Src family kinase inhibitor PP2 efficiently inhibits cervical cancer cell proliferation through down-regulating phospho-Src-Y416 and phospho-EGFR-Y1173

c-Src inhibitor PP2 inhibits head and neck cancer progression through regulation of the epithelial-mesenchymal transition

Head and neck squamous cell carcinoma (HNSCC) is one of the most common cancer, causing considerable mortality and morbidity worldwide. Although HNSCC management has been extensively studied, the treatment outcomes have not improved - the 5-year survival rate of patients with HNSCC is 40%. Recent studies on the development of a novel HNSCC treatment have highlighted proto-oncogene tyrosine-protein kinase Src (c-Src) as one of the major therapeutic targets. However, the clinical efficacy of c-Src inhibitors against HNSCC was not comparable to that obtained in vitro. Furthermore, the molecular mechanisms underlying the efficacy of c-Src inhibitors remain elusive. In this study, we assessed the efficacy of 4-amino-5-(4-chlorophenyl)-7-(dimethylethyl)pyrazolo[3,4-d] pyrimidine (PP2), a selective c-Src inhibitor on HSNCC. Nine HNSCC cell lines (SNU1041, Fraud, SNU46, SNU1076, SNU899, SCC1483, YD15, YD9, and YD10-) were screened, and the effects of PP2 were evaluated using wound healing, apoptosis, and invasion assays. Western blot analysis of downstream markers was conducted to assess the specific mechanism of action of PP2 in HNSCC. The therapeutic efficacy of PP2 was further evaluated in xenograft mice. PP2 reduced tumor cell growth both in vitro and in vivo. Furthermore, it enhanced tumor cell apoptosis in cell lines and prevented metastasis in mice. PP2 also regulated the epithelial-mesenchymal transition pathway downstream of c-Src. More specifically, in SCC1483 and YD15PP2 HNSCC cell lines, PP2 exposure downregulated Erk, Akt/Slug, and Snail but upregulated E-cadherin. These results suggest that PP2 inhibits cell growth and progression in HNSCC by regulating the epithelial-mesenchymal transition pathway.

Pyrazolo[3,4-d]pyrimidine scaffold: A review on synthetic approaches and EGFR and VEGFR inhibitory activities

The pyrazolo[3,4-d]pyrimidine core has received a lot of interest from the medicinal chemistry community as a promising framework for drug design and discovery. It is an isostere of the adenine ring of adenosine triphosphate, which allows it to mimic kinase active site hinge region binding contacts. This scaffold has a wide pharmacological and biological value, one of which is as an anticancer agent. Many successful anticancer medicines have been designed and synthesized using pyrazolo[3,4-d]pyrimidine as a key pharmacophore. The main synthetic routes of pyrazolo[3,4-d]pyrimidines as well as their recent developments as promising anticancer agents acting as endothelial growth factor receptors and vascular endothelial growth factor receptor inhibitors, published in the time frame from 1999 to 2022, are summarized in this review to set the direction for the design and synthesis of novel pyrazolo[3,4-d]pyrimidine derivatives for clinical deployment in cancer treatment.

Phosphorylation-mediated interaction between human E26 transcription factor 1 and specific protein 1 is required for tumor cell migration

Transcription factors, human E26 transcription factor 1 (Ets1) and specific protein 1 (Sp1), are known to induce gene expression in tumorigenicity. High Ets1 expression is often associated with colorectal tumorigenesis. In this study, we discover that metastasis and clone formation in SW480 cells mainly depend on the direct interaction between Ets1 and Sp1 instead of high Ets1 expression. The interaction domains are further addressed to be the segment at Sp1(626-708) and the segment at Ets1(244-331). In addition, the phosphorylation inhibition of Ets1 at Tyr283 by either downregulation of Src kinase or Src family inhibitor treatment decreases the interaction between Sp1 and Ets1 and suppresses SW480 migration. Either administration or overexpression of the peptides harboring the interaction segment strongly inhibits the colony formation and migration of SW480 cells. Our findings suggest that the interaction between Ets1 and Sp1 rather than Ets1 alone promotes transformation in SW480 cells and provide new insight into the Ets1 and Sp1 interaction as an antitumour target in SW480 cells.

Senescent hepatic stellate cells promote liver regeneration through IL-6 and ligands of CXCR2

Senescent cells have long been associated with deleterious effects in aging-related pathologies, although recent studies have uncovered their beneficial roles in certain contexts, such as wound healing. We have found that hepatic stellate cells (HSCs) underwent senescence within 2 days after 2/3 partial hepatectomy (PHx) in young (2–3 months old) mice, and the elimination of these senescent cells by using the senolytic drug ABT263 or by using a genetic mouse model impaired liver regeneration. Senescent HSCs secrete IL-6 and CXCR2 ligands as part of the senescence-associated secretory phenotype, which induces multiple signaling pathways to stimulate liver regeneration. IL-6 activates STAT3, induces Yes-associated protein (YAP) activation through SRC family kinases, and synergizes with CXCL2 to activate ERK1/2 to stimulate hepatocyte proliferation. The administration of either IL-6 or CXCL2 partially restored liver regeneration in mice with senescent cell elimination, and the combination of both fully restored liver weight recovery. Furthermore, the matricellular protein central communication network factor 1 (CCN1, previously called CYR61) was rapidly elevated in response to PHx and induced HSC senescence. Knockin mice expressing a mutant CCN1 unable to bind integrin α₆β₁ were deficient in senescent cells and liver regeneration after PHx. Thus, HSC senescence, largely induced by CCN1, is a programmed response to PHx and plays a critical role in liver regeneration through signaling pathways activated by IL-6 and ligands of CXCR2.

Tyrosine Kinase Src Is a Regulatory Factor of Bone Homeostasis

Osteoclasts, which resorb the bone, and osteoblasts, which form the bone, are the key cells regulating bone homeostasis. Osteoporosis and other metabolic bone diseases occur when osteoclast-mediated bone resorption is increased and bone formation by osteoblasts is decreased. Analyses of tyrosine kinase Src-knockout mice revealed that Src is essential for bone resorption by osteoclasts and suppresses bone formation by osteoblasts. Src-knockout mice exhibit osteopetrosis. Therefore, Src is a potential target for osteoporosis therapy. However, Src is ubiquitously expressed in many tissues and is involved in various biological processes, such as cell proliferation, growth, and migration. Thus, it is challenging to develop effective osteoporosis therapies targeting Src. To solve this problem, it is necessary to understand the molecular mechanism of Src function in the bone. Src expression and catalytic activity are maintained at high levels in osteoclasts. The high activity of Src is essential for the attachment of osteoclasts to the bone matrix and to resorb the bone by regulating actin-related molecules. Src also inhibits the activity of Runx2, a master regulator of osteoblast differentiation, suppressing bone formation in osteoblasts. In this paper, we introduce the molecular mechanisms of Src in osteoclasts and osteoblasts to explore its potential for bone metabolic disease therapy.

Acetylcholine promotes the self-renewal and immune escape of CD133+ thyroid cancer cells through activation of CD133-Akt pathway

Nerves infiltrate the tumor microenvironment and stimulate the growth of cancer cells through the secretion of neurotransmitters. However, the contributions of nerves to the self-renewal capacity of cancer stem cells (CSCs) remain largely unknown. In this study, we found that CD133+ cancer cells were responsible for the initiation of thyroid cancer. Neurons were juxtaposed with CD133+ cells in thyroid cancer tissues. Acetylcholine, one of the most abundant neurotransmitters, promoted CD133 Y828 phosphorylation, and subsequently increased the interaction between CD133 and PI3K regulatory subunit p85, resulting in the activation of the PI3K-Akt pathway. Acetylcholine increased the self-renewal ability of CD133+ thyroid cancer cells through activation of CD133-Akt pathway. Furthermore, acetylcholine promoted the expression of the immune regulator PD-L1 through the activation of the CD133-Akt pathway, resulting in the resistance of CD133+ thyroid cancer cells to CD8⁺ T cells. However, acetylcholine receptor antagonist 4-DAMP blocked the positive effects of acetylcholine on the self-renewal and immune escape of CD133+ thyroid cancer cells. Taken together, these data suggest that acetylcholine increases the self-renewal and immune escape abilities of CD133+ thyroid cancer cells through the activation of the CD133-Akt pathway.

Bosutinib Acts as a Tumor Inhibitor via Downregulating Src/NF-κB/Survivin Expression in HeLa Cells

Efforts have been made to find effective medical drugs for cervical cancer treatment. The incidence of cervical cancer ranks second among women, and is a serious threat to women's health. Aberrant activation of the nonreceptor protein tyrosine kinases such as Src is commonly observed in progressive stages of human tumors. Thus, targeting Src kinase could be a promising strategy for cervical cancer therapy. In this study, we explored the potential utility of bosutinib in the treatment of cervical cancer. We found that bosutinib, as a potent dual Src/Abl inhibitor, could exert anti-tumor effects on cervical cancer. Bosutinib inhibited cervical cancer cells proliferation and colony formation ability in a dose-dependent manner, and also induced apoptosis. Mechanistically, bosutinib effectively decreased the activity of Src/NF-κB/survivin signaling pathway. Our study provided a biological rationale to test bosutinib as a valuable therapeutic option for cervical cancer patients. Anat Rec, 302:2193-2200, 2019. © 2019 American Association for Anatomy.

SMAD4-independent activation of TGF-β signaling by MUC1 in a human pancreatic cancer cell line

Pancreatic Ductal Adenocarcinoma (PDA) has a mortality rate that nearly matches its incidence rate. Transforming Growth Factor Beta (TGF-β) is a cytokine with a dual role in tumor development switching from a tumor suppressor to a tumor promoter. There is limited knowledge of how TGF-β function switches during tumorigenesis. Mucin 1 (MUC1) is an aberrantly glycosylated, membrane-bound, glycoprotein that is overexpressed in >80% of PDA cases and is associated with poor prognosis. In PDA, MUC1 promotes tumor progression and metastasis via signaling through its cytoplasmic tail (MUC1-CT) and interacting with other oncogenic signaling molecules. We hypothesize that high levels of MUC1 in PDA may be partly responsible for the TGF-β functional switch during oncogenesis. We report that overexpression of MUC1 in BxPC3 human PDA cells (BxPC3.MUC1) enhances the induction of epithelial to mesenchymal transition leading to increased invasiveness in response to exogenous TGF-β1. Simultaneously, these cells resist TGF-β induced apoptosis by downregulating levels of cleaved caspases. We show that mutating the tyrosines in MUC1-CT to phenylalanine reverses the TGF-β induced invasiveness. This suggests that the tyrosine residues in MUC1-CT are required for TGF-β induced invasion. Some of these tyrosines are phosphorylated by the tyrosine kinase c-Src. Thus, treatment of BxPC3.MUC1 cells with a c-Src inhibitor (PP2) significantly reduces TGF-β induced invasiveness. Similar observations were confirmed in the Chinese hamster ovarian (CHO) cell line. Data strongly suggests that MUC1 may regulate TGF-β function in PDA cells and thus have potential clinical relevance in the use of TGF-β inhibitors in clinical trials.

Growth inhibitory effect of the Src inhibitor dasatinib in combination with anticancer agents on uterine cervical adenocarcinoma cells

Uterine cervical adenocarcinoma has a poor clinical prognosis when compared with squamous cell carcinoma. Therefore, the development of new treatment strategies for uterine cervical adenocarcinoma is necessary. Src is a proto-oncogene that is important in cancer progression. Dasatinib is a Src inhibitor that has been reported to be effective when used in combination with anticancer drugs. The present study aimed to confirm Src expression in human cervical adenocarcinoma cell lines and to determine the mechanism underlying the inhibitory effect of dasatinib on Src signaling in vitro. Western blot analysis was performed to investigate Src expression in cervical adenocarcinoma cell lines (HeLa and TCO-2 cells). The cells were cultured for 48 h with the addition of different concentrations of anticancer drugs (paclitaxel or oxaliplatin). Viable cell count was measured using a colorimetric (WST-1) assay. The concentrations of anticancer agents were fixed according to the results obtained, and the same experiments were performed using the drugs in combination with dasatinib at various concentrations to determine the concentrations that significantly affected the number of viable cells. The presence or absence of apoptosis was investigated using a caspase-3/7 assay. Signal transduction in each cell line was examined using western blotting. Src was activated in the two cell lines, and cell proliferation was significantly suppressed by each anticancer drug in combination with 10 µM dasatinib. Caspase-3/7 activity was also increased and Src signaling was suppressed by each anticancer drug in combination with dasatinib. In conclusion, Src is overexpressed in cervical adenocarcinoma cell lines, and dasatinib inhibits intracellular Src signaling and causes apoptosis. The results of the present study suggest that Src may be targeted in novel therapeutic strategies for cervical adenocarcinoma.

Epidermal growth factor promotes cyclin G2 degradation via calpain-mediated proteolysis in gynaecological cancer cells

Cyclin G2 (CCNG2) is an atypical cyclin that functions to inhibit cell cycle progression and is often dysregulated in human cancers. We have previously shown that cyclin G2 is highly unstable and can be degraded through the ubiquitin/proteasome pathway. Furthermore, cyclin G2 contains a PEST domain, which has been suggested to act as a signal for degradation by multiple proteases. In this study, we determined if calpains, a family of calcium-dependent proteases, are also involved in cyclin G2 degradation. The addition of calpain inhibitors or silencing of calpain expression by siRNAs strongly enhanced cyclin G2 levels. On the other hand, incubation of cell lysates with purified calpains or increasing the intracellular calcium concentration resulted in a decrease in cyclin G2 levels. Interestingly, the effect of calpain was found to be dependent on the phosphorylation of cyclin G2. Using a kinase inhibitor library, we found that Epidermal Growth Factor (EGF) Receptor is involved in cyclin G2 degradation and treatment with its ligand, EGF, induced cyclin G2 degradation. In addition, the presence of the PEST domain is necessary for calpain and EGF action. When the PEST domain was completely removed, calpain or EGF treatment failed to trigger degradation of cyclin G2. Taken together, these novel findings demonstrate that EGF-induced, calpain-mediated proteolysis contributes to the rapid destruction of cyclin G2 and that the PEST domain is critical for EGF/calpain actions.

NMU signaling promotes endometrial cancer cell progression by modulating adhesion signaling

Neuromedin U (NMU) was originally named based on its strong uterine contractile activity, but little is known regarding its signaling/functions in utero. We identified that NMU and one of its receptors, NMUR2, are not only present in normal uterine endometrium but also co-expressed in endometrial cancer tissues, where the NMU level is correlated with the malignant grades and survival of patients. Cell-based assays further confirmed that NMU signaling can promote cell motility and proliferation of endometrial cancer cells derived from grade II tumors. Activation of NMU pathway in these endometrial cancer cells is required in order to sustain expression of various adhesion molecules, such as CD44 and integrin alpha1, as well as production of their corresponding extracellular matrix ligands, hyaluronan and collagen IV; it also increased the activity of SRC and its downstream proteins RHOA and RAC1. Thus, it is concluded that NMU pathway positively controls the adhesion signaling-SRC-Rho GTPase axis in the tested endometrial cancer cells and that changes in cell motility and proliferation can occur when there is manipulation of NMU signaling in these cells either in vitro or in vivo. Intriguingly, this novel mechanism also explains how NMU signaling promotes the EGFR-driven and TGFβ receptor-driven mesenchymal transitions. Through the above axis, NMU signaling not only can promote malignancy of the tested endometrial cancer cells directly, but also helps these cells to become more sensitive to niche growth factors in their microenvironment.

Src Family Kinases and p38 Mitogen-Activated Protein Kinases Regulate Pluripotent Cell Differentiation in Culture

Multiple pluripotent cell populations, which together comprise the pluripotent cell lineage, have been identified. The mechanisms that control the progression between these populations are still poorly understood. The formation of early primitive ectoderm-like (EPL) cells from mouse embryonic stem (mES) cells provides a model to understand how one such transition is regulated. EPL cells form from mES cells in response to l-proline uptake through the transporter Slc38a2. Using inhibitors of cell signaling we have shown that Src family kinases, p38 MAPK, ERK1/2 and GSK3β are required for the transition between mES and EPL cells. ERK1/2, c-Src and GSK3β are likely to be enforcing a receptive, primed state in mES cells, while Src family kinases and p38 MAPK are involved in the establishment of EPL cells. Inhibition of these pathways prevented the acquisition of most, but not all, features of EPL cells, suggesting that other pathways are required. L-proline activation of differentiation is mediated through metabolism and changes to intracellular metabolite levels, specifically reactive oxygen species. The implication of multiple signaling pathways in the process suggests a model in which the context of Src family kinase activation determines the outcomes of pluripotent cell differentiation.

Oncogene-dependent survival of highly transformed cancer cells under conditions of extreme centrifugal force - implications for studies on extracellular vesicles

Extracellular vesicles (EVs), including exosomes, are a subject of intense interest due to their emission by cancer cells and role in intercellular communication. Earlier reports suggested that oncogenes, such as RAS, MET or EGFR, drive cellular vesiculation. Interestingly, these oncogenes may also traffic between cells using the EV-mediated emission and uptake processes. One of the main tools in the analysis of EVs are ultracentrifugation protocols designed to efficiently separate parental cells from vesicles through a sequence of steps involving increasing g-force. Here we report that ultracentrifugationonly EV preparations from highly transformed cancer cells, driven by the overexpression of oncogenic H-ras (RAS-3) and v-src (SRC-3), may contain clonogenic cancer cells, while preparations of normal or less aggressive human cell lines are generally free from such contamination. Introduction of a filtration step eliminates clonogenic cells from the ultracentrifugate. The survival of RAS-3 and SRC-3 cells under extreme conditions of centrifugal force (110,000 g) is oncogene-induced, as EV preparations of their parental non-tumourigenic cell line (IEC-18) contain negligible numbers of clonogenic cells. Moreover, treatment of SRC-3 cells with the SRC inhibitor (PP2) markedly reduces the presence of such cells in the unfiltered ultracentrifugate. These observations enforce the notion that EV preparations require careful filtration steps, especially in the case of material produced by highly transformed cancer cell types. We also suggest that oncogenic transformation may render cells unexpectedly resistant to extreme physical forces, which may affect their biological properties in vivo.

Janus kinases and Src family kinases in the regulation of EGF-induced vimentin expression in MDA-MB-468 breast cancer cells

Epithelial-mesenchymal transition (EMT) is an important process associated with the metastasis of breast cancer cells. Members of the Janus kinases (JAKs) and Src family kinases (SFKs) are implicated in the regulation of an invasive phenotype in various cancer cell types. Using the pharmacological inhibitors JAK Inhibitor I (a pan-JAK inhibitor) and PP2 we investigated the role of the JAKs and SFKs, respectively, in the regulation of EMT markers in the MDA-MB-468 breast cancer cell line model of epidermal growth factor (EGF)-induced EMT. We identified selective inhibition of EGF induction of the mesenchymal marker vimentin by PP2 and JAK Inhibitor I. The effect of JAK Inhibitor I on vimentin protein induction occurred at a concentration lower than that required to significantly inhibit EGF-mediated signal transducer and activator of transcription 3 (STAT3)-phosphorylation, suggesting involvement of a STAT3-independent mechanism of EGF-induced vimentin regulation by JAKs. Despite our identification of a role for the JAK family in EGF-induced vimentin protein expression, siRNA-mediated silencing of each member of the JAK family was unable to phenocopy pharmacological inhibition, indicating potential redundancy among the JAK family members in this pathway. While SFKs and JAKs do not represent global regulators of the EMT phenotype, our findings have identified a role for members of these signaling pathways in the regulation of EGF-induced vimentin expression in the MDA-MB-468 breast cancer cell line.

Loss of CAR promotes migration and proliferation of HaCaT cells, and accelerates wound healing in rats via Src-p38 MAPK pathway

The coxsackie and adenovirus receptor (CAR) is a cell adhesion molecule mostly localized to cell-cell contacts in epithelial and endothelial cells. CAR is known to regulate tumor progression, however, its physiological role in keratinocyte migration and proliferation, two essential steps in re-epithelialization during wound healing, has less been investigated. Here we showed that CAR was predominantly expressed in the epidermis of human skin, CAR knockdown by RNAi significantly accelerated HaCaT cell migration and proliferation. In addition, knockdown of CAR in vitro increased p-Src, p-p38, and p-JNK protein levels; however, Src inhibitor PP2 prevented the increase of p-Src and p-p38 induced by CAR RNAi, but not p-JNK, and decelerated cell migration and proliferation. More intriguingly, in vivo CAR RNAi on the skin area surrounding the wounds on rat back visually accelerated wound healing and re-epithelialization process, while treatment with PP2 or p38 inhibitor SB203580 obviously inhibited these effects. By contrast, overexpressing CAR in HaCaT cells significantly decelerated cell migration and proliferation. Above results demonstrate that suppression of CAR could accelerate HaCaT cell migration and proliferation, and promote wound healing in rat skin, probably via Src-p38 MAPK pathway. CAR thus might serve as a novel therapeutic target for facilitating wound healing.

Phosphorylation of caveolin-1 on tyrosine-14 induced by ROS enhances palmitate-induced death of beta-pancreatic cells

A considerable body of evidence exists implicating high levels of free saturated fatty acids in beta pancreatic cell death, although the molecular mechanisms and the signaling pathways involved have not been clearly defined. The membrane protein caveolin-1 has long been implicated in cell death, either by sensitizing to or directly inducing apoptosis and it is normally expressed in beta cells. Here, we tested whether the presence of caveolin-1 modulates free fatty acid-induced beta cell death by reexpressing this protein in MIN6 murine beta cells lacking caveolin-1. Incubation of MIN6 with palmitate, but not oleate, induced apoptotic cell death that was enhanced by the presence of caveolin-1. Moreover, palmitate induced de novo ceramide synthesis, loss of mitochondrial transmembrane potential and reactive oxygen species (ROS) formation in MIN6 cells. ROS generation promoted caveolin-1 phosphorylation on tyrosine-14 that was abrogated by the anti-oxidant N-acetylcysteine or the incubation with the Src-family kinase inhibitor, PP2 (4-amino-5-(4-chlorophenyl)-7(dimethylethyl)pyrazolo[3,4-d]pyrimidine). The expression of a non-phosphorylatable caveolin-1 tyrosine-14 to phenylalanine mutant failed to enhance palmitate-induced apoptosis while for MIN6 cells expressing the phospho-mimetic tyrosine-14 to glutamic acid mutant caveolin-1 palmitate sensitivity was comparable to that observed for MIN6 cells expressing wild type caveolin-1. Thus, caveolin-1 expression promotes palmitate-induced ROS-dependent apoptosis in MIN6 cells in a manner requiring Src family kinase mediated tyrosine-14 phosphorylation.

Role of the urokinase-fibrinolytic system in epithelial-mesenchymal transition during lung injury

Alveolar type II epithelial (ATII) cell injury precedes development of pulmonary fibrosis. Mice lacking urokinase-type plasminogen activator (uPA) are highly susceptible, whereas those deficient in plasminogen activator inhibitor (PAI-1) are resistant to lung injury and pulmonary fibrosis. Epithelial-mesenchymal transition (EMT) has been considered, at least in part, as a source of myofibroblast formation during fibrogenesis. However, the contribution of altered expression of major components of the uPA system on ATII cell EMT during lung injury is not well understood. To investigate whether changes in uPA and PAI-1 by ATII cells contribute to EMT, ATII cells from patients with idiopathic pulmonary fibrosis and chronic obstructive pulmonary disease, and mice with bleomycin-, transforming growth factor β-, or passive cigarette smoke-induced lung injury were analyzed for uPA, PAI-1, and EMT markers. We found reduced expression of E-cadherin and zona occludens-1, whereas collagen-I and α-smooth muscle actin were increased in ATII cells isolated from injured lungs. These changes were associated with a parallel increase in PAI-1 and reduced uPA expression. Further, inhibition of Src kinase activity using caveolin-1 scaffolding domain peptide suppressed bleomycin-, transforming growth factor β-, or passive cigarette smoke-induced EMT and restored uPA expression while suppressing PAI-1. These studies show that induction of PAI-1 and inhibition of uPA during fibrosing lung injury lead to EMT in ATII cells.

Thymoquinone induces apoptosis in human colon cancer HCT116 cells through inactivation of STAT3 by blocking JAK2- and Src‑mediated phosphorylation of EGF receptor tyrosine kinase

Thymoquinone (TQ), a compound isolated from black seed oil (Nigella sativa), has been reported to possess anti-inflammatory and anticancer activities. However, the molecular mechanisms underlying the anticancer effects of TQ remain poorly understood. In the present study, we found that TQ significantly reduced the viability of human colon cancer HCT116 cells in a concentration- and time-dependent manner. Treatment of cells with TQ induced apoptosis, which was associated with the upregulation of Bax and inhibition of Bcl-2 and Bcl-xl expression. TQ also activated caspase-9,-7, and -3, and induced the cleavage of poly-(ADP-ribose) polymerase (PARP). Pretreatment with a pan-caspase inhibitor, z-VAD-fmk, abrogated TQ-induced apoptosis by blocking the cleavage of caspase-3 and PARP. Treatment of cells with TQ also diminished the constitutive phosphorylation, nuclear localization and the reporter gene activity of signal transducer and activator of transcription-3 (STAT3). TQ attenuated the expression of STAT3 target gene products, such as survivin, c-Myc, and cyclin-D1, -D2, and enhanced the expression of cell cycle inhibitory proteins p27 and p21. Treatment with TQ attenuated the phosphorylation of upstream kinases, such as Janus-activated kinase-2 (JAK2), Src kinase and epidermal growth factor receptor (EGFR) tyrosine kinase. Pharmacological inhibition of JAK2 and Src blunted tyrosine phosphorylation of EGFR and STAT3, while treatment with an EGFR tyrosine kinase inhibitor gefitinib inhibited phosphorylation of STAT3 without affecting that of JAK2 and Src in HCT116 cells. Collectively, our study revealed that TQ induced apoptosis in HCT116 cells by blocking STAT3 signaling via inhibition of JAK2- and Src-mediated phosphorylation of EGFR tyrosine kinase.

Identification of protein kinase inhibitors with a selective negative effect on the viability of Epstein-Barr virus infected B cell lines

Epstein-Barr virus (EBV) is a human herpesvirus, which is causally associated with the development of several B lymphocytic malignancies that include Burkitt's lymphomas, Hodgkin's disease, AIDS and posttransplant associated lymphomas. The transforming activity of EBV is orchestrated by several latent viral proteins that mimic and modulate cellular growth promoting and antiapoptotic signaling pathways, which involve among others the activity of protein kinases. In an effort to identify small molecule inhibitors of the growth of EBV-transformed B lymphocytes a library of 254 kinase inhibitors was screened. This effort identified two tyrosine kinase inhibitors and two MEK inhibitors that compromised preferentially the viability of EBV-infected human B lymphocytes. Our findings highlight the possible dependence of EBV-infected B lymphocytes on specific kinase-regulated pathways underlining the potential for the development of small molecule-based therapeutics that could target selectively EBV-associated human B lymphocyte malignancies.

Emerging biological treatments for uterine cervical carcinoma

Cervical cancer is the third most common cancer worldwide, and the development of new diagnosis, prognostic, and treatment strategies is a major interest for public health. Cisplatin, in combination with external beam irradiation for locally advanced disease, or as monotherapy for recurrent/metastatic disease, has been the cornerstone of treatment for more than two decades. Other investigated cytotoxic therapies include paclitaxel, ifosfamide and topotecan, as single agents or in combination, revealing unsatisfactory results. In recent years, much effort has been made towards evaluating new drugs and developing innovative therapies to treat cervical cancer. Among the most investigated molecular targets are epidermal growth factor receptor and vascular endothelial growth factor (VEGF) signaling pathways, both playing a critical role in cervical cancer development. Studies with bevacizumab or VEGF receptor tyrosine kinase have given encouraging results in terms of clinical efficacy, without adding significant toxicity. A great number of other molecular agents targeting critical pathways in cervical malignant transformation are being evaluated in preclinical and clinical trials, reporting preliminary promising data.

In the current review, we discuss novel therapeutic strategies which are being investigated for the treatment of advanced cervical cancer.

Cellular functions regulated by phosphorylation of EGFR on Tyr845

The Src gene product (Src) and the epidermal growth factor receptor (EGFR) are prototypes of oncogene products and function primarily as a cytoplasmic non-receptor tyrosine kinase and a transmembrane receptor tyrosine kinase, respectively. The identification of Src and EGFR, and the subsequent extensive investigations of these proteins have long provided cutting edge research in cancer and other molecular and cellular biological studies. In 1995, we reported that the human epidermoid carcinoma cells, A431, contain a small fraction of Src and EGFR in which these two kinase were in physical association with each other, and that Src phosphorylates EGFR on tyrosine 845 (Y845) in the Src-EGFR complex. Y845 of EGFR is located in the activation segment of the kinase domain, where many protein kinases contain kinase-activating autophosphorylation sites (e.g., cAMP-dependent protein kinase, Src family kinases, transmembrane receptor type tyrosine kinases) or trans-phosphorylation sites (e.g., cyclin-dependent protein kinase, mitogen-activated protein kinase, Akt protein kinase). A number of studies have demonstrated that Y845 phosphorylation serves an important role in cancer as well as normal cells. Here we compile the experimental facts involving Src phosphorylation of EGFR on Y845, by which cell proliferation, cell cycle control, mitochondrial regulation of cell metabolism, gamete activation and other cellular functions are regulated. We also discuss the physiological relevance, as well as structural insights of the Y845 phosphorylation.

Activation of Src, Fyn and Yes non-receptor tyrosine kinases in keratinocytes expressing human papillomavirus (HPV) type 16 E7 oncoprotein

BACKGROUND

The Src family tyrosine kinases (SFK) are cellular regulatory proteins that influence cell adhesion, proliferation, invasion and survival during tumor development. Elevated activity of Src was associated with increased cell proliferation and invasivity in human papillomavirus (HPV)-associated malignancies; therefore, transduced human foreskin keratinocytes (HFK) were used to investigate whether SFK activation is a downstream effect of papillomaviral oncoproteins. Activation of ubiquitously expressed SFKs, namely Src, Yes and Fyn, was investigated in both proliferating and differentiating keratinocytes.

RESULTS

In proliferating keratinocytes, Src, Yes and Fyn mRNA levels were not affected by HPV 16 E6 or E7 oncoproteins, while at the protein level as detected by western blot, the presence of both E6 and E7 resulted in substantial increase in Src and Yes expression, but did not alter the high constitutive level of Fyn. Phospo-kinase array revealed that all ubiquitously expressed SFKs are activated by phosphorylation in the presence of HPV 16 E7 oncoprotein. Keratinocyte differentiation led to increased Yes mRNA and protein levels in all transduced cell lines, while it did not influence the Src transcription but resulted in elevated Src protein level in HPV16 E7 expressing lines.

CONCLUSIONS

This study revealed that HPV 16 oncoproteins upregulate Src family kinases Src and Yes via posttranscriptional mechanisms. A further effect of HPV 16 E7 oncoprotein is to enhance the activating phosphorylation of SFKs expressed in keratinocytes.

Analysis of Epithelial Growth Factor-Receptor (EGFR) Phosphorylation in Uterine Smooth Muscle Tumors: Correlation to Mucin-1 and Galectin-3 Expression

Uterine fibroids are the commonest uterine benign tumors. A potential mechanism of malignant transformation from leiomyomas to leiomyosarcomas has been described. Tyrosine phosphorylation is a key mechanism that controls biological functions, such as proliferation and cell differentiation. The aim of the current study was to evaluate the phosphorylation of epithelial growth factor-receptor (EGFR) in normal myometrium, uterine myomas and uterine leiomyosarcomas. Formalin-fixed paraffin-embedded tissue samples from normal myometrium, leiomyomas and leiomyosarcomas were studied. Samples were immunohistochemically (IHC) assessed using the anti-EGFR phosphorylation of Y845 (pEGFR-Y845) and anti-pEGFR-Y1173 phosphorylation-specific antibodies. IHC staining was evaluated using a semiquantitative score. The expression of pEGFR-Y845 was significantly upregulated in leiomyosarcomas (p < 0.001) compared to leiomyomas and normal myometrium. In contrast, pEGFR-Y1173 did not differ significantly between the three groups of the study. Correlation analysis revealed an overall positive correlation between pEGFR Y845 and mucin 1 (MUC1). Further subgroup analysis within the tumoral group (myomas and leiomyosarcomas) revealed an additional negative correlation between pEGFR Y845 and galectin-3 (gal-3) staining. On the contrary no significant correlation was noted within the non-tumoral group. An upregulated EGFR phosphorylation of Y845 in leiomyosarcomas compared to leiomyomas implicates EGFR activation at this special receptor site. Due to these pEGFR-Y845 variations, it can be postulated that MUC1 interacts with it, whereas gal-3 seems to be cleaved from Y845 phosphorylated EGFR. Further research on this field could focus on differences in EGFR pathways as a potentially advantageous diagnostic tool for investigation of benign and malignant signal transduction processes.

Src family kinase inhibitor PP2 accelerates differentiation in human intestinal epithelial cells

The proto-oncogene Src is an important protein tyrosine kinase involved in signaling pathways that control cell adhesion, growth, migration and survival. Here, we investigated the involvement of Src family kinases (SFKs) in human intestinal cell differentiation. We first observed that Src activity peaked in early stages of Caco-2/15 cell differentiation. Inhibition of SFKs with PP2, a selective SFK inhibitor, accelerated the overall differentiation program. Interestingly, all polarization and terminal differentiation markers tested, including sucrase-isomaltase, lactase-phlorizin hydrolase and E and Li-cadherins were found to be significantly up-regulated after only 3 days of treatment in the newly differentiating cells. Further investigation of the effects of PP2 revealed a significant up-regulation of the two main intestinal epithelial cell-specific transcription factors Cdx2 and HNF1α and a reduction of polycomb PRC2-related epigenetic repressing activity as measured by a decrease in H3K27me3, two events closely related to the control of cell terminal differentiation in the intestine. Taken together, these data suggest that SFKs play a key role in the control of intestinal epithelial cell terminal differentiation.

An update on dual Src/Abl inhibitors

c-Src and Bcr-Abl are two cytoplasmatic tyrosine kinases (TKs) involved in the development of malignancies. In particular, Bcr-Abl is the etiologic agent of chronic myeloid leukemia, where Src is also involved; the latter is hyperactivated in several solid tumors. Because of the structural homology between Src and Abl, several compounds originally synthesized as Src inhibitors have also been shown to be Abl inhibitors, useful in overcoming the onset of some types of chronic myeloid leukemia resistances, which frequently appear in the advanced phases of pathology. In recent years, the development of such compounds has been promoted by both excellent preclinical and clinical results, and by the theory that dual or multi-targeted inhibitors might be more effective than selective inhibitors. This review is an update on the most important dual inhibitors already in clinical trials and includes information regarding compounds that have appeared in the literature in recent years.

Cell cycle inhibition without disruption of neurogenesis is a strategy for treatment of aberrant cell cycle diseases: an update

Since publishing our earlier report describing a strategy for the treatment of central nervous system (CNS) diseases by inhibiting the cell cycle and without disrupting neurogenesis (Liu et al. 2010), we now update and extend this strategy to applications in the treatment of cancers as well. Here, we put forth the concept of "aberrant cell cycle diseases" to include both cancer and CNS diseases, the two unrelated disease types on the surface, by focusing on a common mechanism in each aberrant cell cycle reentry. In this paper, we also summarize the pharmacological approaches that interfere with classical cell cycle molecules and mitogenic pathways to block the cell cycle of tumor cells (in treatment of cancer) as well as to block the cell cycle of neurons (in treatment of CNS diseases). Since cell cycle inhibition can also block proliferation of neural progenitor cells (NPCs) and thus impair brain neurogenesis leading to cognitive deficits, we propose that future strategies aimed at cell cycle inhibition in treatment of aberrant cell cycle diseases (i.e., cancers or CNS diseases) should be designed with consideration of the important side effects on normal neurogenesis and cognition.

FMNL2 regulates cell migration and Src and Talin expression in colorectal cancer cells

AIM: To study the role of FMNL2 in regulating the migration of colorectal cancer cells by overexpressing and silencing FMNL2 in these cells, and to evaluate the correlation between the expression of FMNL2 gene and that of Src and Talin.

METHODS: FMNL2-expressing lentivirus was infected into SW480 and HT29 cell lines. RNAi plasmid that expresses a siRNA targeting the FMNL2 gene was designed, constructed, and transfected into SW620 cells line. In vitro invasion assay was performed to investigate the influence of FMNL2 expression on colorectal cell invasion. Western blot was used to detect the expression of FMNL2, Src and Talin in cells and to assess the effect of PP1 on Talin, Src, and FMNL2 expression. Immuno-colocalization assay was used to analyze the interaction of FMNL2 with Src and Talin.

RESULTS: Cell invasion was significantly increased in cells overexpressing FMNL2 (51.20 ± 8.00 vs 38.00 ± 4.00, P < 0.05). FMNL2 expression was positively correlated with Src expression (F = 15.659, P < 0.05), but negatively correlated with Talin expression. Treatment with PP1 prominently decreased Talin expression (^SW480F = 540.595, ^HT29F = 163.816, ^SW620F = 125.507, all P < 0.01), but did not change FMNL2 and Src expression. FMNL2 and Talin were co-localized in the cytoplasm, and FMNL2 and Src were co-localized in the plasma membrane.

CONCLUSION: FMNL2 significantly promotes invasion of colorectal cells. FMNL2 can regulate Src and Talin expression and indirectly control the transition of focal adhesions by regulating Src.

ErbB2, EphrinB1, Src kinase and PTPN13 signaling complex regulates MAP kinase signaling in human cancers

In non-cancerous cells, phosphorylated proteins exist transiently, becoming de-phosphorylated by specific phosphatases that terminate propagation of signaling pathways. In cancers, compromised phosphatase activity and/or expression occur and contribute to tumor phenotype. The non-receptor phosphatase, PTPN13, has recently been dubbed a putative tumor suppressor. It decreased expression in breast cancer correlates with decreased overall survival. Here we show that PTPN13 regulates a new signaling complex in breast cancer consisting of ErbB2, Src, and EphrinB1. To our knowledge, this signaling complex has not been previously described. Co-immunoprecipitation and localization studies demonstrate that EphrinB1, a PTPN13 substrate, interacts with ErbB2. In addition, the oncogenic V660E ErbB2 mutation enhances this interaction, while Src kinase mediates EphrinB1 phosphorylation and subsequent MAP Kinase signaling. Decreased PTPN13 function further enhances signaling. The association of oncogene kinases (ErbB2, Src), a signaling transmembrane ligand (EphrinB1) and a phosphatase tumor suppressor (PTPN13) suggest that EphrinB1 may be a relevant therapeutic target in breast cancers harboring ErbB2-activating mutations and decreased PTPN13 expression.

Direct inhibition of myosin II effectively blocks glioma invasion in the presence of multiple motogens

Anaplastic gliomas, the most common and malignant of primary brain tumors, frequently contain activating mutations and amplifications in promigratory signal transduction pathways. However, targeting these pathways with individual signal transduction inhibitors does not appreciably reduce tumor invasion, because these pathways are redundant; blockade of any one pathway can be overcome by stimulation of another. This implies that a more effective approach would be to target a component at which these pathways converge. In this study, we have investigated whether the molecular motor myosin II represents such a target by examining glioma invasion in a series of increasingly complex models that are sensitive to platelet-derived growth factor, epidermal growth factor, or both. Our results lead to two conclusions. First, malignant glioma cells are stimulated to invade brain through the activation of multiple signaling cascades not accounted for in simple in vitro assays. Second, even though there is a high degree of redundancy in promigratory signaling cascades in gliomas, blocking tumor invasion by directly targeting myosin II remains effective. Our results thus support our hypothesis that myosin II represents a point of convergence for signal transduction pathways that drive glioma invasion and that its inhibition cannot be overcome by other motility mechanisms.

Mammalian Pragmin regulates Src family kinases via the Glu-Pro-Ile-Tyr-Ala (EPIYA) motif that is exploited by bacterial effectors

Several pathogenic bacteria have adopted effector proteins that, upon delivery into mammalian cells, undergo tyrosine phosphorylation at the Glu-Pro-Ile-Tyr-Ala (EPIYA) or EPIYA-like sequence motif by host kinases such as Src family kinases (SFKs). This EPIYA phosphorylation triggers complex formation of bacterial effectors with SH2 domain-containing proteins that results in perturbation of host cell signaling and subsequent pathogenesis. Although the presence of such an anomalous protein interaction suggests the existence of a mammalian EPIYA-containing protein whose function is mimicked or subverted by bacterial EPIYA effectors, no molecule that uses the EPIYA motif for biological function has so far been reported in mammals. Here we show that mammalian Pragmin/SgK223 undergoes tyrosine phosphorylation at the EPIYA motif by SFKs and thereby acquires the ability to interact with the SH2 domain of the C-terminal Src kinase (Csk), a negative regulator of SFKs. The Pragmin-Csk interaction prevents translocalization of Csk from the cytoplasm to the membrane and subsequent inactivation of membrane-associated SFKs. As a result, SFK activity is sustained in cells where Pragmin is phosphorylated at the EPIYA motif. Because EPIYA phosphorylation of Pragmin is mediated by SFKs, cytoplasmic sequestration of Csk by Pragmin establishes a positive feedback regulation of SFK activation. Remarkably, the Helicobacter pylori EPIYA effector CagA binds to the Csk SH2 domain in place of Pragmin and enforces membrane recruitment of Csk and subsequent inhibition of SFKs. This work identifies Pragmin as a mammalian EPIYA effector and suggests that bacterial EPIYA effectors target Pragmin to subvert SFKs for successful infection.