablation of p66^Shc has been shown to be protective against obesity and the insurgence of insulin resistance, but not all the studies available in the literature agree on these points. This review will focus in particular on the role of p66^Shc in the modulation of glucose homeostasis, obesity, body temperature, and respiration/energy expenditure. In view of the obesity and diabetes epidemic, p66^Shc may represent a promising therapeutic target with enormous implications for human health.

The pro-oxidant adaptor p66SHC promotes B cell mitophagy by disrupting mitochondrial integrity and recruiting LC3-II

Macroautophagy/autophagy has emerged as a central process in lymphocyte homeostasis, activation and differentiation. Based on our finding that the p66 isoform of SHC1 (p66SHC) pro-apoptotic ROS-elevating SHC family adaptor inhibits MTOR signaling in these cells, here we investigated the role of p66SHC in B-cell autophagy. We show that p66SHC disrupts mitochondrial function through its CYCS (cytochrome c, somatic) binding domain, thereby impairing ATP production, which results in AMPK activation and enhanced autophagic flux. While p66SHC binding to CYCS is sufficient for triggering apoptosis, p66SHC-mediated autophagy additionally depends on its ability to interact with membrane-associated LC3-II through a specific binding motif within its N terminus. Importantly, p66SHC also has an impact on mitochondria homeostasis by inducing mitochondrial depolarization, protein ubiquitination at the outer mitochondrial membrane, and local recruitment of active AMPK. These events initiate mitophagy, whose full execution relies on the role of p66SHC as an LC3-II receptor which brings phagophore membranes to mitochondria. Importantly, p66SHC also promotes hypoxia-induced mitophagy in B cells. Moreover, p66SHC deficiency enhances B cell differentiation to plasma cells, which is controlled by intracellular ROS levels and the hypoxic germinal center environment. The results identify mitochondrial p66SHC as a novel regulator of autophagy and mitophagy in B cells and implicate p66SHC-mediated coordination of autophagy and apoptosis in B cell survival and differentiation. Abbreviations: ACTB: actin beta; AMPK: AMP-activated protein kinase; ATP: adenosine triphosphate; ATG: autophagy-related; CYCS: cytochrome c, somatic; CLQ: chloroquine; COX: cyclooxygenase; CTR: control; GFP: green fluorescent protein; HIFIA/Hif alpha: hypoxia inducible factor 1 subunit alpha; IMS: intermembrane space; LIR: LC3 interacting region; MAP1LC3B/LC3B: microtubule associated protein 1 light chain 3 beta; MTOR/mTOR: mechanistic target of rapamycin kinase; OA: oligomycin and antimycin A; OMM: outer mitochondrial membrane; PHB: prohibitin; PBS: phosphate-buffered saline; PINK1: PTEN induced putative kinase 1; RFP: red fluorescent protein; ROS: reactive oxygen species; SHC: src Homology 2 domain-containing transforming protein; TMRM: tetramethylrhodamine, methyl ester; TOMM: translocase of outer mitochondrial membrane; ULK1: unc-51 like autophagy activating kinase 1; WT: wild-type.

P66Shc expression in diabetic rat retina

Background

P66Shc is partially localised within the mitochondrial fraction. It is primarily related to the generation of mitochondrial reactive oxygen species and apoptosis. Based on previous studies, we hypothesize that in the retina, p66Shc may exist and affect the development of diabetic retinopathy. The purpose of this study was to investigate p66Shc expression in retinal in streptozotocin-induced diabetic (SD) rats, which may provide a pathway to study the pathogenesis of diabetic retinopathy.

Methods

Reverse transcription-polymerase chain reaction (RT-PCR) and western blot were used to detect retinal p66Shc mRNA and protein expression in SD rats, respectively. Immunohistochemical staining was applied to detect the location of rat retinal p66Shc expression. TUNEL assay was applied to detect the number of apoptotic cells.

Results

P66Shc expression was found in the retina of normal and diabetic rats, and the level of mRNA and protein expression increased with the progression of diabetes mellitus (DM). P66Shc expression was mainly located in the retinal ganglion cell layer and inner nuclear layer. Compared with the normal group, retinal cell tissue apoptosis rate in the D12w group was significantly increased.

Conclusion

Rat retinal p66Shc expression was mainly in the ganglion cell layer and inner nuclear layer. As the degree of DM progressed, p66Shc expression gradually increased, and the number of apoptotic cells also increased.

Expression of the p66Shc protein adaptor is regulated by the activator of transcription STAT4 in normal and chronic lymphocytic leukemia B cells

p66Shc attenuates mitogenic, prosurvival and chemotactic signaling and promotes apoptosis in lymphocytes. Consistently, p66Shc deficiency contributes to the survival and trafficking abnormalities of chronic lymphocytic leukemia (CLL) B cells. The mechanism of p66shc silencing in CLL B cells is methylation-independent, at variance with other cancer cell types. Here we identify STAT4 as a novel transcriptional regulator of p66Shc in B cells. Chromatin immunoprecipitation and reporter gene assays showed that STAT4 binds to and activates the p66shc promoter. Silencing or overexpression of STAT4 resulted in a co-modulation of p66Shc. IL-12-dependent STAT4 activation caused a coordinate increase in STAT4 and p66Shc expression, which correlated with enhanced B cell apoptosis. Treatment with the STAT4 inhibitor lisofylline reverted partly this effect, suggesting that STAT4 phosphorylation is not essential for but enhances p66shc transcription. Additionally, we demonstrate that CLL B lymphocytes have a STAT4 expression defect which partly accounts for their p66Shc deficiency, as supported by reconstitution experiments. Finally, we show that p66Shc participates in a positive feedback loop to promote STAT4 expression. These results provide new insights into the mechanism of p66Shc expression in B cells and its defect in CLL, identifying the STAT4/IL-12 pathway as a potential therapeutic target in this neoplasia.

Ectopic ILT3 controls BCR-dependent activation of Akt in B-cell chronic lymphocytic leukemia

The high proportion of long-term nonprogressors among chronic lymphocytic leukemia (CLL) patients suggests the existence of a regulatory network that restrains the proliferation of tumor B cells. The identification of molecular determinants composing such network is hence fundamental for our understanding of CLL pathogenesis. Based on our previous finding establishing a deficiency in the signaling adaptor p66Shc in CLL cells, we undertook to identify unique phenotypic traits caused by this defect. Here we show that a lack of p66Shc shapes the transcriptional profile of CLL cells and leads to an upregulation of the surface receptor ILT3, the immunoglobulin-like transcript 3 that is normally found on myeloid cells. The ectopic expression of ILT3 in CLL was a distinctive feature of neoplastic B cells and hematopoietic stem cells, thus identifying ILT3 as a selective marker of malignancy in CLL and the first example of phenotypic continuity between mature CLL cells and their progenitors in the bone marrow. ILT3 expression in CLL was found to be driven by Deltex1, a suppressor of antigen receptor signaling in lymphocytes. Triggering of ILT3 inhibited the activation of Akt kinase upon B-cell receptor (BCR) stimulation. This effect was achieved through the dynamic coalescence of ILT3, BCRs, and phosphatidylinositol-3,4,5-trisphosphate 5-phosphatase 1 into inhibitory clusters at the cell surface. Collectively, our findings identify ILT3 as a signature molecule of p66Shc deficiency in CLL and indicate that ILT3 may functionally contribute to a regulatory network controlling tumor progression by suppressing the Akt pathway.

Novel Insights into the PKCβ-dependent Regulation of the Oxidoreductase p66Shc

Dysfunctional mitochondria contribute to the development of many diseases and pathological conditions through the excessive production of reactive oxygen species (ROS), and, where studied, ablation of p66Shc (p66) was beneficial. p66 translocates to the mitochondria and oxidizes cytochrome c to yield H₂O₂, which in turn initiates cell death. PKCβ-mediated phosphorylation of serine 36 in p66 has been implicated as a key regulatory step preceding mitochondrial translocation, ROS production, and cell death, and PKCβ thus may provide a target for therapeutic intervention. We performed a reassessment of PKCβ regulation of the oxidoreductase activity of p66. Although our experiments did not substantiate Ser³⁶ phosphorylation by PKCβ, they instead provided evidence for Ser¹³⁹ and Ser²¹³ as PKCβ phosphorylation sites regulating the pro-oxidant and pro-apoptotic function of p66. Mutation of another predicted PKCβ phosphorylation site also located in the phosphotyrosine binding domain, threonine 206, had no phenotype. Intriguingly, p66 with Thr²⁰⁶ and Ser²¹³ mutated to glutamic acid showed a gain-of-function phenotype with significantly increased ROS production and cell death induction. Taken together, these data argue for a complex mechanism of PKCβ-dependent regulation of p66 activation involving Ser¹³⁹ and a motif surrounding Ser²¹³.

ShcA Protects against Epithelial-Mesenchymal Transition through Compartmentalized Inhibition of TGF-β-Induced Smad Activation

Epithelial–mesenchymal transition (EMT) is a normal cell differentiation event during development and contributes pathologically to carcinoma and fibrosis progression. EMT often associates with increased transforming growth factor-β (TGF-β) signaling, and TGF-β drives EMT, in part through Smad-mediated reprogramming of gene expression. TGF-β also activates the Erk MAPK pathway through recruitment and Tyr phosphorylation of the adaptor protein ShcA by the activated TGF-β type I receptor. We found that ShcA protects the epithelial integrity of nontransformed cells against EMT by repressing TGF-β-induced, Smad-mediated gene expression. p52ShcA competed with Smad3 for TGF-β receptor binding, and down-regulation of ShcA expression enhanced autocrine TGF-β/Smad signaling and target gene expression, whereas increased p52ShcA expression resulted in decreased Smad3 binding to the TGF-β receptor, decreased Smad3 activation, and increased Erk MAPK and Akt signaling. Furthermore, p52ShcA sequestered TGF-β receptor complexes to caveolin-associated membrane compartments, and reducing ShcA expression enhanced the receptor localization in clathrin-associated membrane compartments that enable Smad activation. Consequently, silencing ShcA expression induced EMT, with increased cell migration, invasion, and dissemination, and increased stem cell generation and mammosphere formation, dependent upon autocrine TGF-β signaling. These findings position ShcA as a determinant of the epithelial phenotype by repressing TGF-β-induced Smad activation through differential partitioning of receptor complexes at the cell surface.

The adaptor protein ShcA protects epithelial cells from transitioning toward a mesenchymal phenotype by controlling partitioning of the TGF-β receptor and repressing downstream Smad2/3 activation.

TGF-β family proteins control cell differentiation and various cell functions. Increased TGF-β signaling, acting through heteromeric receptor complexes, contributes to carcinoma progression and fibrosis. TGF-β drives epithelial–mesenchymal transdifferentiation (EMT), which enables cell migration and invasion. Upon TGF-β binding, “type I” receptors activate, through phosphorylation, Smad2 and Smad3 that control target gene transcription. In EMT, Smad complexes activate the expression of EMT “master” transcription factors and cooperate with these to repress the epithelial phenotype and activate mesenchymal gene expression. TGF-β receptors also activate Erk MAPK signaling, involving association of the adaptor protein ShcA and Tyr phosphorylation of ShcA by type I receptors. We now show that the predominant ShcA isoform, p52ShcA, competes with Smad2/3 for binding to type I TGF-β receptors, thus repressing Smad2/3 activation in response to TGF-β and localizing the receptors to caveolar compartments. Consequently, decreased ShcA expression enhanced TGF-β receptor localization in clathrin compartments and autocrine Smad2/3 signaling, repressed the epithelial phenotype, and promoted EMT. The changes following decreased ShcA expression resulted in increased cell migration and invasion, as well as increased stem cell generation, dependent upon autocrine TGF-β signaling. These findings position ShcA as a determinant of the epithelial phenotype by repressing TGF-β-induced Smad activation through differential partitioning of receptor complexes at the cell surface.

Decoding the oxidative stress hypothesis in diabetic embryopathy through proapoptotic kinase signaling

Maternal diabetes-induced birth defects occur in 6-10% of babies born to mothers with pregestational diabetes, representing a significant maternal-fetal health problem. Currently, these congenital malformations represent a significant maternal-fetal medicine issue, but are likely to create an even greater public health threat as 3 million women of reproductive age (19-44 years) have diabetes in the United States alone, and this number is expected to double by 2030. Neural tube defects (NTDs) and congenital heart defects are the most common types of birth defects associated with maternal diabetes. Animal studies have revealed that embryos under hyperglycemic conditions exhibit high levels of oxidative stress resulting from enhanced production of reactive oxygen species and impaired antioxidant capability. Oxidative stress activates a set of proapoptotic kinase signaling intermediates leading to abnormal cell death in the embryonic neural tube, which causes NTD formation. Work in animal models also has revealed that maternal diabetes triggers a series of signaling intermediates: protein kinase C (PKC) isoforms, PKCα, βII and δ; apoptosis signal-regulating kinase 1; c-Jun-N-terminal kinase (JNK)1/2; caspase; and apoptosis. Specifically, maternal diabetes in rodent models activates the proapoptotic unfolded protein response and endoplasmic reticulum (ER) stress. A reciprocal causation between JNK1/2 activation and ER stress exists in diabetic embryopathy. Molecular studies further demonstrate that deletion of the genes for Prkc, Ask1, Jnk1, or Jnk2 abolishes maternal diabetes-induced neural progenitor apoptosis and ameliorates NTD formation. Similar preventive effects are also observed when apoptosis signal-regulating kinase 1, JNK1/2, or ER stress is inhibited. Cell membrane stabilizers and antioxidant supplements are also effective in prevention of diabetes-induced birth defects. Mechanistic studies have revealed important insights into our understanding the cause of diabetic embryopathy and have provided a basis for future interventions against birth defects or other pregnancy complications associated with maternal diabetes. The knowledge of a molecular pathway map identified in animal studies has created unique opportunities to identify molecular targets for therapeutic intervention.

A look behind the scenes: the risk and pathogenesis of primary osteoporosis

Osteoporosis is a common disorder, affecting hundreds of millions of people worldwide, and characterized by decreased bone mineral density and increased fracture risk. Known nonheritable risk factors for primary osteoporosis include advanced age, sex-steroid deficiency and increased oxidative stress. Age is a nonmodifiable risk factor, but the influence of a person's lifestyle (diet and physical activity) on their bone structure and density is modifiable to some extent. Heritable factors influencing bone fragility can be monogenic or polygenic. Osteogenesis imperfecta, juvenile osteoporosis and syndromes of decreased bone density are discussed as examples of monogenic disorders associated with bone fragility. So far, the factors associated with polygenic osteoporosis have been investigated mainly in genome-wide association studies. However, epigenetic mechanisms also contribute to the heritability of polygenic osteoporosis. Identification of these heritable and nonheritable risk factors has already led to the discovery of therapeutic targets for osteoporosis, which emphasizes the importance of research into the pathogenetic mechanisms of osteoporosis. Accordingly, this article discusses the many heritable and nonheritable factors that contribute to the pathogenesis of primary osteoporosis. Although osteoporosis can also develop secondary to many other diseases or their treatment, a discussion of the factors that contribute only to secondary osteoporosis is beyond the scope of this Review.

p66Shc as a switch in bringing about contrasting responses in cell growth: implications on cell proliferation and apoptosis

p66Shc, a member of the ShcA (Src homologous- collagen homologue) adaptor protein family, is one of the three isoforms of this family along with p46Shc and p52Shc. p66Shc, a 66 kDa protein is different from the other isoforms of the ShcA family. p66Shc is the longest isoform of the ShcA family. p66Shc has an additional CH domain at the N-terminal, called the CH2 domain, which is not not present in the other isoforms. This CH2 domain contains a very crucial S36 residue which is phosphorylated in response to oxidative stress and plays a role in apoptosis. Whereas p52Shc and p46Shc are ubiquitously expressed, p66Shc shows constrained expression. This adaptor protein has been shown to be involved in mediating and executing the post effects of oxidative stress and increasing body of evidence is pinpointing to its role in carcinogenesis as well. It shows proto-oncogenic as well as pro-apoptotic properties. This multitasking protein is involved in regulating different networks of cell signaling. On one hand it shows an increased expression profile in different cancers, has a positive role in cell proliferation and migration, whereas on the other hand it promotes apoptosis under oxidative stress conditions by acting as a sensor of ROS (Reactive Oxygen Species). This paradoxical role of p66Shc could be attributed to its involvement in ROS production, as ROS is known to both induce cell proliferation as well as apoptosis. p66Shc by regulating intracellular ROS levels plays a crucial role in regulating longevity and cell senescence. These multi-faceted properties of p66Shc make it a perfect candidate protein for further studies in various cancers and aging related diseases. p66Shc can be targeted in terms of it being used as a possible therapeutic target in various diseases. This review focuses on p66Shc and highlights its role in promoting apoptosis via different cell signaling networks, its role in cell proliferation, along with its presence and role in different forms of cancers.

The small GTPase Rab29 is a common regulator of immune synapse assembly and ciliogenesis

Accumulating evidence underscores the T-cell immune synapse (IS) as a site of intense vesicular trafficking, on which productive signaling and cell activation crucially depend. Although the T-cell antigen receptor (TCR) is known to exploit recycling to accumulate to the IS, the specific pathway that controls this process remains to be elucidated. Here we demonstrate that the small GTPase Rab29 is centrally implicated in TCR trafficking and IS assembly. Rab29 colocalized and interacted with Rab8, Rab11 and IFT20, a component of the intraflagellar transport system that regulates ciliogenesis and participates in TCR recycling in the non-ciliated T cell, as assessed by co-immunoprecipitation and immunofluorescence analysis. Rab29 depletion resulted in the inability of TCRs to undergo recycling to the IS, thereby compromizing IS assembly. Under these conditions, recycling TCRs accumulated in Rab11(+) endosomes that failed to polarize to the IS due to defective Rab29-dependent recruitment of the dynein microtubule motor. Remarkably, Rab29 participates in a similar pathway in ciliated cells to promote primary cilium growth and ciliary localization of Smoothened. These results provide a function for Rab29 as a regulator of receptor recycling and identify this GTPase as a shared participant in IS and primary cilium assembly.

CRIF1 deficiency induces p66shc-mediated oxidative stress and endothelial activation

Mitochondrial dysfunction has been implicated in the pathophysiology of various cardiovascular diseases. CRIF1 is a protein present in the mitochondria associated with large mitoribosomal subunits, and CRIF1 knockdown induces mitochondrial dysfunction and promotes ROS production. p66shc is a redox enzyme implicated in mitochondrial ROS generation and translation of oxidative signals and, therefore, is a key factor for oxidative stress in endothelial cells. In this study, we investigated whether mitochondrial dysfunction induced by CRIF1 knockdown induces p66shc stimulation and plays any role in mitochondrial dysfunction-induced endothelial activation. Knockdown of CRIF1 decreased the expression of mitochondrial oxidative phosphorylation (OXPHOS) complexes I, III and IV, leading to increased mitochondrial ROS (mtROS) and hyperpolarization of the mitochondrial membrane potential. Knockdown of CRIF1 also stimulated phosphorylation of p66shc and increased cytosolic ROS in endothelial cells. Furthermore, the expression of vascular cell adhesion molecule-1 and endoplasmic reticulum stress proteins were increased upon CRIF1 knockdown in endothelial cells. However, p66shc knockdown blunted the alteration in mitochondrial dynamics and ROS production in CRIF1 knockdown endothelial cells. In addition, p66shc knockdown reduced the CRIF1 knockdown-induced increases in adhesion between monocytes and endothelial cells. Taken together, these results suggest that CRIF1 knockdown partially induces endothelial activation via increased ROS production and phosphorylation of p66shc.

Selective inhibition of protein kinase C β2 attenuates the adaptor P66 Shc-mediated intestinal ischemia-reperfusion injury

Apoptosis is a major mode of cell death occurring during ischemia–reperfusion (I/R) induced injury. The p66^Shc adaptor protein, which is mediated by PKCβ, has an essential role in apoptosis under oxidative stress. This study aimed to investigate the role of PKCβ₂/p66^Shc pathway in intestinal I/R injury. In vivo, ischemia was induced by superior mesenteric artery occlusion in mice. Ruboxistaurin (PKCβ inhibitor) or normal saline was administered before ischemia. Then blood and gut tissues were collected after reperfusion for various measurements. In vitro, Caco-2 cells were challenged with hypoxia–reoxygenation (H/R) to simulate intestinal I/R. Translocation and activation of PKCβ₂ were markedly induced in the I/R intestine. Ruboxistaurin significantly attenuated gut damage and decreased the serum levels of tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6). Pharmacological blockade of PKCβ₂ suppressed p66^Shc overexpression and phosphorylation in the I/R intestine. Gene knockdown of PKCβ₂ via small interfering RNA (siRNA) inhibited H/R-induced p66^Shc overexpression and phosphorylation in Caco-2 cells. Phorbol 12-myristate 13-acetate (PMA), which stimulates PKCs, induced p66^Shc phosphorylation and this was inhibited by ruboxistaurin and PKCβ₂ siRNA. Ruboxistaurin attenuated gut oxidative stress after I/R by suppressing the decreased expression of manganese superoxide dismutase (MnSOD), the exhaustion of the glutathione (GSH) system, and the overproduction of malondialdehyde (MDA). As a consequence, ruboxistaurin inhibited intestinal mucosa apoptosis after I/R. Therefore, PKCβ₂ inhibition protects mice from gut I/R injury by suppressing the adaptor p66^Shc-mediated oxidative stress and subsequent apoptosis. This may represent a novel therapeutic approach for the prevention of intestinal I/R injury.

Modulating the p66shc signaling pathway with protocatechuic acid protects the intestine from ischemia-reperfusion injury and alleviates secondary liver damage

Intestinal ischemia-reperfusion (I/R) injury is a serious clinical pathophysiological process that may result in acute local intestine and remote liver injury. Protocatechuic acid (PCA), which has been widely studied as a polyphenolic compound, induces expression of antioxidative genes that combat oxidative stress and cell apoptosis. In this study, we investigated the effect of PCA pretreatment for protecting intestinal I/R-induced local intestine and remote liver injury in mice. Intestinal I/R was established by superior mesenteric artery occlusion for 45 min followed by reperfusion for 90 min. After the reperfusion period, PCA pretreatment markedly alleviated intestine and liver injury induced by intestinal I/R as indicated by histological alterations, decreases in serological damage parameters and nuclear factor-kappa B and phospho-foxo3a protein expression levels, and increases in glutathione, glutathione peroxidase, manganese superoxide dismutase protein expression, and Bcl-xL protein expression in the intestine and liver. These parameters were accompanied by PCA-induced adaptor protein p66shc suppression. These results suggest that PCA has a significant protective effect in the intestine and liver following injury induced by intestinal I/R. The protective effect of PCA may be attributed to the suppression of p66shc and the regulation of p66shc-related antioxidative and antiapoptotic factors.

Negative regulation of chemokine receptor signaling and B-cell chemotaxis by p66Shc

Shc (Src homology 2 domain containing) adaptors are ubiquitous components of the signaling pathways triggered by tyrosine kinase-coupled receptors. In lymphocytes, similar to other cell types, the p52 and p66 isoforms of ShcA/Shc participate in a self-limiting loop where p52Shc acts as a positive regulator of antigen receptor signaling by promoting Ras activation, whereas p66Shc limits this activity by competitively inhibiting p52Shc. Based on the fact that many signaling mediators are shared by antigen and chemokine receptors, including p52Shc, we have assessed the potential implication of p66Shc in the regulation of B-cell responses to chemokines, focusing on the homing receptors CXCR4 (C-X-C chemokine receptor type 4) and CXCR5 (C-X-C chemokine receptor type 5). The results identify p66Shc as a negative regulator of the chemotactic responses triggered by these receptors, including adhesion, polarization and migration. We also provide evidence that this function is dependent on the ability of p66Shc to interact with the chemokine receptors and promote the assembly of an inhibitory complex, which includes the phosphatases SHP-1 (Src homology phosphatase-1) and SHIP-1 (SH2 domain-containing inositol 5'-phosphatase-1), that results in impaired Vav-dependent reorganization of the actin cytoskeleton. This function maps to the phosphorylatable tyrosine residues in the collagen homology 1 (CH1) domain. The results identify p66Shc as a negative regulator of B-cell chemotaxis and suggest a role for this adaptor in the control of B-cell homing.

The adaptor proteins p66Shc and Grb2 regulate the activation of the GTPases ARF1 and ARF6 in invasive breast cancer cells

Signals downstream of growth factor receptors play an important role in mammary carcinogenesis. Recently, we demonstrated that the small GTPases ARF1 and ARF6 were shown to be activated downstream of the epidermal growth factor receptor (EGFR) and act as a key regulator of growth, migration, and invasion of breast cancer cells. However, the mechanism via which the EGFR recruits and activates ARF1 and ARF6 to transmit signals has yet to be fully elucidated. Here, we identify adaptor proteins Grb2 and p66Shc as important regulators mediating ARF activation. We demonstrate that ARF1 can be found in complex with Grb2 and p66Shc upon EGF stimulation of the basal-like breast cancer MDA-MB-231 cell line. However, we report that these two adaptors regulate ARF1 activation differently, with Grb2 promoting ARF1 activation and p66Shc blocking this response. Furthermore, we show that Grb2 is essential for the recruitment of ARF1 to the EGFR, whereas p66Shc hindered ARF1 receptor recruitment. We demonstrate that the negative regulatory role of p66Shc stemmed from its ability to block the recruitment of Grb2/ARF1 to the EGFR. Conversely, p66Shc potentiates ARF6 activation as well as the recruitment of this ARF isoform to the EGFR. Interestingly, we demonstrate that Grb2 is also required for the activation and receptor recruitment of ARF6. Additionally, we show an important role for p66Shc in modulating ARF activation, cell growth, and migration in HER2-positive breast cancer cells. Together, our results highlight a central role for adaptor proteins p66Shc and Grb2 in the regulation of ARF1 and ARF6 activation in invasive breast cancer cells.

The influence of Shc proteins on life span in mice

The signaling molecule p66Shc is often described as a longevity protein. This conclusion is based on a single life span study that used a small number of mice. The purpose of the present studies was to measure life span in a sufficient number of mice to determine if longevity is altered in mice with decreased Shc levels (ShcKO). Studies were completed at UC Davis and the European Institute of Oncology (EIO). At UC Davis, male C57BL/6J WT and ShcKO mice were fed 5% or 40% calorie-restricted (CR) diets. In the 5% CR group, there was no difference in survival curves between genotypes. There was also no difference between genotypes in prevalence of neoplasms or other measures of end-of-life pathology. At 40% calorie restriction group, 70th percentile survival was increased in ShcKO, while there were no differences between genotypes in median or subsequent life span measures. At EIO, there was no increase in life span in ShcKO male or female mice on C57BL/6J, 129Sv, or hybrid C57BL/6J-129Sv backgrounds. These studies indicate that p66Shc is not a longevity protein. However, additional studies are needed to determine the extent to which Shc proteins may influence the onset and severity of specific age-related diseases.

β-Amyloid-evoked apoptotic cell death is mediated through MKK6-p66shc pathway

We have previously shown the involvement of p66shc in mediating apoptosis. Here, we demonstrate the novel mechanism of β-Amyloid-induced toxicity in the mammalian cells. β-Amyloid leads to the phosphorylation of p66shc at the serine 36 residue and activates MKK6, by mediating the phosphorylation at serine 207 residue. Treatment of cells with antioxidants blocks β-Amyloid-induced serine phosphorylation of MKK6, reactive oxygen species (ROS) generation, and hence protected cells against β-Amyloid-induced cell death. Our results indicate that serine phosphorylation of p66shc is carried out by active MKK6. MKK6 knock-down resulted in decreased serine 36 phosphorylation of p66shc. Co-immunoprecipitation results demonstrate a direct physical association between p66shc and WT MKK6, but not with its mutants. Increase in β-Amyloid-induced ROS production was observed in the presence of MKK6 and p66shc, when compared to triple mutant of MKK6 (inactive) and S36 mutant of p66shc. ROS scavengers and knock-down against p66shc, and MKK6 significantly decreased the endogenous level of active p66shc, ROS production, and cell death. Finally, we show that the MKK6-p66shc complex mediates β-Amyloid-evoked apoptotic cell death.

Abnormalities of the cardiac stem and progenitor cell compartment in experimental and human diabetes

Diabetic cardiomyopathy consists of a series of structural and functional changes. Accumulating evidence supports the concept that a "cardiac stem cell compartment disease" plays an important role in the pathophysiology of diabetic cardiomyopathy. In diabetic hearts, human cardiac stem/progenitor cells (CSPC) are reduced and manifest defective proliferative capacity. Hyperglycaemia, hyperlipidemia, inflammation, and the consequent oxidative stress are enhanced in diabetes: these conditions can induce defects in both growth and survival of these cells with an imbalance between cell death and cell replacement, thus favouring the onset of diabetic cardiomyopathy and its progression towards heart failure. The preservation of CSPC compartment can contribute to counteract the negative impact of diabetes on the myocardium. The recent studies summarized in this review have improved our understanding of the development and stem cell biology within the cardiovascular system. However, several issues remain unsolved before cell therapy can become a clinical therapeutically relevant strategy.

Targeting MCT-1 oncogene inhibits Shc pathway and xenograft tumorigenicity

Overexpression of Shc adaptor proteins is associated with mitogenesis, carcinogenesis and metastasis. Multiple copies in T-cell malignancy 1 (MCT-1) oncoprotein promotes cell proliferation, survival and tumorigenic effects. Our current data show that MCT-1 is a novel regulator of Shc-Ras-MEK-ERK signaling and MCT-1 is significantly co-activated with Shc gene in human carcinomas. The knockdown of MCT-1 enhances apoptotic cell death accompanied with the activation of caspases and cleavage of caspase substrates under environmental stress. The cancer cell proliferation, chemo-resistance and tumorigenic capacity are proved to be effectively suppressed by targeting MCT-1. Accordingly, an important linkage between MCT-1 oncogenicity and Shc pathway in tumor development has now been established. Promoting MCT-1 expression by gene hyperactivation may be recognized as a tumor marker and MCT-1 may serve as a molecular target of cancer therapy.

Mitochondrial network in glioma's invadopodia displays an activated state both in situ and in vitro: potential functional implications

Gliomas are typically characterized by their infiltrative nature, and the prognosis can be linked to the invasive nature of the tumoral cells. Glioblastoma multiforme are very invasive cancers and this contributes to their lethality. The invadopodia are considered essential for their motility. Human glioma cell invadopodia were examined with transmission electron and immunofluorescent microscopy. By electron microscopy, in situ gliomas (fibrillary astrocytoma, anaplastic astrocytoma, glioblastoma multiforme, pilocytic astrocytoma) show mitochondria with a dense matrix condensed configuration, indicating an active state. The mitochondria were frequently in close contact with an extended smooth endoplasmic reticulum displaying an endoplasmic reticulum subfraction associated with mitochondria. Mitochondria were seen within the filopodia that were penetrating into the extracellular matrix. The activated mitochondria and smooth endoplasmic reticulum were also detected within the invadopdia, which was associated microblood vessels. Fluorescent microscopy confirmed that D54 and U251 glioma cells growing in vitro also contained filopodia with mitochondria. The U251 glioma cells' filopodia that penetrated through 1.2-μm pores of transwell chambers also contained mitocondria, suggesting that the mitochondria are actively involved in the invasion process. Migration and invasion of tumor cells requires an increase in cellular motility and involves formation of lamellipodia, protrusions of the plasma membrane, and individual filopodia [ 1 ]. Gliomas are typically characterized by their infiltrative nature, resulting in a poorly demarcated interface between tumor and normal brain tissue. Their poor prognosis can be linked to the invasive nature of these cells. The motility of these tumor cells is correlated with the presence of invadopodia [ 2 ], and, consequently, more insight is necessary into their structural and molecular aspects. Evidence of robust invadopodia activity in glioblastoma multiforme cells has been reported [ 3 , 4 ]. Because of the significant impact of invadopodia in oncological events such as cell invasion and matrix degradation, more insight into structural and molecular aspects is needed [ 2 ]. The dynamic assembly of invadopodia is still not well understood [ 2 ], and little is known of the alterations in mitochondrial structure and function that contribute to cell mobility [ 5 ]. This paper describes two prominent structural features of the mitochondrial network present within the glioma´s invadopodia that we have recently observed. We believe these two features (activated mitochondria and smooth ER, along with mitochondria contained within the filopodia) might provide researchers with possible targets for future therapies that can control glioma invasiveness.

Feedback loop between p66(Shc) and Nrf2 promotes lung cancer progression

p66(Shc), one of the SHC1 gene encoding proteins, promotes cell death and reports cell anchorage status, mediating anoikis in vitro and functioning as a metastasis suppressor in vivo. However, very little is known about p66(Shc) gene regulation in cancer cells. Here, we show that methylation of a specific CpG site in the early post-transcriptional region correlates with p66(Shc) repression in clinical human lung cancer samples and cancer cell lines. We also find that the stress related transcription factor Nrf2 associates with p66(Shc) gene promoter in the methylated region, and promotes p66(Shc) transcription. However, p66(Shc) induction by Nrf2 requires demethylation of the Nrf2 binding site in p66(Shc) promoter. Knock-down of p66(Shc) leads to a positive feedback upregulation of Nrf2 expression and accordingly, Nrf2 is found to be highly expressed in tumors with low p66(Shc) expression. Further, Nrf2 expression level positively correlates with tumor grade of patients. Thus, we propose that epigenetic repression of p66(Shc) in cancer cells might be a key factor leading to Nrf2 upregulation, increased cell survival, and tumor progression.

Deletion of p66Shc in mice increases the frequency of size-change mutations in the lacZ transgene

Upon oxidative challenge the genome accumulates adducts and breaks that activate the DNA damage response to repair, arrest, or eliminate the damaged cell. Thus, reactive oxygen species (ROS) generated by endogenous oxygen metabolism are thought to affect mutation frequency. However, few studies determined the mutation frequency when oxidative stress is reduced. To test whether in vivo spontaneous mutation frequency is altered in mice with reduced oxidative stress and cell death rate, we crossed p66Shc knockout (p66KO) mice, characterized by reduced intracellular concentration of ROS and by impaired apoptosis, with a transgenic line harboring multiple copies of the lacZ mutation reporter gene as part of a plasmid that can be recovered from organs into Escherichia coli to measure mutation rate. Liver and small intestine from 2- to 24-month-old, lacZ (p66Shc+/+) and lacZp66KO mice, were investigated revealing no difference in overall mutation frequency but a significant increase in the frequency of size-change mutations in the intestine of lacZp66KO mice. This difference was further increased upon irradiation of mice with X-ray. In addition, we found that knocking down cyclophilin D, a gene that facilitates mitochondrial apoptosis acting downstream of p66Shc, increased the size-change mutation frequency in small intestine. Size-change mutations also accumulated in death-resistant embryonic fibroblasts from lacZp66KO mice treated with H2 O2 . These results indicate that p66Shc plays a role in the accumulation of DNA rearrangements and suggest that p66Shc functions to clear damaged cells rather than affect DNA metabolism.

P66Shc-rac1 pathway-mediated ROS production and cell migration is downregulated by ascorbic acid

The oxidative role(s) of p66Shc protein has been increasingly expanded over the last decade. However, its relation with the most potent antioxidant molecule, i.e. ascorbic acid has never been studied. We have previously shown that p66Shc mediates rac1 activation, reactive oxygen species (ROS) production and cell death. Here we studied the effect of ascorbic acid on the pathway involving p66Shc and rac1. Our results indicate a decrease in the expression of p66Shc in a dose- and time-dependent manner. We studied the effect of ascorbic acid on rac1 expression and its activity. Ascorbic acid has no effect on total rac1 expression; however, rac1 activation was inhibited in a dose-dependent manner. Results suggest that the decrease in rac1 activity is mediated through ascorbic acid-modulated p66Shc expression. The decrease in rac1 activity was evident in cells transfected with the p66shc mutant (proline motif mutant, at residues P47 to P50). Our studies indicate that p66Shc-mediated ROS upregulation is significantly decreased in the presence of ascorbic acid. Cell migration experiments point towards the inhibition of p66Shc-rac1-mediated migration in the presence of ascorbic acid. Finally, results are suggestive that ascorbic acid-mediated decrease in Shc expression occurs through an increased Shc ubiquitination. Overall, the study brings out the novel role of ascorbic acid in antioxidant signal transduction.

Chronic nicotine exposure augments renal oxidative stress and injury through transcriptional activation of p66shc

BACKGROUND

Chronic nicotine (Ch-NIC) exposure exacerbates ischemia/reperfusion (I/R)-induced oxidative stress and acute kidney injury (AKI), and mitochondrial production of reactive oxygen species (ROS) in cultured renal proximal tubule cells (RPTCs). Because Ser36-phosphorylated p66shc modulates mitochondrial ROS production and injury of RPTCs, we hypothesized that Ch-NIC exacerbates AKI by increasing stress-induced phosphorylation of p66shc.

METHODS

We first tested whether Ch-NIC augments I/R-AKI-induced expression and phosphorylation of p66shc in vivo. We then examined whether knocking down p66shc, or impairing its Ser36 phosphorylation or binding to cytochrome c, alters the effects of Ch-NIC on oxidative stress (H₂O₂)-induced production of ROS, mitochondrial depolarization and injury in RPTCs in vitro.

RESULTS

We found that Ch-NIC increased the expression of p66shc in the control and ischemic kidneys, but only increased its Ser36 phosphorylation after renal I/R. Knocking down p66shc or impairing phosphorylation of its Ser36 residue, via the S36A mutation (but not the phosphomimetic S36D mutation), blunted Ch-NIC + H2O2-dependent ROS production, mitochondrial depolarization and injury in RPTCs. Additionally, Ch-NIC + H2O2-dependent binding of p66shc to mitochondrial cytochrome c was attenuated by S36A mutation of p66shc, and impairing cytochrome c binding (via W134F mutation) abolished ROS production, mitochondrial depolarization and injury, while ectopic overexpression of p66shc (which mimics Ch-NIC treatment) augmented oxidant injury. We determined that Ch-NIC stimulates the p66shc promoter through p53- and epigenetic modification (promoter hypomethylation).

CONCLUSIONS

Ch-NIC worsens oxidative stress-dependent acute renal injury by increasing expression and consequent oxidative stress-dependent Ser36 phosphorylation of p66shc. Thus, targeting this pathway may have therapeutic relevance in preventing/ameliorating tobacco-related kidney injury.

S1P1 expression is controlled by the pro-oxidant activity of p66Shc and is impaired in B-CLL patients with unfavorable prognosis

Although intrinsic apoptosis defects are causal to the extended survival of chronic lymphocytic leukemia (CLL) B cells, several lines of evidence support a contribution of the peripheral lymphoid organs and BM microenvironment to the extended lifespan of leukemic B cells. Lymphocyte trafficking is controlled by homing signals provided by stromal cell-derived chemokines and egress signals provided by sphingosine-1-phosphate (S1P). In the present study, we show that expression of S1P1, the S1P receptor responsible for lymphocyte egress, is selectively reduced in CLL B cells with unmutated IGHV. Expression of S1P2, which controls B-cell homeostasis, is also impaired in CLL B cells but independently of the IGHV mutational status. We provide evidence herein that p66Shc, a Shc adaptor family member the deficiency of which is implicated in the apoptosis defects of CLL B cells, controls S1P1 expression through its pro-oxidant activity. p66Shc also controls the expression of the homing receptor CCR7, which opposes S1P1 by promoting lymphocyte retention in peripheral lymphoid organs. The results of the present study provide insights into the regulation of S1P1 expression in B cells and suggest that defective egress caused by impaired S1P1 expression contributes to the extended survival of CLL B cells by prolonging their residency in the prosurvival niche of peripheral lymphoid organs.

The phosphoinositide 3-kinase signaling pathway in normal and malignant B cells: activation mechanisms, regulation and impact on cellular functions

The phosphoinositide 3-kinase (PI3K) pathway is a central signal transduction axis controlling normal B cell homeostasis and activation in humoral immunity. The p110δ PI3K catalytic subunit has emerged as a critical mediator of multiple B cell functions. The activity of this pathway is regulated at multiple levels, with inositol phosphatases PTEN and SHIP both playing critical roles. When deregulated, the PI3K pathway can contribute to B cell malignancies and autoantibody production. This review summarizes current knowledge on key mechanisms that activate and regulate the PI3K pathway and influence normal B cell functional responses including the development of B cell subsets, antigen presentation, immunoglobulin isotype switch, germinal center responses, and maintenance of B cell anergy. We also discuss PI3K pathway alterations reported in select B cell malignancies and highlight studies indicating the functional significance of this pathway in malignant B cell survival and growth within tissue microenvironments. Finally, we comment on early clinical trial results, which support PI3K inhibition as a promising treatment of chronic lymphocytic leukemia.