Shoc2 is targeted to late endosomes and required for Erk1/2 activation in EGF-stimulated cells

The expression of congenital Shoc2 variants induces AKT-dependent feedback activation of the ERK1/2 pathway

The Shoc2 scaffold protein is crucial in transmitting signals within the Epidermal Growth Factor Receptor (EGFR)-mediated Extracellular signal-regulated Kinase (ERK1/2) pathway. While the significance of Shoc2 in this pathway is well-established, the precise mechanisms through which Shoc2 governs signal transmission remain to be fully elucidated. Hereditary mutations in Shoc2 are responsible for Noonan Syndrome with Loose anagen Hair (NSLH). However, due to the absence of known enzymatic activity in Shoc2, directly assessing how these mutations affect its function is challenging. ERK1/2 phosphorylation is used as a primary parameter of Shoc2 function, but the impact of Shoc2 mutants on the pathway activation is unclear. This study investigates how the NSLH-associated Shoc2 variants influence EGFR signals in the context of the ERK1/2 and AKT downstream signaling pathways. We show that when the ERK1/2 pathway is a primary signaling pathway activated downstream of EGFR, Shoc2 variants cannot upregulate ERK1/2 phosphorylation to the level of the WT Shoc2. Yet, when the AKT and ERK1/2 pathways were activated, in cells expressing Shoc2 variants, ERK1/2 phosphorylation was higher than in cells expressing WT Shoc2. We found that, in cells expressing the Shoc2 NSLH mutants, the AKT signaling pathway triggers the PAK activation, followed by phosphorylation and Raf-1/MEK1/2 /ERK1/2 signaling axis activation. Hence, our studies reveal a previously unrecognized feedback regulation downstream of the EGFR and provide evidence for the Shoc2 role as a "gatekeeper" in controlling the selection of downstream effectors within the EGFR signaling network.

A Leucine-Rich Repeat Protein Provides a SHOC2 the RAS Circuit: a Structure-Function Perspective

SHOC2 is a prototypical leucine-rich repeat protein that promotes downstream receptor tyrosine kinase (RTK)/RAS signaling and plays important roles in several cellular and developmental processes. Gain-of-function germ line mutations of SHOC2 drive the RASopathy Noonan-like syndrome, and SHOC2 mediates adaptive resistance to mitogen-activated protein kinase (MAPK) inhibitors. Similar to many scaffolding proteins, SHOC2 facilitates signal transduction by enabling proximal protein interactions and regulating the subcellular localization of its binding partners. Here, we review the structural features of SHOC2 that mediate its known functions, discuss these elements in the context of various binding partners and signaling pathways, and highlight areas of SHOC2 biology where a consensus view has not yet emerged.

The leucine-rich repeat signaling scaffolds Shoc2 and Erbin: cellular mechanism and role in disease

Leucine-rich repeat-containing proteins (LRR proteins) are involved in supporting a large number of cellular functions. In this review, we summarize recent advancements in understanding functions of the LRR proteins as signaling scaffolds. In particular, we explore what we have learned about the mechanisms of action of the LRR scaffolds Shoc2 and Erbin and their roles in normal development and disease. We discuss Shoc2 and Erbin in the context of their multiple known interacting partners in various cellular processes and summarize often unexpected functions of these proteins through analysis of their roles in human pathologies. We also review these LRR scaffold proteins as promising therapeutic targets and biomarkers with potential application across various pathologies.

Single-domain antibodies for functional targeting of the signaling scaffold Shoc2

The accurate transmission of signals by the canonical ERK1/2 kinase pathway critically relies on the proper assembly of an intricate multiprotein complex by the scaffold protein Shoc2. However, the details of the mechanism by which Shoc2 guides ERK1/2 signals are not clear, in part, due to the lack of research tools targeting specific protein binding moieties of Shoc2. We report generation and characterization of single domain antibodies against human Shoc2 using a universal synthetic library of humanized nanobodies. Our results identify eight synthetic single-domain antibodies and show that two evaluated antibodies have binding affinities to Shoc2 in the nanomolar range. High affinity antibodies were uniquely suited for the analysis of the Shoc2 complex assembly. Selected single-domain antibodies were also functional in intracellular assays. This study illustrates that Shoc2 single-domain antibodies can be used to understand functional mechanisms governing complex multiprotein signaling modules and have promise in application for therapies that require modulation of the ERK1/2-associated diseases.

Hematopoietic and neural crest defects in zebrafish shoc2 mutants: a novel vertebrate model for Noonan-like syndrome

The extracellular signal-related kinase 1 and 2 (ERK1/2) pathway is a highly conserved signaling cascade with numerous essential functions in development. The scaffold protein Shoc2 amplifies the activity of the ERK1/2 pathway and is an essential modulator of a variety of signaling inputs. Germline mutations in Shoc2 are associated with the human developmental disease known as the Noonan-like syndrome with loose anagen hair. Clinical manifestations of this disease include congenital heart defects, developmental delays, distinctive facial abnormalities, reduced growth and cognitive deficits along with hair anomalies. The many molecular details of pathogenesis of the Noonan-like syndrome and related developmental disorders, cumulatively called RASopathies, remain poorly understood. Mouse knockouts for Shoc2 are embryonic lethal, emphasizing the need for additional animal models to study the role of Shoc2 in embryonic development. Here, we characterize a zebrafish shoc2 mutant, and show that Shoc2 is essential for development, and that its loss is detrimental for the development of the neural crest and for hematopoiesis. The zebrafish model of the Noonan-like syndrome described here provides a novel system for the study of structure-function analyses and for genetic screens in a tractable vertebrate system.

VCP/p97 controls signals of the ERK1/2 pathway transmitted via the Shoc2 scaffolding complex: novel insights into IBMPFD pathology

Valosin-containing protein (VCP), also named p97, is an essential hexameric AAA+ ATPase with diverse functions in the ubiquitin system. Here we demonstrate that VCP is critical in controlling signals transmitted via the essential Shoc2-ERK1/2 signaling axis. The ATPase activity of VCP modulates the stoichiometry of HUWE1 in the Shoc2 complex as well as HUWE1-mediated allosteric ubiquitination of the Shoc2 scaffold and the RAF-1 kinase. Abrogated ATPase activity leads to augmented ubiquitination of Shoc2/RAF-1 and altered phosphorylation of RAF-1. We found that in fibroblasts from patients with inclusion body myopathy with Paget’s disease of bone and frontotemporal dementia (IBMPFD) that harbor germline mutations in VCP, the levels of Shoc2 ubiquitination and ERK1/2 phosphorylation are imbalanced. This study provides a mechanistic basis for the critical role of VCP in the regulation of the ERK1/2 pathway and reveals a previously unrecognized function of the ERK1/2 pathway in the pathogenesis of IBMPFD.

M-Ras/Shoc2 signaling modulates E-cadherin turnover and cell-cell adhesion during collective cell migration

Collective cell migration is required for normal embryonic development and contributes to various biological processes, including wound healing and cancer cell invasion. The M-Ras GTPase and its effector, the Shoc2 scaffold, are proteins mutated in the developmental RASopathy Noonan syndrome, and, here, we report that activated M-Ras recruits Shoc2 to cell surface junctions where M-Ras/Shoc2 signaling contributes to the dynamic regulation of cell-cell junction turnover required for collective cell migration. MCF10A cells expressing the dominant-inhibitory M-Ras^S27N variant or those lacking Shoc2 exhibited reduced junction turnover and were unable to migrate effectively as a group. Through further depletion/reconstitution studies, we found that M-Ras/Shoc2 signaling contributes to junction turnover by modulating the E-cadherin/p120-catenin interaction and, in turn, the junctional expression of E-cadherin. The regulatory effect of the M-Ras/Shoc2 complex was mediated at least in part through the phosphoregulation of p120-catenin and required downstream ERK cascade activation. Strikingly, cells rescued with the Noonan-associated, myristoylated-Shoc2 mutant (Myr-Shoc2) displayed a gain-of-function (GOF) phenotype, with the cells exhibiting increased junction turnover and reduced E-cadherin/p120-catenin binding and migrating as a faster but less cohesive group. Consistent with these results, Noonan-associated C-Raf mutants that bypass the need for M-Ras/Shoc2 signaling exhibited a similar GOF phenotype when expressed in Shoc2-depleted MCF10A cells. Finally, expression of the Noonan-associated Myr-Shoc2 or C-Raf mutants, but not their WT counterparts, induced gastrulation defects indicative of aberrant cell migration in zebrafish embryos, further demonstrating the function of the M-Ras/Shoc2/ERK cascade signaling axis in the dynamic control of coordinated cell movement.

SHOC2 subcellular shuttling requires the KEKE motif-rich region and N-terminal leucine-rich repeat domain and impacts on ERK signalling

SHOC2 is a scaffold protein composed almost entirely by leucine-rich repeats (LRRs) and having an N-terminal region enriched in alternating lysine and glutamate/aspartate residues (KEKE motifs). SHOC2 acts as a positive modulator of the RAS-RAF-MEK-ERK signalling cascade by favouring stable RAF1 interaction with RAS. We previously reported that the p.Ser2Gly substitution in SHOC2 underlies Mazzanti syndrome, a RASopathy clinically overlapping Noonan syndrome, promoting N-myristoylation and constitutive targeting of the mutant to the plasma membrane. We also documented transient nuclear translocation of wild-type SHOC2 upon EGF stimulation, suggesting a more complex function in signal transduction.Here, we characterized the domains controlling SHOC2 shuttling between the nucleus and cytoplasm, and those contributing to SHOC2^S2G mistargeting to the plasma membrane, analysed the structural organization of SHOC2's LRR motifs, and determined the impact of SHOC2 mislocalization on ERK signalling. We show that LRRs 1 to 13 constitute a structurally recognizable domain required for SHOC2 import into the nucleus and constitutive targeting of SHOC2^S2G to the plasma membrane, while the KEKE motif-rich region is necessary to achieve efficient SHOC2 export from the nucleus. We also document that SHOC2^S2G localizes both in raft and non-raft domains, and that it translocates to the non-raft domains following stimulation. Finally, we demonstrate that SHOC2 trapping at different subcellular sites has a diverse impact on ERK signalling strength and dynamics, suggesting a dual counteracting modulatory role of SHOC2 in the control of ERK signalling exerted at different intracellular compartments.

The function of Shoc2: A scaffold and beyond

The extracellular signal-regulated kinase (ERK1/2) cascade regulates a myriad of functions in multicellular organisms. Scaffold proteins provide critical spatial and temporal control over the specificity of signaling. Shoc2 is a scaffold that accelerates activity of the ERK1/2 pathway. Loss of Shoc2 expression in mice results in embryonic lethality, thus highlighting the essential role of Shoc2 in embryogenesis. In agreement, patients carrying mutated Shoc2 suffer from a wide spectrum of developmental deficiencies. Efforts to understand the mechanisms by which Shoc2 controls ERK1/2 activity revealed the intricate machinery that governs the ability of Shoc2 to transduce signals of the ERK1/2 pathway. Understanding the mechanisms by which Shoc2 contributes to a high degree of specificity of ERK1/2 signaling as well as deciphering the biological functions of Shoc2 in development and human disorders are major unresolved questions.

Shoc2-tranduced ERK1/2 motility signals--Novel insights from functional genomics

The extracellular signal-regulated kinase 1 and 2 (ERK1/2) pathway plays a central role in defining various cellular fates. Scaffold proteins modulating ERK1/2 activity control growth factor signals transduced by the pathway. Here, we analyzed signals transduced by Shoc2, a critical positive modulator of ERK1/2 activity. We found that loss of Shoc2 results in impaired cell motility and delays cell attachment. As ERKs control cellular fates by stimulating transcriptional response, we hypothesized that the mechanisms underlying changes in cell adhesion could be revealed by assessing the changes in transcription of Shoc2-depleted cells. Using quantitative RNA-seq analysis, we identified 853 differentially expressed transcripts. Characterization of the differentially expressed genes showed that Shoc2 regulates the pathway at several levels, including expression of genes controlling cell motility, adhesion, crosstalk with the transforming growth factor beta (TGFβ) pathway, and expression of transcription factors. To understand the mechanisms underlying delayed attachment of cells depleted of Shoc2, changes in expression of the protein of extracellular matrix (lectin galactoside-binding soluble 3-binding protein; LGALS3BP) were functionally analyzed. We demonstrated that delayed adhesion of the Shoc2-depleted cells is a result of attenuated expression and secretion of LGALS3BP. Together our results suggest that Shoc2 regulates cell motility by modulating ERK1/2 signals to cell adhesion.

Unconventional EGF-induced ERK1/2-mediated Kv1.3 endocytosis

The potassium channel Kv1.3 plays roles in immunity, neuronal development and sensory discrimination. Regulation of Kv1.3 by kinase signaling has been studied. In this context, EGF binds to specific receptors (EGFR) and triggers tyrosine kinase-dependent signaling, which down-regulates Kv1.3 currents. We show that Kv1.3 undergoes EGF-dependent endocytosis. This EGF-mediated mechanism is relevant because is involved in adult neural stem cell fate determination. We demonstrated that changes in Kv1.3 subcellular distribution upon EGFR activation were due to Kv1.3 clathrin-dependent endocytosis, which targets the Kv1.3 channels to the lysosomal degradative pathway. Interestingly, our results further revealed that relevant tyrosines and other interacting motifs, such as PDZ and SH3 domains, were not involved in the EGF-dependent Kv1.3 internalization. However, a new, and yet undescribed mechanism, of ERK1/2-mediated threonine phosphorylation is crucial for the EGF-mediated Kv1.3 endocytosis. Our results demonstrate that EGF triggers the down-regulation of Kv1.3 activity and its expression at the cell surface, which is important for the development and migration of adult neural progenitors.

Spatial control of Shoc2-scaffold-mediated ERK1/2 signaling requires remodeling activity of the ATPase PSMC5

The scaffold protein Shoc2 accelerates activity of the ERK1 and ERK2 (ERK1/2, also known as MAPK3 and MAPK1) pathway. Mutations in Shoc2 result in Noonan-like RASopathy, a developmental disorder with a wide spectrum of symptoms. The amplitude of the ERK1/2 signals transduced through the complex is fine-tuned by the HUWE1-mediated ubiquitylation of Shoc2 and its signaling partner RAF-1. Here, we provide a mechanistic basis of how ubiquitylation of Shoc2 and RAF-1 is controlled. We demonstrate that the newly identified binding partner of Shoc2, the (AAA+) ATPase PSMC5, triggers translocation of Shoc2 to endosomes. At the endosomes, PSMC5 displaces the E3 ligase HUWE1 from the scaffolding complex to attenuate ubiquitylation of Shoc2 and RAF-1. We show that a RASopathy mutation that changes the subcellular distribution of Shoc2 leads to alterations in Shoc2 ubiquitylation due to the loss of accessibility to PSMC5. In summary, our results demonstrate that PSMC5 is a new and important player involved in regulating ERK1/2 signal transmission through the remodeling of Shoc2 scaffold complex in a spatially-defined manner.

Research Resource: Androgen Receptor Activity Is Regulated Through the Mobilization of Cell Surface Receptor Networks

The aberrant expression of androgen receptor (AR)-dependent transcriptional programs is a defining pathology of the development and progression of prostate cancers. Transcriptional cofactors that bind AR are critical determinants of prostate tumorigenesis. To gain a deeper understanding of the proteins linked to AR-dependent gene transcription, we performed a DNA-affinity chromatography-based proteomic screen designed to identify proteins involved in AR-mediated gene transcription in prostate tumor cells. Functional experiments validated the coregulator roles of known AR-binding proteins in AR-mediated transcription in prostate tumor cells. More importantly, novel coregulatory functions were detected in components of well-established cell surface receptor-dependent signal transduction pathways. Further experimentation demonstrated that components of the TNF, TGF-β, IL receptor, and epidermal growth factor signaling pathways modulated AR-dependent gene transcription and androgen-dependent proliferation in prostate tumor cells. Collectively, our proteomic dataset demonstrates that the cell surface receptor- and AR-dependent pathways are highly integrated, and provides a molecular framework for understanding how disparate signal-transduction pathways can influence AR-dependent transcriptional programs linked to the development and progression of human prostate cancers.

Shoc2/Sur8 protein regulates neurite outgrowth

The Shoc2 protein has been implicated in the positive regulation of the Ras-ERK pathway by increasing the functional binding interaction between Ras and Raf, leading to increased ERK activity. Here we found that Shoc2 overexpression induced sustained ERK phosphorylation, notably in the case of EGF stimulation, and Shoc2 knockdown inhibited ERK activation. We demonstrate that ectopic overexpression of human Shoc2 in PC12 cells significantly promotes neurite extension in the presence of EGF, a stimulus that induces proliferation rather than differentiation in these cells. Finally, Shoc2 depletion reduces both NGF-induced neurite outgrowth and ERK activation in PC12 cells. Our data indicate that Shoc2 is essential to modulate the Ras-ERK signaling outcome in cell differentiation processes involved in neurite outgrowth.

A Novel SHOC2 Variant in Rasopathy

Rasopathies are a group of genetic disorders caused by germline mutations in multiple genes of the Extracellular signal-Regulated Kinases 1 and 2 (ERK1/2) pathway. The only previously identified missense mutation in SHOC2, a scaffold protein of the ERK1/2 pathway, led to Noonan-like syndrome with loose anagen hair. Here, we report a novel mutation in SHOC2(c.519G>A; p.M173I) that leads to a Rasopathy with clinical features partially overlapping those occurring in Noonan and cardiofaciocutaneous syndromes. Studies to clarify the significance of this SHOC2 variant revealed that the mutant protein has impaired capacity to interact with protein phosphatase 1c (PP1c), leading to insufficient activation of RAF-1 kinase. This SHOC2 variant thus is unable to fully rescue ERK1/2 activity in cells depleted of endogenous SHOC2. We conclude that SHOC2 mutations can cause a spectrum of Rasopathy phenotypes in heterozygous individuals. Importantly, our work suggests that individuals with mild Rasopathy symptoms may be underdiagnosed.

HUWE1 is a molecular link controlling RAF-1 activity supported by the Shoc2 scaffold

Scaffold proteins play a critical role in controlling the activity of the extracellular signal-regulated kinase 1/2 (ERK1/2) pathway. Shoc2 is a leucine-rich repeat scaffold protein that acts as a positive modulator of ERK1/2 signaling. However, the precise mechanism by which Shoc2 modulates the activity of the ERK1/2 pathway is unclear. Here we report the identification of the E3 ubiquitin ligase HUWE1 as a binding partner and regulator of Shoc2 function. HUWE1 mediates ubiquitination and, consequently, the levels of Shoc2. Additionally, we show that both Shoc2 and HUWE1 are necessary to control the levels and ubiquitination of the Shoc2 signaling partner, RAF-1. Depletion of HUWE1 abolishes RAF-1 ubiquitination, with corresponding changes in ERK1/2 pathway activity occurring. Our results indicate that the HUWE1-mediated ubiquitination of Shoc2 is the switch that regulates the transition from an active to an inactive state of the RAF-1 kinase. Taken together, our results demonstrate that HUWE1 is a novel player involved in regulating ERK1/2 signal transmission through the Shoc2 scaffold complex.

Visualizing of signaling proteins on endosomes utilizing knockdown and reconstitution approach

Spatial distribution of intracellular signaling molecules and assembly of signaling complexes are yet to be fully understood. Studies of signaling events in time or space present a particular challenge due to the adverse effects that overexpression of signaling proteins may have on their functions and localization. To follow the distribution of signaling proteins in living cells we developed a methodology named knockdown and reconstitution (KDAR) that allows one to visualize proteins at levels of expression that are close to physiological. This methodology provides a stable expression of "endogenous" shRNA for long-term silencing of the targeted gene and simultaneous expression of a DNA cassette coding for a fluorescently labeled protein, which is insensitive to the targeting shRNA. In this chapter we discuss the needed reagents and outline two experimental approaches to generate KDAR stable cell lines. First, we demonstrate how the plasmid-mediated KDAR approach is successfully utilized to visualize spatial distribution of the GFP-labeled MEK2 in living cells. We then show how the lentivirus-mediated KDAR approach is used to reconstitute and visualize expression of the ERK1/2 scaffold protein Shoc2.

The neuropilin 1 cytoplasmic domain is required for VEGF-A-dependent arteriogenesis

Neuropilin 1 (NRP1) plays an important but ill-defined role in VEGF-A signaling and vascular morphogenesis. We show that mice with a knockin mutation that ablates the NRP1 cytoplasmic tail (Nrp1^cyto) have normal angiogenesis but impaired developmental and adult arteriogenesis. The arteriogenic defect was traced to the absence of a PDZ-dependent interaction between NRP1 and VEGF receptor 2 (VEGFR2) complex and synectin, which delayed trafficking of endocytosed VEGFR2 from Rab5+ to EAA1+ endosomes. This led to increased PTPN1 (PTP1b)-mediated dephosphorylation of VEGFR2 at Y¹¹⁷⁵, the site involved in activating ERK signaling. The Nrp1^cyto mutation also impaired endothelial tubulogenesis in vitro, which could be rescued by expressing full-length NRP1 or constitutively active ERK. These results demonstrate that the NRP1 cytoplasmic domain promotes VEGFR2 trafficking in a PDZ-dependent manner to regulate arteriogenic ERK signaling and establish a role for NRP1 in VEGF-A signaling during vascular morphogenesis.

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The NRP1 cytoplasmic domain promotes VEGF receptor (VEGFR) 2 endocytic trafficking

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In its absence, VEGR2 trafficking is delayed in sorting endosomes

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PTP1b binds to Rab5+ sorting endosomes and dephosphorylates the Y¹¹⁷⁵ site of VEGFR2

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Loss of the NRP1 cytoplasmic domain impairs developmental and adult arteriogenesis

Functional Integration of the Conserved Domains of Shoc2 Scaffold

Shoc2 is a positive regulator of signaling to extracellular signal-regulated protein kinases 1 and 2 (ERK1/2). Shoc2 is also proposed to interact with RAS and Raf-1 in order to accelerate ERK1/2 activity. To understand the mechanisms by which Shoc2 regulates ERK1/2 activation by the epidermal growth factor receptor (EGFR), we dissected the role of Shoc2 structural domains in binding to its signaling partners and its role in regulating ERK1/2 activity. Shoc2 is comprised of two main domains: the 21 leucine rich repeats (LRRs) core and the N-terminal non-LRR domain. We demonstrated that the N-terminal domain mediates Shoc2 binding to both M-Ras and Raf-1, while the C-terminal part of Shoc2 contains a late endosomal targeting motif. We found that M-Ras binding to Shoc2 is independent of its GTPase activity. While overexpression of Shoc2 did not change kinetics of ERK1/2 activity, both the N-terminal and the LRR-core domain were able to rescue ERK1/2 activity in cells depleted of Shoc2, suggesting that these Shoc2 domains are involved in modulating ERK1/2 activity.

Desmoglein-1/Erbin interaction suppresses ERK activation to support epidermal differentiation

Genetic disorders of the Ras/MAPK pathway, termed RASopathies, produce numerous abnormalities, including cutaneous keratodermas. The desmosomal cadherin, desmoglein-1 (DSG1), promotes keratinocyte differentiation by attenuating MAPK/ERK signaling and is linked to striate palmoplantar keratoderma (SPPK). This raises the possibility that cutaneous defects associated with SPPK and RASopathies share certain molecular faults. To identify intermediates responsible for executing the inhibition of ERK by DSG1, we conducted a yeast 2-hybrid screen. The screen revealed that Erbin (also known as ERBB2IP), a known ERK regulator, binds DSG1. Erbin silencing disrupted keratinocyte differentiation in culture, mimicking aspects of DSG1 deficiency. Furthermore, ERK inhibition and the induction of differentiation markers by DSG1 required both Erbin and DSG1 domains that participate in binding Erbin. Erbin blocks ERK signaling by interacting with and disrupting Ras-Raf scaffolds mediated by SHOC2, a protein genetically linked to the RASopathy, Noonan-like syndrome with loose anagen hair (NS/LAH). DSG1 overexpression enhanced this inhibitory function, increasing Erbin-SHOC2 interactions and decreasing Ras-SHOC2 interactions. Conversely, analysis of epidermis from DSG1-deficient patients with SPPK demonstrated increased Ras-SHOC2 colocalization and decreased Erbin-SHOC2 colocalization, offering a possible explanation for the observed epidermal defects. These findings suggest a mechanism by which DSG1 and Erbin cooperate to repress MAPK signaling and promote keratinocyte differentiation.

Spatial regulation of epidermal growth factor receptor signaling by endocytosis

Signaling by cell surface receptors appears to be relatively straight-forward: ligand binds to the extracellular domain of the receptor and biochemical changes are communicated into the cell. However, this process is more complex than it first seems due to the various mechanisms that regulate signaling. In order to effectively target these receptors for pharmacological purposes, a more complete understanding of how their signaling is regulated is needed. Here, how the endocytic pathway regulates receptor signaling is discussed, using the epidermal growth factor receptor (EGFR) as a model. In particular, the spatial regulation of signaling is examined. Areas of discussion include: how endocytic trafficking affects biology/pathology, varying approaches for studying the relationship between receptor endocytosis and signaling, and developments in how the endocytic pathway controls EGFR:effector communication and EGFR-mediated cell biology.

Genetic basis of the impaired renal myogenic response in FHH rats

This study examined the effect of substitution of a 2.4-megabase pair (Mbp) region of Brown Norway (BN) rat chromosome 1 (RNO1) between 258.8 and 261.2 Mbp onto the genetic background of fawn-hooded hypertensive (FHH) rats on autoregulation of renal blood flow (RBF), myogenic response of renal afferent arterioles (AF-art), K(+) channel activity in renal vascular smooth muscle cells (VSMCs), and development of proteinuria and renal injury. FHH rats exhibited poor autoregulation of RBF, while FHH.1BN congenic strains with the 2.4-Mbp BN region exhibited nearly perfect autoregulation of RBF. The diameter of AF-art from FHH rats increased in response to pressure but decreased in congenic strains containing the 2.4-Mbp BN region. Protein excretion and glomerular and interstitial damage were significantly higher in FHH rats than in congenic strains containing the 2.4-Mbp BN region. K(+) channel current was fivefold greater in VSMCs from renal arterioles of FHH rats than cells obtained from congenic strains containing the 2.4-Mbp region. Sequence analysis of the known and predicted genes in the 2.4-Mbp region of FHH rats revealed amino acid-altering variants in the exons of three genes: Add3, Rbm20, and Soc-2. Quantitative PCR studies indicated that Mxi1 and Rbm20 were differentially expressed in the renal vasculature of FHH and FHH.1BN congenic strain F. These data indicate that transfer of this 2.4-Mbp region from BN to FHH rats restores the myogenic response of AF-art and autoregulation of RBF, decreases K(+) current, and slows the progression of proteinuria and renal injury.