Pharmacologic PPAR-γ Activation Reprograms Bone Marrow Macrophages and Partially Rescues HSPC Mobilization in Human and Murine Diabetes.

Mobilization of hematopoietic stem/progenitor cells (HSPC) from the bone marrow (BM) is impaired in diabetes. Excess oncostatin M (OSM) produced by M1 macrophages in the diabetic BM signals through p66Shc to induce Cxcl12 in stromal cells and retain HSPC. BM adipocytes are another source of CXCL12 that blunts mobilization. We tested a strategy of pharmacologic macrophage reprogramming to rescue HSPC mobilization. In vitro, PPAR-γ activation with pioglitazone switched macrophages from M1 to M2, reduced Osm expression, and prevented transcellular induction of Cxcl12 In diabetic mice, pioglitazone treatment downregulated Osm, p66Shc, and Cxcl12 in the hematopoietic BM, restored the effects of granulocyte-colony stimulation factor (G-CSF), and partially rescued HSPC mobilization, but it increased BM adipocytes. Osm deletion recapitulated the effects of pioglitazone on adipogenesis, which was p66Shc independent, and double knockout of Osm and p66Shc completely rescued HSPC mobilization. In the absence of OSM, BM adipocytes produced less CXCL12, being arguably devoid of HSPC-retaining activity, whereas pioglitazone failed to downregulate Cxcl12 in BM adipocytes. In patients with diabetes on pioglitazone therapy, HSPC mobilization after G-CSF was partially rescued. In summary, pioglitazone reprogrammed BM macrophages and suppressed OSM signaling, but sustained Cxcl12 expression by BM adipocytes could limit full recovery of HSPC mobilization.

p66Shc promotes HCC progression in the tumor microenvironment via STAT3 signaling.

The development of hepatocellular carcinoma (HCC) is strongly associated with chronic inflammation. p66Shc is an oxidase previously shown to promote androgen-independent cell growth through generation of reactive oxygen species. However, the importance and biologic functions of p66Shc in HCC are unclear. The clinical significance of p66Shc was assessed in a large cohort of patients with HCC. High Shc1 expression was closely correlated with poor clinical outcomes and early recurrence of HCC. p66Shc expression was also determined in HCC samples and cell lines and found to be increased. Moreover, knockdown of p66Shc significantly inhibited cell proliferation, motility in vitro and tumor growth in vivo and could attenuate the proliferation, and motility of cells stimulated by activated macrophage conditioned media. Mechanically, p66Shc knockdown inhibited phosphorylation of STAT3 on serine 727 in vitro and in vivo. Our results show that high p66Shc expression in HCC predicts a worse prognosis for survival. Furthermore, p66Shc may serve as a novel candidate target for HCC therapy.

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.

Perturbations in mitochondrial dynamics by p66Shc lead to renal tubular oxidative injury in human diabetic nephropathy.

Renal tubular injury is increasingly being recognized as an early characteristic of diabetic nephropathy (DN). Mitochondrial dynamic alterations and redox protein p66Shc-mediated oxidative stress are both critical for ensuing diabetic tubular cell injury and apoptosis; whether these two processes are interlinked remains unclear. In the present study, we observed changes in mitochondrial morphology and expression of associated proteins in tubules of patients with DN. We demonstrated mitochondrial fragmentation as an important pathogenic feature of tubular cell injury that is linked to oxidative stress and p66Shc up-regulation. In renal proximal tubular cells, alterations in mitochondrial dynamics and expression of fission-fusion proteins were observed under high glucose (HG) ambience, along with p66Shc Ser36 phosphorylation. Gene ablation of p66Shc alleviated HG-induced mitochondrial fragmentation, down-regulated Fis1 and reduced p66Shc-Fis1 binding, increased Mfn1 expression, and disrupted interactions between Mfn1 and proapoptotic Bak. Overexpression of p66Shc exacerbated these changes, whereas overexpression of dominant-negative p66Shc Ser36 mutant had a marginal effect under HG, indicating that p66Shc phosphorylation as a prerequisite in the modulation of mitochondrial dynamics. Disrupted mitochondrial dynamics and enhanced Mfn1-Bak interactions modulated by p66Shc led to loss of mitochondrial voltage potential, cytochrome C release, excessive ROS generation, and apoptosis. Taken together, these results link p66Shc to mitochondrial dynamic alterations in the pathogenesis of DN and unveil a novel mechanism by which p66Shc mediates HG-induced mitochondrial fragmentation and proapoptotic signaling that results in oxidative injury and apoptosis in the tubular compartment in human diabetic nephropathy.

Heritable, Allele-Specific Chromosomal Looping between Tandem Promoters Specifies Promoter Usage of SHC1.

One-half of the genes in the human genome contain alternative promoters, some of which generate products with opposing functions. Aberrant silencing or activation of such alternative promoters is associated with multiple diseases, including cancer, but little is known regarding the molecular mechanisms that control alternative promoter choice. The SHC1 gene encodes p46Shc/p52Shc and p66Shc, proteins oppositely regulating anchorage-independent growth that are produced by transcription initiated from the upstream and downstream tandem promoters of SHC1, respectively. Here we demonstrate that activation of these promoters is mutually exclusive on separate alleles in single primary endothelial cells in a heritable fashion, ensuring expression of both transcripts by the cell. Peripheral blood lymphocytes that do not transcribe p66Shc transcribed p52Shc biallelically. This distinct monoallelic transcription pattern is established by allele-specific chromosomal looping between tandem promoters, which silences the upstream promoter. Our results reveal a new mechanism to control alternative promoter usage through higher-order chromatin structure.

p66Shc regulates migration of castration-resistant prostate cancer cells.

Metastatic castration-resistant (CR) prostate cancer (PCa) is a lethal disease for which no effective treatment is currently available. p66Shc is an oxidase previously shown to promote androgen-independent cell growth through generation of reactive oxygen species (ROS) and is elevated in clinical PCa and multiple CR PCa cell lines. We hypothesize p66Shc also increases the migratory activity of PCa cells through ROS and investigate the associated mechanism. Using the transwell assay, our study reveals that the level of p66Shc protein correlates with cell migratory ability across several PCa cell lines. Furthermore, we show hydrogen peroxide treatment induces migration of PCa cells that express low levels of p66Shc in a dose-dependent manner, while antioxidants inhibit migration. Conversely, PCa cells that express high levels of endogenous p66Shc or by cDNA transfection possess increased cell migration which is mitigated upon p66Shc shRNA transfection or expression of oxidase-deficient dominant-negative p66Shc W134F mutant. Protein microarray and immunoblot analyses reveal multiple proteins, including ErbB-2, AKT, mTOR, ERK, FOXM1, PYK2 and Rac1, are activated in p66Shc-elevated cells. Their involvement in PCa migration was examined using respective small-molecule inhibitors. The role of Rac1 was further validated using cDNA transfection and, significantly, p66Shc is found to promote lamellipodia formation through Rac1 activation. In summary, the results of our current studies clearly indicate p66Shc also regulates PCa cell migration through ROS-mediated activation of migration-associated proteins, notably Rac1.

Role of p66shc in skeletal muscle function.

p66shc is a growth factor adaptor protein that contributes to mitochondrial ROS production. p66shc is involved in insulin signaling and its deletion exerts a protective effect against diet-induced obesity. In light of the role of skeletal muscle activity in the control of systemic metabolism and obesity, we investigated which is the contribution of p66shc in regulating muscle structure and function. Here, we show that p66shc-/- muscles are undistinguishable from controls in terms of size, resistance to denervation-induced atrophy, and force. However, p66shc-/- mice perform slightly better than wild type animals during repetitive downhill running. Analysis of the effects after placing mice on a high fat diet (HFD) regimen demonstrated that running distance is greatly reduced in obese wild type animals, but not in overweight-resistant p66shc-/- mice. In addition, muscle force measured after exercise decreases upon HFD in wild type mice while p66shc-/- animals are protected. Our data indicate that p66shc affect the response to damage of adult muscle in chow diet, and it determines the maintenance of muscle force and exercise performance upon a HFD regimen.

Inhibition of p66Shc-mediated mitochondrial apoptosis via targeting prolyl-isomerase Pin1 attenuates intestinal ischemia/reperfusion injury in rats.

Intestinal epithelial oxidative stress and apoptosis constitute key pathogenic mechanisms underlying intestinal ischemia/reperfusion (I/R) injury. We previously reported that the adaptor 66 kDa isoform of the adaptor molecule ShcA (p66Shc)-mediated pro-apoptotic pathway was activated after intestinal I/R. However, the upstream regulators of the p66Shc pathway involved in intestinal I/R remain to be fully identified. Here, we focused on the role of a prolyl-isomerase, peptidyl-prolyl cis-trans isomerase (Pin1), in the regulation of p66Shc activity during intestinal I/R. Intestinal I/R was induced in rats by superior mesenteric artery (SMA) occlusion. Juglone (Pin1 inhibitor) or vehicle was injected intraperitoneally before I/R challenge. Caco-2 cells were exposed to hypoxia/reoxygenation (H/R) in vitro to simulate an in vivo I/R model. We found that p66Shc was significantly up-regulated in the I/R intestine and that this up-regulation resulted in the accumulation of intestinal mitochondrial reactive oxygen species (ROS) and massive epithelial apoptosis. Moreover, intestinal I/R resulted in elevated protein expression and enzyme activity of Pin1 as well as increased interaction between Pin1 and p66Shc. This Pin1 activation was responsible for the translocation of p66Shc to the mitochondria during intestinal I/R, as Pin1 suppression by juglone or siRNA markedly blunted p66Shc mitochondrial translocation and the subsequent ROS generation and cellular apoptosis. Additionally, Pin1 inhibition alleviated gut damage and secondary lung injury, leading to improvement of survival after I/R. Collectively, our findings demonstrate for the first time that Pin1 inhibition protects against intestinal I/R injury, which could be partially attributed to the p66Shc-mediated mitochondrial apoptosis pathway. This may represent a novel prophylactic target for intestinal I/R injury.

Detachment-Based Equilibrium of Anoikic Cell Death and Autophagic Cell Survival Through Adaptor Protein p66(Shc).

Anoikis (detachment-induced cell death) confers a tumor-suppressive function in metastatic cancer cells. Autophagy, a conserved self-degradative process, enhances the anoikis resistance of detached cancer cells by maintaining cellular homeostasis. However, the mechanism of regulating cell fate-decision by balancing anoikis and autophagy has been poorly understood. Our previous studies have shown that the adaptor protein p66(Shc) mediates anoikis through RhoA activation and inhibits tumor metastasis in vivo. We also found that p66(Shc) depletion mitigates nutrient-deprivation-induced autophagy. These findings suggest p66(Shc) may coordinately regulate these two processes. To verify this hypothesis, we investigated the effect of p66(Shc) on the cell death of detached lung cancer cells, and measured autophagy markers and autophagic flux. Results showed that p66(Shc) depletion significantly inhibited anoikis, and reduced the formation of LC3B-II and the degradation of Sequestosome 1 (SQSTM1, p62) in detachment-induced cells. Using monodansylcadaverine (MDC)-LysoTracker double staining and monomeric Cherry (mCherry)-GFP-LC3 assay, we found that the autophagic flux was also mitigated by p66(Shc) depletion. In addition, p66(Shc) knockdown increased the formation of full-length X-linked inhibitor of apoptosis (XIAP)-associated factor 1 (XAF1), which enhances anoikis sensitivity. In conclusion, p66(Shc) plays an essential role in detachment-based equilibrium of anoikic cell death and autophagic cell survival.