Altered regulation of SHP-2 and PTP 1B tyrosine phosphatases in cystic kidneys from bcl-2 -/- mice

SHP2: its association and roles in systemic lupus erythematosus

OBJECTIVE

Systemic lupus erythematosus (SLE) is an autoimmune inflammatory disease. Src homology 2 domain containing protein tyrosine phosphatase (SHP2) is a member of the protein tyrosine phosphatases (PTPs) family. To date, relationship between SHP2 and SLE pathogenesis is not elucidated.

METHOD

We measured plasma levels of SHP2 in 328 SLE patients, 78 RA patients, 80 SS patients and 79 healthy controls by ELISA, and discussed association of SHP2 in SLE patients, potential of plasma SHP2 as a SLE biomarker. Moreover, histological and serological changes were evaluated by flow cytometry, HE/Masson examination, immunofluorescence test in pristane-induced lupus mice after SHP2 inhibitor injection to reveal role of SHP2 in lupus development.

RESULTS

Results indicated that SHP2 plasma levels were upregulated in SLE patients and correlated with some clinical, laboratory characteristics such as proteinuria, pyuria, and may be a potential biomarker for SLE. After SHP2 inhibitor treatment, hepatosplenomegaly and histological severity of the kidney in lupus mice were improved. SHP2 inhibitor reversed DCs, Th1, and Th17 cells differentiation and downregulated inflammatory cytokines (IL-4, IL-6, IL-10, IL-17A, IFN-γ and TNF-α) and autoantibodies (ANA, anti-dsDNA) production in pristane-lupus mice.

CONCLUSION

In summary, SHP2 correlated with SLE pathogenesis and promoted the development of lupus.

GDF15 is a heart-derived hormone that regulates body growth

The endocrine system is crucial for maintaining whole-body homeostasis. Little is known regarding endocrine hormones secreted by the heart other than atrial/brain natriuretic peptides discovered over 30 years ago. Here, we identify growth differentiation factor 15 (GDF15) as a heart-derived hormone that regulates body growth. We show that pediatric heart disease induces GDF15 synthesis and secretion by cardiomyocytes. Circulating GDF15 in turn acts on the liver to inhibit growth hormone (GH) signaling and body growth. We demonstrate that blocking cardiomyocyte production of GDF15 normalizes circulating GDF15 level and restores liver GH signaling, establishing GDF15 as a bona fide heart-derived hormone that regulates pediatric body growth. Importantly, plasma GDF15 is further increased in children with concomitant heart disease and failure to thrive (FTT). Together these studies reveal a new endocrine mechanism by which the heart coordinates cardiac function and body growth. Our results also provide a potential mechanism for the well-established clinical observation that children with heart diseases often develop FTT.

Reduced FAK-STAT3 signaling contributes to ER stress-induced mitochondrial dysfunction and death in endothelial cells

Excessive endoplasmic reticulum (ER) stress leads to cell loss in many diseases, e.g., contributing to endothelial cell loss after spinal cord injury. Here, we determined whether ER stress-induced mitochondrial dysfunction could be explained by interruption of the focal adhesion kinase (FAK)-mitochondrial STAT3 pathway we recently discovered. ER stress was induced in brain-derived mouse bEnd5 endothelial cells by thapsigargin or tunicamycin and caused apoptotic cell death over a 72h period. In concert, ER stress caused mitochondrial dysfunction as shown by reduced bioenergetic function, loss of mitochondrial membrane potential and increased mitophagy. ER stress caused a reduction in mitochondrial phosphorylated S727-STAT3, known to be important for maintaining mitochondrial function. Normal activation or phosphorylation of the upstream cytoplasmic FAK was also reduced, through mechanisms that involve tyrosine phosphatases and calcium signaling, as shown by pharmacological inhibitors, bisperoxovanadium (bpV) and 2-aminoethoxydiphenylborane (APB), respectively. APB mitigated the reduction in FAK and STAT3 phosphorylation, and improved endothelial cell survival caused by ER stress. Transfection of cells rendered null for STAT3 using CRISPR technology with STAT3 mutants confirmed the specific involvement of S727-STAT3 inhibition in ER stress-mediated cell loss. These data suggest that loss of FAK signaling during ER stress causes mitochondrial dysfunction by reducing the protective effects of mitochondrial STAT3, leading to endothelial cell death. We propose that stimulation of the FAK-STAT3 pathway is a novel therapeutic approach against pathological ER stress.

Liver kinase B1 expression promotes phosphatase activity and abrogation of receptor tyrosine kinase phosphorylation in human cancer cells

Aberrant receptor tyrosine kinase phosphorylation (pRTK) has been associated with diverse pathological conditions, including human neoplasms. In lung cancer, frequent liver kinase B1 (LKB1) mutations correlate with tumor progression, but potential links with pRTK remain unknown. Heightened and sustained receptor activation was demonstrated by LKB1-deficient A549 (lung) and HeLaS3 (cervical) cancer cell lines. Depletion (siRNA) of endogenous LKB1 expression in H1792 lung cancer cells also correlated with increased pRTK. However, ectopic LKB1 expression in A549 and HeLaS3 cell lines, as well as H1975 activating-EGF receptor mutant lung cancer cell resulted in dephosphorylation of several tumor-enhancing RTKs, including EGF receptor, ErbB2, hepatocyte growth factor receptor (c-Met), EphA2, rearranged during transfection (RET), and insulin-like growth factor I receptor. Receptor abrogation correlated with attenuation of phospho-Akt and increased apoptosis. Global phosphatase inhibition by orthovanadate or depletion of protein tyrosine phosphatases (PTPs) resulted in the recovery of receptor phosphorylation. Specifically, the activity of SHP-2, PTP-1β, and PTP-PEST was enhanced by LKB1-expressing cells. Our findings provide novel insight on how LKB1 loss of expression or function promotes aberrant RTK signaling and rapid growth of cancer cells.

Necrotic renal epithelial cell inhibits renal interstitial fibroblast activation: role of protein tyrosine phosphatase 1B

Our recent studies showed that contents of necrotic renal proximal tubular cells (RPTC) from 2 × 10(6) cells/ml directly induced death of cultured renal interstitial fibroblasts. However, it remains unknown whether nonlethal number of necrotic RPTC would also alter the fate of renal interstitial fibroblasts. To address this issue, renal interstitial fibroblasts (NRK-49F) were exposed to necrotic RPTC supernatant (RPTC-Sup) obtained from 2 × 10(4) to 5 × 10(5) cells/ml. These concentrations of RPTC did not induce cell death, but led to inactivation of renal fibroblasts as indicated by reduced expression of α-smooth muscle actin and fibronectin, two hallmarks of activated fibroblasts. Concurrently, the same doses of necrotic RPTC-Sup suppressed phosphorylation of epidermal growth factor receptor (EGFR) and signal transducers and activators of transcription-3 (STAT3) in a time- and dose-dependent manner, but did not affect phosphorylation of platelet-derived growth factor receptor-β, AKT, and extracellular signal-regulated kinase 1/2. The presence of sodium orthovanadate, a general protein tyrosine phosphatase (PTP) inhibitor or TCS-401 (a selective PTP1B inhibitor), abrogated those effects of RPTC-Sup, whereas coincubation with the EGFR inhibitor (Gefitinib) or silencing of EGFR with siRNA preserved the ability of RPTC-Sup in suppressing renal fibroblast activation and STAT3 phosphorylation. Moreover, RPTC-Sup treatment induced PTP1B phosphorylation and its interaction with EGFR. Collectively, these results indicate that nonlethal necrotic RPTC-Sup can induce inactivation of renal interstitial fibroblasts, which occurs through a mechanism involved in PTP1B-mediated inhibition of EGFR signaling.

Rescue of renal hypoplasia and cystic dysplasia in Bcl-2 -/- mice expressing Bcl-2 in ureteric bud derived epithelia

Bcl-2 is the founding member of a family of proteins that influence apoptosis. Loss of bcl-2 results in renal hypoplasia/cystic dysplasia at birth. Here, we examined whether re-expression of bcl-2 throughout the ureteric bud and its derived epithelia would restore a normal renal phenotype in bcl-2 -/- mice. Re-expression of bcl-2 in the ureteric bud/collecting duct of bcl-2 -/- mice increased nephron numbers, diminished glomerular hypertrophy, and increased nephrogenic zone size. Unlike bcl-2 -/- mice which have gross renal cyst formation, few renal cysts were present in mice re-expressing bcl-2. We have previously shown increased apoptosis and proliferation, as well as aberrant protein tyrosine phosphatase 1B expression, accompanied cystic changes in bcl-2 -/- mice. These changes were not observed when bcl-2 was re-expressed in the ureteric bud/collecting duct system. Thus, expression of bcl-2 in the ureteric bud/collecting duct resulted in increased nephron numbers partially rescuing renal hypoplasia/cystic dysplasia in bcl-2 -/- mice.

Disruption of FAK signaling: a side mechanism in cytotoxicity

Focal adhesion kinase (FAK) is a non-receptor protein tyrosine kinase (PTK) which acts as an early modulator in the integrin signaling cascade. FAK phosphorylation and its consequent activation regulate several basic biological cellular functions. On the contrary, dysregulation of FAK signaling is implicated in the malignant transformation of cells, as well as in nonmalignant pathological conditions. With respect to cytotoxicity, accumulating data indicate that FAK participates in the mechanism of action of the known cytotoxic reactive oxygen species (ROS). Additionally, evidence was presented that different cytotoxic substances, such as arsenic (As), lead (Pb), acrylamide, methylisothiazolinone (MIT), dichlorovinylcysteine (DCVC) and halothane, acted, at least in part, by downregulating FAK tyrosine phosphorylation, while the bacterial toxins Pasteurella multocida toxin and Escherichia coli cytotoxic necrotizing factor, have been shown to exert cytotoxic effects by inducing FAK tyrosine phosphorylation. The observation that upregulation as well as downregulation of FAK activity both result in cytotoxic effects seems contradictory. Even though a common mode of action, with respect to the dysregulation of FAK signaling, for these cytotoxic substances has not yet been discovered, a cumulative approach could be established by focusing on FAK activation and signaling cascade. According to these data, interfering with FAK signaling might be of a potential use in blocking these cytotoxic effects. Further studies are needed on the possible implication of FAK in substance-induced cytotoxicity, as well as the possibility that such effects might be hindered or even blocked by restoring FAK signaling.

Structural basis of interaction between protein tyrosine phosphatase PCP-2 and beta-catenin

PCP-2 is a member of receptor-like protein tyrosine phosphatase of the MAM domain family. To investigate which part of PCP-2 was involved in its interaction with beta-catenin, we constructed various deletion mutants of PCP-2. These PCP-2 mutants and wild-type PCP-2 were co-transfected into BHK-21 cells with beta-catenin individually. An in vivo binding assay revealed that the expression of wild-type PCP-2, PCP-2 deltaC1C2 (deleted PCP-2 without both PTP domains) and PCP-2 deltaC2 (deleted PCP-2 without the second PTP domain) could be immunoprecipitated by anti-catenin antibody in every co-transfection, but PCP-2 EXT (deleted PCP-2 without the juxtamembrane region and both PTP domains) was missing, which implied that PCP-2 and beta-catenin could associate directly and the juxtamembrane region in PCP-2 was sufficient for the process.

Cytoskeletal remodeling in vascular smooth muscle cells in response to angiotensin II-induced activation of the SHP-2 tyrosine phosphatase

Angiotensin II is an octapeptide that regulates diverse cellular responses including the actin cytoskeletal organization. In this study, stable cell lines overexpressing wild-type or catalytically inactive SHP-2 were employed to elucidate the signaling pathway utilized by the SHP-2 tyrosine phosphatase that mediates an angiotensin II-induced reorganization of the actin cytoskeleton in vascular smooth muscle cells (VSMC). The expression of wild-type SHP-2 prevented an angiotensin II dependent increase in stress fiber formation. In contrast, the catalytically inactive mutant SHP-2 increased stress fiber formation. Additional observations further established that SHP-2 regulates the reorganization of the actin cytoskeleton through RhoA- and Vav2-dependent signaling pathways. The expression of wild-type SHP-2 caused a dephosphorylation of several focal adhesion associated proteins including paxillin, p130Cas, and tensin in VSMC. This dephosphorylation of focal adhesion associated proteins was accompanied by significantly decreased numbers of focal adhesions within cells. These results demonstrate a unique role for SHP-2 in the regulation of the cellular architecture of VSMC, suggesting the possibility that this phosphatase might be instrumental in vascular remodeling.

Protein phosphatase-2A regulates protein tyrosine phosphatase activity in Lewis lung carcinoma tumor variants

Cellular adherence and motility are processes that are controlled by focal adhesion assembly and disassembly. Consequently, the dynamics of focal adhesions regulate tumor cell metastasis and are influenced by the tyrosine phosphorylation state of paxillin. Metastatic LLC cells are more migratory and have reduced paxillin tyrosine phosphorylation as compared to nonmetastatic LLC cells. In nonmetastatic Lewis lung carcinoma (LLC) tumor cells, inhibition of the serine/threonine protein phosphatase-2A (PP-2A) activity results in increased motility that is associated with a reduction in the phosphotyrosine content of paxillin. Studies to determine if PP-2A can regulate protein tyrosine phosphatase activity showed that blocking PP-2A activity of nonmetastatic LLC-C8 tumor cells with okadaic acid reduces protein tyrosine phosphatase activity. Among the tyrosine phosphatases whose activity was inhibited upon PP-2A inhibition is Shp-2. In contrast, protein levels of Shp-2 are unaffected by PP-2A inhibition. While these results do not fully identify how inhibition of PP-2A results in tyrosine dephosphorylation of paxillin, they do demonstrate that PP-2A can link serine/threonine and tyrosine signaling pathways by regulating protein tyrosine phosphatases.

Angiotensin II triggers EGFR tyrosine kinase-dependent Ca2+ influx in afferent arterioles

We previously reported that inhibition of epidermal growth factor receptor tyrosine kinase activity attenuates renal arteriolar contractile responses to angiotensin II. We performed the present experiments to determine if epidermal growth factor receptor tyrosine kinase activity contributes to the afferent arteriolar intracellular [Ca2+] response to angiotensin II. Afferent arterioles were dissected from rat kidney and intracellular [Ca2+] was monitored with the use of fura-2. In normal Ringer's bath containing 1.5 mmol/L Ca2+, basal intracellular [Ca2+] averaged 95+/-7 nmol/L and 100 nmol/L angiotensin II caused a rapid rise (peak Delta=75+/-10 nmol/L) that waned to a plateau averaging 24+/-5 nmol/L above baseline. Pretreatment with 100 nmol/L AG1478 (epidermal growth factor receptor tyrosine kinase inhibitor) reduced both the peak and the plateau stages of the angiotensin II response (peak Delta=42+/-7 nmol/L; plateau Delta=8+/-4 nmol/L). A structurally unrelated epidermal growth factor receptor tyrosine kinase inhibitor also suppressed the peak response to angiotensin II, whereas tyrosine phosphatase inhibition enhanced the plateau phase of the response. In the presence of 100 nmol/L extracellular Ca2+, the angiotensin II response was characterized by a peak of diminished magnitude (Delta=49+/-10 nmol/L; P<0.05 versus the response in normal Ringer's bath) with no plateau, and this response was unaffected by AG1478. Moreover, angiotensin II stimulation of divalent cation influx (Mn2+ quench of fura-2 fluorescence) was decreased significantly by AG1478. We conclude that epidermal growth factor receptor tyrosine kinase activity contributes to the afferent arteriolar intracellular [Ca2+] response to angiotensin II and that this process involves promotion of Ca2+ influx.

Sustained activation of MAPK/ERKs signaling pathway in cystic kidneys from bcl-2 -/- mice

Cell proliferation, survival, and differentiation are carefully orchestrated processes during nephrogenesis that become aberrant during renal cyst formation. Signaling through focal adhesion kinase (FAK) impacts these processes, although its role during nephrogenesis requires further delineation. We previously demonstrated that phosphorylation of FAK and paxillin is not downregulated in cystic kidneys from B cell lymphoma/leukemia-2 (bcl-2) -/- mice. Here we examine whether FAK downstream signaling pathways are affected in these cystic kidneys. Cystic kidneys from bcl-2 -/- mice exhibited sustained phosphorylation of Src and mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK, ERK1). However, similar levels of expression were noted for phosphorylated c-Jun NH(2)-terminal kinase, phosphatidylinositol-3-kinase, and its target protein kinase B/ATP-dependent tyrosine kinase in kidneys from postnatal day 20 bcl-2 +/+ and bcl-2 -/- mice. We also examined expression of the adapter protein Shc, implicated in growth and apoptosis. Expression of p66(Shc) decreases to low levels in postnatal kidneys, whereas p52/p46(Shc) was constitutively expressed during nephrogenesis. Shc expression was similar in normal and cystic kidneys. Therefore, sustained activation of MAPK/ERKs through the Src/FAK pathway may contribute to the hyperproliferation observed in cystic kidneys from bcl-2 -/- mice.