Gain-of-function/Noonan syndrome SHP-2/Ptpn11 mutants enhance calcium oscillations and impair NFAT signaling

From Stem to Sternum: The Role of Shp2 in the Skeleton

Src homology-2 domain-containing phosphatase 2 (SHP2) is a ubiquitously expressed phosphatase that is vital for skeletal development and maintenance of chondrocytes, osteoblasts, and osteoclasts. Study of SHP2 function in small animal models has led to insights in phenotypes observed in SHP2-mutant human disease, such as Noonan syndrome. In recent years, allosteric SHP2 inhibitors have been developed to specifically target the protein in neoplastic processes. These inhibitors are highly specific and have great potential for disease modulation in cancer and other pathologies, including bone disorders. In this review, we discuss the importance of SHP2 and related signaling pathways (e.g., Ras/MEK/ERK, JAK/STAT, PI3K/Akt) in skeletal development. We review rodent models of pathologic processes caused by germline mutations that activate SHP2 enzymatic activity, with a focus on the skeletal phenotype seen in these patients. Finally, we discuss SHP2 inhibitors in development and their potential for disease modulation in these genetic diseases, particularly as it relates to the skeleton.

Friend or foe? Unraveling the complex roles of protein tyrosine phosphatases in cardiac disease and development

Regulation of protein tyrosine phosphorylation is critical for most, if not all, fundamental cellular processes. However, we still do not fully understand the complex and tissue-specific roles of protein tyrosine phosphatases in the normal heart or in cardiac pathology. This review compares and contrasts the various roles of protein tyrosine phosphatases known to date in the context of cardiac disease and development. In particular, it will be considered how specific protein tyrosine phosphatases control cardiac hypertrophy and cardiomyocyte contractility, how protein tyrosine phosphatases contribute to or ameliorate injury induced by ischaemia / reperfusion or hypoxia / reoxygenation, and how protein tyrosine phosphatases are involved in normal heart development and congenital heart disease. This review delves into the newest developments and current challenges in the field, and highlights knowledge gaps and emerging opportunities for future research.

The Extracellular Signal-Regulated Kinase Mitogen-Activated Protein Kinase Pathway in Osteoblasts

Extracellular signal-regulated kinases (ERKs) are evolutionarily ancient signal transducers of the mitogen-activated protein kinase (MAPK) family that have long been linked to the regulation of osteoblast differentiation and bone formation. Here, we review the physiological functions, biochemistry, upstream activators, and downstream substrates of the ERK pathway. ERK is activated in skeletal progenitors and regulates osteoblast differentiation and skeletal mineralization, with ERK serving as a key regulator of Runt-related transcription factor 2, a critical transcription factor for osteoblast differentiation. However, new evidence highlights context-dependent changes in ERK MAPK pathway wiring and function, indicating a broader set of physiological roles associated with changes in ERK pathway components or substrates. Consistent with this importance, several human skeletal dysplasias are associated with dysregulation of the ERK MAPK pathway, including neurofibromatosis type 1 and Noonan syndrome. The continually broadening array of drugs targeting the ERK pathway for the treatment of cancer and other disorders makes it increasingly important to understand how interference with this pathway impacts bone metabolism, highlighting the importance of mouse studies to model the role of the ERK MAPK pathway in bone formation.

Double-edged roles of protein tyrosine phosphatase SHP2 in cancer and its inhibitors in clinical trials

Phosphorylation is a reversible post-translational modification regulated by phosphorylase and dephosphorylase to mediate important cellular events. Src homology-2-containing protein tyrosine phosphatase 2 (SHP2) encoded by PTPN11 is the first identified oncogenic protein in protein tyrosine phosphatases family. Serving as a convergent node, SHP2 is involved in multiple cascade signaling pathways including Ras-Raf-MEK-ERK, PI3K-AKT, JAK-STAT and PD-1/PD-L1 pathways. Especially, the double-edged roles of SHP2 based on the substrate specificity in various biological contexts dramatically increase the effect complexity in different SHP2-associated diseases. Evidences suggest that by collaborating with other mutations in associated pathways, dysregulation of SHP2 contributes to the pathogenesis of different cancers, making SHP2 a promising therapeutic target for cancer treatment. SHP2 can either act as oncogenic factor or tumor suppressor in different diseases, and both the conserved catalytic dephosphorylation mechanism and the unique allosteric regulation mechanism of SHP2 provide opportunities for the development of SHP2 inhibitors and activators. To date, several small-molecule SHP2 inhibitors have advanced into clinical trials for mono- or combined therapy of cancers. Moreover, SHP2 activators and proteolysis-targeting chimera (PROTAC)-based degraders also display therapeutic promise. In this review, we comprehensively summarize the overall structures, regulation mechanisms, double-edged roles of SHP2 in both physiological and carcinogenic pathways, and SHP2 inhibitors in clinical trials. SHP2 activators and degraders are also briefly discussed. This review aims to provide in-depth understanding of the biological roles of SHP2 and highlight therapeutic potential of targeting SHP2.

Multiple versus solitary giant cell lesions of the jaw: Similar or distinct entities?

The majority of giant cell lesions of the jaw present as a solitary focus of disease in bones of the maxillofacial skeleton. Less frequently they occur as multifocal lesions. This raises the clinical dilemma if these should be considered distinct entities and therefore each need a specific therapeutic approach. Solitary giant cell lesions of the jaw present with a great diversity of symptoms. Recent molecular analysis revealed that these are associated with somatic gain-of-function mutations in KRAS, FGFR1 or TRPV4 in a large component of the mononuclear stromal cells which all act on the RAS/MAPK pathway. For multifocal lesions, a small group of neoplastic multifocal giant cell lesions of the jaw remain after ruling out hyperparathyroidism. Strikingly, most of these patients are diagnosed with jaw lesions before the age of 20 years, thus before the completion of dental and jaw development. These multifocal lesions are often accompanied by a diagnosis or strong clinical suspicion of a syndrome. Many of the frequently reported syndromes belong to the so-called RASopathies, with germline or mosaic mutations leading to downstream upregulation of the RAS/MAPK pathway. The other frequently reported syndrome is cherubism, with gain-of-function mutations in the SH3BP2 gene leading through assumed and unknown signaling to an autoinflammatory bone disorder with hyperactive osteoclasts and defective osteoblastogenesis. Based on this extensive literature review, a RAS/MAPK pathway activation is hypothesized in all giant cell lesions of the jaw. The different interaction between and contribution of deregulated signaling in individual cell lineages and crosstalk with other pathways among the different germline- and non-germline-based alterations causing giant cell lesions of the jaw can be explanatory for the characteristic clinical features. As such, this might also aid in the understanding of the age-dependent symptomatology of syndrome associated giant cell lesions of the jaw; hopefully guiding ideal timing when installing treatment strategies in the future.

In vitro differentiation of W8B2+ human cardiac stem cells: gene expression of ionic channels and spontaneous calcium activity

Background

Human cardiac stem cells expressing the W8B2 marker (W8B2⁺ CSCs) were recently identified and proposed as a new model of multipotent CSCs capable of differentiating into smooth muscle cells, endothelial cells and immature myocytes. Nevertheless, no characterization of ion channel or calcium activity during the differentiation of these stem cells has been reported.

Methods

The objectives of this study were thus to analyze (using the TaqMan Low-Density Array technique) the gene profile of W8B2⁺ CSCs pertaining to the regulation of ion channels, transporters and other players involved in the calcium homeostasis of these cells. We also analyzed spontaneous calcium activity (via the GCaMP calcium probe) during the in vitro differentiation of W8B2⁺ CSCs into cardiac myocytes.

Results

Our results show an entirely different electrophysiological genomic profile between W8B2⁺ CSCs before and after differentiation. Some specific nodal genes, such as Tbx3, HCN, ICaT, L, KV, and NCX, are overexpressed after this differentiation. In addition, we reveal spontaneous calcium activity or a calcium clock whose kinetics change during the differentiation process. A pharmacological study carried out on differentiated W8B2⁺ CSCs showed that the NCX exchanger and IP3 stores play a fundamental role in the generation of these calcium oscillations.

Conclusions

Taken together, the present results provide important information on ion channel expression and intrinsic calcium dynamics during the differentiation process of stem cells expressing the W8B2 marker.

Human ex vivo spinal cord slice culture as a useful model of neural development, lesion, and allogeneic neural cell therapy

Background

There are multiple promising treatment strategies for central nervous system trauma and disease. However, to develop clinically potent and safe treatments, models of human-specific conditions are needed to complement in vitro and in vivo animal model-based studies.

Methods

We established human brain stem and spinal cord (cross- and longitudinal sections) organotypic cultures (hOCs) from first trimester tissues after informed consent by donor and ethical approval by the Regional Human Ethics Committee, Stockholm (lately referred to as Swedish Ethical Review Authority), and The National Board of Health and Welfare, Sweden. We evaluated the stability of hOCs with a semi-quantitative hOC score, immunohistochemistry, flow cytometry, Ca²⁺ signaling, and electrophysiological analysis. We also applied experimental allogeneic human neural cell therapy after injury in the ex vivo spinal cord slices.

Results

The spinal cord hOCs presented relatively stable features during 7–21 days in vitro (DIV) (except a slightly increased cell proliferation and activated glial response). After contusion injury performed at 7 DIV, a significant reduction of the hOC score, increase of the activated caspase-3⁺ cell population, and activated microglial populations at 14 days postinjury compared to sham controls were observed. Such elevation in the activated caspase-3⁺ population and activated microglial population was not observed after allogeneic human neural cell therapy.

Conclusions

We conclude that human spinal cord slice cultures have potential for future structural and functional studies of human spinal cord development, injury, and treatment strategies.

The Noonan Syndrome Gene Lztr1 Controls Cardiovascular Function by Regulating Vesicular Trafficking

RATIONALE

Noonan syndrome (NS) is one of the most frequent genetic disorders. Bleeding problems are among the most common, yet poorly defined complications associated with NS. A lack of consensus on the management of bleeding complications in patients with NS indicates an urgent need for new therapeutic approaches.

OBJECTIVE

Bleeding disorders have recently been described in patients with NS harboring mutations of LZTR1 (leucine zipper-like transcription regulator 1), an adaptor for CUL3 (CULLIN3) ubiquitin ligase complex. Here, we assessed the pathobiology of LZTR1-mediated bleeding disorders.

METHODS AND RESULTS

Whole-body and vascular specific knockout of Lztr1 results in perinatal lethality due to cardiovascular dysfunction. Lztr1 deletion in blood vessels of adult mice leads to abnormal vascular leakage. We found that defective adherent and tight junctions in Lztr1-depleted endothelial cells are caused by dysregulation of vesicular trafficking. LZTR1 affects the dynamics of fusion and fission of recycling endosomes by controlling ubiquitination of the ESCRT-III (endosomal sorting complex required for transport III) component CHMP1B (charged multivesicular protein 1B), whereas NS-associated LZTR1 mutations diminish CHMP1B ubiquitination. LZTR1-mediated dysregulation of CHMP1B ubiquitination triggers endosomal accumulation and subsequent activation of VEGFR2 (vascular endothelial growth factor receptor 2) and decreases blood levels of soluble VEGFR2 in Lztr1 haploinsufficient mice. Inhibition of VEGFR2 activity by cediranib rescues vascular abnormalities observed in Lztr1 knockout mice Conclusions: Lztr1 deletion phenotypically overlaps with bleeding diathesis observed in patients with NS. ELISA screening of soluble VEGFR2 in the blood of LZTR1-mutated patients with NS may predict both the severity of NS phenotypes and potential responders to anti-VEGF therapy. VEGFR inhibitors could be beneficial for the treatment of bleeding disorders in patients with NS.

Pediatric Evans syndrome is associated with a high frequency of potentially damaging variants in immune genes

Evans syndrome (ES) is a rare severe autoimmune disorder characterized by the combination of autoimmune hemolytic anemia and immune thrombocytopenia. In most cases, the underlying cause is unknown. We sought to identify genetic defects in pediatric ES (pES), based on a hypothesis of strong genetic determinism. In a national, prospective cohort of 203 patients with early-onset ES (median [range] age at last follow-up: 16.3 years ([1.2-41.0 years]) initiated in 2004, 80 nonselected consecutive individuals underwent genetic testing. The clinical data were analyzed as a function of the genetic findings. Fifty-two patients (65%) received a genetic diagnosis (the M+ group): 49 carried germline mutations and 3 carried somatic variants. Thirty-two (40%) had pathogenic mutations in 1 of 9 genes known to be involved in primary immunodeficiencies (TNFRSF6, CTLA4, STAT3, PIK3CD, CBL, ADAR1, LRBA, RAG1, and KRAS), whereas 20 patients (25%) carried probable pathogenic variants in 16 genes that had not previously been reported in the context of autoimmune disease. Lastly, no genetic abnormalities were found in the remaining 28 patients (35%, the M- group). The M+ group displayed more severe disease than the M- group, with a greater frequency of additional immunopathologic manifestations and a greater median number of lines of treatment. Six patients (all from the M+ group) died during the study. In conclusion, pES was potentially genetically determined in at least 65% of cases. Systematic, wide-ranging genetic screening should be offered in pES; the genetic findings have prognostic significance and may guide the choice of a targeted treatment.

Protein tyrosine phosphatases in cardiac physiology and pathophysiology

More than any other organ, the heart is particularly sensitive to gene expression deregulation, often leading in the long run to impaired contractile performances and excessive fibrosis deposition progressing to heart failure. Recent investigations provide evidences that the protein phosphatases (PPs), as their counterpart protein kinases, are important regulators of cardiac physiology and development. Two main groups, the protein serine/threonine phosphatases and the protein tyrosine phosphatases (PTPs), constitute the PPs family. Here, we provide an overview of the role of PTP subfamily in the development of the heart and in cardiac pathophysiology. Based on recent in silico studies, we highlight the importance of PTPs as therapeutic targets for the development of new drugs to restore PTPs signaling in the early and late events of heart failure.

Requirements for band-pass activation of Ca2+-sensitive proteins such as NFAT

Several proteins are sensitive to frequency-modulated oscillations of calcium levels. Most of them exhibit increased activities for faster frequencies, a characteristic here referred to as high-pass activation. In contrast, the transcription factor NFAT is optimally activated at a specific frequency, a behaviour we call band-pass activation. We constructed a kinetic model of NFAT activation, confirming its ability for band-pass activation at experimentally observed frequencies. To characterise the requirements for band-pass activation further, we developed a minimal model, identifying antagonistic, calcium-dependent regulation with differently responsive regulators as essential for band-pass activation. Further, in optimisations cooperative binding proved to be an important feature for distinct frequency-decoding in models of high- and band-pass activation. A subsequent analysis of the optimised parameter sets revealed the most sensitive parameters along with additional preconditions for efficient decoding. Our analysis is not limited to NFAT, but potentially applies to any protein showing high- or band-pass activation.

Mapping genes for calcium signaling and their associated human genetic disorders

Motivation

Signal transduction via calcium ions (Ca²⁺) represents a fundamental signaling pathway in all eukaryotic cells. A large portion of the human genome encodes proteins used to assemble signaling systems that can transduce signals with diverse spatial and temporal dynamics.

Results

Here, we provide a map of all of the genes involved in Ca²⁺ signaling and link these genes to human genetic disorders. Using Gene Ontology terms and genome databases, 1805 genes were identified as regulators or targets of intracellular Ca²⁺ signals. Associating these 1805 genes with human genetic disorders uncovered 1470 diseases with mutated ‘Ca²⁺ genes’. A network with scale-free properties appeared when the Ca²⁺ genes were mapped to their associated genetic disorders.

Availability and Implementation

The Ca²⁺ genome database is freely available at http://cagedb.uhlenlab.org and will foster studies of gene functions and genetic disorders associated with Ca²⁺ signaling.

Supplementary information

Supplementary data are available at Bioinformatics online.

SHP2 associates with nuclear localization of STAT3: significance in progression and prognosis of colorectal cancer

Tyrosine phosphatase SHP2, encoded by PTPN11, has been implicated in many physiologic and pathologic processes in neoplastic progression. However, controversies are emerging from many studies, indicating SHP2 has a dual role in different types of tumors. We aimed to explore the role of SHP2 in progression and prognosis of colorectal cancer (CRC). SHP2 inhibited CRC cell proliferation and migration, and the phosphorylation of STAT3 was negatively regulated by SHP2 in CRC. SHP2 and nuclear STAT3 were examined in 270 CRC tissues. SHP2 was significantly correlated with nuclear STAT3 (Spearman’s rho = −0.408, P ≤ 0.001). Based on Cox regression analysis, patients with high levels of SHP2 and low levels of nuclear STAT3 had longer disease-specific survival (DSS) (HR, 0.362; 95% CI, 0.165–0.794) and disease-free survival (DFS) (HR, 0.447; 95% CI, 0.227–0.877). Further, low levels of SHP2 and high levels of nuclear STAT3 were independently associated with adverse outcomes in the whole cohort (DFS; HR, 2.353; 95% CI, 1.199–4.619). These results suggest that combination of SHP2 and nuclear STAT3 is a strong prognostic predictor in CRC.

Dissipative structures and biological rhythms

Sustained oscillations abound in biological systems. They occur at all levels of biological organization over a wide range of periods, from a fraction of a second to years, and with a variety of underlying mechanisms. They control major physiological functions, and their dysfunction is associated with a variety of physiological disorders. The goal of this review is (i) to give an overview of the main rhythms observed at the cellular and supracellular levels, (ii) to briefly describe how the study of biological rhythms unfolded in the course of time, in parallel with studies on chemical oscillations, (iii) to present the major roles of biological rhythms in the control of physiological functions, and (iv) the pathologies associated with the alteration, disappearance, or spurious occurrence of biological rhythms. Two tables present the main examples of cellular and supracellular rhythms ordered according to their period, and their role in physiology and pathophysiology. Among the rhythms discussed are neural and cardiac rhythms, metabolic oscillations such as those occurring in glycolysis in yeast, intracellular Ca⁺⁺ oscillations, cyclic AMP oscillations in Dictyostelium amoebae, the segmentation clock that controls somitogenesis, pulsatile hormone secretion, circadian rhythms which occur in all eukaryotes and some bacteria with a period close to 24 h, the oscillatory dynamics of the enzymatic network driving the cell cycle, and oscillations in transcription factors such as NF-ΚB and tumor suppressors such as p53. Ilya Prigogine's concept of dissipative structures applies to temporal oscillations and allows us to unify within a common framework the various rhythms observed at different levels of biological organization, regardless of their period and underlying mechanism.

Cellular interplay via cytokine hierarchy causes pathological cardiac hypertrophy in RAF1-mutant Noonan syndrome

Noonan syndrome (NS) is caused by mutations in RAS/ERK pathway genes, and is characterized by craniofacial, growth, cognitive and cardiac defects. NS patients with kinase-activating RAF1 alleles typically develop pathological left ventricular hypertrophy (LVH), which is reproduced in Raf1^L613V/+ knock-in mice. Here, using inducible Raf1^L613V expression, we show that LVH results from the interplay of cardiac cell types. Cardiomyocyte Raf1^L613V enhances Ca²⁺ sensitivity and cardiac contractility without causing hypertrophy. Raf1^L613V expression in cardiomyocytes or activated fibroblasts exacerbates pressure overload-evoked fibrosis. Endothelial/endocardial (EC) Raf1^L613V causes cardiac hypertrophy without affecting contractility. Co-culture and neutralizing antibody experiments reveal a cytokine (TNF/IL6) hierarchy in Raf1^L613V-expressing ECs that drives cardiomyocyte hypertrophy in vitro. Furthermore, postnatal TNF inhibition normalizes the increased wall thickness and cardiomyocyte hypertrophy in vivo. We conclude that NS-cardiomyopathy involves cardiomyocytes, ECs and fibroblasts, TNF/IL6 signalling components represent potential therapeutic targets, and abnormal EC signalling might contribute to other forms of LVH.

The human congenital disorder Noonan Syndrome (NS) is caused by germ-line mutations that hyperactivate the RAS/ERK signalling pathway, and can feature pathologic cardiac enlargement. Here, the authors find that a complex cellular and molecular interplay involving a cytokine hierarchy underlies cardiac hypertrophy caused by a NS-associated Raf allele.

A tyrosine phosphatase SHP2 gain-of-function mutation enhances malignancy of breast carcinoma

Background: Evidence suggests that Src homologous protein phosphotyrosyl phosphatase 2 (SHP2) mutations promote cancer development in several solid tumours. In this study, we focused on the in vivo and in vitro effects of an SHP2 mutation on the breast cancer phenotype to determine whether this mutation is correlated with a malignant phenotype.

Methods: Mutant PTPN11 cDNA (D61G) was transduced into MDA-MB231 and MCF-7 cells. The effects of the D61G mutation on tumourigenesis and malignant behaviours, such as cell adhesion, proliferation, migration and invasion, were examined. Potential underlying molecular mechanisms, i.e., activation of the Gab1-Ras-Erk axis, were also examined.

Results:In vitro experiments revealed that tumour adhesion, proliferation, migration and invasion were significantly increased in the SHP2 D61G mutant groups. Consistently, in vivo experiments also showed that the tumour sizes and weights were increased significantly in the SHP2 D61G-MB231 group (p < 0.001) in association with tumour metastasis. Mechanistically, the PTPN11 mutation resulted in activation of the Ras-ErK pathway. The binding between Gab1 and mutant SHP2 was significantly increased.

Conclusion: Mutant SHP2 significantly promotes tumour migration and invasion at least partially through activation of the Gab1-Ras-Erk axis. This finding could have direct implications for breast cancer therapy.

Low-dose dasatinib rescues cardiac function in Noonan syndrome

Noonan syndrome (NS) is a common autosomal dominant disorder that presents with short stature, craniofacial dysmorphism, and cardiac abnormalities. Activating mutations in the PTPN11 gene encoding for the Src homology 2 (SH2) domain-containing protein tyrosine phosphatase-2 (SHP2) causes approximately 50% of NS cases. In contrast, NS with multiple lentigines (NSML) is caused by mutations that inactivate SHP2, but it exhibits some overlapping abnormalities with NS. Protein zero-related (PZR) is a SHP2-binding protein that is hyper-tyrosyl phosphorylated in the hearts of mice from NS and NSML, suggesting that PZR and the tyrosine kinase that catalyzes its phosphorylation represent common targets for these diseases. We show that the tyrosine kinase inhibitor, dasatinib, at doses orders of magnitude lower than that used for its anticancer activities inhibited PZR tyrosyl phosphorylation in the hearts of NS mice. Low-dose dasatinib treatment of NS mice markedly improved cardiomyocyte contractility and functionality. Remarkably, a low dose of dasatinib reversed the expression levels of molecular markers of cardiomyopathy and reduced cardiac fibrosis in NS and NSML mice. These results suggest that PZR/SHP2 signaling is a common target of both NS and NSML and that low-dose dasatinib may represent a unifying therapy for the treatment of PTPN11-related cardiomyopathies.

Hepatic Inositol 1,4,5 Trisphosphate Receptor Type 1 Mediates Fatty Liver

Fatty liver is the most common type of liver disease, affecting nearly one third of the US population and more than half a billion people worldwide. Abnormalities in ER calcium handling and mitochondrial function each have been implicated in abnormal lipid droplet formation. Here we show that the type 1 isoform of the inositol 1,4,5-trisphosphate receptor (InsP₃R1) specifically links ER calcium release to mitochondrial calcium signaling and lipid droplet formation in hepatocytes. Moreover, liver-specific InsP₃R1 knockout mice have impaired mitochondrial calcium signaling, decreased hepatic triglycerides, reduced lipid droplet formation and are resistant to development of fatty liver. Patients with non-alcoholic steatohepatitis, the most malignant form of fatty liver, have increased hepatic expression of InsP₃R1 and the extent of ER-mitochondrial co-localization correlates with the degree of steatosis in human liver biopsies.

CONCLUSION

InsP₃R1 plays a central role in lipid droplet formation in hepatocytes and the data suggest that it is involved in the development of human fatty liver disease.

Contribution of Post-translational Phosphorylation to Sarcomere-Linked Cardiomyopathy Phenotypes

Secondary shifts develop in post-translational phosphorylation of sarcomeric proteins in multiple animal models of inherited cardiomyopathy. These signaling alterations together with the primary mutation are predicted to contribute to the overall cardiac phenotype. As a result, identification and integration of post-translational myofilament signaling responses are identified as priorities for gaining insights into sarcomeric cardiomyopathies. However, significant questions remain about the nature and contribution of post-translational phosphorylation to structural remodeling and cardiac dysfunction in animal models and human patients. This perspective essay discusses specific goals for filling critical gaps about post-translational signaling in response to these inherited mutations, especially within sarcomeric proteins. The discussion focuses primarily on pre-clinical analysis of animal models and defines challenges and future directions in this field.

The role of the protein tyrosine phosphatase SHP2 in cardiac development and disease

Congenital heart disease is the most common human developmental disorder, affecting ∼1:100 newborns, and is the primary cause of birth-defect related deaths worldwide. As a major regulator of receptor tyrosine kinase (RTK), cytokine and G-protein coupled receptor signaling, the non-receptor protein tyrosine phosphatase SHP2 plays a critical role in normal cardiac development and function. Indeed, SHP2 participates in a wide variety of cellular functions, including proliferation, survival, differentiation, migration, and cell-cell communication. Moreover, human activating and inactivating mutations of SHP2 are responsible for two related developmental disorders called Noonan and LEOPARD Syndromes, respectively, which are both characterized, in part, by congenital heart defects. Structural, enzymologic, biochemical, and SHP2 mouse model studies have together greatly enriched our knowledge of SHP2 and, as such, have also uncovered the diverse roles for SHP2 in cardiac development, including its contribution to progenitor cell specification, cardiac morphogenesis, and maturation of cardiac valves and myocardial chambers. By delineating the precise mechanisms by which SHP2 is involved in regulating these processes, we can begin to better understand the pathogenesis of cardiac disease and find more strategic and effective therapies for treatment of patients with congenital heart disorders.

Osteoblastic differentiation enhances expression of TRPV4 that is required for calcium oscillation induced by mechanical force

Mechanical stress is known to alter bone mass and the loss of force stimuli leads to reduction of bone mass. However, molecules involved in this phenomenon are incompletely understood. As mechanical force would affect signaling events in cells, we focused on a calcium channel, TRPV4 regarding its role in the effects of force stimuli on calcium in osteoblasts. TRPV4 expression levels were enhanced upon differentiation of osteoblasts in culture. We found that BMP-2 treatment enhanced TRPV4 gene expression in a dose dependent manner. BMP-2 effects on TRPV4 expression were suppressed by inhibitors for transcription and new protein synthesis. In these osteoblasts, a TRPV4-selective agonist, 4α-PDD, enhanced calcium signaling and the effects of 4α-PDD were enhanced in differentiated osteoblasts compared to the control cells. Fluid flow, as a mechanical stimulation, induced intracellular calcium oscillation in wild type osteoblasts. In contrast, TRPV4 deficiency suppressed calcium oscillation significantly even when the cells were subjected to fluid flow. These data suggest that TRPV4 is involved in the flow-induced calcium signaling in osteoblasts.

Novel role for SHP-2 in nutrient-responsive control of S6 kinase 1 signaling

Amino acids are required for the activation of the mammalian target of rapamycin complex 1 (mTORC1), which plays a critical role in cell growth, proliferation, and metabolism. The branched-chain amino acid leucine is an essential nutrient that stimulates mTORC1 to promote protein synthesis by activating p70 S6 kinase 1 (S6K1). Here we show that the protein tyrosine phosphatase SHP-2 is required for leucine-induced activation of S6K1 in skeletal myoblasts. In response to leucine, S6K1 activation is inhibited in myoblasts either lacking SHP-2 expression or overexpressing a catalytically inactive mutant of SHP-2. Activation of S6K1 by leucine requires the mobilization of intracellular calcium (Ca(2+)), which we show is mediated by SHP-2 in an inositol-1,4,5-trisphosphate-dependent manner. Ectopic Ca(2+) mobilization rescued the S6K1 activation defect in SHP-2-deficient myoblasts. SHP-2 was identified to act upstream of phospholipase C β4, linking it to the generation of nutrient-induced Ca(2+) release and S6K1 phosphorylation. Consistent with these results, SHP-2-deficient myoblasts exhibited impaired leucine sensing, leading to defective autophagy and reduced myoblast size. These data define a new role for SHP-2 as a nutrient-sensing regulator in skeletal myoblasts that is required for the activation of S6K1.

The role of SH3BP2 in the pathophysiology of cherubism

Cherubism is a rare bone dysplasia that is characterized by symmetrical bone resorption limited to the jaws. Bone lesions are filled with soft fibrous giant cell-rich tissue that can expand and cause severe facial deformity. The disorder typically begins in children at ages of 2-5 years and the bone resorption and facial swelling continues until puberty; in most cases the lesions regress spontaneously thereafter. Most patients with cherubism have germline mutations in the gene encoding SH3BP2, an adapter protein involved in adaptive and innate immune response signaling. A mouse model carrying a Pro416Arg mutation in SH3BP2 develops osteopenia and expansile lytic lesions in bone and some soft tissue organs. In this review we discuss the genetics of cherubism, the biological functions of SH3BP2 and the analysis of the mouse model. The data suggest that the underlying cause for cherubism is a systemic autoinflammatory response to physiologic challenges despite the localized appearance of bone resorption and fibrous expansion to the jaws in humans.

TSLP signaling network revealed by SILAC-based phosphoproteomics

Thymic stromal lymphopoietin (TSLP) is a cytokine that plays diverse roles in the regulation of immune responses. TSLP requires a heterodimeric receptor complex consisting of IL-7 receptor α subunit and its unique TSLP receptor (gene symbol CRLF2) to transmit signals in cells. Abnormal TSLP signaling (e.g. overexpression of TSLP or its unique receptor TSLPR) contributes to the development of a number of diseases including asthma and leukemia. However, a detailed understanding of the signaling pathways activated by TSLP remains elusive. In this study, we performed a global quantitative phosphoproteomic analysis of the TSLP signaling network using stable isotope labeling by amino acids in cell culture. By employing titanium dioxide in addition to antiphosphotyrosine antibodies as enrichment methods, we identified 4164 phosphopeptides on 1670 phosphoproteins. Using stable isotope labeling by amino acids in cell culture-based quantitation, we determined that the phosphorylation status of 226 proteins was modulated by TSLP stimulation. Our analysis identified activation of several members of the Src and Tec families of kinases including Btk, Lyn, and Tec by TSLP for the first time. In addition, we report TSLP-induced phosphorylation of protein phosphatases such as Ptpn6 (SHP-1) and Ptpn11 (Shp2), which has also not been reported previously. Co-immunoprecipitation assays showed that Shp2 binds to the adapter protein Gab2 in a TSLP-dependent manner. This is the first demonstration of an inducible protein complex in TSLP signaling. A kinase inhibitor screen revealed that pharmacological inhibition of PI-3 kinase, Jak family kinases, Src family kinases or Btk suppressed TSLP-dependent cellular proliferation making them candidate therapeutic targets in diseases resulting from aberrant TSLP signaling. Our study is the first phosphoproteomic analysis of the TSLP signaling pathway that greatly expands our understanding of TSLP signaling and provides novel therapeutic targets for TSLP/TSLPR-associated diseases in humans.

Stem cells and calcium signaling

The increasing interest in stem cell research is linked to the promise of developing treatments for many lifethreatening, debilitating diseases, and for cell replacement therapies. However, performing these therapeutic innovations with safety will only be possible when an accurate knowledge about the molecular signals that promote the desired cell fate is reached. Among these signals are transient changes in intracellular Ca(2+) concentration [Ca(2+)](i). Acting as an intracellular messenger, Ca(2+) has a key role in cell signaling pathways in various differentiation stages of stem cells. The aim of this chapter is to present a broad overview of various moments in which Ca(2+)-mediated signaling is essential for the maintenance of stem cells and for promoting their development and differentiation, also focusing on their therapeutic potential.

Inositol 1,4,5-trisphosphate receptor subtype-specific regulation of calcium oscillations

Oscillatory fluctuations in the cytosolic concentration of free calcium ions (Ca²⁺) are considered a ubiquitous mechanism for controlling multiple cellular processes. Inositol 1,4,5-trisphosphate (IP₃) receptors (IP₃R) are intracellular Ca²⁺ release channels that mediate Ca²⁺ release from endoplasmic reticulum (ER) Ca²⁺ stores. The three IP₃R subtypes described so far exhibit differential structural, biophysical, and biochemical properties. Subtype specific regulation of IP₃R by the endogenous modulators IP₃, Ca²⁺, protein kinases and associated proteins have been thoroughly examined. In this article we will review the contribution of each IP₃R subtype in shaping cytosolic Ca²⁺ oscillations.

Calcium signaling in placenta

The placenta sustains the developing fetus throughout gestation and its major functions include nutrition, gas and waste exchange via a variety of passive or active mechanisms. Up to 30 g of calcium (Ca(2+)) actively crosses the trophoblast layer during human pregnancy. The Ca(2+) ion not only plays an important role for skeletal development but is also an essential second messenger. This review is intended to highlight the implications of Ca(2+) signaling during reproduction and specifically placentation. Initially, a Ca(2+) wave induces fertilization of the oocyte. The intracellular Ca(2+) concentration is key for the blastocyst implantation, proper placental development and function. Current knowledge of many proteins involved in placental Ca(2+) regulation and their function in pathologic conditions is largely limited. Recent studies, however, point to alterations in Ca(2+) homeostasis in placental pathologies such as pre-eclampsia (PE) and intrauterine growth restriction (IUGR). A broader understanding of the role of Ca(2+) signaling during human reproduction may offer insight into impaired pregnancy outcomes.

Paclitaxel accelerates spontaneous calcium oscillations in cardiomyocytes by interacting with NCS-1 and the InsP3R

Paclitaxel (Taxol) is a microtubule-stabilizing compound that is used for cancer chemotherapy. However, Taxol administration is limited by serious side effects including cardiac arrhythmia, which cannot be explained by its microtubule-stabilizing effect. Recently, neuronal calcium sensor 1 (NCS-1), a calcium binding protein that modulates the inositol-1,4,5-trisphosphate receptor (InsP(3)R), was described as a binding partner of Taxol and as a substrate of calpain. We examined calcium signaling processes in cardiomyocytes after treatment with Taxol to investigate the basis of Taxol-induced cardiac arrhythmia. After treating isolated neonatal rat ventricular myocytes with a therapeutic concentration of Taxol for several hours live cell imaging experiments showed that the frequency of spontaneous calcium oscillations significantly increased. This effect was not mimicked by other tubulin-stabilizing agents. However, it was prevented by inhibiting the InsP(3)R. Taxol treated cells had increased expression of NCS-1, an effect also detectable after Taxol administration in vivo. Short hairpin RNA mediated knockdown of NCS-1 decreased InsP(3)R dependent intracellular calcium release, whereas Taxol treatment, that increased NCS-1 levels, increased InsP(3)R dependent calcium release. The effects of Taxol were ryanodine receptor independent. At the single channel level Taxol and NCS-1 mediated an increase in InsP(3)R activity. Calpain activity was not affected by Taxol in cardiomyocytes suggesting a calpain independent signaling pathway. In short, our study shows that Taxol impacts calcium signaling and calcium oscillations in cardiomyocytes through NCS-1 and the InsP(3)R.

The tyrosine phosphatase Shp2 in development and cancer

Deregulation of signaling pathways, through mutation or other molecular changes, can ultimately result in disease. The tyrosine phosphatase Shp2 has emerged as a major regulator of receptor tyrosine kinase (RTK) and cytokine receptor signaling. In the last decade, germline mutations in the human PTPN11 gene, encoding Shp2, were linked to Noonan (NS) and LEOPARD syndromes, two multisymptomatic developmental disorders that are characterized by short stature, craniofacial defects, cardiac defects, and mental retardation. Somatic Shp2 mutations are also associated with several types of human malignancies, such as the most common juvenile leukemia, juvenile myelomonocytic leukemia (JMML). Whereas NS and JMML are caused by gain-of-function (GOF) mutations of Shp2, loss-of-function (LOF) mutations are thought to be associated with LEOPARD syndrome. Animal models that carry conditional LOF and GOF mutations have allowed a better understanding of the mechanism of Shp2 function in disease, and shed light on the role of Shp2 in signaling pathways that control decisive events during embryonic development or during cellular transformation/tumorigenesis.

Regulation of myofibroblast activities: calcium pulls some strings behind the scene

Myofibroblast-induced remodeling of collagenous extracellular matrix is a key component of our body's strategy to rapidly and efficiently repair damaged tissues; thus myofibroblast activity is considered crucial in assuring the mechanical integrity of vital organs and tissues after injury. Typical examples of beneficial myofibroblast activities are scarring after myocardial infarct and repair of damaged connective tissues including dermis, tendon, bone, and cartilage. However, deregulation of myofibroblast contraction causes the tissue deformities that characterize hypertrophic scars as well as organ fibrosis that ultimately leads to heart, lung, liver and kidney failure. The phenotypic features of the myofibroblast, within a spectrum going from the fibroblast to the smooth muscle cell, raise the question as to whether it regulates contraction in a fibroblast- or muscle-like fashion. In this review, we attempt to elucidate this point with a particular focus on the role of calcium signaling. We suggest that calcium plays a central role in myofibroblast biological activity not only in regulating contraction but also in mediating intracellular and extracellular mechanical signals, structurally organizing the contractile actin-myosin cytoskeleton, and establishing lines of intercellular communication.

A new lock-step mechanism of matrix remodelling based on subcellular contractile events

Myofibroblasts promote tissue contractures during fibrotic diseases. To understand how spontaneous changes in the intracellular calcium concentration, [Ca(2+)](i), contribute to myofibroblast contraction, we analysed both [Ca(2+)](i) and subcellular contractions. Contractile events were assessed by tracking stress-fibre-linked microbeads and measured by atomic force microscopy. Myofibroblasts exhibit periodic (approximately 100 seconds) [Ca(2+)](i) oscillations that control small (approximately 400 nm) and weak (approximately 100 pN) contractions. Whereas depletion of [Ca(2+)](i) reduces these microcontractions, cell isometric tension is unaffected, as shown by growing cells on deformable substrates. Inhibition of Rho- and ROCK-mediated Ca(2+)-independent contraction has no effect on microcontractions, but abolishes cell tension. On the basis of this two-level regulation of myofibroblast contraction, we propose a single-cell lock-step model. Rho- and ROCK-dependent isometric tension generates slack in extracellular matrix fibrils, which are then accessible for the low-amplitude and high-frequency contractions mediated by [Ca(2+)](i). The joint action of both contraction modes can result in macroscopic tissue contractures of approximately 1 cm per month.

Functional effects of PTPN11 (SHP2) mutations causing LEOPARD syndrome on epidermal growth factor-induced phosphoinositide 3-kinase/AKT/glycogen synthase kinase 3beta signaling

LEOPARD syndrome (LS), a disorder with multiple developmental abnormalities, is mainly due to mutations that impair the activity of the tyrosine phosphatase SHP2 (PTPN11). How these alterations cause the disease remains unknown. We report here that fibroblasts isolated from LS patients displayed stronger epidermal growth factor (EGF)-induced phosphorylation of both AKT and glycogen synthase kinase 3beta (GSK-3beta) than fibroblasts from control patients. Similar results were obtained in HEK293 cells expressing LS mutants of SHP2. We found that the GAB1/phosphoinositide 3-kinase (PI3K) complex was more abundant in fibroblasts from LS than control subjects and that both AKT and GSK-3beta hyperphosphorylation were prevented by reducing GAB1 expression or by overexpressing a GAB1 mutant unable to bind to PI3K. Consistently, purified recombinant LS mutants failed to dephosphorylate GAB1 PI3K-binding sites. These mutants induced PI3K-dependent increase in cell size in a model of chicken embryo cardiac explants and in transcriptional activity of the atrial natriuretic factor (ANF) gene in neonate rat cardiomyocytes. In conclusion, SHP2 mutations causing LS facilitate EGF-induced PI3K/AKT/GSK-3beta stimulation through impaired GAB1 dephosphorylation, resulting in deregulation of a novel signaling pathway that could be involved in LS pathology.

The Rho guanine nucleotide exchange factor AKAP13 (BRX) is essential for cardiac development in mice

A fundamental biologic principle is that diverse biologic signals are channeled through shared signaling cascades to regulate development. Large scaffold proteins that bind multiple proteins are capable of coordinating shared signaling pathways to provide specificity to activation of key developmental genes. Although much is known about transcription factors and target genes that regulate cardiomyocyte differentiation, less is known about scaffold proteins that couple signals at the cell surface to differentiation factors in developing heart cells. Here we show that AKAP13 (also known as Brx-1, AKAP-Lbc, and proto-Lbc), a unique protein kinase A-anchoring protein (AKAP) guanine nucleotide exchange region belonging to the Dbl family of oncogenes, is essential for cardiac development. Cardiomyocytes of Akap13-null mice had deficient sarcomere formation, and developing hearts were thin-walled and mice died at embryonic day 10.5-11.0. Disruption of Akap13 was accompanied by reduced expression of Mef2C. Consistent with a role of AKAP13 upstream of MEF2C, Akap13 siRNA led to a reduction in Mef2C mRNA, and overexpression of AKAP13 augmented MEF2C-dependent reporter activity. The results suggest that AKAP13 coordinates Galpha(12) and Rho signaling to an essential transcription program in developing cardiomyocytes.

Biological functions of the low and high molecular weight protein isoforms of fibroblast growth factor-2 in cardiovascular development and disease

Fibroblast growth factor 2 (FGF2) consists of multiple protein isoforms (low molecular weight, LMW, and high molecular weight, HMW) produced by alternative translation from the Fgf2 gene. These protein isoforms are localized to different cellular compartments, indicating unique biological activity. FGF2 isoforms in the heart have distinct roles in many pathological circumstances in the heart including cardiac hypertrophy, ischemia-reperfusion injury, and atherosclerosis. These studies suggest distinct biological activities of FGF2 LMW and HMW isoforms both in vitro and in vivo. Yet, due to the limitations that only the recombinant FGF2 LMW isoform is readily available and that the FGF2 antibody is nonspecific with regards to its isoforms, much remains to be determined regarding the role(s) of the FGF2 LMW and HMW isoforms in cellular behavior and in cardiovascular development and pathophysiology. This review summarizes the activities of LMW and HMW isoforms of FGF2 in cardiovascular development and disease.

AQP4 knockout impairs proliferation, migration and neuronal differentiation of adult neural stem cells

Aquaporin-4 (AQP4), a key molecule for maintaining water and ion homeostasis in the central nervous system, is expressed in adult neural stem cells (ANSCs) as well as astrocytes. However, little is known about the functions of AQP4 in the ANSCs in vitro. Here we show that AQP4 knockout inhibits the proliferation, survival, migration and neuronal differentiation of ANSCs derived from the subventricular zone of adult mice. Flow cytometric cell cycle analysis revealed that AQP4 knockout increased the basal apoptosis and induced a G2-M arrest in ANSCs. Using Fluo-3 Ca2+ imaging, we show that AQP4 knockout alters the spontaneous Ca2+ oscillations by frequency enhancement and amplitude suppression, and suppresses KCl-induced Ca2+ influx. AQP4 knockout downregulated the expression of connexin43 and the L-type voltage-gated Ca2+ channel CaV1.2 subtype in ANSCs. Together, these findings suggest that AQP4 plays a crucial role in regulating the proliferation, migration and differentiation of ANSCs, and this function of AQP4 is probably mediated by its action on intracellular Ca2+ dynamics.

Myofibroblast communication is controlled by intercellular mechanical coupling

Neoformation of intercellular adherens junctions accompanies the differentiation of fibroblasts into contractile myofibroblasts, a key event during development of fibrosis and in wound healing. We have previously shown that intercellular mechanical coupling of stress fibres via adherens junctions improves contraction of collagen gels by myofibroblasts. By assessing spontaneous intracellular Ca2+ oscillations, we here test whether adherens junctions mechanically coordinate myofibroblast activities. Periodic Ca2+ oscillations are synchronised between physically contacting myofibroblasts and become desynchronised upon dissociation of adherens junctions with function-blocking peptides. Similar uncoupling is obtained by inhibiting myofibroblast contraction using myosin inhibitors and by blocking mechanosensitive ion channels using Gd3+ and GSMTx4. By contrast, gap junction uncouplers do not affect myofibroblast coordination. We propose the following model of mechanical coupling for myofibroblasts: individual cell contraction is transmitted via adherens junctions and leads to the opening of mechanosensitive ion channels in adjacent cells. The resulting Ca2+ influx induces a contraction that can feed back on the first cell and/or stimulate other contacting cells. This mechanism could improve the remodelling of cell-dense tissue by coordinating the activity of myofibroblasts.

The tyrosine phosphatase Shp2 (PTPN11) in cancer

Diverse cellular processes are regulated by tyrosyl phosphorylation, which is controlled by protein-tyrosine kinases (PTKs) and protein-tyrosine phosphatases (PTPs). De-regulated tyrosyl phosphorylation, evoked by gain-of-function mutations and/or over-expression of PTKs, contributes to the pathogenesis of many cancers and other human diseases. PTPs, because they oppose the action of PTKs, had been considered to be prime suspects for potential tumor suppressor genes. Surprisingly, few, if any, tumor suppressor PTPs have been identified. However, the Src homology-2 domain-containing phosphatase Shp2 (encoded by PTPN11) is a bona fide proto-oncogene. Germline mutations in PTPN11 cause Noonan and LEOPARD syndromes, whereas somatic PTPN11 mutations occur in several types of hematologic malignancies, most notably juvenile myelomonocytic leukemia and, more rarely, in solid tumors. Shp2 also is an essential component in several other oncogene signaling pathways. Elucidation of the events underlying Shp2-evoked transformation may provide new insights into oncogenic mechanisms and novel targets for anti-cancer therapy.

Noonan syndrome-associated SHP-2/Ptpn11 mutants enhance SIRPalpha and PZR tyrosyl phosphorylation and promote adhesion-mediated ERK activation

Noonan syndrome (NS) is an autosomal dominant disorder that is associated with multiple developmental abnormalities. Activated mutations of the protein-tyrosine phosphatase, SHP-2/PTPN11, have been reported in approximately 50% of NS cases. Despite being activated, NS-associated SHP-2 mutants require plasma membrane proximity to evoke disease-associated signaling. Here we show that NS-associated SHP-2 mutants induce hypertyrosyl phosphorylation of the transmembrane glycoproteins, SIRPalpha (signal-regulatory protein alpha) and PZR (protein zero-related), resulting in their increased association with NS-associated SHP-2 mutants. NS-associated SHP-2 mutants enhanced SIRPalpha and PZR tyrosyl phosphorylation either by impairing SIRPalpha dephosphorylation or by promoting PZR tyrosyl phosphorylation. Importantly, during embryogenesis in a mouse model of NS, SIRPalpha and PZR were hypertyrosyl-phosphorylated and bound increased levels of the NS-associated SHP-2 mutant. SIRPalpha and PZR have been implicated in extracellular matrix-dependent signaling. Mouse embryonic fibroblasts derived from a mouse model of NS displayed enhanced ERK activation in response to fibronectin plating. Knockdown of SIRPalpha and PZR in these cells attenuated the enhanced activation of ERK following fibronectin plating. Thus, SIRPalpha and PZR serve as scaffolds that facilitate plasma membrane recruitment and signaling of NS-associated SHP-2 mutants.

Chromogranin B regulates calcium signaling, nuclear factor kappaB activity, and brain natriuretic peptide production in cardiomyocytes

Altered regulation of signaling pathways can lead to pathologies including cardiac hypertrophy and heart failure. We report that neonatal and adult cardiomyocytes express chromogranin B (CGB), a Ca(2+) binding protein that modulates Ca(2+) release by the inositol 1,4,5-trisphosphate receptor (InsP(3)R). Using fluorescent Ca(2+) indicator dyes, we found that CGB regulates InsP(3)-dependent Ca(2+) release in response to angiotensin II, an octapeptide hormone that promotes cardiac hypertrophy. ELISA experiments and luciferase reporter assays identified angiotensin II as a potent inducer of brain natriuretic peptide (BNP), a hormone that recently emerged as an important biomarker in cardiovascular disease. CGB was found to regulate angiotensin II-stimulated and basal secretion, expression and promoter activity of BNP that depend on the InsP(3)R. Moreover, we provide evidence that CGB acts via the transcription activity of nuclear factor kappaB in an InsP(3)/Ca(2+)-dependent manner but independent of nuclear factor of activated T cells. In vivo experiments further showed that cardiac hypertrophy induced by angiotensin II, a condition characterized by increased ventricular BNP production, is associated with upregulation of ventricular CGB expression. Overexpression of CGB in cardiomyocytes, in turn, induced the BNP promoter. The evidence presented in this study identifies CGB as a novel regulator of cardiomyocyte InsP(3)/Ca(2+)-dependent signaling, nuclear factor kappaB activity, and BNP production.

Deletion of Ptpn11 (Shp2) in cardiomyocytes causes dilated cardiomyopathy via effects on the extracellular signal-regulated kinase/mitogen-activated protein kinase and RhoA signaling pathways

BACKGROUND

Heart failure is the leading cause of death in the United States. By delineating the pathways that regulate cardiomyocyte function, we can better understand the pathogenesis of cardiac disease. Many cardiomyocyte signaling pathways activate protein tyrosine kinases. However, the role of specific protein tyrosine phosphatases (PTPs) in these pathways is unknown.

METHODS AND RESULTS

Here, we show that mice with muscle-specific deletion of Ptpn11, the gene encoding the SH2 domain-containing PTP Shp2, rapidly develop a compensated dilated cardiomyopathy without an intervening hypertrophic phase, with signs of cardiac dysfunction appearing by the second postnatal month. Shp2-deficient primary cardiomyocytes are defective in extracellular signal-regulated kinase/mitogen-activated protein kinase (Erk/MAPK) activation in response to a variety of soluble agonists and pressure overload but show hyperactivation of the RhoA signaling pathway. Treatment of primary cardiomyocytes with Erk1/2- and RhoA pathway-specific inhibitors suggests that both abnormal Erk/MAPK and RhoA activities contribute to the dilated phenotype of Shp2-deficient hearts.

CONCLUSIONS

Our results identify Shp2 as the first PTP with a critical role in adult cardiac function, indicate that in the absence of Shp2 cardiac hypertrophy does not occur in response to pressure overload, and demonstrate that the cardioprotective role of Shp2 is mediated via control of both the Erk/MAPK and RhoA signaling pathways.