Activation of Src and transformation by an RPTPα splice mutant found in human tumours

Glucose-mediated N-glycosylation of RPTPα affects its subcellular localization and Src activation

Receptor-type protein tyrosine phosphatase α (RPTPα) is one of the typical PTPs that play indispensable roles in many cellular processes associated with cancers. It has been considered as the most powerful regulatory oncogene for Src activation, however it is unclear how its biological function is regulated by post-translational modifications. Here, we show that the extracellular segment of RPTPα is highly N-glycosylated precisely at N21, N36, N68, N80, N86, N104 and N124 sites. Such N-glycosylation modifications mediated by glucose concentration alter the subcellular localization of RPTPα from Golgi apparatus to plasma membrane, enhance the interaction of RPTPα with Src, which in turn enhances the activation of Src and ultimately promotes tumor development. Our results identified the N-glycosylation modifications of RPTPα, and linked it to glucose starvation and Src activation for promoting tumor development, which provides new evidence for the potential antitumor therapy.

Regulation of Src Family Kinases during Colorectal Cancer Development and Its Clinical Implications

Src family kinases (SFKs) are non-receptor kinases that play a critical role in the pathogenesis of colorectal cancer (CRC). The expression and activity of SFKs are upregulated in patients with CRC. Activation of SFKs promotes CRC cell proliferation, metastases to other organs and chemoresistance, as well as the formation of cancer stem cells (CSCs). The enhanced expression level of Src is associated with decreased survival in patients with CRC. Src-mediated regulation of CRC progression involves various membrane receptors, modulators, and suppressors, which regulate Src activation and its downstream targets through various mechanisms. This review provides an overview of the current understanding of the correlations between Src and CRC progression, with a special focus on cancer cell proliferation, invasion, metastasis and chemoresistance, and formation of CSCs. Additionally, this review discusses preclinical and clinical strategies to improve the therapeutic efficacy of drugs targeting Src for treating patients with CRC.

PTPRA Phosphatase Regulates GDNF-Dependent RET Signaling and Inhibits the RET Mutant MEN2A Oncogenic Potential

The RET proto-oncogene encodes receptor tyrosine kinase, expressed primarily in tissues of neural crest origin. De-regulation of RET signaling is implicated in several human cancers. Recent phosphatome interactome analysis identified PTPRA interacting with the neurotrophic factor (GDNF)-dependent RET-Ras-MAPK signaling-axis. Here, by identifying comprehensive interactomes of PTPRA and RET, we reveal their close physical and functional association. The PTPRA directly interacts with RET, and using the phosphoproteomic approach, we identify RET as a direct dephosphorylation substrate of PTPRA both in vivo and in vitro. The protein phosphatase domain-1 is indispensable for the PTPRA inhibitory role on RET activity and downstream Ras-MAPK signaling, whereas domain-2 has only minor effect. Furthermore, PTPRA also regulates the RET oncogenic mutant variant MEN2A activity and invasion capacity, whereas the MEN2B is insensitive to PTPRA. In sum, we discern PTPRA as a novel regulator of RET signaling in both health and cancer.

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PTPRA inhibits ligand (GDNF-GFRα1)-mediated RET activity on Ras-MAPK signaling axis

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PTPRA dephosphorylate RET on key functional phosphotyrosine sites

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PTPRA catalytic (PTPase) domain 1 regulates RET-driven signaling

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PTPRA suppresses RET oncogenic mutant MEN2A in both Ras-MAPK and cell invasion models

Protein tyrosine phosphatases: promising targets in pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is the most common type of pancreatic cancer. It is the fourth leading cause of cancer-related death and is associated with a very poor prognosis. KRAS driver mutations occur in approximately 95% of PDAC cases and cause the activation of several signaling pathways such as mitogen-activated protein kinase (MAPK) pathways. Regulation of these signaling pathways is orchestrated by feedback loops mediated by the balance between protein tyrosine kinases (PTKs) and protein tyrosine phosphatases (PTPs), leading to activation or inhibition of its downstream targets. The human PTPome comprises 125 members, and these proteins are classified into three distinct families according to their structure. Since PTP activity description, it has become clear that they have both inhibitory and stimulatory effects on cancer-associated signaling processes and that deregulation of PTP function is closely associated with tumorigenesis. Several PTPs have displayed either tumor suppressor or oncogenic characteristics during the development and progression of PDAC. In this sense, PTPs have been presented as promising candidates for the treatment of human pancreatic cancer, and many PTP inhibitors have been developed since these proteins were first associated with cancer. Nevertheless, some challenges persist regarding the development of effective and safe methods to target these molecules and deliver these drugs. In this review, we discuss the role of PTPs in tumorigenesis as tumor suppressor and oncogenic proteins. We have focused on the differential expression of these proteins in PDAC, as well as their clinical implications and possible targeting for pharmacological inhibition in cancer therapy.

Protein tyrosine phosphatase alpha inhibits hypothalamic leptin receptor signaling and regulates body weight in vivo

Understanding how body weight is regulated at the molecular level is essential for treating obesity. We show that female mice genetically lacking protein tyrosine phosphatase (PTP) receptor type α (PTPRA) exhibit reduced weight and adiposity and increased energy expenditure, and are more resistant to diet-induced obesity than matched wild-type control mice. These mice also exhibit reduced levels of circulating leptin and are leptin hypersensitive, suggesting that PTPRA inhibits leptin signaling in the hypothalamus. Male and female PTPRA-deficient mice fed a high-fat diet were leaner and displayed increased metabolic rates and lower circulating leptin levels, indicating that the effects of loss of PTPRA persist in the obese state. Molecularly, PTPRA down-regulates leptin receptor signaling by dephosphorylating the receptor-associated kinase JAK2, with which the phosphatase associates constitutively. In contrast to the closely related tyrosine phosphatase ε, leptin induces only weak phosphorylation of PTPRA at its C-terminal regulatory site Y789, and this does not affect the activity of PTPRA toward JAK2. PTPRA is therefore an inhibitor of hypothalamic leptin signaling in vivo and may prevent premature activation of leptin signaling, as well as return signaling to baseline after exposure to leptin.-Cohen-Sharir, Y., Kuperman, Y., Apelblat, D., den Hertog, J., Spiegel, I., Knobler, H., Elson, A. Protein tyrosine phosphatase alpha inhibits hypothalamic leptin receptor signaling and regulates body weight in vivo.

Dasatinib, a Src inhibitor, sensitizes liver metastatic colorectal carcinoma to oxaliplatin in tumors with high levels of phospho-Src

Despite the development of new antineoplastic agents for the treatment of colorectal cancer (CRC), oxaliplatin and fluoropyrimidines remain the most commonly employed drugs for the treatment of both early and advanced disease. Intrinsic or acquired resistance is, however, an important limitation to pharmacological therapy, and the development of chemosensitization strategies constitute a major goal with important clinical implications. In the present work, we determined that high levels of activated Src kinase, measured as phospho-Src at the Tyr419 residue in CRC cell lines, can promote colorectal carcinoma cell resistance to oxaliplatin, but not to 5-fluorouracil (5FU), and that inhibition of this protein restores sensitivity to oxaliplatin. Similar results were observed with in vivo patient-derived xenograft (PDX) models that were orthotopically grown in murine livers. In PDX tumor lines derived from human CRC liver metastasis, dasatinib, a Src inhibitor, increases sensitivity to oxaliplatin only in tumors with high p-Src. However, dasatinib did not modify sensitivity to 5FU in any of the models. Our data suggest that chemoresistance induced by p-Src is specific to oxaliplatin, and that p-Src levels can be used to identify patients who may benefit from this combination therapy. These results are relevant for clinicians as they identify a novel biomarker of drug resistance that is suitable to pharmacological manipulation.

Src SUMOylation Inhibits Tumor Growth Via Decreasing FAK Y925 Phosphorylation

Src, a non-receptor tyrosine kinase protein, plays a critical role in cell proliferation and tumorigenesis. SUMOylation, a reversible ubiquitination-like post-translational modification, is vital for tumor progression. Here, we report that the Src protein can be SUMOylated at lysine 318 both in vitro and in vivo. Hypoxia can induce a decrease of Src SUMOylation along with an increase of Y419 phosphorylation, a phosphorylation event required for Src activation. On the other hand, treatment with hydrogen peroxide can enhance Src SUMOylation. Significantly, ectopic expression of SUMO-defective mutation, Src K318R, promotes tumor growth more potently than that of wild-type Src, as determined by migration assay, soft agar assay, and tumor xenograft experiments. Consistently, Src SUMOylation leads to a decrease of Y925 phosphorylation of focal adhesion kinase (FAK), an established regulatory event of cell migration. Our results suggest that SUMOylation of Src at lysine 318 negatively modulate its oncogenic function by, at least partially, inhibiting Src-FAK complex activity.

Stepping out of the shadows: Oncogenic and tumor-promoting protein tyrosine phosphatases

Protein tyrosine phosphorylation is critical for proper function of cells and organisms. Phosphorylation is regulated by the concerted but generically opposing activities of tyrosine kinases (PTKs) and tyrosine phosphatases (PTPs), which ensure its proper regulation, reversibility, and ability to respond to changing physiological situations. Historically, PTKs have been associated mainly with oncogenic and pro-tumorigenic activities, leading to the generalization that protein dephosphorylation is anti-oncogenic and hence that PTPs are tumor-suppressors. In many cases PTPs do suppress tumorigenesis. However, a growing body of evidence indicates that PTPs act as dominant oncogenes and drive cell transformation in a number of contexts, while in others PTPs support transformation that is driven by other oncogenes. This review summarizes the known transforming and tumor-promoting activities of the classical, tyrosine specific PTPs and highlights their potential as drug targets for cancer therapy.

Csk-homologous kinase (Chk) is an efficient inhibitor of Src-family kinases but a poor catalyst of phosphorylation of their C-terminal regulatory tyrosine

Background

C-terminal Src kinase (Csk) and Csk-homologous kinase (Chk) are the major endogenous inhibitors of Src-family kinases (SFKs). They employ two mechanisms to inhibit SFKs. First, they phosphorylate the C-terminal tail tyrosine which stabilizes SFKs in a closed inactive conformation by engaging the SH2 domain in cis. Second, they employ a non-catalytic inhibitory mechanism involving direct binding of Csk and Chk to the active forms of SFKs that is independent of phosphorylation of their C-terminal tail. Csk and Chk are co-expressed in many cell types. Contributions of the two mechanisms towards the inhibitory activity of Csk and Chk are not fully clear. Furthermore, the determinants in Csk and Chk governing their inhibition of SFKs by the non-catalytic inhibitory mechanism are yet to be defined.

Methods

We determined the contributions of the two mechanisms towards the inhibitory activity of Csk and Chk both in vitro and in transduced colorectal cancer cells. Specifically, we assayed the catalytic activities of Csk and Chk in phosphorylating a specific peptide substrate and a recombinant SFK member Src. We employed surface plasmon resonance spectroscopy to measure the kinetic parameters of binding of Csk, Chk and their mutants to a constitutively active mutant of the SFK member Hck. Finally, we determined the effects of expression of recombinant Chk on anchorage-independent growth and SFK catalytic activity in Chk-deficient colorectal cancer cells.

Results

Our results revealed Csk as a robust enzyme catalysing phosphorylation of the C-terminal tail tyrosine of SFKs but a weak non-catalytic inhibitor of SFKs. In contrast, Chk is a poor catalyst of SFK tail phosphorylation but binds SFKs with high affinity, enabling it to efficiently inhibit SFKs with the non-catalytic inhibitory mechanism both in vitro and in transduced colorectal cancer cells. Further analyses mapped some of the determinants governing this non-catalytic inhibitory mechanism of Chk to its kinase domain.

Conclusions

SFKs are activated by different upstream signals to adopt multiple active conformations in cells. SFKs adopting these conformations can effectively be constrained by the two complementary inhibitory mechanisms of Csk and Chk. Furthermore, the lack of this non-catalytic inhibitory mechanism accounts for SFK overactivation in the Chk-deficient colorectal cancer cells.

Electronic supplementary material

The online version of this article (doi:10.1186/s12964-017-0186-x) contains supplementary material, which is available to authorized users.

Increased PTPRA expression leads to poor prognosis through c-Src activation and G1 phase progression in squamous cell lung cancer

PTPRA is reported to be involved in cancer development and progression through activating the Src family kinase (SFK) signaling pathways, however, the roles of PTPRA in the squamous cell lung cancer (SCC) development are unclear. The purpose of this study was to clarify the clinical relevance and biological roles of PTPRA in SCC. We found that PTPRA was upregulated in squamous cell lung cancer compared to matched normal tissues at the mRNA (N=20, P=0.004) and protein expression levels (N=75, P<0.001). Notably, high mRNA level of PTPRA was significantly correlated with poorer prognosis in 675 SCC patients from the Kaplan-Meier plotter database. With 75 cases, we found that PTPRA protein expression was significantly correlated with tumor size (P=0.002), lymph node metastasis (P=0.008), depth of tumor invasion (P<0.001) and clinical stage (P<0.001). The Kaplan-Meier plot suggested that high expression of PTPRA had poorer overall survival in SCC patients (P=0.009). Multivariate Cox regression analysis suggested that PTPRA expression was an independent prognostic factor in SCC patients. In the cellular models, PTPRA promotes SCC cell proliferation through modulating Src activation as well as cell cycle progression. In conclusion, higher PTPRA level was associated with worse prognosis of SCC patients and PTPRA could promote the cell cycle progression through stimulating the c-Src signaling pathways.

Cell Transformation by PTP1B Truncated Mutants Found in Human Colon and Thyroid Tumors

Expression of wild-type protein tyrosine phosphatase (PTP) 1B may act either as a tumor suppressor by dysregulation of protein tyrosine kinases or a tumor promoter through Src dephosphorylation at Y527 in human breast cancer cells. To explore whether mutated PTP1B is involved in human carcinogenesis, we have sequenced PTP1B cDNAs from human tumors and found splice mutations in ~20% of colon and thyroid tumors. The PTP1BΔE6 mutant expressed in these two tumor types and another PTP1BΔE5 mutant expressed in colon tumor were studied in more detail. Although PTP1BΔE6 revealed no phosphatase activity compared with wild-type PTP1B and the PTP1BΔE5 mutant, its expression induced oncogenic transformation of rat fibroblasts without Src activation, indicating that it involved signaling pathways independent of Src. The transformed cells were tumourigenic in nude mice, suggesting that the PTP1BΔE6 affected other molecule(s) in the human tumors. These observations may provide a novel therapeutic target for colon and thyroid cancer.

Regulation of RPTPα-c-Src signalling pathway by miR-218

Receptor protein tyrosine phosphatase alpha (RPTPα), an activator of Src family kinases, is found significantly overexpressed in human cancer tissues. However, little is known about the regulation of RPTPα expression. miRNAs target multiple genes and play important roles in many cancer processes. Here, we identified a miRNA, miR-218 that binds directly to the 3'-UTR of RPTPα. Ectopic overexpression of miR-218 decreased RPTPα protein leading to decreased dephosphorylation of c-Src and decreased tumour growth in vitro and in vivo. A feedback loop between c-Src and miR-218 was revealed where c-Src inhibits transcription of SLIT2, which intronically hosts miR-218. These results show a novel regulatory pathway for RPTPα-c-Src signalling.

An RPTPα/Src family kinase/Rap1 signaling module recruits myosin IIB to support contractile tension at apical E-cadherin junctions

Cell-cell adhesion couples the contractile cortices of epithelial cells together, generating tension to support a range of morphogenetic processes. E-cadherin adhesion plays an active role in generating junctional tension by promoting actin assembly and cortical signaling pathways that regulate myosin II. Multiple myosin II paralogues accumulate at mammalian epithelial cell-cell junctions. Earlier, we found that myosin IIA responds to Rho-ROCK signaling to support junctional tension in MCF-7 cells. Although myosin IIB is also found at the zonula adherens (ZA) in these cells, its role in junctional contractility and its mode of regulation are less well understood. We now demonstrate that myosin IIB contributes to tension at the epithelial ZA. Further, we identify a receptor type-protein tyrosine phosphatase alpha-Src family kinase-Rap1 pathway as responsible for recruiting myosin IIB to the ZA and supporting contractile tension. Overall these findings reinforce the concept that orthogonal E-cadherin-based signaling pathways recruit distinct myosin II paralogues to generate the contractile apparatus at apical epithelial junctions.

Focal adhesion kinase regulates the phosphorylation protein tyrosine phosphatase-α at Tyr789 in breast cancer cells

Protein tyrosine phosphatase (PTP)‑α regulates the phosphorylation of focal adhesion kinase (FAK), which is important in cellular signal transduction and integration of proteins. It has been demonstrated that a FAK‑Del33 mutation (deletion of exon 33; KF437463) in breast cancer tissues regulates cell migration through FAK/Src signaling activation. However, the detailed pathway for Src activation with FAK‑Del33 remains to be elucidated. The present study used a retroviral expression system to examine changes in PTPα phosphorylation affected by the FAK‑Del33 protein in breast cancer cells. Small interfering (si)RNA targeting PTPα interfered with the phosphorylation of Src. Wound‑healing and migration assays were performed to identify cell morphology and quantitative analysis was performed by examining band color depth in western blot analysis. Significant differences were observed in the phosphorylation level of PTPα at Tyr789 between the FAK‑Del33 and the wild‑type breast cancer cells, suggesting that FAK regulated the phosphorylation level of PTPα at Tyr789 in breast cancer mutant FAK‑Del33 cells. The gene expression profile with FAK siRNA did not alter the levels of phosphorylation in other mutants, including autophosphorylation disability (Y397F), ATP kinase dominant negative (K454R) and protein 4.1, ezrin, radixin, moesin domain attenuate (Δ375). FAK RNAi inhibited the activity of the FAK‑Del33 at the Src site and rescued the elevated cell migration and invasion. The present study demonstrated for the first time, to the best of our knowledge, an increase in the phosphorylation level of PTPα‑Tyr789 by its upstream activator, FAK‑Del33, leading to Src activation in certain breast cancer cells, which has significant implications for metastatic potential.

SUMOylation of Grb2 enhances the ERK activity by increasing its binding with Sos1

Background

Grb2 (Growth factor receptor-bound protein 2) is a key adaptor protein in maintaining the ERK activity via linking Sos1 (Son of sevenless homolog 1) or other proteins to activated RTKs, such as EGFR. Currently, little knowledge is available concerning the post-translational modification (PTM) of Grb2 except for its phosphorylation. Since emerging evidences have highlighted the importance of SUMOylation (Small ubiquitin-related modifier), a reversible PTM, in modulating protein functions, we wondered if Grb2 could be SUMOylated and thereby influences its functions especially involved in the Ras/MEK/ERK pathway.

Methods

SUMOylation of Grb2 was analyzed with the in vivo SUMOylation assay using the Ni²⁺-NTA affinity pulldown and the in vitro E.coli-based SUMOylation assay. To test the ERK activity and cell transformation, the murine fibroblast cell line NIH/3T3 and the murine colon cancer cell line CMT-93 were used for the experiments including Grb2 knockdown, ectopic re-expression, cell transformation and migration. Immunoprecipitation (IP) was employed for seeking proteins that interact with SUMO modified Grb2. Xenograft tumor model in mice was conducted to verify that Grb2 SUMOylation regulated tumorigenesis in vivo.

Results

Grb2 can be SUMOylated by SUMO1 at lysine 56 (K⁵⁶), which is located in the linker region between the N-terminal SH3 domain and the SH2 domain. Knockdown of Grb2 reduced the ERK activity and suppressed cell motility and tumorigenesis in vitro and in vivo, which were all rescued by stable ectopic re-expression of wild-type Grb2 but not the mutant Grb2^K56R. Furthermore, Grb2 SUMOylation at K⁵⁶ increased the formation of Grb2-Sos1 complex, which sequentially leads to the activation of Ras/MEK/MAPK pathway.

Conclusions

Our results provide evidences that Grb2 is SUMOylated in vivo and this modification enhances ERK activities via increasing the formation of Grb2-Sos1 complex, and may consequently promote cell motility, transformation and tumorigenesis.

RPTPα controls epithelial adherens junctions, linking E-cadherin engagement to c-Src-mediated phosphorylation of cortactin

Epithelial junctions are fundamental determinants of tissue organization, subject to regulation by tyrosine phosphorylation. Homophilic binding of E-cadherin activates tyrosine kinases, such as Src, that control junctional integrity. Protein tyrosine phosphatases (PTPs) also contribute to cadherin-based adhesion and signaling, but little is known about their specific identity or functions at epithelial junctions. Here, we report that the receptor PTP RPTPα (human gene name PTPRA) is recruited to epithelial adherens junctions at the time of cell-cell contact, where it is in molecular proximity to E-cadherin. RPTPα is required for appropriate cadherin-dependent adhesion and for cyst architecture in three-dimensional culture. Loss of RPTPα impairs adherens junction integrity, as manifested by defective E-cadherin accumulation and peri-junctional F-actin density. These effects correlate with a role for RPTPα in cellular (c)-Src activation at sites of E-cadherin engagement. Mechanistically, RPTPα is required for appropriate tyrosine phosphorylation of cortactin, a major Src substrate and a cytoskeletal actin organizer. Expression of a phosphomimetic cortactin mutant in RPTPα-depleted cells partially rescues F-actin and E-cadherin accumulation at intercellular contacts. These findings indicate that RPTPα controls cadherin-mediated signaling by linking homophilic E-cadherin engagement to cortactin tyrosine phosphorylation through c-Src.

Receptor protein-tyrosine phosphatase α regulates focal adhesion kinase phosphorylation and ErbB2 oncoprotein-mediated mammary epithelial cell motility

We investigated the role of protein-tyrosine phosphatase α (PTPα) in regulating signaling by the ErbB2 oncoprotein in mammary epithelial cells. Using this model, we demonstrated that activation of ErbB2 led to the transient inactivation of PTPα, suggesting that attenuation of PTPα activity may contribute to enhanced ErbB2 signaling. Furthermore, RNAi-induced suppression of PTPα led to increased cell migration in an ErbB2-dependent manner. The ability of ErbB2 to increase cell motility in the absence of PTPα was characterized by prolonged interaction of GRB7 with ErbB2 and increased association of ErbB2 with a β1-integrin-rich complex, which depended on GRB7-SH2 domain interactions. Finally, suppression of PTPα resulted in increased phosphorylation of focal adhesion kinase on Tyr-407, which induced the recruitment of vinculin and the formation of a novel focal adhesion kinase complex in response to ErbB2 activation in mammary epithelial cells. Collectively, these results reveal a new role for PTPα in the regulation of motility of mammary epithelial cells in response to ErbB2 activation.

Protein tyrosine phosphatases as novel targets in breast cancer therapy

Breast cancer is linked to hyperactivation of protein tyrosine kinases (PTKs), and recent studies have unveiled that selective tyrosine dephosphorylation by protein tyrosine phosphatases (PTPs) of specific substrates, including PTKs, may activate or inactivate oncogenic pathways in human breast cancer cell growth-related processes. Here, we review the current knowledge on the involvement of PTPs in breast cancer, as major regulators of breast cancer therapy-targeted PTKs, such as HER1/EGFR, HER2/Neu, and Src. The functional interplay between PTKs and PTK-activating or -inactivating PTPs, and its implications in novel breast cancer therapies based on targeting of specific PTPs, are discussed.

PTPα-mediated Src activation by EGF in human breast cancer cells

Protein tyrosine phosphatase alpha (PTPα) functions as an activator of Src by dephosphorylating Tyr527/530, a critical negative regulatory site. The increase of PTPα catalytic activity requires its phosphorylation at Ser180 and/or Ser204 and its dissociation from PTPα/Grb2 complex. Here, we show that epidermal growth factor (EGF) stimulation increases the ability of PTPα to activate Src by dephosphorylating Tyr530 in BT-20 and SKBR3 breast cancer cell lines. Treatment of these cells with EGF transiently decreased the association of PTPα with Grb2 and enhanced PTPα catalytic activity via Ser180 and Ser204 phosphorylation that was blocked by the protein kinase C delta (PKCδ) inhibitor rottlerin or knockdown of PKCδ by siRNA or by the overexpression of PTPαS180A/S204A mutant. PTPα siRNA blocked EGF-mediated Src activation in cancer cells and inhibited on colony formation, whereas control siRNA did not. These results suggested that PTPα links activation of epidermal growth factor receptor (EGFR) signaling with Src activation and may provide a novel therapeutic target for treatment of breast cancer.

Protein tyrosine phosphatases in cancer: friends and foes!

Tyrosine phosphorylation of proteins serves as an exquisite switch in controlling several key oncogenic signaling pathways involved in cell proliferation, apoptosis, migration, and invasion. Since protein tyrosine phosphatases (PTPs) counteract protein kinases by removing phosphate moieties on target proteins, one may intuitively think that PTPs would act as tumor suppressors. Indeed, one of the most described PTPs, namely, the phosphatase and tensin homolog (PTEN), is a tumor suppressor. However, a growing body of evidence suggests that PTPs can also function as potent oncoproteins. In this chapter, we provide a broad historical overview of the PTPs, their mechanism of action, and posttranslational modifications. Then, we focus on the dual properties of classical PTPs (receptor and nonreceptor) and dual-specificity phosphatases in cancer and summarize the current knowledge of the signaling pathways regulated by key PTPs in human cancer. In conclusion, we present our perspective on the potential of these PTPs to serve as therapeutic targets in cancer.

Oncogenic signaling by tyrosine kinases of the SRC family in advanced colorectal cancer

The non-receptor tyrosine kinases of the SRC family (SFK) play important roles in signal transduction induced by a large variety of extracellular stimuli, including growth factors and Integrins. When deregulated, SFKs show oncogenic activity, as originally reported for v-Src, the transforming product of the avian retrovirus RSV, and then, in many human cancers, particularly colorectal cancer (CRC). In CRC, SFK deregulation largely occurs in the absence of mutations of the corresponding genes, but the underlying molecular mechanisms involved are still unclear. In addition to a role in early tumor progression, SFK deregulation may also be important in advanced CRC, as suggested by the association between increased SFK activity and poor clinical outcome. However, SFK contribution to CRC metastasis formation is still poorly documented. Here, we will review recent findings that broaden our understanding of the mechanisms underlying SFK deregulation and signaling in advanced CRC. We will also discuss the implication of these observations for SFK-based therapy in metastatic CRC.

Traditional Chinese medicine as dual guardians against hypertension and cancer?

This study utilizes the comprehensive traditional Chinese medicine database TCM Database@Taiwan ( http://tcm.cmu.edu.tw/ ) in conjunction with structure-based and ligand-based drug design to identify multi-function Src inhibitors. The three potential TCM candidates identified as having suitable docking conformations and bioactivity profiles were Angeliferulate, (3R)-2'-hydroxy-3',4'-dimethoxyisoflavan-7-O-beta-D-glucoside (HMID), and 3-[2',6-dihydroxy-5'-(2-propenyl)[1,1'-biphenyl]3-yl]-(E)-2-propenoic acid (3PA). Molecular dynamics simulation demonstrated that the TCM candidates have more stable interactions with the cleft and in complex with Src kinase compared to Saracatinib. Angeliferulate and HMID, both originated from Angelica sinensis, not only interact with Lys298 and amino acids from different loops in the cleft, but also with Asp407 located on the activation loop. These interactions are important to reduce the opening of the activation loop due to phosphorylation, hence stabilize the Src kinase cleft structure and inhibit activation. The TCM candidates also exhibited high affinity to other cancer-related target proteins (EGFR, HER2, and HSP90). Our observations suggest that the TCM candidates might have multi-targeting effects in hypertension and cancer.