Signal-transducing adaptor molecules STAM1 and STAM2 are required for T-cell development and survival

STAM2 negatively regulates the MyD88-mediated NF-κB signaling pathway in miiuy croaker, Miichthys miiuy

Signal transducing adapter molecule 2 (STAM2), a member of the Signal Transducing Adapter Molecule (STAM) family, is a protein with significant implications in diverse signaling pathways and endocytic membrane trafficking. However, the role of the STAM2, especially in fish, remains largely unknown. In this study, we discovered that STAM2 negatively regulates the NF-κB signaling pathway, and its inhibitory effect is enhanced upon LPS induction. Our study confirmed that STAM2 can enhance the degradation of myeloid differentiation primary-response protein 88 (MyD88), an upstream regulator of NF-κB pathway. Furthermore, the UIM domain of STAM2 is important for the inhibition of MyD88. Mechanistically, STAM2 inhibits the NF-κB signaling pathway by targeting the MyD88 autophagy pathway. In addition, we showed that STAM2 promotes the proliferation of Vibrio harveyi. In summary, our study reveals that STAM2 inhibits NF-κB signaling activation and mediates innate immunity in teleost via the autophagy pathway.

ESCRT-dependent control of craniofacial morphogenesis with concomitant perturbation of NOTCH signaling

Craniofacial development is orchestrated by transcription factor-driven regulatory networks, epigenetic modifications, and signaling pathways. Signaling molecules and their receptors rely on endo-lysosomal trafficking to prevent accumulation on the plasma membrane. ESCRT (Endosomal Sorting Complexes Required for Transport) machinery is recruited to endosomal membranes enabling degradation of such endosomal cargoes. Studies in vitro and in invertebrate models established the requirements of the ESCRT machinery in membrane remodeling, endosomal trafficking, and lysosomal degradation of activated membrane receptors. However, investigations during vertebrate development have been scarce. By ENU-induced mutagenesis, we isolated a mouse line, Vps25ENU/ENU, carrying a hypomorphic allele of the ESCRT-II component Vps25, with craniofacial anomalies resembling features of human congenital syndromes. Here, we assessed the spatiotemporal dynamics of Vps25 and additional ESCRT-encoding genes during murine development. We show that these genes are ubiquitously expressed although enriched in discrete domains of the craniofacial complex, heart, and limbs. ESCRT-encoding genes, including Vps25, are expressed in both cranial neural crest-derived mesenchyme and epithelium. Unlike constitutive ESCRT mutants, Vps25ENU/ENU embryos display late lethality. They exhibit hypoplastic lower jaw, stunted snout, dysmorphic ear pinnae, and secondary palate clefting. Thus, we provide the first evidence for critical roles of ESCRT-II in craniofacial morphogenesis and report perturbation of NOTCH signaling in craniofacial domains of Vps25ENU/ENU embryos. Given the known roles of NOTCH signaling in the developing cranium, and notably the lower jaw, we propose that the NOTCH pathway partly mediates the craniofacial defects of Vps25ENU/ENU mouse embryos.

A Systematic Compilation of Human SH3 Domains: A Versatile Superfamily in Cellular Signaling

SRC homology 3 (SH3) domains are fundamental modules that enable the assembly of protein complexes through physical interactions with a pool of proline-rich/noncanonical motifs from partner proteins. They are widely studied modular building blocks across all five kingdoms of life and viruses, mediating various biological processes. The SH3 domains are also implicated in the development of human diseases, such as cancer, leukemia, osteoporosis, Alzheimer's disease, and various infections. A database search of the human proteome reveals the existence of 298 SH3 domains in 221 SH3 domain-containing proteins (SH3DCPs), ranging from 13 to 720 kilodaltons. A phylogenetic analysis of human SH3DCPs based on their multi-domain architecture seems to be the most practical way to classify them functionally, with regard to various physiological pathways. This review further summarizes the achievements made in the classification of SH3 domain functions, their binding specificity, and their significance for various diseases when exploiting SH3 protein modular interactions as drug targets.

Carbon Monoxide Activates PERK-Regulated Autophagy to Induce Immunometabolic Reprogramming and Boost Antitumor T-cell Function

Mitochondria and endoplasmic reticulum (ER) share structural and functional networks and activate well-orchestrated signaling processes to shape cells' fate and function. While persistent ER stress (ERS) response leads to mitochondrial collapse, moderate ERS promotes mitochondrial function. Strategies to boost antitumor T-cell function by targeting ER-mitochondria cross-talk have not yet been exploited. Here, we used carbon monoxide (CO), a short-lived gaseous molecule, to test whether engaging moderate ERS conditions can improve mitochondrial and antitumor functions in T cells. In melanoma antigen-specific T cells, CO-induced transient activation of ERS sensor protein kinase R-like endoplasmic reticulum kinase (PERK) significantly increased antitumor T-cell function. Furthermore, CO-induced PERK activation temporarily halted protein translation and induced protective autophagy, including mitophagy. The use of LC3-GFP enabled differentiation between the cells that prepare themselves to undergo active autophagy (LC3-GFPpos) and those that fail to enter the process (LC3-GFPneg). LC3-GFPpos T cells showed strong antitumor potential, whereas LC3-GFPneg cells exhibited a T regulatory-like phenotype, harbored dysfunctional mitochondria, and accumulated abnormal metabolite content. These anomalous ratios of metabolites rendered the cells with a hypermethylated state and distinct epigenetic profile, limiting their antitumor activity. Overall, this study shows that ERS-activated autophagy pathways modify the mitochondrial function and epigenetically reprogram T cells toward a superior antitumor phenotype to achieve robust tumor control.

SIGNIFICANCE

Transient activation of ER stress with carbon monoxide drives mitochondrial biogenesis and protective autophagy that elicits superior antitumor T-cell function, revealing an approach to improving adoptive cell efficacy therapy.

OTUB1 Recruits Tumor Infiltrating Lymphocytes and Is a Prognostic Marker in Digestive Cancers

Background

The deubiquitinating enzyme (DUB) OTUB1 can regulate the process of ubiquitination, but the influence of OTUB1 on immunity, apoptosis, autophagy, and the prognosis of digestive cancers requires further exploration.

Methods

OTUB1 expression was analyzed with the Oncomine and TIMER database. Kaplan-Meier plotter was used to calculate the association between OTUB1 and clinical prognosis. The regulation of OTUB1 on cancer immunocyte infiltration was determined by the TIMER database. The interaction between OTUB1 and immune genes, gene expression profiling (GEP), key genes of apoptosis and autophagy were analyzed via GEPIA. Protein-protein interaction (PPI), gene expression profiling (GEP), and functional pathway enrichment were also performed with the STRING and Pathway Common databases, respectively.

Results

High OTUB1 expression was found in CHOL, LIHC, READ, ESCA, and COAD, which was significantly associated with the poorer OS of LIHC (HR = 2.07, 95% CI = 1.30-3.30, P = 0.002), with modifications by sex, stage, grade, and mutant burden. OTUB1 can promote the recruitment of B cells, CD8 + T cells, macrophages in ESCA, B cells, and neutrophils in LIHC. We determined a significant interaction between OTUB1 and USP8, RNF128, LRIG1, UBB, UBC, STAM2, RNF41, EGFR, RPS27A, and HGS by PPI. This functional pathway indicates the regulatory role of OTUB1on immune, apoptosis, and autophagy through its interaction with TP53 and ATG.

Conclusions

OTUB1 performed as a molecular indicator of poor prognosis in digestive cancers, regulated the infiltration of tumor immunocytes, and exerted a significant influence on apoptosis and autophagy. OTUB1 is a potential antitumor target for digestive tumors.

A risk signature with four autophagy-related genes for predicting survival of glioblastoma multiforme

Glioblastoma multiforme (GBM) is a devastating brain tumour without effective treatment. Recent studies have shown that autophagy is a promising therapeutic strategy for GBM. Therefore, it is necessary to identify novel biomarkers associated with autophagy in GBM. In this study, we downloaded autophagy-related genes from Human Autophagy Database (HADb) and Gene Set Enrichment Analysis (GSEA) website. Least absolute shrinkage and selection operator (LASSO) regression and multivariate Cox regression analysis were performed to identify genes for constructing a risk signature. A nomogram was developed by integrating the risk signature with clinicopathological factors. Time-dependent receiver operating characteristic (ROC) curve and calibration plot were used to evaluate the efficiency of the prognostic model. Finally, four autophagy-related genes (DIRAS3, LGALS8, MAPK8 and STAM) were identified and were used for constructing a risk signature, which proved to be an independent risk factor for GBM patients. Furthermore, a nomogram was developed based on the risk signature and clinicopathological factors (IDH1 status, age and history of radiotherapy or chemotherapy). ROC curve and calibration plot suggested the nomogram could accurately predict 1-, 3- and 5-year survival rate of GBM patients. For function analysis, the risk signature was associated with apoptosis, necrosis, immunity, inflammation response and MAPK signalling pathway. In conclusion, the risk signature with 4 autophagy-related genes could serve as an independent prognostic factor for GBM patients. Moreover, we developed a nomogram based on the risk signature and clinical traits which was validated to perform better for predicting 1-, 3- and 5-year survival rate of GBM.

All roads lead to the vacuole-autophagic transport as part of the endomembrane trafficking network in plants

Plants regulate their development and response to the changing environment by sensing and interpreting environmental signals. Intracellular trafficking pathways including endocytic-, vacuolar-, and autophagic trafficking are important for the various aspects of responses in plants. Studies in the last decade have shown that the autophagic transport pathway uses common key components of endomembrane trafficking as well as specific regulators. A number of factors previously described for their function in endosomal trafficking have been discovered to be involved in the regulation of autophagy in plants. These include conserved endocytic machineries, such as the endosomal sorting complex required for transport (ESCRT), subunits of the HOPS and exocyst complexes, SNAREs, and RAB GTPases as well as plant-specific proteins. Defects in these factors have been shown to cause impairment of autophagosome formation, transport, fusion, and degradation, suggesting crosstalk between autophagy and other intracellular trafficking processes. In this review, we focus mainly on possible functions of endosomal trafficking components in autophagy.

Identification of STAM1 as a novel effector of ventral projection of spinal motor neurons

During spinal cord development, motor neuron (MN) axons exit the spinal cord ventrally, although the molecular basis for this process remains poorly understood. STAM1 and Hrs form a complex involved with endosomal targeting of cargo proteins, including the chemokine receptor CXCR4. Interestingly, the absence of CXCR4 signaling in spinal MNs is known to enforce improper extension of the axons into the dorsal side of the spinal cord. Here we report that the MN-specific Isl1-Lhx3 complex directly transactivates the Stam1 gene and STAM1 functions in determining the ventral spinal MN axonal projections. STAM1 is co-expressed with Hrs in embryonic spinal MNs, and knock-down of STAM1 in the developing chick spinal cord results in down-regulation of the expression of CXCR4, accompanied by dorsally projecting motor axons. Interestingly, overexpression of STAM1 or CXCR4 also results in dorsal projection of motor axons, suggesting that proper CXCR4 protein level is critical for the ventral motor axon trajectory. Our results reveal a critical regulatory axis for the ventral axonal trajectory of developing spinal MNs, consisting of the Isl1-Lhx3 complex, STAM1 and CXCR4.

ESCRT-II/Vps25 constrains digit number by endosome-mediated selective modulation of FGF-SHH signaling

Sorting and degradation of receptors and associated signaling molecules maintain homeostasis of conserved signaling pathways during cell specification and tissue development. Yet, whether machineries that sort signaling proteins act preferentially on different receptors and ligands in different contexts remains mysterious. Here, we show that Vacuolar protein sorting 25, Vps25, a component of ESCRT-II (Endosomal Sorting Complex Required for Transport II), directs preferential endosome-mediated modulation of FGF signaling in limbs. By ENU-induced mutagenesis, we isolated a polydactylous mouse line carrying a hypomorphic mutation of Vps25 (Vps25(ENU)). Unlike Vps25-null embryos we generated, Vps25(ENU/ENU) mutants survive until late gestation. Their limbs display FGF signaling enhancement and consequent hyperactivation of the FGF-SHH feedback loop causing polydactyly, whereas WNT and BMP signaling remain unperturbed. Notably, Vps25(ENU/ENU) Mouse Embryonic Fibroblasts exhibit aberrant FGFR trafficking and degradation; however, SHH signaling is unperturbed. These studies establish that the ESCRT-II machinery selectively limits FGF signaling in vertebrate skeletal patterning.

The role of the endosomal sorting complexes required for transport (ESCRT) in tumorigenesis

The endosomal sorting complexes required for transport (ESCRT) are needed for three distinct cellular functions in higher eukaryotes: (i) Multivesicular body formation for the degradation of transmembrane proteins in lysosomes, (ii) midbody abscission during cytokinesis and (iii) retroviral budding. Not surprisingly, loss of ESCRT function has severe consequences, which include the failure to down-regulate growth factor receptors leading to deregulated mitogenic signaling. While it is clear that the function of the ESCRT machinery is important for embryonic development, its role in cancer is more controversial. Various experimental approaches in different model organisms arrive at partially divergent conclusions regarding the contribution of ESCRTs to tumorigenesis. Therefore the aim of this review is to provide an overview on different model systems used to study the role of the ESCRT machinery in cancer development, to highlight common grounds and present certain controversies in the field.

Hepatocyte growth factor regulated tyrosine kinase substrate in the peripheral development and function of B-cells

Hepatocyte growth factor (HGF)-regulated tyrosine kinase substrate (Hrs) is a vesicular sorting protein that functions as one of the endosomal-sorting proteins required for transport (ESCRT). Hrs, which binds to ubiquitinated proteins through its ubiquitin-interacting motif (UIM), contributes to the lysosomal transport and degradation of ubiquitinated membrane proteins. However, little is known about the relationship between B-cell functions and ESCRT proteins in vivo. Here we examined the immunological roles of Hrs in B-cell development and functions using B-cell-specific Hrs-deficient (Hrs(flox/flox);mb1(cre/)(+):Hrs-cKO) mice, which were generated using a cre-LoxP recombination system. Hrs deficiency in B-cells significantly reduced T-cell-dependent antibody production in vivo and impaired the proliferation of B-cells treated in vitro with an anti-IgM monoclonal antibody but not with LPS. Although early development of B-cells in the bone marrow was normal in Hrs-cKO mice, there was a significant decrease in the number of the peripheral transitional B-cells and marginal zone B-cells in the spleen of Hrs-cKO mice. These results indicate that Hrs plays important roles during peripheral development and physiological functions of B lymphocytes.

A genome-wide association study of chemotherapy-induced alopecia in breast cancer patients

INTRODUCTION

Chemotherapy-induced alopecia is one of the most common adverse events caused by conventional cytotoxic chemotherapy, yet there has been very little progress in the prevention or treatment of this side effect. Although this is not a life-threatening event, alopecia is very psychologically difficult for many women to manage. In order to improve the quality of life for these women, it is important to elucidate the molecular mechanisms of chemotherapy-induced alopecia and develop ways to effectively prevent and/or treat it. To identify the genetic risk factors associated with chemotherapy-induced alopecia, we conducted a genome-wide association study (GWAS) using DNA samples from breast cancer patients who were treated with chemotherapy.

METHODS

We performed a case-control association study of 303 individuals who developed grade 2 alopecia, and compared them with 880 breast cancer patients who did not show hair loss after being treated with conventional chemotherapy. In addition, we separately analyzed a subset of patients who received specific combination therapies by GWASs and applied the weighted genetic risk scoring (wGRS) system to investigate the cumulative effects of the associated SNPs.

RESULTS

We identified an SNP significantly associated with drug-induced grade 2 alopecia (rs3820706 in CACNB4 (calcium channel voltage-dependent subunit beta 4) on 2q23, P = 8.13 × 10(-9), OR = 3.71) and detected several SNPs that showed some suggestive associations by subgroup analyses. We also classified patients into four groups on the basis of wGRS analysis and found that patients who classified in the highest risk group showed 443 times higher risk of antimicrotubule agents-induced alopecia than the lowest risk group.

CONCLUSIONS

Our study suggests several associated genes and should shed some light on the molecular mechanism of alopecia in chemotherapy-treated breast cancer patients and hopefully will contribute to development of interventions that will improve the quality of life (QOL) of cancer patients.

Novel roles for the E3 ubiquitin ligase atrophin-interacting protein 4 and signal transduction adaptor molecule 1 in G protein-coupled receptor signaling

The CXCL12/CXCR4 signaling axis plays an important role in human health and disease; however, the molecular mechanisms mediating CXCR4 signaling remain poorly understood. Ubiquitin modification of CXCR4 by the E3 ubiquitin ligase AIP4 is required for lysosomal sorting and degradation, which is mediated by the endosomal sorting complex required for transport (ESCRT) machinery. CXCR4 sorting is regulated by an interaction between endosomal localized arrestin-2 and STAM-1, an ESCRT-0 component. Here, we report a novel role for AIP4 and STAM-1 in regulation of CXCR4 signaling that is distinct from their function in CXCR4 trafficking. Depletion of AIP4 and STAM-1 by siRNA caused significant inhibition of CXCR4-induced ERK-1/2 activation, whereas overexpression of these proteins enhanced CXCR4 signaling. We further show that AIP4 and STAM-1 physically interact and that the proline-rich region in AIP4 and the SH3 domain in STAM-1 are essential for the interaction. Overexpression of an AIP4 catalytically inactive mutant and a mutant that shows poor binding to STAM-1 fails to enhance CXCR4-induced ERK-1/2 signaling, as compared with wild-type AIP4, suggesting that the interaction between AIP4 and STAM-1 and the ligase activity of AIP4 are essential for ERK-1/2 activation. Remarkably, a discrete subpopulation of AIP4 and STAM-1 resides in caveolar microdomains with CXCR4 and appears to mediate ERK-1/2 signaling. We propose that AIP4-mediated ubiquitination of STAM-1 in caveolae coordinates activation of ERK-1/2 signaling. Thus, our study reveals a novel function for ubiquitin in the regulation of CXCR4 signaling, which may be broadly applicable to other G protein-coupled receptors.

T cell receptor (TCR)-induced tyrosine phosphorylation dynamics identifies THEMIS as a new TCR signalosome component

Stimulation of the T cell antigen receptor (TCR) induces formation of a phosphorylation-dependent signaling network via multiprotein complexes, whose compositions and dynamics are incompletely understood. Using stable isotope labeling by amino acids in cell culture (SILAC)-based quantitative proteomics, we investigated the kinetics of signal propagation after TCR-induced protein tyrosine phosphorylation. We confidently assigned 77 proteins (of 758 identified) as a direct or indirect consequence of tyrosine phosphorylation that proceeds in successive "signaling waves" revealing the temporal pace at which tyrosine kinases activate cellular functions. The first wave includes thymocyte-expressed molecule involved in selection (THEMIS), a protein recently implicated in thymocyte development but whose signaling role is unclear. We found that tyrosine phosphorylation of THEMIS depends on the presence of the scaffold proteins Linker for activation of T cells (LAT) and SH2 domain-containing lymphocyte protein of 76 kDa (SLP-76). THEMIS associates with LAT, presumably via the adapter growth factor receptor-bound protein 2 (Grb2) and with phospholipase Cγ1 (PLC-γ1). RNAi-mediated THEMIS knock-down inhibited TCR-induced IL-2 gene expression due to reduced ERK and nuclear factor of activated T cells (NFAT)/activator protein 1 (AP-1) signaling, whereas JNK, p38, or nuclear factor κB (NF-κB) activation were unaffected. Our study reveals the dynamics of TCR-dependent signaling networks and suggests a specific role for THEMIS in early TCR signalosome function.

PTP1B targets the endosomal sorting machinery: dephosphorylation of regulatory sites on the endosomal sorting complex required for transport component STAM2

Dephosphorylation and endocytic down-regulation are distinct processes that together control the signaling output of a variety of receptor tyrosine kinases (RTKs). PTP1B can directly dephosphorylate several RTKs, but it can also promote activation of downstream pathways through largely unknown mechanisms. These positive signaling functions likely contribute to the tumor-promoting effect of PTP1B in mouse cancer models. Here, we have identified STAM2, an endosomal protein involved in sorting activated RTKs for lysosomal degradation, as a substrate of PTP1B. PTP1B interacts with STAM2 at defined phosphotyrosine sites, and knockdown of PTP1B expression augments STAM2 phosphorylation. Intriguingly, manipulating the expression and phosphorylation state of STAM2 did not have a general effect on epidermal growth factor (EGF)-induced EGF receptor trafficking, degradation, or signaling. Instead, phosphorylated STAM2 specifically suppressed Akt activation, and a phosphorylation-deficient STAM2 mutant displayed prolonged localization on endosomes following EGF stimulation. These results reveal a novel link between the dephosphorylation and endocytic machinery and suggest that PTP1B can affect RTK signaling in a previously unrecognized manner.

Arrestin-2 interacts with the endosomal sorting complex required for transport machinery to modulate endosomal sorting of CXCR4

The chemokine receptor CXCR4, a G protein-coupled receptor, is targeted for lysosomal degradation via a ubiquitin-dependent mechanism that involves the endosomal sorting complex required for transport (ESCRT) machinery. We have reported recently that arrestin-2 also targets CXCR4 for lysosomal degradation; however, the molecular mechanisms by which this occurs remain poorly understood. Here, we show that arrestin-2 interacts with ESCRT-0, a protein complex that recognizes and sorts ubiquitinated cargo into the degradative pathway. Signal-transducing adaptor molecule (STAM)-1, but not related STAM-2, interacts directly with arrestin-2 and colocalizes with CXCR4 on early endosomal antigen 1-positive early endosomes. Depletion of STAM-1 by RNA interference and disruption of the arrestin-2/STAM-1 interaction accelerates agonist promoted degradation of CXCR4, suggesting that STAM-1 via its interaction with arrestin-2 negatively regulates CXCR4 endosomal sorting. Interestingly, disruption of this interaction blocks agonist promoted ubiquitination of hepatocyte growth factor-regulated tyrosine kinase substrate (HRS) but not CXCR4 and STAM-1 ubiquitination. Our data suggest a mechanism whereby arrestin-2 via its interaction with STAM-1 modulates CXCR4 sorting by regulating the ubiquitination status of HRS.

STAM adaptor proteins interact with COPII complexes and function in ER-to-Golgi trafficking

Signal-transducing adaptor molecules (STAMs) are involved in growth factor and cytokine signaling as well as receptor degradation, and they form complexes with a number of endocytic proteins, including Hrs and Eps15. In this study, we demonstrate that STAM proteins also localize prominently to early exocytic compartments and profoundly regulate Golgi morphology. Upon STAM overexpression in cells, the Golgi apparatus becomes extensively fragmented and dispersed, but when STAMs are depleted, the Golgi becomes highly condensed. Under both scenarios, vesicular stomatitis virus G protein-green fluorescent protein trafficking to the plasma membrane is markedly inhibited, and recovery of Golgi morphology after Brefeldin A treatment is substantially impaired in STAM-depleted cells. Furthermore, STAM proteins interact with coat protein II (COPII) proteins, probably at endoplasmic reticulum (ER) exit sites, and Sar1 activity is required to maintain the localization of STAMs at discrete sites. Thus, in addition to their roles in signaling and endocytosis, STAMs function prominently in ER-to-Golgi trafficking, most likely through direct interactions with the COPII complex.

MEK1/2 induces STAT5-mediated germline transcription of the TCRgamma locus in response to IL-7R signaling

The IL-7R plays an essential role in gammadelta T cell development by inducing V-J recombination of the TCRgamma locus through STAT5. Although tyrosine residues in the intracellular domain of the mouse IL-7R alpha-chain (IL-7Ralpha) have been implicated in STAT5 activation, it is still unknown whether they are essential for gammadelta T cell development. In this study, we showed that those IL-7Ralpha tyrosine residues are not essential for gammadelta T cell development, because phenylalanine replacement of four intracellular tyrosine residues (IL-7R-FFFF) partially rescued gammadelta T cell development of IL-7Ralpha-/- progenitors. To examine signaling pathways activated by IL-7R-FFFF, we introduced a chimeric receptor consisting of the human IL-4R alpha-chain and mouse IL-7R-FFFF (4R/7R-FFFF) into an IL-7-dependent pre-B cell line and found that 4R/7R-FFFF induced TCRgamma germline transcription and STAT5 activation. Treatment of cells with MEK1/2 inhibitors significantly decreased levels of TCRgamma germline transcription and STAT5 tyrosine phosphorylation mediated by 4R/7R-FFFF, suggesting that MEK1/2 plays an alternative role in STAT5 activation by IL-7R. MEK1/2 associated with STAT5 and induced STAT5 tyrosine phosphorylation and DNA binding activity. Furthermore, MEK1 directly phosphorylated a STAT5 tyrosine residue in vitro. Finally, active MEK1 partially rescued TCRgamma germline transcription by IL-7R in a pre-T cell line. These results demonstrate that MEK1/2 induces TCRgamma germline transcription by phosphorylating STAT5 through IL-7R-FFFF and suggest a potential role for MAPK in IL-7R tyrosine-independent activation of STAT5.

Endosomal sorting complex required for transport proteins in cancer pathogenesis, vesicular transport, and non-endosomal functions

Endosomal sorting complex required for transport (ESCRT) proteins form a multicomplex sorting machinery that controls multivesicular body (MVB) formation and the sorting of ubiquitinated membrane proteins to the endosomes. Being sorted to the MVB generally results in the lysosome-dependent degradation of cell-surface receptors, and defects in this machinery induce dysregulated receptor traffic and turnover. Recent lessons from gene targeting and silencing methodologies have implicated the ESCRT in normal development, cell differentiation, and growth, as well as in the budding of certain enveloped viruses. Furthermore, it is becoming apparent that the dysregulation of ESCRT proteins is involved in the development of various human diseases, including many types of cancers and neurodegenerative disorders. Here, we summarize the roles of ESCRT proteins in MVB sorting processes and the regulation of tumor cells, and we discuss some of their other functions that are unrelated to vesicular transport.

The related adaptors, adaptor in lymphocytes of unknown function X and Rlk/Itk-binding protein, have nonredundant functions in lymphocytes

Adaptors play a critical role in regulating signaling pathways that control lymphocyte development and activation. Adaptor in lymphocytes of unknown function X (ALX) and Rlk/Itk-binding protein (RIBP) are adaptors related by structure and sequence, coexpressed in T cells. Mice deficient for each adaptor demonstrated that ALX and RIBP, respectively, negatively and positively regulate T cell activation in response to TCR/CD28 stimulation. However, these results did not preclude that they may function redundantly in other cell populations, or in response to other stimuli. Therefore, to understand the relationship between these related adaptors, ALX/RIBP-deficient mice were generated. We demonstrate that although ALX and RIBP are expressed throughout T cell development, T cell development occurs normally in these mice. Using the H-Y TCR transgenic model, positive and negative selection were found to proceed unimpeded in the absence of ALX and RIBP. We demonstrate that RIBP is also expressed in B cells; however, RIBP- and ALX/RIBP-deficient mice had normal B cell development, and responded equivalently to wild type in response to IgM, CD40, B cell-activating factor/B lymphocyte stimulator, CpG, and LPS. Interestingly, T cells deficient in both ALX and RIBP behaved similarly to those deficient in ALX alone during T cell activation in response to TCR/CD28, exhibiting increased IL-2 production, CD25 expression, and proliferation, thus showing that ALX deficiency masked the effect of RIBP deficiency. ALX/RIBP-deficient T cells did not have any alterations in either activation-induced cell death or Th1/2 polarization. Therefore, we did not find any functional redundancy or synergy during lymphocyte development, selection, activation, or survival in ALX/RIBP-deficient mice, demonstrating that these molecules function independently.

Transcriptional responses in spleens from mice exposed to Yersinia pestis CO92

Yersinia pestis is one of the most threatening biological agents due to the associated high mortality and history of plague pandemics. Identifying molecular players in the host response to infection may enable the development of medical countermeasures against Y. pestis. In this study, microarrays were used to identify the host splenic response mechanisms to Y. pestis infection. Groups of Balb/c mice were injected intraperitoneally with 2-257CFU of Y. pestis strain CO92 or vehicle. One group was assessed for mortality rates and another group for transcriptional analysis. The time to death at the 8 and 257CFU challenge doses were 5.0+/-2.3 and 3.8+/-0.4 days, respectively. Gene profiling using Affymetrix Mouse Genome 430 2.0 Arrays revealed no probe sets were significantly altered for all five mice in the low-dose group when compared to the vehicle controls. However, 534 probe sets were significantly altered in the high dose versus vehicle controls; 384 probe sets were down-regulated and 150 probe sets were up-regulated. The predominant biological processes identified were immune function, cytoskeletal, apoptosis, cell cycle, and protein degradation. This study provides new information on the underlying transcriptional mechanisms in mice to Y. pestis infection.

Impairment of organ-specific T cell negative selection by diabetes susceptibility genes: genomic analysis by mRNA profiling

BACKGROUND

T cells in the thymus undergo opposing positive and negative selection processes so that the only T cells entering circulation are those bearing a T cell receptor (TCR) with a low affinity for self. The mechanism differentiating negative from positive selection is poorly understood, despite the fact that inherited defects in negative selection underlie organ-specific autoimmune disease in AIRE-deficient people and the non-obese diabetic (NOD) mouse strain

RESULTS

Here we use homogeneous populations of T cells undergoing either positive or negative selection in vivo together with genome-wide transcription profiling on microarrays to identify the gene expression differences underlying negative selection to an Aire-dependent organ-specific antigen, including the upregulation of a genomic cluster in the cytogenetic band 2F. Analysis of defective negative selection in the autoimmune-prone NOD strain demonstrates a global impairment in the induction of the negative selection response gene set, but little difference in positive selection response genes. Combining expression differences with genetic linkage data, we identify differentially expressed candidate genes, including Bim, Bnip3, Smox, Pdrg1, Id1, Pdcd1, Ly6c, Pdia3, Trim30 and Trim12.

CONCLUSION

The data provide a molecular map of the negative selection response in vivo and, by analysis of deviations from this pathway in the autoimmune susceptible NOD strain, suggest that susceptibility arises from small expression differences in genes acting at multiple points in the pathway between the TCR and cell death.

Rin1 interacts with signal-transducing adaptor molecule (STAM) and mediates epidermal growth factor receptor trafficking and degradation

Rin1, the prototype of a new family of multidomain Rab5 exchange factors, has been shown to play an important role in the endocytosis of the epidermal growth factor receptor (EGFR). Herein, we examined the role of Rin1 in the down-regulation of EGFR following EGF stimulation. We observed that overexpression of Rin1 accelerates EGFR degradation in EGF-stimulated cells. In concordance, depletion of endogenous Rin1 by RNA interference resulted in a substantial reduction of EGFR degradation. We showed that Rin1 interacts with signal-transducing adaptor molecule 2 (STAM2), a protein that associates with hepatocyte growth factor-regulated substrate and plays a key role in the endosomal sorting machinery. Green fluorescent protein (GFP)-Rin1 co-localizes with hemagglutinin (HA)-STAM2 and with endogenous hepatocyte growth factor-regulated substrate. Furthermore, wild type STAM2, but not a deletion mutant lacking the SH3 domain, co-immunoprecipitates with endogenous Rin1. This interaction is dependent on the proline-rich domain (PRD) of Rin1 as Rin1DeltaPRD, a mutant lacking the PRD, does not interact with STAM2. Moreover, EGFR degradation was not accelerated by expression of the Rin1DeltaPRD mutant. Together these results suggest that Rin1 regulates EGFR degradation in cooperation with STAM, defining a novel role for Rin1 in regulating endosomal trafficking.

SSeCKS/Gravin/AKAP12 attenuates expression of proliferative and angiogenic genes during suppression of v-Src-induced oncogenesis

Background

SSeCKS is a major protein kinase C substrate with kinase scaffolding and metastasis-suppressor activity whose expression is severely downregulated in Src- and Ras-transformed fibroblast and epithelial cells and in human prostate, breast, and gastric cancers. We previously used NIH3T3 cells with tetracycline-regulated SSeCKS expression plus a temperature-sensitive v-Src allele to show that SSeCKS re-expression inhibited parameters of v-Src-induced oncogenic growth without attenuating in vivo Src kinase activity.

Methods

We use cDNA microarrays and semi-quantitative RT-PCR analysis to identify changes in gene expression correlating with i) SSeCKS expression in the absence of v-Src activity, ii) activation of v-Src activity alone, and iii) SSeCKS re-expression in the presence of active v-Src.

Results

SSeCKS re-expression resulted in the attenuation of critical Src-induced proliferative and pro-angiogenic gene expression including Afp, Hif-1α, Cdc20a and Pdgfr-β, and conversely, SSeCKS induced several cell cycle regulatory genes such as Ptpn11, Gadd45a, Ptplad1, Cdkn2d (p19), and Rbbp7.

Conclusion

Our data provide further evidence that SSeCKS can suppress Src-induced oncogenesis by modulating gene expression downstream of Src kinase activity.

SSeCKS/Gravin/AKAP12 Metastasis Suppressor Inhibits Podosome Formation via RhoA- and Cdc42-Dependent Pathways

Podosomes are poorly understood actin-rich structures notably found in cancer cell lines or in v-Src-transformed cells that are thought to facilitate some of the invasive properties involved in tumor metastasis. The enrichment of the Tks5/Fish protein, a v-Src substrate, is required for formation of podosomes. We showed previously that the tetracycline-regulated reexpression of the Src-suppressed C kinase substrate (SSeCKS, also known as Gravin/AKAP12) inhibited variables of v-Src-induced oncogenic growth in NIH3T3, correlating with the induction of normal actin cytoskeletal structures and cell morphology but not with gross inhibition of Src phosphorylation activity in the cell. Here, we show that SSeCKS reexpression at physiologic levels suppresses podosome formation, correlating with decreases in Matrigel invasiveness, whereas there is no effect on total cellular tyrosine phosphorylation or on the phosphorylation of Tks5/Fish. Activated forms of RhoA and Cdc42 were capable of rescuing podosome formation in v-Src cells reexpressing SSeCKS, and this correlated with the ability of SSeCKS to inhibit RhoA and Cdc42 activity levels by >5-fold. Interestingly, although activated Rac I had little effect on podosome formation, it could partner with activated RhoA to reverse the cell flattening induced by SSeCKS. These data suggest that v-Src-induced Tks5 tyrosine phosphorylation is insufficient for podosome formation in the absence of RhoA- and/or Cdc42-mediated cytoskeletal remodeling. Additionally, they strengthen the notion that SSeCKS suppresses Src-induced oncogenesis by reestablishing actin-based cytoskeletal architecture.

Allograft rejection requires STAT5a/b-regulated antiapoptotic activity in T cells but not B cells

STATs play key roles in immune function. We examined the role of STAT5a/b in allograft rejection. STAT5a/b-deficient mice showed a 4-fold increased survival time of heart allografts (p < 0.01). Unlike wild type, purified STAT5a/b-/- T cells transferred to Rag1-/- recipients failed to mediate heart allograft rejection until supplemented with STAT5a/b-/- B cells. In vitro, STAT5a/b-/- T cells did not proliferate in response to Con A or alloantigens but entered apoptosis within 48 h (95%). Activated STAT5a/b-/- T cells showed increased expression of proapoptotic (caspases, DNA repair genes, TNF/TNFR-associated factor family genes) and decreased antiapoptotic mRNAs in microarrays, while Western blots confirmed reduced antiapoptotic Bcl-2 and elevated proapoptotic Bax protein expression. Interestingly, at 24 h postactivation, STAT5a/b+/+ and STAT5a/b-/- T cells produced similar levels of IL-2, IL-4, IL-10, and IFN-gamma mRNA; ELISPOT assay showed an equivalent number of IL-4- and IFN-gamma-producing T cells in both STAT5a/b+/+ and STAT5a/b-/- splenic populations. Sera from STAT5a/b+/+ and STAT5a/b-/- rejectors had donor-specific IgM, IgG1, IgG2a, and IgG2b Ab, while STAT5a/b deficiency had no impact on B cell survival or proliferation in response to LPS. Compared with allografts from STAT5a/b+/+ recipients, heart allografts from STAT5a/b-/- recipients had markedly reduced infiltration by CD4 and CD8 T cells but increased infiltration by B cells and dense endothelial deposition of C4d, a marker of humoral rejection. Thus, activated STAT5a/b-/- T cells produce cytokines prior to entering apoptosis, thereby promoting differentiation of B cells yielding donor-specific IgM and IgG Ab that mediate allograft rejection.

Identification and Characterization of Survival-Related Gene, a Novel Cell Survival Gene Controlling Apoptosis and Tumorigenesis

Apoptosis plays a critical role in cellular homeostasis during development, immune responses, and tumorigenesis. Recent studies have identified a number of genes that control this process. We report here our identification of a novel cell survival-related gene (SRG) from a human expression cDNA library by functional cloning. SRG shows no significant nucleotide sequence homology to any known genes in the Genbank. Our fluorescence in situ hybridization analysis has estimated that SRG is located at 1p36, agreeing with the location at 1p36.22 in the human genome sequence. SRG encodes a putative protein of 172 amino acids, which is mainly located in the perinuclear region. Northern blotting analysis indicates that SRG is highly expressed in many human cancer cell lines although it is low in most tissues except liver and placenta. To investigate the function of SRG in apoptosis, we transfected SRG cDNA into BAF/BO3 and B16/F0 cells and induced apoptosis by cytokine/serum deprivation. We found that SRG-transfected cells are resistant to apoptosis induced by cytokine/serum deprivation. In addition, mice bearing SRG-transfected melanoma had more tumor formation and larger tumor growth. Melanoma transfected with antisense SRG showed significantly less tumor formation and smaller tumor growth. Interestingly, mouse SRG gene was also identified on chromosome 4 and blocking SRG expression with small interfering RNA promoted serum deprivation-induced apoptosis of NIH3T3 cells. Our results show that SRG is a novel cell survival gene that critically controls apoptosis and tumor formation.

Cell biology of IL-7, a key lymphotrophin

IL-7 is essential for the development and survival of T lymphocytes. This review is primarily from the perspective of the cell biology of the responding T cell. Beginning with IL-7 receptor structure and regulation, the major signaling pathways appear to be via PI3K and Stat5, although the requirement for either has yet to be verified by published knockout experiments. The proliferation pathway induced by IL-7 differs from conventional growth factors and is primarily through posttranslational regulation of p27, a Cdk inhibitor, and Cdc25a, a Cdk-activating phosphatase. The survival function of IL-7 is largely through maintaining a favorable balance of bcl-2 family members including Bcl-2 itself and Mcl-1 on the positive side, and Bax, Bad and Bim on the negative side. There are also some remarkable metabolic effects of IL-7 withdrawal. Studies of IL-7 receptor signaling have yet to turn up unique pathways, despite the unique requirement for IL-7 in T cell biology. There remain significant questions regarding IL-7 production and the major producing cells have yet to be fully characterized.

Hrs, a mammalian master molecule in vesicular transport and protein sorting, suppresses the degradation of ESCRT proteins signal transducing adaptor molecule 1 and 2

The degradation and sorting of cytoplasmic and cell-surface proteins are crucial steps in the control of cellular functions. We previously identified three mammalian Vps (vacuolar protein sorting) proteins, Hrs (hepatocyte growth factor-regulated tyrosine kinase substrate) and signal transducing adaptor molecule (STAM) 1 and -2, which are tyrosine-phosphorylated upon cytokine/growth factor stimulation. Hrs and the STAMs each contain a ubiquitin-interacting motif and through formation of a complex are involved in the vesicle transport of early endosomes. To explore the mechanism and cellular function of this complex in mammalian cells, we established an Hrs-defective fibroblastoid cell line (hrs(-/-)); embryos with this genotype died in utero. In the hrs(-/-) cells only trace amounts of STAM1 and STAM2 were detected. Introduction of wild-type Hrs or an Hrs mutant with an intact STAM binding domain (Hrs-dFYVE) fully restored STAM1 and STAM2 expression, whereas mutants with no STAM binding ability (Hrs-dC2, Hrs-dM) failed to express the STAMs. This regulated control of STAM expression by Hrs was independent of transcription. Interestingly, STAM1 degradation was mediated by proteasomes and was partially dependent on the ubiquitin-interacting motif of STAM1. Revertant Hrs expression in hrs(-/-) cells not only led to the accumulation of ubiquitinated proteins, including intracytoplasmic vesicles, but also restored STAM1 levels in early endosomes and eliminated the enlarged endosome phenotype caused by the absence of Hrs. These results suggest that Hrs is a master molecule that controls in part the degradation of STAM1 and the accumulation of ubiquitinated proteins.

Effects of deficiencies of STAMs and Hrs, mammalian class E Vps proteins, on receptor downregulation

The STAM family proteins, STAM1 and STAM2/EAST/Hbp, are phosphotyrosine proteins that contain SH3 domains and ubiquitin-interacting motifs. Their yeast homologue, Hse1, and its binding protein, Vps27, are involved in the vacuolar membrane transport machinery. Here we show that STAM1 and STAM2 are localized to the endosomal membrane. Some of these complexes contain Eps15, an endocytic protein, which accumulates in clumps upon expression of a dominant-negative form of Vps4-A, an AAA-type ATPase, that is required for normal endosome function. These results support the idea that the STAMs are mammalian vacuolar protein sorting (Vps) proteins. We also demonstrate that ligand-mediated epidermal growth factor receptor (EGFR) degradation is partially but not completely impaired in both Hrs(-/-) and STAM1(-/-)STAM2(-/-) mouse embryonic fibroblasts. Furthermore, endosome swelling is seen in both Hrs(-/-) and STAM1(-/-)STAM2(-/-) cells. These results suggest that the STAMs and Hrs play important roles in the mammalian endosomal/vacuolar protein sorting pathway.

Cloning and characterization of ALX, an adaptor downstream of CD28

T cell activation requires two signals: specific recognition of antigen through the T cell receptor (TCR) and a costimulatory signal provided primarily by CD28 in naïve T cells. We cloned a novel gene with considerable homology to RIBP/TSAd/Lad, an adaptor involved in T cell activation and interleukin-2 (IL-2) promoter activation. Expression of this gene is limited to the spleen and thymus. We have named this gene ALX, adaptor in lymphocytes of unknown function X. Because the related adaptor RIBP is involved in IL-2 regulation, we investigated whether ALX had a similar function. ALX overexpression in Jurkat T cells results in inhibition of IL-2 promoter activation after stimulation with superantigen. The IL-2 promoter contains several binding sites for transcription factors including the composite element RE/AP, which is the primary site of CD28 transcriptional activation. ALX overexpression had the greatest effect on the activation of a RE/AP reporter as opposed to an AP-1 reporter. Interestingly, ALX overexpression strongly inhibited RE/AP activation in response to anti-CD28/phorbol 12-myristate 13-acetate (PMA) stimulation but had minimal effect when anti-TCR/PMA was used. Therefore, it appears that ALX may function downstream of CD28 costimulation during T cell activation. In addition, the mobility of ALX shifts upon TCR/CD28 costimulation to a greater extent than what is observed with either stimulus alone demonstrating that ALX is a target of both TCR and CD28 costimulatory signaling pathways.

HIV Gag mimics the Tsg101-recruiting activity of the human Hrs protein

The HIV-1 Gag protein recruits the cellular factor Tsg101 to facilitate the final stages of virus budding. A conserved P(S/T)AP tetrapeptide motif within Gag (the "late domain") binds directly to the NH2-terminal ubiquitin E2 variant (UEV) domain of Tsg101. In the cell, Tsg101 is required for biogenesis of vesicles that bud into the lumen of late endosomal compartments called multivesicular bodies (MVBs). However, the mechanism by which Tsg101 is recruited from the cytoplasm onto the endosomal membrane has not been known. Now, we report that Tsg101 binds the COOH-terminal region of the endosomal protein hepatocyte growth factor-regulated tyrosine kinase substrate (Hrs; residues 222-777). This interaction is mediated, in part, by binding of the Tsg101 UEV domain to the Hrs 348PSAP351 motif. Importantly, Hrs222-777 can recruit Tsg101 and rescue the budding of virus-like Gag particles that are missing native late domains. These observations indicate that Hrs normally functions to recruit Tsg101 to the endosomal membrane. HIV-1 Gag apparently mimics this Hrs activity, and thereby usurps Tsg101 and other components of the MVB vesicle fission machinery to facilitate viral budding.

Identification of AMSH-LP containing a Jab1/MPN domain metalloenzyme motif

We have isolated a cDNA clone encoding a new AMSH (associated molecule with the SH3 domain of STAM) family protein, termed AMSH-like protein (AMSH-LP). AMSH-LP has similar characteristics to AMSH; both AMSH-LP and AMSH are expressed ubiquitously in various human tissues, contain a putative nuclear localization signal (NLS), an Mpr/Pad1/N-terminal (MPN) domain, and a Jab1/MPN domain metalloenzyme (JAMM) motif in their structures, and are excluded from the nucleus when lacking either the NLS or MPN domain. Moreover, we observed an enhancement of interleukin 2 (IL-2)-mediated c-myc induction in AMSH-LP-transfected cells similar to that seen in AMSH-transfected cells, suggesting a functional similarity between AMSH-LP and AMSH. However, the present study demonstrated that AMSH-LP, unlike AMSH, fails to bind to the SH3 domains of STAM1 (signal transducing adaptor molecule 1) and Grb2. These results suggest that AMSH-LP and AMSH may have different functions.

Interaction of the deafness-dystonia protein DDP/TIMM8a with the signal transduction adaptor molecule STAM1

The Mohr-Tranebjaerg-Jensen deafness-dystonia-optic atrophy protein DDP/TIMM8a is translated on cytoplasmic ribosomes but targeted ultimately to the mitochondrial intermembrane space, where it is involved in mitochondrial protein import. STAM1 is a cytoplasmic signal-transducing adaptor molecule implicated in cytokine signaling. We report here a direct interaction between DDP and STAM1, identified by yeast two-hybrid screening and confirmed by co-immunoprecipitation, fusion protein "pull downs," and nuclear redistribution assays. DDP coordinates Zn(2+), and Zn(2+) was found to stimulate the DDP-STAM1 interaction in vitro. Endogenous STAM1 localizes predominantly to early endosomes, and we found no evidence that STAM1 is imported into mitochondria in vitro. Thus, the DDP-STAM1 interaction likely occurs in the cytoplasm or at the mitochondrial outer membrane. The DDP-STAM1 interaction requires a coiled-coil region in STAM1 that overlaps with the immunoreceptor tyrosine-based activation motif (ITAM), a region previously shown to be important for interaction with Jak2/3 and hepatocyte growth factor-regulated tyrosine kinase substrate (Hrs). Thus, DDP binding may alter the interactions of STAM1 with several cytoplasmic proteins involved in cell signaling and endosomal trafficking.

STAM and Hrs are subunits of a multivalent ubiquitin-binding complex on early endosomes

STAM1 and STAM2, which have been identified as regulators of receptor signaling and trafficking, interact directly with Hrs, which mediates the endocytic sorting of ubiquitinated membrane proteins. The STAM proteins interact with the same coiled-coil domain that is involved in the targeting of Hrs to endosomes. In this work, we show that STAM1 and STAM2, as well as an endocytic regulator protein, Eps15, can be co-immunoprecipitated with Hrs both from membrane and cytosolic fractions and that recombinant Hrs, STAM1/STAM2, and Eps15 form a ternary complex. We find that overexpression of Hrs causes a strong recruitment of STAM2 to endosome membranes. Moreover, STAM2, like Hrs and Eps15, binds ubiquitin, and Hrs, STAM2, and Eps15 colocalize with ubiquitinated proteins in clathrin-containing endosomal microdomains. The localization of Hrs, STAM2, Eps15, and clathrin to endosome membranes is controlled by the AAA ATPase mVps4, which has been implicated in multivesicular body formation. Depletion of cellular Hrs by small interfering RNA results in a strongly reduced recruitment of STAM2 to endosome membranes and an impaired degradation of endocytosed epidermal growth factor receptors. We propose that Hrs, Eps15, and STAM proteins function in a multivalent complex that sorts ubiquitinated proteins into the multivesicular body pathway.