Teaching an old dogma new tricks: twenty years of Shc adaptor signalling

Critical role of mitogen-inducible gene 6 in restraining endothelial cell permeability to maintain vascular homeostasis

Although mitogen-inducible gene 6 (MIG6) is highly expressed in vascular endothelial cells, it remains unknown whether MIG6 affects vascular permeability. Here, we show for the first time a critical role of MIG6 in limiting vascular permeability. We unveil that genetic deletion of Mig6 in mice markedly increased VEGFA-induced vascular permeability, and MIG6 knockdown impaired endothelial barrier function. Mechanistically, we reveal that MIG6 inhibits VEGFR2 phosphorylation by binding to the VEGFR2 kinase domain 2, and MIG6 knockdown increases the downstream signaling of VEGFR2 by enhancing phosphorylation of PLCγ1 and eNOS. Moreover, MIG6 knockdown disrupted the balance between RAC1 and RHOA GTPase activation, leading to endothelial cell barrier breakdown and the elevation of vascular permeability. Our findings demonstrate an essential role of MIG6 in maintaining endothelial cell barrier integrity and point to potential therapeutic implications of MIG6 in the treatment of diseases involving vascular permeability. Xing et al. (2022) investigated the critical role of MIG6 in vascular permeability. MIG6 deficiency promotes VEGFA-induced vascular permeability via activation of PLCγ1-Ca²⁺-eNOS signaling and perturbation of the balance in RAC1/RHOA activation, resulting in endothelial barrier disruption.

ShcA promotes chondrocyte hypertrophic commitment and osteoarthritis in mice through RunX2 nuclear translocation and YAP1 inactivation

OBJECTIVE

Chondrocyte hypertrophic differentiation, a key process in endochondral ossification, is also a feature of osteoarthritis leading to cartilage destruction. Here we investigated the role of the adaptor protein Src homology and Collagen A (ShcA) in chondrocyte differentiation and osteoarthritis.

METHODS

Mice ablated for ShcA in osteochondroprogenitor cells were generated by crossing mice carrying the Twist2-Cre transgene with ShcA^flox/flox mice. Their phenotype (n = 5 to 14 mice per group) was characterized using histology, immuno-histology and western-blot. To identify the signaling mechanisms involved, in vitro experiments were conducted on wild type and ShcA deficient chondrocytes (isolated from n = 4 to 7 littermates) and the chondroprogenitor cell line ATDC5 (n = 4 independent experiments) using western-blot, cell fractionation and confocal microscopy.

RESULTS

Deletion of ShcA decreases the hypertrophic zone of the growth plate (median between group difference -11.37% [95% confidence interval -17.34 to -8.654]), alters the endochondral ossification process, and leads to dwarfism (3 months old male mice nose-to-anus length -1.48 cm [-1.860 to -1.190]). ShcA promotes ERK1/2 activation, nuclear translocation of RunX2, the master transcription factor for chondrocyte hypertrophy, while maintaining the Runx2 inhibitor, YAP1, in its cytosolic inactive form. This leads to hypertrophic commitment and expression of markers of hypertrophy, such as Collagen X. In addition, loss of ShcA protects from age-related osteoarthritis development in mice (2 years old mice OARSI score -6.67 [-14.25 to -4.000]).

CONCLUSION

This study reveals ShcA as a new player in the control of chondrocyte hypertrophic differentiation and its deletion slows down osteoarthritis development.

A Study of Combined Genotype Effects of SHCBP1 on Wool Quality Traits in Chinese Merino

SHCBP1 (Shc SH2-domain binding protein 1) is a member of the Src and collagen homolog (Shc) protein family and is closely associated with multiple signaling pathways that play important roles during hair follicle induction, morphogenesis, and cycling. The purpose of this study was to investigate SHCBP1 gene expression, polymorphisms, and the association between SHCBP1 and wool quality traits in Chinese Merino sheep. The SHCBP1 gene was shown, by qPCR, to be ubiquitously expressed in sheep tissues and differentially expressed in the adult skin of Chinese Merino and Suffolk sheep. Four SNPs (termed SHCBP1SNPs 1-4) were identified by Sanger sequencing and were located in exon 2, intron 9, intron 12, and exon 13 of the sheep SHCBP1 gene, respectively. SHCBP1SNPs 3 and 4 (rs411176240 and rs160910635) were significantly associated with wool crimp (P < 0.05). The combined polymorphism (SHCBP1SNP3-SHCBP1SNP4) was significantly associated with wool crimp (P < 0.05). Bioinformatics analysis showed that the SNPs associated with wool crimp (SHCBP1SNPs 3 and 4) might affect the pre-mRNA splicing by creating binding sites for serine-arginine-rich proteins and that SHCBP1SNP4 might alter the SHCBP1 mRNA and protein secondary structure. Our results suggest that SHCBP1 influences wool crimp and SHCBP1SNPs 3 and 4 might be useful markers for marker-assisted selection and sheep breeding.

WNT16 is Robustly Increased by Oncostatin M in Mouse Calvarial Osteoblasts and Acts as a Negative Feedback Regulator of Osteoclast Formation Induced by Oncostatin M

Background

Bone loss is often observed adjacent to inflammatory processes. The WNT signaling pathways have been implicated as novel regulators of both immune responses and bone metabolism. WNT16 is important for cortical bone mass by inhibiting osteoclast differentiation, and we have here investigated the regulation of WNT16 by several members of the pro-inflammatory gp130 cytokine family.

Methods

The expression and regulation of Wnt16 in primary murine cells were studied by qPCR, scRNAseq and in situ hybridization. Signaling pathways were studied by siRNA silencing. The importance of oncostatin M (OSM)-induced WNT16 expression for osteoclastogenesis was studied in cells from Wnt16-deficient and wild-type mice.

Results

We found that IL-6/sIL-6R and OSM induce the expression of Wnt16 in primary mouse calvarial osteoblasts, with OSM being the most robust stimulator. The induction of Wnt16 by OSM was dependent on gp130 and OSM receptor (OSMR), and downstream signaling by the SHC1/STAT3 pathway, but independent of ERK. Stimulation of the calvarial cells with OSM resulted in enhanced numbers of mature, oversized osteoclasts when cells were isolated from Wnt16 deficient mice compared to cells from wild-type mice. OSM did not affect Wnt16 mRNA expression in bone marrow cell cultures, explained by the finding that Wnt16 and Osmr are expressed in distinctly different cells in bone marrow, nor was osteoclast differentiation different in OSM-stimulated bone marrow cell cultures isolated from Wnt16^−/- or wild-type mice. Furthermore, we found that Wnt16 expression is substantially lower in cells from bone marrow compared to calvarial osteoblasts.

Conclusion

These findings demonstrate that OSM is a robust stimulator of Wnt16 mRNA in calvarial osteoblasts and that WNT16 acts as a negative feedback regulator of OSM-induced osteoclast formation in the calvarial bone cells, but not in the bone marrow.

Downregulation of SHCBP1 Inhibits Proliferation, Migration, and Invasion in Human Nasopharyngeal Carcinoma Cells

Background

SHC SH2 domain-binding protein 1 (SHCBP1), one of the members of Src homolog and collagen homolog (Shc) family, has been reported to be overexpressed in several malignant cancers and involved in tumor progression. However, the expression of SHCBP1 in nasopharyngeal carcinoma (NPC) remains unclear, and its clinical significance remains to be further elucidated.

Methods

The expression of SHCBP1 mRNA in 35 pair samples of NPC and adjacent normal tissues of NPC was detected by RT-qPCR. The expression level of SHCBP1 protein and mRNA in the selected cells was detected by western blot and RT-qPCR, respectively. The effects of SHCBP1 on NPC in vitro were observed by MTT method, colony formation assay, apoptosis assay, cell cycle assay, wound healing assay, transwell migration assay, and transwell invasion assay.

Results

SHCBP1 was highly expressed in clinical tissues and NPC cell lines, and SHCBP1 knockdown significantly inhibited NPC cell proliferation. Overexpression of SHCBP1 promoted NPC cell proliferation, migration, and invasion in NPC cell lines. Silencing SHCBP1 expression can delay cell cycle and inhibit cell apoptosis.

Conclusion

Our results suggest that SHCBP1 may promote proliferation and metastasis of NPC cells, which represents that SHCBP1 may act as a new indicator for predicting the prognosis of NPC and a new target for clinical treatment.

Double p52Shc/p46Shc Rat Knockout Demonstrates Severe Gait Abnormalities Accompanied by Dilated Cardiomyopathy

The ubiquitously expressed adaptor protein Shc exists in three isoforms p46Shc, p52Shc, and p66Shc, which execute distinctly different actions in cells. The role of p46Shc is insufficiently studied, and the purpose of this study was to further investigate its functional significance. We developed unique rat mutants lacking p52Shc and p46Shc isoforms (p52Shc/46Shc-KO) and carried out histological analysis of skeletal and cardiac muscle of parental and genetically modified rats with impaired gait. p52Shc/46Shc-KO rats demonstrate severe functional abnormalities associated with impaired gait. Our analysis of p52Shc/46Shc-KO rat axons and myelin sheets in cross-sections of the sciatic nerve revealed the presence of significant anomalies. Based on the lack of skeletal muscle fiber atrophy and the presence of sciatic nerve abnormalities, we suggest that the impaired gait in p52Shc/46Shc-KO rats might be due to the sensory feedback from active muscle to the brain locomotor centers. The lack of dystrophin in some heart muscle fibers reflects damage due to dilated cardiomyopathy. Since rats with only p52Shc knockout do not display the phenotype of p52Shc/p46Shc-KO, abnormal locomotion is likely to be caused by p46Shc deletion. Our data suggest a previously unknown role of 46Shc actions and signaling in regulation of gait.

Adaptor Protein ShcD/SHC4 Interacts with Tie2 Receptor to Synergistically Promote Glioma Cell Invasion

Gliomas are characterized by diffuse infiltration of tumor cells into surrounding brain tissue, and this highly invasive nature contributes to disease recurrence and poor patient outcomes. The molecular mechanisms underlying glioma cell invasion remain incompletely understood, limiting development of new targeted therapies. Here, we have identified phosphotyrosine adaptor protein ShcD as upregulated in malignant glioma and shown that it associates with receptor tyrosine kinase Tie2 to facilitate invasion. In human glioma cells, we find that expression of ShcD and Tie2 increases invasion, and this significant synergistic effect is disrupted with a ShcD mutant that cannot bind Tie2 or hyperphosphorylate the receptor. Expression of ShcD and/or Tie2 further increases invadopodia formation and matrix degradation in U87 glioma cells. In a coculture model, we show that U87-derived tumor spheroids expressing both ShcD and Tie2 display enhanced infiltration into cerebral organoids. Mechanistically, we identify changes in focal adhesion kinase phosphorylation in the presence of ShcD and/or Tie2 in U87 cells upon Tie2 activation. Finally, we identify a strong correlation between transcript levels of ShcD and Tie2 signaling components as well as N-cadherin in advanced gliomas and those with classical or mesenchymal subtypes, and we show that elevated expression of ShcD correlates with a significant reduction in patient survival in higher grade gliomas with mesenchymal signature. Altogether, our data highlight a novel Tie2-ShcD signaling axis in glioma cell invasion, which may be of clinical significance. IMPLICATIONS: ShcD cooperates with Tie2 to promote glioma cell invasion and its elevated expression correlates with poor patient outcome in advanced gliomas.

Shc3 promotes hepatocellular carcinoma stemness and drug resistance by interacting with β-catenin to inhibit its ubiquitin degradation pathway

Hepatocellular carcinoma (HCC) is one of the most common cancers with an insidious onset, strong invasiveness, insensitivity to chemotherapy, and poor prognosis, thus makes clinical treatment challenging. The mechanisms require further elucidation for developing novel therapies and targeting drug resistance. Here, we observed high Shc3 expression in patients with chemoresistant and recurrent HCCs. Shc3 overexpression induced a significant increase in MDR1/P-glycoprotein expression, whereas Shc3 knockdown impaired this expression. Further, Shc3 inhibition significantly restored HCC cell sensitivity to doxorubicin and sorafenib. Mechanistically, Shc3 interacted with β-catenin, inhibited destruction complex stability, promoted β-catenin release, and dampened β-catenin ubiquitination. Shc3 bound β-catenin and facilitated its nuclear translocation, prompting the β-catenin/TCF pathway to elevate MDR1 transcription. β-catenin blockage abolished the discrepancy in drug resistance between Shc3-depleted HCC cells and control cells, which further validating that β-catenin is required for Shc3-mediated liver chemotherapy. We also determined the effect of Shc3 on the sensitivity of HCC to chemotherapy in vivo. Collectively, this study provides a potential strategy to target these pathways concurrently with systemic chemotherapy that can improve the clinical treatment of HCC.

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.

Mitogen-Inducible Gene 6 Inhibits Angiogenesis by Binding to SHC1 and Suppressing Its Phosphorylation

The mitogen-inducible gene 6 (MIG6) is an adaptor protein widely expressed in vascular endothelial cells. However, it remains unknown thus far whether it plays a role in angiogenesis. Here, using comprehensive in vitro and in vivo model systems, we unveil a potent anti-angiogenic effect of MIG6 in retinal development and neovascularization and the underlying molecular and cellular mechanisms. Loss of function assays using genetic deletion of Mig6 or siRNA knockdown increased angiogenesis in vivo and in vitro, while MIG6 overexpression suppressed pathological angiogenesis. Moreover, we identified the cellular target of MIG6 by revealing its direct inhibitory effect on vascular endothelial cells (ECs). Mechanistically, we found that the anti-angiogenic effect of MIG6 is fulfilled by binding to SHC1 and inhibiting its phosphorylation. Indeed, SHC1 knockdown markedly diminished the effect of MIG6 on ECs. Thus, our findings show that MIG6 is a potent endogenous inhibitor of angiogenesis that may have therapeutic value in anti-angiogenic therapy.

Receptor Tyrosine Kinase Signaling and Targeting in Glioblastoma Multiforme

Glioblastoma multiforme (GBM) is amongst the deadliest of human cancers, with a median survival rate of just over one year following diagnosis. Characterized by rapid proliferation and diffuse infiltration into the brain, GBM is notoriously difficult to treat, with tumor cells showing limited response to existing therapies and eventually developing resistance to these interventions. As such, there is intense interest in better understanding the molecular alterations in GBM to guide the development of more efficient targeted therapies. GBM tumors can be classified into several molecular subtypes which have distinct genetic signatures, and they show aberrant activation of numerous signal transduction pathways, particularly those connected to receptor tyrosine kinases (RTKs) which control glioma cell growth, survival, migration, invasion, and angiogenesis. There are also non-canonical modes of RTK signaling found in GBM, which involve G-protein-coupled receptors and calcium channels. This review uses The Cancer Genome Atlas (TCGA) GBM dataset in combination with a data-mining approach to summarize disease characteristics, with a focus on select molecular pathways that drive GBM pathogenesis. We also present a unique genomic survey of RTKs that are frequently altered in GBM subtypes, as well as catalog the GBM disease association scores for all RTKs. Lastly, we discuss current RTK targeted therapies and highlight emerging directions in GBM research.

Low-density lipoprotein receptor (LDLR) regulates NLRP3-mediated neuronal pyroptosis following cerebral ischemia/reperfusion injury

BACKGROUND

Inflammatory response has been recognized as a pivotal pathophysiological process during cerebral ischemic stroke. NLRP3 inflammasome, involved in the regulation of inflammatory cascade, can simultaneously lead to GSDMD-executed pyroptosis in cerebral ischemia. Low-density lipoprotein receptor (LDLR), responsible for cholesterol uptake, was noted to exert potential anti-inflammatory bioactivities. Nevertheless, the role of LDLR in neuroinflammation mobilized by cerebral ischemia/reperfusion (I/R) has not been investigated.

METHODS

Ischemic stroke mice model was accomplished by middle cerebral artery occlusion. Oxygen-glucose deprivation was employed after primary cortical neuron was extracted and cultured. A pharmacological inhibitor of NLRP3 (CY-09) was administered to suppress NLPR3 activation. Histological and biochemical analysis were performed to assess the neuronal death both in vitro and in vivo. In addition, neurological deficits and behavioral deterioration were evaluated in mice.

RESULTS

The expression of LDLR was downregulated following cerebral I/R injury. Genetic knockout of Ldlr enhanced caspase-1-dependent cleavage of GSDMD and resulted in severe neuronal pyroptosis. LDLR deficiency contributed to excessive NLRP3-mediated maturation and release of IL-1β and IL-18 under in vitro and in vivo ischemic conditions. These influences ultimately led to aggravated neurological deficits and long-term cognitive dysfunction. Blockade of NLRP3 substantially retarded neuronal pyroptosis in Ldlr^-/- mice and cultured Ldlr^-/- neuron after experimental stroke.

CONCLUSIONS

These results demonstrated that LDLR modulates NLRP3-mediated neuronal pyroptosis and neuroinflammation following ischemic stroke. Our findings characterize a novel role for LDLR as a potential therapeutic target in neuroinflammatory responses to acute cerebral ischemic injury.

The Role of Shcbp1 in Signaling and Disease

Src homolog and collagen homolog (Shc) proteins have been identified as adapter proteins associated with cell surface receptors and have been shown to play important roles in signaling and disease. Shcbp1 acts as a Shc SH2-domain binding protein 1 and is involved in the regulation of signaling pathways, such as FGF, NF-κB, MAPK/ERK, PI3K/AKT, TGF-β1/Smad and β -catenin signaling. Shcbp1 participates in T cell development, the regulation of downstream signal transduction pathways, and cytokinesis during mitosis and meiosis. In addition, Shcbp1 has been demonstrated to correlate with Burkitt-like lymphoma, breast cancer, lung cancer, gliomas, synovial sarcoma, human hepatocellular carcinoma and other diseases. Shcbp1 may play an important role in tumorigenesis and progression. Accordingly, recent studies are reviewed herein to discuss and interpret the role of Shcbp1 in normal cell proliferation and differentiation, tumorigenesis and progression, as well as its interactions with proteins.

Functional maintenance of calcium store by ShcB adaptor protein in cerebellar Purkinje cells

Intracellular Ca²⁺ levels are changed by influx from extracellular medium and release from intracellular stores. In the central nervous systems, Ca²⁺ release is involved in various physiological events, such as neuronal excitability and transmitter release. Although stable Ca²⁺ release in response to stimulus is critical for proper functions of the nervous systems, regulatory mechanisms relating to Ca²⁺ release are not fully understood in central neurons. Here, we demonstrate that ShcB, an adaptor protein expressed in central neurons, has an essential role in functional maintenance of Ca²⁺ store in cerebellar Purkinje cells (PCs). ShcB-knockout (KO) mice showed defects in cerebellar-dependent motor function and long-term depression (LTD) at cerebellar synapse. The reduced LTD was accompanied with an impairment of intracellular Ca²⁺ release. Although the expression of Ca²⁺ release channels and morphology of Ca²⁺ store looked intact, content of intracellular Ca²⁺ store and activity of sarco/endoplasmic reticular Ca²⁺-ATPase (SERCA) were largely decreased in the ShcB-deficient cerebellum. Furthermore, when ShcB was ectopically expressed in the ShcB-KO PCs, the Ca²⁺ release and its SERCA-dependent component were restored. These data indicate that ShcB plays a key role in the functional maintenance of ER Ca²⁺ store in central neurons through regulation of SERCA activity.

RNA-seq analysis of the key long noncoding RNAs and mRNAs related to cognitive impairment after cardiac arrest and cardiopulmonary resuscitation

Cardiac arrest (CA) is the leading cause of death around the world. Survivors after CA and cardiopulmonary resuscitation (CPR) develop moderate to severe cognitive impairment up to 60% at 3 months. Accumulating evidence demonstrated that long non-coding RNAs (lncRNAs) played a pivotal role in ischemic brain injury. This study aimed to identify potential key lncRNAs associated with early cognitive deficits after CA/CPR. LncRNA and mRNA expression profiles of the hippocampus in CA/CPR or sham group were analyzed via high-throughput RNA sequencing, which exhibited 1920 lncRNAs and 1162 mRNAs were differentially expressed. These differentially expressed genes were confirmed to be primarily associated with inflammatory or apoptotic signaling pathways through GO and KEGG pathway enrichment analysis and coding-noncoding co-expression network analysis. Among which, five key pairs of lncRNA-mRNA were further analyzed by qRT-PCR and western blot. We found that the lncRNANONMMUT113601.1 and mRNA Shc1, an inflammation and apoptosis-associated gene, exhibited the most significant changes in hippocampus of CA/CPR mice. Furthermore, we found that the correlations between this lncRNA and mRNA mainly happened in neurons of hippocampus by in situ hybridization. These results suggested that the critical pairs of lncRNA-mRNA may act as essential regulators in early cognitive deficits after resuscitation.

The genomic landscape of metastasis in treatment-naïve breast cancer models

Metastasis remains the principle cause of mortality for breast cancer and presents a critical challenge because secondary lesions are often refractory to conventional treatments. While specific genetic alterations are tightly linked to primary tumor development and progression, the role of genetic alteration in the metastatic process is not well-understood. The theory of tumor evolution postulated by Peter Nowell in 1976 has yet to be proven in the context of metastasis. Therefore, in order to investigate how somatic evolution contributes to breast cancer metastasis, we performed exome, whole genome, and RNA sequencing of matched metastatic and primary tumors from pre-clinical mouse models of breast cancer. Here we show that in a treatment-naïve setting, recurrent single nucleotide variants and copy number variation, but not gene fusion events, play key metastasis-driving roles in breast cancer. For instance, we identified recurrent mutations in Kras, a known driver of colorectal and lung tumorigenesis that has not been previously implicated in breast cancer metastasis. However, in a set of in vivo proof-of-concept experiments we show that the Kras G12D mutation is sufficient to significantly promote metastasis using three syngeneic allograft models. The work herein confirms the existence of metastasis-driving mutations and presents a novel framework to identify actionable metastasis-targeted therapies.

The majority of breast cancer-associated deaths are due to metastatic disease, the process where cancerous cells leave the primary tumor and spread to a new location in the body, because metastatic tumors often become insensitive to the same therapies that were successful in treating the primary tumor. To date, this complex process has been attributed to dynamic changes in tumor cell gene expression regulated by epigenetic factors. Interestingly, while genomic alterations are accepted drivers of neoplastic transformation, it is unknown if such events contribute to metastatic spread. One reason for this is the limited availability of matched and treatment-naïve primary tumor and metastatic tumor samples from patients for comparative genomic testing. Here we use two pre-clinical mouse models of metastatic breast cancer to test if genomic alterations can drive metastatic capacity. We identified metastasis-specific events of single nucleotide variation and gene amplification in well-known oncogenic genes, as well as lesser known factors. We also show that expression of these mutant factors can drive metastasis of weakly and non-metastatic mouse mammary cancer cell lines when implanted in mice. Crucially, by observing and reporting this untested etiology of metastatic disease, specific genomic events can now be included in efforts to develop targets for metastasis-specific therapies.

p66ShcA functions as a contextual promoter of breast cancer metastasis

Background

The p66ShcA redox protein is the longest isoform of the Shc1 gene and is variably expressed in breast cancers. In response to a variety of stress stimuli, p66ShcA becomes phosphorylated on serine 36, which allows it to translocate from the cytoplasm to the mitochondria where it stimulates the formation of reactive oxygen species (ROS). Conflicting studies suggest both pro- and anti-tumorigenic functions for p66ShcA, which prompted us to examine the contribution of tumor cell-intrinsic functions of p66ShcA during breast cancer metastasis.

Methods

We tested whether p66ShcA impacts the lung-metastatic ability of breast cancer cells. Breast cancer cells characteristic of the ErbB2+/luminal (NIC) or basal (4T1) subtypes were engineered to overexpress p66ShcA. In addition, lung-metastatic 4T1 variants (4T1-537) were engineered to lack endogenous p66ShcA via Crispr/Cas9 genomic editing. p66ShcA null cells were then reconstituted with wild-type p66ShcA or a mutant (S36A) that cannot translocate to the mitochondria, thereby lacking the ability to stimulate mitochondrial-dependent ROS production. These cells were tested for their ability to form spontaneous metastases from the primary site or seed and colonize the lung in experimental (tail vein) metastasis assays. These cells were further characterized with respect to their migration rates, focal adhesion dynamics, and resistance to anoikis in vitro. Finally, their ability to survive in circulation and seed the lungs of mice was assessed in vivo.

Results

We show that p66ShcA increases the lung-metastatic potential of breast cancer cells by augmenting their ability to navigate each stage of the metastatic cascade. A non-phosphorylatable p66ShcA-S36A mutant, which cannot translocate to the mitochondria, still potentiated breast cancer cell migration, lung colonization, and growth of secondary lung metastases. However, breast cancer cell survival in the circulation uniquely required an intact p66ShcA S36 phosphorylation site.

Conclusion

This study provides the first evidence that both mitochondrial and non-mitochondrial p66ShcA pools collaborate in breast cancer cells to promote their maximal metastatic fitness.

Localization of phosphotyrosine adaptor protein ShcD/SHC4 in the adult rat central nervous system

Background

Mammalian Shc (Src homology and collagen) proteins comprise a family of four phosphotyrosine adaptor molecules which exhibit varied spatiotemporal expression and signaling functions. ShcD is the most recently discovered homologue and it is highly expressed in the developing central nervous system (CNS) and adult brain. Presently however, its localization within specific cell types of mature neural structures has yet to be characterized.

Results

In the current study, we examine the expression profile of ShcD in the adult rat CNS using immunohistochemistry, and compare with those of the neuronally enriched ShcB and ShcC proteins. ShcD shows relatively widespread distribution in the adult brain and spinal cord, with prominent levels of staining throughout the olfactory bulb, as well as in sub-structures of the cerebellum and hippocampus, including the subgranular zone. Co-localization studies confirm the expression of ShcD in mature neurons and progenitor cells. ShcD immunoreactivity is primarily localized to axons and somata, consistent with the function of ShcD as a cytoplasmic adaptor. Regional differences in expression are observed among neural Shc proteins, with ShcC predominating in the hippocampus, cerebellum, and some fiber tracts. Interestingly, ShcD is uniquely expressed in the olfactory nerve layer and in glomeruli of the main olfactory bulb.

Conclusions

Together our findings suggest that ShcD may provide a distinct signaling contribution within the olfactory system, and that overlapping expression of ShcD with other Shc proteins may allow compensatory functions in the brain.

Downregulation of p66Shc can reduce oxidative stress and apoptosis in oxidative stress model of marginal cells of stria vascularis in Sprague Dawley rats

Background

p66Shc, a Src homologue and collagen homologue (Shc) adaptor protein, mediates oxidative stress signaling. The p66Shc-null mice have increased lifespan and enhanced resistance to oxidative stress. Studies have also indicated its potential role in inner ear aging, which can lead to deafness.

Objective

The aim of this study was to determine the effects of p66Shc down-regulation on the marginal cells (MCs) of the inner ear stria vascularis.

Methods

Primary MCs were isolated from neonatal rats and treated with glucose oxidase to induce oxidative stress. The cells were transduced with adenovirus expressing siRNA, and the knockdown was verified by Western blotting. The reactive oxygen species (ROS) levels and apoptosis were analyzed using the DCFH-DA probe and Annexin-V/7-AAD staining respectively. The ultrastructure of the differentially-treated cells was examined by transmission electron microscopy (TEM).

Results: The in vitro oxidative stress model was established successfully in rat MCs. Knockdown of p66Shc alleviated the high ROS levels and apoptosis in the glucose oxidase-treated cells. In addition, glucose oxidase significantly increased the number of peroxisomes in the MCs, which was decreased by p66Shc inhibition.

Conclusion

Oxidative stress increases p66Shc levels in the marginal cells of the inner ear, which aggravates ROS production and cellular injury. Blocking p66Shc expression can effectively reduce oxidative stress and protect the MCs.

Activation of Shc1 Allows Oncostatin M to Induce RANKL and Osteoclast Formation More Effectively Than Leukemia Inhibitory Factor

Background and Purpose: The gp130 family of cytokines signals through receptors dimerizing with the gp130 subunit. Downstream signaling typically activates STAT3 but also SHP2/Ras/MAPK pathways. Oncostatin M (OSM) is a unique cytokine in this family since the receptor (OSMR) activates a non-redundant signaling pathway by recruitment of the adapter Shc1. We have studied the functional relevance of Shc1 for OSM-induced bone resorption.

Experimental Approach: Osteoblasts were stimulated with OSM and STAT3 and Shc1 activations were studied using real-time PCR and Western blots. The role of STAT3 and Shc1 for OSM-induced RANKL expression and osteoclast formation was studied by silencing their mRNA expressions. Effects of OSM were compared to those of the closely related cytokine leukemia inhibitory factor (LIF).

Key Results: OSM, but not LIF, induced the mRNA and protein expression of Shc1 and activated phosphorylation of Shc1 in the osteoblasts. Silencing of Shc1 decreased OSM-induced activation of STAT3 and RANKL expression. Silencing of STAT3 had no effect on activation of Shc1, but prevented the OSM-mediated increase of RANKL expression. Silencing of either Shc1 or STAT3 in osteoblasts decreased formation of osteoclasts in OSM-stimulated co-cultures of osteoblasts and macrophages. In agreement with these observations, OSM was a more potent and robust stimulator than LIF of RANKL formation and bone resorption in mouse calvariae and osteoclast formation in bone marrow cultures.

Conclusions and Implications: Activation of the Shc1-dependent STAT3 signaling is crucial for OSM-induced osteoclast formation. Inhibition of Shc1 is a potential mechanism to specifically inhibit OSM-induced bone resorption.

[Functional roles of phosphotyrosine adaptor Shc in the brain]

Adaptor molecules (adaptor proteins) have indispensable roles in cellular signaling, essential for cellular proliferation, development and metabolism. Shc (Src homology and collagen homology)-family molecule is a group of adaptor molecules, and indicated to be involved in intracellular phosphotyrosine signaling. Shc family has 4 subtypes, ShcA-ShcD, and there are long and short isoforms in ShcA and ShcC whereas ShcB and ShcD have short isoform only. There are three domains conserved in all Shc-family isoforms: phosphotyrosine-binding (PTB) domain, collagen-homology 1 (CH1) domain and Src-homology 2 (SH2) domain, from the N-terminal to C-terminal. PTB and SH2 domains recognize and bind to phosphotyrosine in other molecules, and CH1 domain is recognized and bind to SH2 domain in Grb2, an adaptor molecule, when the tyrosine residues in the domain are phosphorylated. Expression of ShcA is observed in all tissues except for brain in adult animals, although ShcA mRNA is detected in brain during embryonic days. On the other hand, in adult brain, expressions of ShcB, ShcC, and ShcD are observed. Analysis of single knockout mice (ShcA (neuron specific), ShcB, ShcC) and double knockout mice for ShcB and C indicated essential roles of Shc-family molecules in proliferation and survival of cells in various brain regions as well as synaptic plasticity and higher brain functions such as learning and memory. Studies on multiple-knockout mice of Shc-family molecules may further clarify possible involvements of Shc family in physiological and pathophysiological functions in brain.

Designing Motif-Engineered Receptors To Elucidate Signaling Molecules Important for Proliferation of Hematopoietic Stem Cells

The understanding of signaling events is critical for attaining long-term expansion of hematopoietic stem cells ex vivo. In this study, we aim to analyze the contribution of multiple signaling molecules in proliferation of hematopoietic stem cells. To this end, we design a bottom-up engineered receptor with multiple tyrosine motifs, which can recruit multiple signaling molecules of interest. This is followed by a top-down approach, where one of the multiple tyrosine motifs in the bottom-up engineered receptor is functionally knocked out by tyrosine-to-phenylalanine mutation. The combination of these two approaches demonstrates the importance of Shc in cooperation with STAT3 or STAT5 in the proliferation of hematopoietic stem cells. The platform developed herein may be applied for analyzing other cells and/or other cell fate regulation systems.

A Link Between Alzheimer's and Type II Diabetes Mellitus? Ca+2 -Mediated Signal Control and Protein Localization

We propose protein localization dependent signal activation (PLDSA) as a model to describe pre-existing protein partitioning between the cytosol, and membrane surface, as a means to modulate signal activation, specificity, and robustness. We apply PLDSA to explain possible molecular links between type II diabetes mellitus (T2DM) and Alzheimer's disease (AD) by describing Ca+2 -mediated interactions between the Src non-receptor tyrosine kinase and p52Shc adaptor protein. We suggest that these interactions may serve as a contributing factor to disease development and progression. In particular, we propose that signaling response is regulated, in part, by Ca+2 -mediated partitioning of lipid-bound and soluble forms of Src and p52shc. Thus, protein-protein interactions that drive signaling in response to extracellular ligand binding are also mediated by partitioning of signaling proteins between membrane-bound and soluble populations. We propose that PLDSA effects may explain, in part, the evolutionary basis of promiscuous protein interaction domains and their importance in cellular function.

Loss of the adaptor protein ShcA in endothelial cells protects against monocyte macrophage adhesion, LDL-oxydation, and atherosclerotic lesion formation

ShcA is an adaptor protein that binds to the cytoplasmic tail of receptor tyrosine kinases and of the Low Density Lipoprotein-related receptor 1 (LRP1), a trans-membrane receptor that protects against atherosclerosis. Here, we examined the role of endothelial ShcA in atherosclerotic lesion formation. We found that atherosclerosis progression was markedly attenuated in mice deleted for ShcA in endothelial cells, that macrophage content was reduced at the sites of lesions, and that adhesion molecules such as the intercellular adhesion molecule-1 (ICAM-1) were severely reduced. Our data indicate that transcriptional regulation of ShcA by the zinc-finger E-box-binding homeobox 1 (ZEB1) and the Hippo pathway effector YAP, promotes ICAM-1 expression independently of p-NF-κB, the primary driver of adhesion molecules expressions. In addition, ShcA suppresses endothelial Akt and nitric oxide synthase (eNOS) expressions. Thus, through down regulation of eNOS and ZEB1-mediated ICAM-1 up regulation, endothelial ShcA promotes monocyte-macrophage adhesion and atherosclerotic lesion formation. Reducing ShcA expression in endothelial cells may represent an obvious therapeutic approach to prevent atherosclerosis.

Phosphorylation of threonine residues on Shc promotes ligand binding and mediates crosstalk between MAPK and Akt pathways in breast cancer cells

Scaffold proteins play important roles in regulating signalling network fidelity, the absence of which is often the basis for diseases such as cancer. In the present work, we show that the prototypical scaffold protein Shc is phosphorylated by the extracellular signal-regulated kinase, Erk. In addition, Shc threonine phosphorylation is specifically up-regulated in two selected triple-negative breast cancer (TNBC) cell lines. To explore how Erk-mediated threonine phosphorylation on Shc might play a role in the dysregulation of signalling events, we investigated how Shc affects pathways downstream of EGF receptor. Using an in vitro model and biophysical analysis, we show that Shc threonine phosphorylation is responsible for elevated Akt and Erk signalling, potentially through the recruitment of the 14-3-3 ζ and Pin-1 proteins.

Regulation of insulin-like growth factor receptors by Ubiquilin1

Insulin-like growth factor-1 receptor (IGF1R) is a receptor tyrosine kinase that mediates growth, proliferation and survival. Dysregulation of IGF pathway contributes to the initiation, progression and metastasis of cancer and is also involved in diseases of glucose metabolism, such as diabetes. We have identified Ubiquilin1 (UBQLN1) as a novel interaction partner of IGF1R, IGF2R and insulin receptor (INSR). UBQLN family of proteins have been studied primarily in the context of protein quality control and in the field of neurodegenerative disorders. Our laboratory discovered a link between UBQLN1 function and tumorigenesis, such that UBQLN1 is lost and underexpressed in 50% of human lung adenocarcinoma cases. We demonstrate here that UBQLN1 regulates the expression and activity of IGF1R. Following loss of UBQLN1 in lung adenocarcinoma cells, there is accelerated loss of IGF1R. Despite decreased levels of total receptors, the ratio of active : total receptors is higher in cells that lack UBQLN1. UBQLN1 also regulates INSR and IGF2R post-stimulation with ligand. We conclude that UBQLN1 is essential for normal regulation of IGF receptors. UBQLN-1-deficient cells demonstrate increased cell viability compared with control when serum-starved and stimulation of IGF pathway in these cells increased their migratory potential by 3-fold. As the IGF pathway is involved in processes of normal growth, development, metabolism and cancer progression, understanding its regulation by Ubiquilin1 can be of tremendous value to many disciplines.

Differential effects of epidermal growth factor (EGF) receptor ligands on receptor binding, downstream signalling pathways and DNA synthesis in hepatocytes

Hepatocytes are responsive to mitogenic effects of several ligands acting via EGFR. Studying primary cultures of rat hepatocytes, we found that, as compared to EGF, HB-EGF had a markedly higher affinity of the EGFR, while AR and TGFα had lower affinity. HB-EGF was also more potent compared to the other growth factors regarding phosphorylation of EGFR, Shc, ERK1/2 and Akt. All ligands induced phosphorylation of ErbB2, indicating receptor heterodimerization. TGFα, despite having much lower receptor affinity, was about equally potent and efficacious as HB-EGF as a stimulator of DNA synthesis. In contrast, EGF had relatively high affinity but markedly lower efficacy in stimulation of DNA synthesis. The results suggest that amplifying and/or inhibitory mechanisms may modulate the mitogenic responses downstream of the initial signalling steps, and that this may affect the effects of the EGFR ligands differentially.

ShcA Adaptor Protein Promotes Nephrin Endocytosis and Is Upregulated in Proteinuric Nephropathies

Nephrin is a key structural component of the podocyte slit diaphragm, and proper expression of nephrin on the cell surface is critical to ensure integrity of the blood filtration barrier. Maintenance of nephrin within this unique cell junction has been proposed to require dynamic phosphorylation events and endocytic recycling, although the molecular mechanisms that control this interplay are poorly understood. Here, we investigated the possibility that the phosphotyrosine adaptor protein ShcA regulates nephrin turnover. Western blotting and immunostaining analysis confirmed that ShcA is expressed in podocytes. In immunoprecipitation and pulldown assays, ShcA, via its SH2 domain, was associated with several phosphorylated tyrosine residues on nephrin. Overexpression of ShcA promoted nephrin tyrosine phosphorylation and reduced nephrin signaling and cell surface expression in vitro In a rat model of reversible podocyte injury and proteinuria, phosphorylated nephrin temporally colocalized with endocytic structures coincident with upregulation of ShcA expression. In vivo biotinylation assays confirmed that nephrin expression decreased at the cell surface and correspondingly increased in the cytosol during the injury time course. Finally, immunostaining in kidney biopsy specimens demonstrated overexpression of ShcA in several human proteinuric kidney diseases compared with normal conditions. Our results suggest that increases in ShcA perturb nephrin phosphosignaling dynamics, leading to aberrant nephrin turnover and slit diaphragm disassembly.

The ShcD phosphotyrosine adaptor subverts canonical EGF receptor trafficking

Shc family signalling adaptors connect activated transmembrane receptors to proximal effectors, and most also contain a sequence involved in clathrin-mediated receptor endocytosis. Notably, this AP2 adaptin-binding motif (AD) is absent from the ShcD (also known as Shc4) homolog, which also uniquely promotes ligand-independent phosphorylation of the epidermal growth factor receptor (EGFR). We now report that cultured cells expressing ShcD exhibit reduced EGF uptake, commensurate with a decrease in EGFR surface presentation. Under basal conditions, ShcD colocalises with the EGFR and facilitates its phosphorylation, ubiquitylation and accumulation in juxtanuclear vesicles identified as Rab11-positive endocytic recycling compartments. Accordingly, ShcD also functions as a constitutive binding partner for the E3 ubiquitin ligase Cbl. EGFR phosphorylation and focal accumulation likewise occur upon ShcD co-expression in U87 glioma cells. Loss of ShcD phosphotyrosine-binding function or insertion of the ShcA AD sequence each restore ligand acquisition through distinct mechanisms. The AD region also contains a nuclear export signal, indicating its multifunctionality. Overall, ShcD appears to possess several molecular permutations that actively govern the EGFR, which may have implications in development and disease.

Identification of STS-1 as a novel ShcA-binding protein

ShcA is a cytoplasmic signaling protein that supports signal transduction by receptor protein-tyrosine kinases by providing auxiliary tyrosine phosphorylation sites that engage additional signaling proteins. The principal binding partner for tyrosine phosphorylation sites on ShcA is Grb2. In the current study, we have used phosphotyrosine-containing peptides to isolate and identify STS-1 as a novel ShcA-binding protein. Our results further show that the interaction between STS-1 and ShcA is regulated in response to EGF receptor activation.

Acute Ethanol Increases IGF-I-Induced Phosphorylation of ERKs by Enhancing Recruitment of p52-Shc to the Grb2/Shc Complex

Ethanol plays a detrimental role in the development of the brain. Multiple studies have shown that ethanol inhibits insulin-like growth factor I receptor (IGF-IR) function. Because the IGF-IR contributes to brain development by supporting neural growth, survival, and differentiation, we sought to determine the molecular mechanism(s) involved in ethanol's effects on this membrane-associated tyrosine kinase. Using multiple neuronal cell types, we performed Western blot, immunoprecipitation, and GST-pulldowns following acute (1-24 h) or chronic (3 weeks) treatment with ethanol. Surprisingly, exposure of multiple neuronal cell types to acute (up to 24 h) ethanol (50 mM) enhanced IGF-I-induced phosphorylation of extracellular regulated kinases (ERKs), without affecting IGF-IR tyrosine phosphorylation itself, or Akt phosphorylation. This acute increase in ERKs phosphorylation was followed by the expected inhibition of the IGF-IR signaling following 3-week ethanol exposure. We then expressed a GFP-tagged IGF-IR construct in PC12 cells and used them to perform fluorescence recovery after photobleaching (FRAP) analysis. Using these fluorescently labeled cells, we determined that 50 mM ethanol decreased the half-time of the IGF-IR-associated FRAP, which implied that cell membrane-associated signaling events could be affected. Indeed, co-immunoprecipitation and GST-pulldown studies demonstrated that the acute ethanol exposure increased the recruitment of p52-Shc to the Grb2-Shc complex, which is known to engage the Ras-Raf-ERKs pathway following IGF-1 stimulation. These experiments indicate that even a short and low-dose exposure to ethanol may dysregulate function of the receptor, which plays a critical role in brain development. J. Cell. Physiol. 232: 1275-1286, 2017. © 2016 Wiley Periodicals, Inc.

Signaling adaptor ShcD suppresses extracellular signal-regulated kinase (Erk) phosphorylation distal to the Ret and Trk neurotrophic receptors

Proteins of the Src homology and collagen (Shc) family are typically involved in signal transduction events involving Ras/MAPK and PI3K/Akt pathways. In the nervous system, they function proximal to the neurotrophic factors that regulate cell survival, differentiation, and neuron-specific characteristics. The least characterized homolog, ShcD, is robustly expressed in the developing and mature nervous system, but its contributions to neural cell circuitry are largely uncharted. We now report that ShcD binds to active Ret, TrkA, and TrkB neurotrophic factor receptors predominantly via its phosphotyrosine-binding (PTB) domain. However, in contrast to the conventional Shc adaptors, ShcD suppresses distal phosphorylation of the Erk MAPK. Accordingly, genetic knock-out of mouse ShcD enhances Erk phosphorylation in the brain. In cultured cells, this capacity is tightly aligned to phosphorylation of ShcD CH1 region tyrosine motifs, which serve as docking platforms for signal transducers, such as Grb2. Erk suppression is relieved through independent mutagenesis of the PTB domain and the CH1 tyrosine residues, and successive substitution of these tyrosines breaks the interaction between ShcD and Grb2, thereby promoting TrkB-Grb2 association. Erk phosphorylation can also be restored in the presence of wild type ShcD through Grb2 overexpression. Conversely, mutation of the ShcD SH2 domain results in enhanced repression of Erk. Although the SH2 domain is a less common binding interface in Shc proteins, we demonstrate that it associates with the Ptpn11 (Shp2) phosphatase, which in turn regulates ShcD tyrosine phosphorylation. We therefore propose a model whereby ShcD competes with neurotrophic receptors for Grb2 binding and opposes activation of the MAPK cascade.

DNA methylation and substance-use risk: a prospective, genome-wide study spanning gestation to adolescence

Epigenetic processes have been implicated in addiction; yet, it remains unclear whether these represent a risk factor and/or a consequence of substance use. Here, we believe we conducted the first genome-wide, longitudinal study to investigate whether DNA methylation patterns in early life prospectively associate with substance use in adolescence. The sample comprised of 244 youth (51% female) from the Avon Longitudinal Study of Parents and Children (ALSPAC), with repeated assessments of DNA methylation (Illumina 450k array; cord blood at birth, whole blood at age 7) and substance use (tobacco, alcohol and cannabis use; age 14-18). We found that, at birth, epigenetic variation across a tightly interconnected genetic network (n=65 loci; q<0.05) associated with greater levels of substance use during adolescence, as well as an earlier age of onset amongst users. Associations were specific to the neonatal period and not observed at age 7. Key annotated genes included PACSIN1, NEUROD4 and NTRK2, implicated in neurodevelopmental processes. Several of the identified loci were associated with known methylation quantitative trait loci, and consequently likely to be under significant genetic control. Collectively, these 65 loci were also found to partially mediate the effect of prenatal maternal tobacco smoking on adolescent substance use. Together, findings lend novel insights into epigenetic correlates of substance use, highlight birth as a potentially sensitive window of biological vulnerability and provide preliminary evidence of an indirect epigenetic pathway linking prenatal tobacco exposure and adolescent substance use.

Unravelling the Mechanism of TrkA-Induced Cell Death by Macropinocytosis in Medulloblastoma Daoy Cells

Macropinocytosis is a normal cellular process by which cells internalize extracellular fluids and nutrients from their environment and is one strategy that Ras-transformed pancreatic cancer cells use to increase uptake of amino acids to meet the needs of rapid growth. Paradoxically, in non-Ras transformed medulloblastoma brain tumors, we have shown that expression and activation of the receptor tyrosine kinase TrkA overactivates macropinocytosis, resulting in the catastrophic disintegration of the cell membrane and in tumor cell death. The molecular basis of this uncontrolled form of macropinocytosis has not been previously understood. Here, we demonstrate that the overactivation of macropinocytosis is caused by the simultaneous activation of two TrkA-mediated pathways: (i) inhibition of RhoB via phosphorylation at Ser(185) by casein kinase 1, which relieves actin stress fibers, and (ii) FRS2-scaffolded Src and H-Ras activation of RhoA, which stimulate actin reorganization and the formation of lamellipodia. Since catastrophic macropinocytosis results in brain tumor cell death, improved understanding of the mechanisms involved will facilitate future efforts to reprogram tumors, even those resistant to apoptosis, to die.

Up-regulation of N-cadherin by Collagen I-activated Discoidin Domain Receptor 1 in Pancreatic Cancer Requires the Adaptor Molecule Shc1

Pancreatic ductal adenocarcinomas are highly malignant cancers characterized by extensive invasion into surrounding tissues, metastasis to distant organs, and a limited response to therapy. A main feature of pancreatic ductal adenocarcinomas is desmoplasia, which leads to extensive deposition of collagen I. We have demonstrated that collagen I can induce epithelial-mesenchymal transition (EMT) in pancreatic cancer cells. A hallmark of EMT is an increase in the expression of the mesenchymal cadherin N-cadherin. Previously we showed up-regulation of N-cadherin promotes tumor cell invasion and that collagen I-induced EMT is mediated by two collagen receptors, α2β1-integrin and discoidin domain receptor 1 (DDR1). DDR1 is a receptor-tyrosine kinase widely expressed during embryonic development and in many adult tissues and is also highly expressed in many different cancers. In the signaling pathway initiated by collagen, we have shown proline-rich tyrosine kinase 2 (Pyk2) is downstream of DDR1. In this study we found isoform b of DDR1 is responsible for collagen I-induced up-regulation of N-cadherin and tyrosine 513 of DDR1b is necessary. Knocking down Shc1, which binds to tyrosine 513 of DDR1b via its PTB (phosphotyrosine binding) domain, eliminates the up-regulation of N-cadherin. The signaling does not require a functional SH2 domain or the tyrosine residues commonly phosphorylated in Shc1 but is mediated by the interaction between a short segment of the central domain of Shc1 and the proline-rich region of Pyk2. Taken together, these data illustrate DDR1b, but not DDR1a, mediates collagen I-induced N-cadherin up-regulation, and Shc1 is involved in this process by coupling to both DDR1 and Pyk2.

Non-canonical dynamic mechanisms of interaction between the p66Shc protein and Met receptor

The present study identifies a novel and unexpected mechanism underscoring the diversification of p66Shc among other Shc (Src homology and collagen homology) proteins, with respect to its mode of interaction with the receptor Met and impacts on key binding effectors of Met-regulated signalling.

Met receptor tyrosine kinase (RTK) is known to bind to the three distinct protein isoforms encoded by the ShcA (Shc) gene. Structure–function studies have unveiled critical roles for p52Shc-dependent signalling pathways in Met-regulated biological functions. The molecular basis of the interaction between the Met and p52Shc proteins is well-defined, but not for the longest protein isoform, p66Shc. In the present study, co-immunoprecipitation assays were performed in human embryonic kidney 293 (HEK293) cells, transiently co-transfected with Met and p66Shc mutants, in order to define the molecular determinants involved in mediating Met–p66Shc interaction. Our results show that p66Shc interacts constitutively with the receptor Met, and the Grb2 (growth factor receptor-bound protein-2) and Gab1 (Grb2-associated binder-1) adaptor proteins. Although its phosphotyrosine-binding domain (PTB) and Src homology 2 (SH2) domains co-ordinate p66Shc binding to non-activated Met receptor, these phosphotyrosine-binding modules, and its collagen homology domain 2 (CH2) region, exert negative constraints. In contrast, p66Shc interaction with the activated Met depends mainly on the integrity of its PTB domain, and to a lesser extent of its SH2 domain. Even though not required for the recruitment of p66Shc, tyrosine phosphorylation of p66Shc by activated Met enhances these interactions by mechanisms not reliant on the integrity of the Met multisubstrate-binding site. In turn, this increases phosphotyrosine-dependent p66Shc–Grb2–Gab1 complex formation away from the receptor, while blocking Grb2 and Gab1 recruitment to activated Met. In conclusion, we identify, for the first time, a novel non-canonical dynamic mode of interaction between Met and the p66 protein isoform of Shc and its effects on rewiring binding effector complexes according to the activation state of the receptor.

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.

EGF-receptor specificity for phosphotyrosine-primed substrates provides signal integration with Src

Aberrant activation of the EGF receptor (EGFR) contributes to many human cancers by activating the Ras-MAPK pathway and other pathways. EGFR signaling is augmented by Src-family kinases, but the mechanism is poorly understood. Here, we show that human EGFR preferentially phosphorylates peptide substrates that are primed by a prior phosphorylation. Using peptides based on the sequence of the adaptor protein Shc1, we show that Src mediates the priming phosphorylation, thus promoting subsequent phosphorylation by EGFR. Importantly, the doubly phosphorylated Shc1 peptide binds more tightly than singly phosphorylated peptide to the Ras activator Grb2; this binding is a key step in activating the Ras-MAPK pathway. Finally, a crystal structure of EGFR in complex with a primed Shc1 peptide reveals the structural basis for EGFR substrate specificity. These results provide a molecular explanation for the integration of Src and EGFR signaling with downstream effectors such as Ras.

PI3 kinase is indispensable for oncogenic transformation by the V560D mutant of c-Kit in a kinase-independent manner

Oncogenic mutants of c-Kit are often found in mastocytosis, gastrointestinal stromal tumors and acute myeloid leukemia. The activation mechanism of the most commonly occurring mutation, D816V in exon 17 of c-Kit, has been well-studied while other mutations remain fairly uncharacterized in this respect. In this study, we show that the constitutive activity of the exon 11 mutant V560D is weaker than the D816V mutant. Phosphorylation of downstream signaling proteins induced by the ligand for c-Kit, stem cell factor, was stronger in c-Kit/V560D expressing cells than in cells expressing c-kit/D816V. Although cells expressing c-Kit/V560D showed increased ligand-independent proliferation and survival compared to wild-type c-Kit-expressing cells, these biological effects were weaker than in c-Kit/D816V-expressing cells. In contrast to cells expressing wild-type c-Kit, cells expressing c-Kit/V560D were independent of Src family kinases for downstream signaling. However, the independence of Src family kinases was not due to a Src-like kinase activity that c-Kit/D816V displayed. Point mutations that selectively block the association of PI3 kinase with c-Kit/V560D inhibited ligand-independent activation of the receptor, while inhibition of the kinase activity of PI3 kinase with pharmacological inhibitors did not affect the kinase activity of the receptor. This suggests a lipid kinase-independent key role of PI3 kinase in c-Kit/V560D-mediated oncogenic signal transduction. Thus, PI3 kinase is an attractive therapeutic target in malignancies induced by c-Kit mutations independent of its lipid kinase activity.

Identification of SHIP-1 and SHIP-2 homologs in channel catfish, Ictalurus punctatus

Src homology domain 2 (SH2) domain-containing inositol 5'-phosphatases (SHIP) proteins have diverse roles in signal transduction. SHIP-1 and SHIP-2 homologs were identified in channel catfish, Ictalurus punctatus, based on sequence homology to murine and human SHIP sequences. Full-length cDNAs for catfish SHIP-1 and SHIP-2 (IpSHIP-1 and IpSHIP-2) were obtained using 5' and 3' RACE protocols. Catfish SHIP molecules share a high degree of sequence identity to their respective SHIP sequences from diverse taxa and both are encoded by single copy genes. IpSHIP-1 and IpSHIP-2 transcripts were expressed in all catfish tissues analyzed except for skin, and IpSHIP-1 message was more abundant than IpSHIP-2 message in lymphoid tissues. Catfish clonal B, cytotoxic T, and macrophage cell lines also expressed message for both molecules. IpSHIP-1 and IpSHIP-2 SH2 domains were expressed as recombinant proteins and were both found to be bound by cross-reacting rabbit anti-mouse SHIP-1 pAb. The anti-mouse SHIP-1 pAb also reacted with cell lysates from the cytotoxic T cell lines, macrophages and stimulated PBL. SHIP-1 is also phosphorylated at a conserved tyrosine residue, as shown by immunoprecipitation studies.

Conformation-Dependent Human p52Shc Phosphorylation by Human c-Src

Phosphorylation of the human p52Shc adaptor protein is a key determinant in modulating signaling complex assembly in response to tyrosine kinase signaling cascade activation. The underlying mechanisms that govern p52Shc phosphorylation status are unknown. In this study, p52Shc phosphorylation by human c-Src was investigated using purified proteins to define mechanisms that affect the p52Shc phosphorylation state. We conducted biophysical characterizations of both human p52Shc and human c-Src in solution as well as membrane-mimetic environments using the acidic lipid phosphatidylinositol 4-phosphate or a novel amphipathic detergent (2,2-dihexylpropane-1,3-bis-β-D-glucopyranoside). We then identified p52Shc phosphorylation sites under various solution conditions, and the amount of phosphorylation at each identified site was quantified using mass spectrometry. These data demonstrate that the p52Shc phosphorylation level is altered by the solution environment without affecting the fraction of active c-Src. Mass spectrometry analysis of phosphorylated p52Shc implies functional linkage among phosphorylation sites. This linkage may drive preferential coupling to protein binding partners during signaling complex formation, such as during initial binding interactions with the Grb2 adaptor protein leading to activation of the Ras/MAPK signaling cascade. Remarkably, tyrosine residues involved in Grb2 binding were heavily phosphorylated in a membrane-mimetic environment. The increased phosphorylation level in Grb2 binding residues was also correlated with a decrease in the thermal stability of purified human p52Shc. A schematic for the phosphorylation-dependent interaction between p52Shc and Grb2 is proposed. The results of this study suggest another possible therapeutic strategy for altering protein phosphorylation to regulate signaling cascade activation.

ShcC proteins: brain aging and beyond

To date, most studies of Shc family of signaling adaptor proteins have been focused on the near-ubiquitously expressed ShcA, indicating its relevance to age-related diseases and longevity. Although the role of the neuronal ShcC protein is much less investigated, accumulated evidence suggests its importance for neuroprotection against such aging-associated conditions as brain ischemia and oxidative stress. Here, we summarize more than decade of studies on the ShcC expression and function in normal brain, age-related brain pathologies and immune disorders with a focus on the interactions of ShcC with signaling proteins/pathways, and the possible implications of these interactions for changes associated with aging.

The Src homology and collagen A (ShcA) adaptor protein is required for the spatial organization of the costamere/Z-disk network during heart development

Src homology and collagen A (ShcA) is an adaptor protein that binds to tyrosine kinase receptors. Its germ line deletion is embryonic lethal with abnormal cardiovascular system formation, and its role in cardiovascular development is unknown. To investigate its functional role in cardiovascular development in mice, ShcA was deleted in cardiomyocytes and vascular smooth muscle cells by crossing ShcA flox mice with SM22a-Cre transgenic mice. Conditional mutant mice developed signs of severe dilated cardiomyopathy, myocardial infarctions, and premature death. No evidence of a vascular contribution to the phenotype was observed. Histological analysis of the heart revealed aberrant sarcomeric Z-disk and M-band structures, and misalignments of T-tubules with Z-disks. We find that not only the ErbB3/Neuregulin signaling pathway but also the baroreceptor reflex response, which have been functionally associated, are altered in the mutant mice. We further demonstrate that ShcA interacts with Caveolin-1 and the costameric protein plasma membrane Ca(2+)/calmodulin-dependent ATPase (PMCA), and that its deletion leads to abnormal dystrophin signaling. Collectively, these results demonstrate that ShcA interacts with crucial proteins and pathways that link Z-disk and costamere.

Understanding and applying tyrosine biochemical diversity

This review highlights some of the recent advances made in our understanding of the diversity of tyrosine biochemistry and shows how this has inspired novel applications in numerous areas of molecular design and synthesis, including chemical biology and bioconjugation. The pathophysiological implications of tyrosine biochemistry will be presented from a molecular perspective and the opportunities for therapeutic intervention explored.

[Control of insulin signalisation and action by the Grb14 protein]

The action of insulin on metabolism and cell growth is mediated by a specific receptor tyrosine kinase, which, through phosphorylation of several substrates, triggers the activation of two major signaling pathways, the phosphatidylinositol 3-kinase (PI3-K)/Akt pathway and the Ras/extracellular signal-regulated kinase (ERK) pathway. Insulin-induced activation of the receptor and downstream signaling is also subjected to a negative feedback control involving several mechanisms, among which the interaction of the insulin receptor and its substrates with inhibitory proteins. After summarizing the major mechanisms underlying the activation and attenuation of insulin signaling, this review focuses on its control by the Grb14 adaptor protein. Grb14 has been identif-ied as an inhibitor of insulin signaling and action, and is involved in insulin resistance associated with type 2 diabetes and obesity. Studies on the molecular mechanism of action of Grb14 have shown that, through interaction with the activated insulin receptor, Grb14 inhibits its catalytic activity and the activation of downstream signaling. However, the consequences of Grb14 gene invalidation are complex and tissue-specific, and some effects of Grb14 on insulin signaling appear to be linked to its interaction with effector proteins downstream the insulin receptor. Pharmacological inhibition of Grb14 should allow to enhance insulin sensitivity and improve energy homeostasis in insulin-resistant states.

Evidence for a novel antioxidant function and isoform-specific regulation of the human p66Shc gene

p66Shc, but not p52Shc or p46Shc, is regulated by the Nrf2-ARE system, indicative of p66Shc as an antioxidant gene. p66Shc serves as an antioxidant protein in the cytoplasm, protecting cells from ROS toxicity and maintaining expression of other ARE-regulated genes. Finally, p66Shc is essential for erythroid differentiation.

The mammalian Shc family, composed of p46, p52, and p66 isoforms, serves as an adaptor protein in cell growth and stress response. p66Shc was shown to be a negative lifespan regulator by acting as a prooxidant protein in mitochondria; however, the regulatory mechanisms of p66Shc expression and function are incompletely understood. This study provides evidence for new features of p66Shc serving as an antioxidant and critical protein in cell differentiation. Unique among the Shc family, transcription of p66Shc is activated through the antioxidant response element (ARE)–nuclear factor erythroid 2–related factor 2 (Nrf2) pathway in K562 human erythroleukemia and other cell types after treatment with hemin, an iron-containing porphyrin. Phosphorylated p66Shc at Ser-36, previously reported to be prone to mitochondrial localization, is increased by hemin treatment, but p66Shc remains exclusively in the cytoplasm. p66Shc knockdown inhibits hemin-induced erythroid differentiation, in which reactive oxygen species production and apoptosis are significantly enhanced in conjunction with suppression of other ARE-dependent antioxidant genes. Conversely, p66Shc overexpression is sufficient for inducing erythroid differentiation. Collectively these results demonstrate the isoform-specific regulation of the Shc gene by the Nrf2-ARE pathway and a new antioxidant role of p66Shc in the cytoplasm. Thus p66Shc is a bifunctional protein involved in cellular oxidative stress response and differentiation.

Adapter protein Shc regulates Janus kinase 3 phosphorylation

Although constitutive activation of Janus kinase 3 (Jak3) leads to different cancers, the mechanism of trans-molecular regulation of Jak3 activation is not known. Previously we reported that Jak3 interactions with adapter protein p52ShcA (Shc) facilitate mucosal homeostasis. In this study, we characterize the structural determinants that regulate the interactions between Jak3 and Shc and demonstrate the trans-molecular mechanism of regulation of Jak3 activation by Shc. We show that Jak3 autophosphorylation was the rate-limiting step during Jak3 trans-phosphorylation of Shc where Jak3 directly phosphorylated two tyrosine residues in Src homology 2 (SH2) domain and one tyrosine residue each in calponin homology 1 (CH1) domain and phosphotyrosine interaction domain (PID) of Shc. Direct interactions between mutants of Jak3 and Shc showed that although FERM domain of Jak3 was sufficient for binding to Shc, CH1 and PID domains of Shc were responsible for binding to Jak3. Functionally Jak3 was autophosphorylated under IL-2 stimulation in epithelial cells. However, Shc recruited tyrosine phosphatases SHP2 and PTP1B to Jak3 and thereby dephosphorylated Jak3. Thus we not only characterize Jak3 interaction with Shc, but also demonstrate the molecular mechanism of intracellular regulation of Jak3 activation where Jak3 interactions with Shc acted as regulators of Jak3 dephosphorylation through direct interactions of Shc with both Jak3 and tyrosine phosphatases.