The suppressor of cytokine signaling (SOCS)-7 interacts with the actin cytoskeleton through vinexin

Cloning of suppressor of cytokine signaling 7 from silkworm (Bombyx mori) and its response to the infection of Bombyx mori nucleopolyhedrovirus

Suppressors of cytokine signaling (SOCS) play important roles in the regulation of growth, development, and immunity of eukaryotic organisms. SOCS7 is an important member of the SOCS family, but its physiological and pathological functions remain largely unknown in invertebrates including insects. Here, we first report the cloning of a SOCS7 gene from a domesticated silkworm (Bombyx mori), named BmSOCS7. We have characterized BmSOCS7 expression profiles in silkworm varieties susceptible or resistant to the infection of Bombyx mori nucleopolyhedrovirus (BmNPV) using the real-time fluorescence quantitative PCR. BmSOCS7 expresses highly in embryogenesis and lowly in metamorphosis in resistant silkworms but does in opposite contrast in susceptible silkworms. Its expression is at very low level in the fat body of resistant silkworms but is relatively high in the fat body of susceptible ones. BmNPV inoculation induces a transient downregulation and then a general upregulation of BmSOCS7 expression in BmN cells, while it induces a general downregulation in silkworm midgut, fat body and hemolymph with more pronounced effect in resistant silkworms than susceptible ones and more prominent in the fat body and hemolymph than the midgut. Together, our work reveals that downregulation of BmSOCS7 expression may be an important strategy for silkworm anti-BmNPV immune response, and BmSOCS7 may mainly function in the fat body and hemolymph rather than the midgut to participate in BmNPV infection process.

miR-221 promotes keratinocyte proliferation and migration by targeting SOCS7 and is regulated by YB-1

Proliferation and migration of keratinocytes are vital processes for the successful epithelization specifically after wounding. MiR‐221 has been identified to play a potential role in promoting wound regeneration by inducing blood vessel formation. However, little is known about the role of miR‐221 in the keratinocyte proliferation and migration during wound healing. An in vivo mice wound‐healing model was generated; the expression levels of miR‐221 were assessed by qRT‐PCR and fluorescence in situ hybridization. Initially, we found that miR‐221 was upregulated in the proliferative phase of wound healing. Further, in an in vivo wound‐healing mice model, targeted delivery of miR‐221 mimics accelerated wound healing. Contrastingly, inhibition of miR‐221 delayed healing. Additionally, we observed that overexpression of miR‐221 promoted cell proliferation and migration, while inhibition of miR‐221 had the opposite effects. Moreover, we identified SOCS7 as a direct target of miR‐221 in keratinocytes and overexpression of SOCS7 reversed the effects of miR‐221 in HaCaT keratinocytes. Finally, we identified that YB‐1 regulates the expression of miR‐221 in HaCaT keratinocytes. Overall, our experiments suggest that miR‐221 is regulated by YB‐1 in HaCaT keratinocytes and acts on SOCS7, thereby playing an important role in HaCaT keratinocyte proliferation and migration during wound healing.

SOCS1: Regulator of T Cells in Autoimmunity and Cancer

SOCS1 is a negative feedback regulator of cytokine and growth factor receptor signaling, and plays an indispensable role in attenuating interferon gamma signaling. Studies on SOCS1-deficient mice have established a crucial role for SOCS1 in regulating CD8⁺ T cell homeostasis. In the thymus, SOCS1 prevents thymocytes that had failed positive selection from surviving and expanding, ensures negative selection and prevents inappropriate developmental skewing toward the CD8 lineage. In the periphery, SOCS1 not only controls production of T cell stimulatory cytokines but also attenuates the sensitivity of CD8⁺ T cells to synergistic cytokine stimulation and antigen non-specific activation. As cytokine stimulation of CD8⁺ T lymphocytes increases their sensitivity to low affinity TCR ligands, SOCS1 likely contributes to peripheral T cell tolerance by putting brakes on aberrant T cell activation driven by inflammatory cytokines. In addition, SOCS1 is critical to maintain the stability of T regulatory cells and control their plasticity to become pathogenic Th17 and Th1 cells under the harmful influence of inflammatory cytokines. SOCS1 also regulates T cell activation by dendritic cells via modulating their generation, maturation, antigen presentation, costimulatory signaling, and cytokine production. The above control mechanisms of SOCS1 on T cells, T regulatory cells and dendritic cells collectively contribute to immunological tolerance and prevent autoimmune manifestation. On other hand, silencing SOCS1 in dendritic cells or CD8⁺ T cells stimulates efficient antitumor immunity. Thus, even though SOCS1 is not a cell surface checkpoint inhibitor, its regulatory functions on T cell responses qualify SOCS1as a "non-classical" checkpoint blocker. SOCS1 also functions as a tumor suppressor in cancer cells by regulating oncogenic signal transduction pathways. The loss of SOCS1 expression observed in many tumors may have an impact on classical checkpoint pathways. The potential to exploit SOCS1 to treat inflammatory/autoimmune diseases and elicit antitumor immunity is discussed.

Cell regulation by phosphotyrosine-targeted ubiquitin ligases

Three classes of E3 ubiquitin ligases, members of the Cbl, Hakai, and SOCS-Cul5-RING ligase families, stimulate the ubiquitination of phosphotyrosine-containing proteins, including receptor and nonreceptor tyrosine kinases and their phosphorylated substrates. Because ubiquitination frequently routes proteins for degradation by the lysosome or proteasome, these E3 ligases are able to potently inhibit tyrosine kinase signaling. Their loss or mutational inactivation can contribute to cancer, autoimmunity, or endocrine disorders, such as diabetes. However, these ligases also have biological functions that are independent of their ubiquitination activity. Here we review relevant literature and then focus on more-recent developments in understanding the structures, substrates, and pathways through which the phosphotyrosine-specific ubiquitin ligases regulate diverse aspects of cell biology.

SOCS proteins in regulation of receptor tyrosine kinase signaling

Receptor tyrosine kinases (RTKs) are a family of cell surface receptors that play critical roles in signal transduction from extracellular stimuli. Many in this family of kinases are overexpressed or mutated in human malignancies and thus became an attractive drug target for cancer treatment. The signaling mediated by RTKs must be tightly regulated by interacting proteins including protein-tyrosine phosphatases and ubiquitin ligases. The suppressors of cytokine signaling (SOCS) family proteins are well-known negative regulators of cytokine receptors signaling consisting of eight structurally similar proteins, SOCS1-7, and cytokine-inducible SH2-containing protein (CIS). A key feature of this family of proteins is the presence of an SH2 domain and a SOCS box. Recent studies suggest that SOCS proteins also play a role in RTK signaling. Activation of RTK results in transcriptional activation of SOCS-encoding genes. These proteins associate with RTKs through their SH2 domains and subsequently recruit the E3 ubiquitin machinery through the SOCS box, and thereby limit receptor stability by inducing ubiquitination. In a similar fashion, SOCS proteins negatively regulate mitogenic signaling by RTKs. It is also evident that RTKs can sometimes bypass SOCS regulation and SOCS proteins can even potentiate RTKs-mediated mitogenic signaling. Thus, apart from negative regulation of receptor signaling, SOCS proteins may also influence signaling in other ways.

SOCS6 is a selective suppressor of receptor tyrosine kinase signaling

The suppressors of cytokine signaling (SOCS) are well-known negative regulators of cytokine receptor signaling. SOCS6 is one of eight members of the SOCS family of proteins. Similar to other SOCS proteins, SOCS6 consists of an uncharacterized extended N-terminal region followed by an SH2 domain and a SOCS box. Unlike other SOCS proteins, SOCS6 is mainly involved in negative regulation of receptor tyrosine kinase signaling. SOCS6 is widely expressed in many tissues and is found to be downregulated in many cancers including colorectal cancer, gastric cancer, lung cancer, ovarian cancer, stomach cancer, thyroid cancer, hepatocellular carcinoma, and pancreatic cancer. SOCS6 is involved in negative regulation of receptor signaling by increasing degradation mediated by ubiquitination of receptors or substrate proteins and induces apoptosis by targeting mitochondrial proteins. Therefore, SOCS6 turns out as an important regulator of survival signaling and its activity is required for controlling receptor tyrosine kinase signaling.

Suppressor of cytokine signalling (SOCS) proteins as guardians of inflammatory responses critical for regulating insulin sensitivity

Overactivation of immune pathways in obesity is an important cause of insulin resistance and thus new approaches aimed to limit inflammation or its consequences may be effective for treating Type 2 diabetes. The SOCS (suppressors of cytokine signalling) are a family of proteins that play an essential role in mediating inflammatory responses in both immune cells and metabolic organs such as the liver, adipose tissue and skeletal muscle. In the present review we discuss the role of SOCS1 and SOCS3 in controlling immune cells such as macrophages and T-cells and the impact this can have on systemic inflammation and insulin resistance. We also dissect the mechanisms by which SOCS (1-7) regulate insulin signalling in different tissues including their impact on the insulin receptor and insulin receptor substrates. Lastly, we discuss the important findings from SOCS whole-body and tissue-specific null mice, which implicate an important role for these proteins in controlling insulin action and glucose homoeostasis in obesity.

In vitro and in vivo effects of suppressor of cytokine signalling 7 knockdown in breast cancer: the influence on cellular response to hepatocyte growth factor

Purpose. Suppressor of cytokine signaling 7 (SOCS7) is a member of the SOCS family and is known to interact with phospholipase Cγ-1 (PLCγ-1), a key downstream mediator of the hepatocyte growth factor (HGF)/C-MET axis. Here, we report our observations of the effect of knocking down SOCS7 gene on the behaviour of breast cancer cells both in vitro and in vivo and to elucidate whether this involves HGF/C-MET pathway using the PLCγ-1 blocker U73122. Methods. MCF7 and MDA-MB-231 breast cancer cells were transfected with anti-SOCS7 ribozymal transgene, to create sublines with SOCS7 knockdown. The in vitro growth and migration of the cells were evaluated in basic conditions and with HGF and U73122 treatment using growth assays, scratch-wound, and electrical cell impedance sensing (ECIS) migration assays. MCF7 and MDA-MB-231 in vivo tumour xenograft growth were also studied. Results. Basal in vitro growth and migration of both cellular lines and the in vivo MCF7 xenograft growth were significantly enhanced with SOCS7 knockdown. In vitro HGF treatment has further influenced the growth and migration when SOCS7 gene was knocked-down in both cellular lines (P < 0.05). PLCγ-1 pharmacological inhibition of the HGF/C-MET cascade during their in vitro growth and migration seemed to only occur when SOCS7 gene was knocked down. Conclusions. We report a unique regulatory role for SOCS7 in controlling the malignant behaviour of breast cancer lines MCF7 and MDA-MB-231 in vitro and the MCF7 tumour xenografts in vivo. We also report a regulatory role for SOCS7 during the in vitro HGF-induced growth and migration in these cells as HGF treatment and SOCS7 loss have synergistically enhanced these functions. This SOCS7 knockdown-attributed effect could be due to a precise anti-PLCγ-1 role.

The WAVE regulatory complex links diverse receptors to the actin cytoskeleton

The WAVE regulatory complex (WRC) controls actin cytoskeletal dynamics throughout the cell by stimulating the actin-nucleating activity of the Arp2/3 complex at distinct membrane sites. However, the factors that recruit the WRC to specific locations remain poorly understood. Here, we have identified a large family of potential WRC ligands, consisting of ∼120 diverse membrane proteins, including protocadherins, ROBOs, netrin receptors, neuroligins, GPCRs, and channels. Structural, biochemical, and cellular studies reveal that a sequence motif that defines these ligands binds to a highly conserved interaction surface of the WRC formed by the Sra and Abi subunits. Mutating this binding surface in flies resulted in defects in actin cytoskeletal organization and egg morphology during oogenesis, leading to female sterility. Our findings directly link diverse membrane proteins to the WRC and actin cytoskeleton and have broad physiological and pathological ramifications in metazoans.

The role of suppressors of cytokine signalling in human neoplasms

Suppressors of cytokine signalling 1-7 (SOCS1-7) and cytokine-inducible SH2-containing protein (CIS) are a group of intracellular proteins that are well known as JAK-STAT and several other signalling pathways negative feedback regulators. More recently several members have been identified as tumour suppressors and dysregulation of their biological roles in controlling cytokine and growth factor signalling may contribute to the development of many solid organ and haematological malignancies. This review explores their biological functions and their possible tumour suppressing role in human neoplasms.

The N-terminal domains of SOCS proteins: a conserved region in the disordered N-termini of SOCS4 and 5

Suppressors of cytokine signaling (SOCS) proteins function as negative regulators of cytokine signaling and are involved in fine tuning the immune response. The structure and role of the SH2 domains and C-terminal SOCS box motifs of the SOCS proteins are well characterized, but the long N-terminal domains of SOCS4-7 remain poorly understood. Here, we present bioinformatic analyses of the N-terminal domains of the mammalian SOCS proteins, which indicate that these domains of SOCS4, 5, 6, and 7 are largely disordered. We have also identified a conserved region of about 70 residues in the N-terminal domains of SOCS4 and 5 that is predicted to be more ordered than the surrounding sequence. The conservation of this region can be traced as far back as lower vertebrates. As conserved regions with increased structural propensity that are located within long disordered regions often contain molecular recognition motifs, we expressed the N-terminal conserved region of mouse SOCS4 for further analysis. This region, mSOCS4₈₆₋₁₅₅, has been characterized by circular dichroism and nuclear magnetic resonance spectroscopy, both of which indicate that it is predominantly unstructured in aqueous solution, although it becomes helical in the presence of trifluoroethanol. The high degree of sequence conservation of this region across different species and between SOCS4 and SOCS5 nonetheless implies that it has an important functional role, and presumably this region adopts a more ordered conformation in complex with its partners. The recombinant protein will be a valuable tool in identifying these partners and defining the structures of these complexes.

Transcriptome analysis revealed unique genes as targets for the anti-inflammatory action of activated protein C in human macrophages

Background

Activated protein C (APC) has been introduced as a therapeutic agent for treatment of patients with severe sepsis due to its unique anticoagulant and anti-inflammatory properties in the vascular system. In this study we investigated novel targets for the anti-inflammatory action of APC in human macrophages.

Methods

Using a genome-wide approach, effects of APC on the expression profile in inflammatory activated human macrophages were analyzed.

Results

We identified, for the first time, genes that are specifically regulated by APC under inflammatory conditions, such as chromatin binding protein 4B (CHMP4B) and p300/CBP-associated factor (PCAF), thus indicating a role of APC in the epigenetic control of gene transcription. A functional assay showed the influence of APC in the acetyltransferase/deacetylase activity of nuclear extracts from inflamed macrophages.

Conclusion

Our data sheds new light on APC targets in inflammation and opens new lines of investigation that may be explored in order to further elucidate its unique molecule properties.

Epithelial induction of porcine suppressor of cytokine signaling 2 (SOCS2) gene expression in response to Entamoeba histolytica

Suppressor of cytokine signaling (SOCS) proteins are key physiological regulators of both innate and adaptive immunity. These proteins belong to the three major classes of modulators of cytokines signaling. In the following article, we used porcine polarized intestinal cells to study early response to the protozoan, Entamoeba histolytica, and we identified by rapid amplification of cDNA ends (RACE) PCR porcine SOCS1, SOCS4, SOCS5 and SOCS6 encoding sequences. With more than 92% identity predicted porcine SOCS proteins are very similar to their human counterparts. Among SOCS transcripts, only SOCS2 mRNA was significantly induced in epithelial intestinal cells in response to the cytolytic activity of the parasite. The transcriptomic profile obtained after 3h of co-culture of polarized intestinal cells with E. histolytica was clearly oriented toward inflammation and the recruitment of neutrophils. These transcriptomic data have been normalized with accuracy by the utilisation of multiple validated reference genes. The analysis offers a first set of reference genes useful for future studies in porcine intestinal cells. Our data shed light on the understanding of the early response of polarized intestinal cells to E. histolytica and identified a potential involvement of SOCS2 in the parasite regulation of the host response.

SCO-ping out the mechanisms underlying the etiology of hydrocephalus

The heterogeneous nature of congenital hydrocephalus has hampered our understanding of the molecular basis of this common clinical problem. However, disease gene identification and characterization of multiple transgenic mouse models has highlighted the importance of the subcommissural organ (SCO) and the ventricular ependymal (vel) cells. Here, we review how altered development and function of the SCO and vel cells contributes to hydrocephalus.

Nck adapter proteins: functional versatility in T cells

Nck is a ubiquitously expressed adapter protein that is almost exclusively built of one SH2 domain and three SH3 domains. The two isoproteins of Nck are functionally redundant in many aspects and differ in only few amino acids that are mostly located in the linker regions between the interaction modules. Nck proteins connect receptor and non-receptor tyrosine kinases to the machinery of actin reorganisation. Thereby, Nck regulates activation-dependent processes during cell polarisation and migration and plays a crucial role in the signal transduction of a variety of receptors including for instance PDGF-, HGF-, VEGF- and Ephrin receptors. In most cases, the SH2 domain mediates binding to the phosphorylated receptor or associated phosphoproteins, while SH3 domain interactions lead to the formation of larger protein complexes. In T lymphocytes, Nck plays a pivotal role in the T cell receptor (TCR)-induced reorganisation of the actin cytoskeleton and the formation of the immunological synapse. However, in this context, two different mechanisms and adapter complexes are discussed. In the first scenario, dependent on an activation-induced conformational change in the CD3epsilon subunits, a direct binding of Nck to components of the TCR/CD3 complex was shown. In the second scenario, Nck is recruited to the TCR complex via phosphorylated Slp76, another central constituent of the membrane proximal activation complex. Over the past years, a large number of putative Nck interactors have been identified in different cellular systems that point to diverse additional functions of the adapter protein, e.g. in the control of gene expression and proliferation.

Chapter 3: Role of SOCS in allergic and innate immune responses

Cytokines are powerful mediators of the immune response that, following initial release by components of the innate system, drive effector functions as well as stimulate the additional arms of the response. Their individual functions are diverse, with stimulatory and inhibitory actions, with the resultant systemic immune response a summation of these actions. The frequently opposing effects of cytokines determine that the blockade of one results in the functional augmentation of the other. Thus, the differential regulation of cytokines profoundly influences the character of the immune response. The suppressor of cytokine signaling proteins are a family of molecules pivotal to this critical regulation. In this review, we will discuss their structural components and functions and our understanding of their impact on the systemic immune response.

Septins regulate actin organization and cell-cycle arrest through nuclear accumulation of NCK mediated by SOCS7

Mammalian septins are GTP-binding proteins the functions of which are not well understood. Knockdown of SEPT2, 6, and 7 causes stress fibers to disintegrate and cells to lose polarity. We now show that this phenotype is induced by nuclear accumulation of the adaptor protein NCK, as the effects can be reversed or induced by cytoplasmic or nuclear NCK, respectively. NCK is carried into the nucleus by SOCS7 (suppressor of cytokine signaling 7), which possesses nuclear import/export signals. SOCS7 interacts with septins and NCK through distinct domains. DNA damage induces actin and septin rearrangement and rapid nuclear accumulation of NCK and SOCS7. Moreover, NCK expression is essential for cell-cycle arrest. The septin-SOCS7-NCK axis intersects with the canonical DNA damage cascade downstream of ATM/ATR and is essential for p53 Ser15 phosphorylation. These data illuminate an unanticipated connection between septins, SOCS7, NCK signaling, and the DNA damage response.

Involvement of phosphatases in the anchorage-dependent regulation of ERK2 activation

Activation of extracellular signal-regulated kinase (ERK) is known to be regulated by cell adhesion, namely "anchorage dependence". Most studies on the anchorage-dependent regulation have focused on the upstream activating components. We previously reported that the focal adhesion protein vinexin beta can induce the anchorage-independent activation of ERK2. We show here that vinexin beta-induced anchorage-independent activation of ERK2 involves prevention of the dephosphorylation of ERK2, but not the promotion of MEK1 or Raf1 activity. Furthermore, knockdown of vinexin beta resulted in a faster dephosphorylation of ERK2 in A549 cells. Moreover, the coexpression of MKP3/rVH6, an ERK2 specific phosphatase, suppressed the anchorage-independent activation of ERK2 induced by vinexin beta. These results suggest that vinexin beta can prevent the dephosphorylation of ERK2 stimulated by cell detachment, leading to the anchorage-independent activation of ERK2. Furthermore, we found that phosphatase activity directed against activated ERK2 was higher in suspended cells than in adherent cells. In addition, orthovanadate efficiently induces anchorage-independent activation of ERK2 without marked activation of MEK1 in NIH3T3 cells. These observations suggest that the anchorage dependence of ERK1/2 activation is regulated not only by upstream kinases, Raf1 and MEK, but also by phosphatases acting against ERK1/2 and that vinexin beta can induce anchorage-independent activation of ERK by preventing the inactivation of ERK1/2.

Suppressor of cytokine signaling in allergic inflammation

The immunopathological hallmark of allergic diseases is elevated total and allergen specific serum IgE levels along with inflammation. This inflammation results from the activation of a cadre of hematopoietic and nonhematopoetic cells. This coordinated activation is the result of the increased production of a variety of soluble factors including chemokines and cytokines. The magnitude and the duration of cytokine action will determine the response to an allergen, either mounting a low-grade immunologic response or resulting in exaggerated reaction such as asthma or atopic dermatitis. Thus, the action of cytokines is tightly regulated both developmentally and within the cell. The suppressor of cytokine signaling (SOCS) protein family represents a novel group of cytoplasmic negative feedback regulators of type I and II cytokines. Several of the signaling pathways regulated by SOCS proteins are important in allergic immune responses. Thus, SOCS proteins may be important regulators of atopy.

DDR1 signaling is essential to sustain Stat5 function during lactogenesis

Postnatal development of the mammary gland is achieved by an interplay of endocrine and extracellular matrix-derived signals. Despite intense research, a comprehensive understanding of the temporal and spatial coordination of these hormonal and basement membrane stimuli is still lacking. Here, we address the role of the collagen-receptor DDR1 in integrating extracellular matrix-derived signaling with the lactogenic pathway initiated by the prolactin receptor. We found that stimulation of DDR1-overexpressing mammary epithelial HC11 cells with collagen and prolactin resulted in stronger and more sustained induction of Stat5 phosphorylation as compared to control cells. Enhanced Stat5 activity in HC11-DDR1 cells correlated with increased beta-casein gene expression. In contrast, cells derived from DDR1-null mice showed reduced Stat5 activation upon lactogenic stimulation and completely failed to induce beta-casein expression. The cell-autonomous role of DDR1 in controlling ductal branching and alveologenesis prior to the onset of lactogenesis was corroborated by mammary tissue transplantation experiments. Our results show that aside from hormone- and cytokine receptors, DDR1 signaling establishes a third matrix-derived pathway vital to maintain mammary gland function.

Deletion of SOCS7 leads to enhanced insulin action and enlarged islets of Langerhans

NIDDM is characterized by progressive insulin resistance and the failure of insulin-producing pancreatic beta cells to compensate for this resistance. Hyperinsulinemia, inflammation, and prolonged activation of the insulin receptor (INSR) have been shown to induce insulin resistance by decreasing INSR substrate (IRS) protein levels. Here we describe a role for SOCS7 in regulating insulin signaling. Socs7-deficient mice exhibited lower glucose levels and prolonged hypoglycemia during an insulin tolerance test and increased glucose clearance in a glucose tolerance test. Six-month-old Socs7-deficient mice exhibited increased growth of pancreatic islets with mildly increased fasting insulin levels and hypoglycemia. These defects correlated with increased IRS protein levels and enhanced insulin action in cells lacking SOCS7. Additionally, SOCS7 associated with the INSR and IRS1--molecules that are essential for normal regulation of insulin action. These data suggest that SOCS7 is a potent regulator of glucose homeostasis and insulin signaling.

Suppressor of cytokine signaling 7 inhibits prolactin, growth hormone, and leptin signaling by interacting with STAT5 or STAT3 and attenuating their nuclear translocation

We report here the role of one of the less studied members of the family of suppressors of cytokine signaling (SOCS), namely SOCS-7, in cytokine signaling. We demonstrate that SOCS-7 inhibits prolactin (PRL), growth hormone (GH), or leptin (LEP) signaling mediated through STAT3 and STAT5 in a dose-dependent manner. SOCS-7 also attenuated STAT3 and STAT5 signaling induced by overexpression of JH1, the catalytic subdomain of JAK2. Since SOCS-7 interacted with phosphorylated STAT3 or STAT5, we assumed that SOCS-7 acts at the level of STAT proteins. Indeed, we showed that SOCS-7 inhibits PRL- and leptin-induced STAT5 and STAT3 phosphorylation and prevented the nuclear translocation of activated STAT3. Taken together, our results indicate that SOCS-7 is a physiological dysregulator of PRL, leptin, and probably also GH signaling and that its mode of action is a novel variation of SOCS protein inhibition of cytokine-inducible STAT-mediated signal transduction.

Development of hydrocephalus in mice lacking SOCS7

SOCS7 is a member of the suppressor of cytokine signaling (SOCS) family of proteins (SOCS1-SOCS7 and CIS). SOCS proteins are composed of an N-terminal domain of variable length, a central Src homology 2 domain, and a C-terminal SOCS box. Biochemical and genetic studies have revealed that SOCS1, SOCS2, SOCS3, and CIS play an important role in the termination of cytokine and growth factor signaling. However, the biological actions of other SOCS proteins are less well defined. To investigate the physiological role of SOCS7, we have used gene targeting to generate mice that lack expression of the Socs7 gene. Socs7-/- mice were born in expected numbers, were fertile, and did not exhibit defects in hematopoiesis or circulating glucose or insulin concentrations. However, Socs7-/- mice were 7-10% smaller than their wild-type littermates, and within 15 weeks of age approximately 50% of the Socs7-/- mice died as a result of hydrocephalus that was characterized by cranial distortion, dilation of the ventricular system, reduced thickness of the cerebral cortex, and disorganization of the subcommissural organ. In situ hybridization studies revealed prominent expression of Socs7 in the brain, suggestive of an important functional role of SOCS7 in this organ.