Breast cancer cells proliferation is regulated by tyrosine phosphatase SHP1 through c-jun N-terminal kinase and cooperative induction of RFX-1 and AP-4 transcription factors

Identification of RFX5 as prognostic biomarker and associated with immune infiltration in stomach adenocarcinoma

Background

Regulatory factor X (RFX) gene family is a series of encodes transcription factors with a highly conserved DNA binding domain. RFXs played a vital role in the development and progression of cancer. However, the significance of RFXs in stomach adenocarcinoma (STAD) has not been fully clarified.

Methods

Online bioinformatics tools such as GSCALite, Kaplan–Meier Plotter, TIMER, LinkedOmics were used to explore the immunomodulatory function and clinical value of RFXs in STAD.

Results

The mRNA level of RFX1, RFX3, RFX4, RFX5, RFX7 and RFX8 was significantly elevated in STAD tissue versus adjacent normal tissue. We also summarize the copy number variation, single nucleotide variants and drug sensitivity of RFXs in STAD. Prognostic analysis indicated that STAD patients with high RFX5 and RFX7 expression had a better overall survival, first progression, and post-progression survival. Moreover, RFX5 expression was significantly associated with the abundance of immune cells, the expression of immune biomarkers and tumor mutational burden score in STAD. Functional enrichment analysis revealed that RFX5 and its related genes were mainly involved in T cell activation, antigen receptor-mediated signaling pathway, cell adhesion molecules, and Th17 cell differentiation. Validation study further verified the expression and prognosis of RFX5 in STAD. Further univariate and multivariate analyses suggested that pathological stage and RFX5 could be a potential independent prognostic factor for STAD.

Conclusions

RFX5 was a candidate prognostic biomarker and associated with immune infiltration in STAD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40001-022-00794-w.

Small Molecule Inhibitors for Hepatocellular Carcinoma: Advances and Challenges

According to data provided by World Health Organization, hepatocellular carcinoma (HCC) is the sixth most common cause of deaths due to cancer worldwide. Tremendous progress has been achieved over the last 10 years developing novel agents for HCC treatment, including small-molecule kinase inhibitors. Several small molecule inhibitors currently form the core of HCC treatment due to their versatility since they would be more easily absorbed and have higher oral bioavailability, thus easier to formulate and administer to patients. In addition, they can be altered structurally to have greater volumes of distribution, allowing them to block extravascular molecular targets and to accumulate in a high concentration in the tumor microenvironment. Moreover, they can be designed to have shortened half-lives to control for immune-related adverse events. Most importantly, they would spare patients, healthcare institutions, and society as a whole from the burden of high drug costs. The present review provides an overview of the pharmaceutical compounds that are licensed for HCC treatment and other emerging compounds that are still investigated in preclinical and clinical trials. These molecules are targeting different molecular targets and pathways that are proven to be involved in the pathogenesis of the disease.

KBoost: a new method to infer gene regulatory networks from gene expression data

Reconstructing gene regulatory networks is crucial to understand biological processes and holds potential for developing personalized treatment. Yet, it is still an open problem as state-of-the-art algorithms are often not able to process large amounts of data within reasonable time. Furthermore, many of the existing methods predict numerous false positives and have limited capabilities to integrate other sources of information, such as previously known interactions. Here we introduce KBoost, an algorithm that uses kernel PCA regression, boosting and Bayesian model averaging for fast and accurate reconstruction of gene regulatory networks. We have benchmarked KBoost against other high performing algorithms using three different datasets. The results show that our method compares favorably to other methods across datasets. We have also applied KBoost to a large cohort of close to 2000 breast cancer patients and 24,000 genes in less than 2 h on standard hardware. Our results show that molecularly defined breast cancer subtypes also feature differences in their GRNs. An implementation of KBoost in the form of an R package is available at: https://github.com/Luisiglm/KBoost and as a Bioconductor software package.

Identification of Phomoxanthone A and B as Protein Tyrosine Phosphatase Inhibitors

Phomoxanthone A and B (PXA and PXB) are xanthone dimers and isolated from the endophytic fungus Phomopsis sp. By254. The results demonstrated that PXB and PXA are noncompetitive inhibitors of SHP2 and PTP1B and competitive inhibitors of SHP1. Molecular docking studies showed that PXB and PXA interact with conserved domains of protein tyrosine phosphatases such as the β5-β6 loop, WPD loop, P loop, and Q loop. PXA and PXB could significantly inhibit the cell proliferation in MCF7 cells. Our results indicated that these two compounds do not efficiently inhibit PTP1B and SHP2 activity. RNA sequencing showed that PXA and PXB may inhibit SHP1 activity in MCF7 cells leading to the upregulation of inflammatory factors. In addition to PTP inhibition, PXA and PXB are multitarget compounds to inhibit the proliferation of tumor cells. In conclusion, both compounds show inhibition of cancer cells and a certain degree of inflammatory stimulation, which make them promising for tumor immunotherapy.

Evaluating the prognostic value and functional roles of transcription factor AP4 in colorectal cancer

The basic helix-loop-helix transcription factor AP4 (TFAP4) gene serves an important function in the genesis and progression of tumors. However, few studies to date have defined the role of this gene in colorectal cancer (CRC). The aim of the present study was to assess the expression of TFAP4 in CRC and its impact on the prognosis of patients with CRC. In the present study, the expression of TFAP4 was detected in 30 matched pairs of fresh CRC tissues, 187 cases of clinical paraffin-embedded CRC tissues and CRC cell lines using the reverse transcriptase-quantitative polymerase chain reaction, immunohistochemistry or western blot analysis. Survival analysis was based on TFAP4 expression. The effects of TFAP4 on CRC cell function were investigated by ectopic expression or knockdown of TFAP4 in vitro. TFAP4 expression was revealed to be increased in human CRC tissues and cell lines. The overall survival (OS) time of patients with high TFAP4 expression was significantly decreased compared with patients with low TFAP4 expression (P<0.001). In addition, TFAP4 was revealed to be an independent prognostic factor for the OS time of patients with CRC (hazard ratio, 2.607; 95% confidence interval, 1.469-4.627; P=0.001). Ectopic TFAP4 expression promoted CRC cell proliferation, migration and invasion in vitro, and the silencing of TFAP4 expression resulted in the inhibition of these events. These results demonstrated that TFAP4, which was overexpressed in CRC tissues and cell lines, increased the malignant potential of CRC cells and may serve as an indicator for poor prognosis in patients with CRC.

AP4 positively regulates LAPTM4B to promote hepatocellular carcinoma growth and metastasis, while reducing chemotherapy sensitivity

Polymorphisms of the lysosomal-associated protein transmembrane-4 beta (LAPTM4B) gene are related to various forms of tumour susceptibility, which led us to hypothesize that some unique transcription factors targeting this polymorphism region may affect the biological function of LAPTM4B in tumour progression. In this study, we found that the transcription factor AP4 directly binds to the polymorphism region of the LAPTM4B gene promoter and induces its transcription. In addition, we demonstrated that AP4 promotes hepatocellular carcinoma (HCC) cell proliferation and metastasis and depresses chemotherapy sensitivity via LAPTM4B by activating the PI3K/AKT signalling pathway and caspase-dependent pathway. Interestingly, we found that AP4 could not only regulate LAPTM4B by directly binding to the promoter, but also be regulated via a positive feedback mechanism involving LAPTM4B acting on c-myc. Finally, we showed that AP4 and LAPTM4B are highly coexpressed in HCC tissues, and their coexpression may be a marker of poor prognosis. These findings provide evidence of the expression and functional coupling between AP4 and LAPTM4B and shed light on the regulation of LAPTM4B and its function in liver cancer.

The Transcription Factor AP4 Promotes Oncogenic Phenotypes and Cisplatin Resistance by Regulating LAPTM4B Expression

Lysosomal-associated protein transmembrane-4 beta (LAPTM4B) is a novel oncogene, whose overexpression is involved in cancer occurrence and progression. However, the mechanism of LAPTM4B transcriptional regulation remains unclear. In this study, the results of transcription factor (TF) profiling plate arrays indicated that AP4 was a potential transcription factor regulating LAPTM4B expression. LAPTM4B was positively correlated with AP4 and they were both associated with poor overall and disease-free survival. Luciferase and electrophoretic mobility shift assay assays confirmed that AP4 directly bound to the polymorphism region of LAPTM4B promoter and modulated its transcription. Functionally, AP4 promoted cell proliferation, migration, invasion, and assisted drug resistance in part through upregulation of LAPTM4B. Taken together, these findings identify LAPTM4B as a direct AP4 target gene and the interaction of AP4 and LAPTM4B plays an important role in breast cancer progression.Implications: This study demonstrates that AP4 promotes cell growth, migration, invasion, and cisplatin resistance through upregulation of LAPTM4B expression, thus representing an attractive therapeutic target for breast cancer. Mol Cancer Res; 16(5); 857-68. ©2018 AACR.

Differential regulation of pro-inflammatory cytokine signalling by protein tyrosine phosphatases in pancreatic β-cells

Type 1 diabetes (T1D) is characterized by the destruction of insulin-producing β-cells by immune cells in the pancreas. Pro-inflammatory including TNF-α, IFN-γ and IL-1β are released in the islet during the autoimmune assault and signal in β-cells through phosphorylation cascades, resulting in pro-apoptotic gene expression and eventually β-cell death. Protein tyrosine phosphatases (PTPs) are a family of enzymes that regulate phosphorylative signalling and are associated with the development of T1D. Here, we observed expression of PTPN6 and PTPN1 in human islets and islets from non-obese diabetic (NOD) mice. To clarify the role of these PTPs in β-cells/islets, we took advantage of CRISPR/Cas9 technology and pharmacological approaches to inactivate both proteins. We identify PTPN6 as a negative regulator of TNF-α-induced β-cell death, through JNK-dependent BCL-2 protein degradation. In contrast, PTPN1 acts as a positive regulator of IFN-γ-induced STAT1-dependent gene expression, which enhanced autoimmune destruction of β-cells. Importantly, PTPN1 inactivation by pharmacological modulation protects β-cells and primary mouse islets from cytokine-mediated cell death. Thus, our data point to a non-redundant effect of PTP regulation of cytokine signalling in β-cells in autoimmune diabetes.

Tamoxifen promotes apoptosis and inhibits invasion in estrogen‑positive breast cancer MCF‑7 cells

Tamoxifen (TAM) is the earliest non-steroidal antiestrogen drug, which has been widely used in endocrine therapy targeting breast cancer. The aim of the present study was to investigate the effect of TAM on the proliferation, apoptosis, migration and invasion of the estrogen‑positive (ER+) breast cancer cell line MCF‑7 in vitro, and elucidate its mechanisms. It was demonstrated that TAM suppressed proliferation, migration and invasion, and induced apoptosis in MCF‑7 cells. Further investigation revealed that the mitochondrial membrane potential and the amount of ATP were significantly decreased following the treatment of MCF‑7 cells with TAM. Mitochondria are an important source of reactive oxygen species (ROS) and they are also the target of ROS as well. In the present study, TAM promoted the formation of ROS in MCF‑7 cells. In conclusion, these results reveal the underlying mechanism by which TAM induces ER+ breast cancer cell apoptosis and inhibits invasion, thereby supporting the use of TAM in breast cancer treatment.

Silencing of AP-4 inhibits proliferation, induces cell cycle arrest and promotes apoptosis in human lung cancer cells

Activating enhancer-binding protein (AP)-4 is a member of the basic helix-loop-helix transcription factors, and is involved in tumor biology. However, the role of AP-4 in human lung cancer remains to be fully elucidated. In the present study, the expression of AP-4 in human lung cancer tissues and cells was investigated by reverse transcription-quantitative polymerase chain reaction, and it was observed that the level of AP-4 was increased in tumor tissues and cells compared with their normal counterparts. AP-4 expression was knocked down by transfection with a specific small interfering RNA (siRNA) in lung cancer cells, and this indicated that siRNA-mediated silencing of AP-4 inhibited cell proliferation, arrested the cell cycle at the G0/G1 phase and induced apoptosis by modulating the expression of p21 and cyclin D1. The results of the present study suggest that AP-4 may be an oncoprotein that has a significant role in lung cancer, and that siRNA-mediated silencing of AP-4 may have therapeutic potential as a strategy for the treatment of lung cancer.

DephosSite: a machine learning approach for discovering phosphotase-specific dephosphorylation sites

Protein dephosphorylation, which is an inverse process of phosphorylation, plays a crucial role in a myriad of cellular processes, including mitotic cycle, proliferation, differentiation, and cell growth. Compared with tyrosine kinase substrate and phosphorylation site prediction, there is a paucity of studies focusing on computational methods of predicting protein tyrosine phosphatase substrates and dephosphorylation sites. In this work, we developed two elegant models for predicting the substrate dephosphorylation sites of three specific phosphatases, namely, PTP1B, SHP-1, and SHP-2. The first predictor is called MGPS-DEPHOS, which is modified from the GPS (Group-based Prediction System) algorithm with an interpretable capability. The second predictor is called CKSAAP-DEPHOS, which is built through the combination of support vector machine (SVM) and the composition of k-spaced amino acid pairs (CKSAAP) encoding scheme. Benchmarking experiments using jackknife cross validation and 30 repeats of 5-fold cross validation tests show that MGPS-DEPHOS and CKSAAP-DEPHOS achieved AUC values of 0.921, 0.914 and 0.912, for predicting dephosphorylation sites of the three phosphatases PTP1B, SHP-1, and SHP-2, respectively. Both methods outperformed the previously developed kNN-DEPHOS algorithm. In addition, a web server implementing our algorithms is publicly available at http://genomics.fzu.edu.cn/dephossite/ for the research community.

Involvement of DDX6 gene in radio- and chemoresistance in glioblastoma

CCRT (concomitant chemotherapy and radiation therapy) is often used for glioblastoma multiforme (GBM) treatment after surgical therapy, however, patients treated with CCRT undergo poor prognosis due to development of treatment resistant recurrence. Many studies have been performed to overcome these problems and to discover genes influencing treatment resistance. To discover potential genes inducing CCRT resistance in GBM, we used whole genome screening by infecting shRNA pool in patient-derived cell. The cells infected ~8,000 shRNAs were implanted in mouse brain and treated RT/TMZ as in CCRT treated patients. We found DDX6 as the candidate gene for treatment resistance after screening and establishing DDX6 knock down cells for functional validation. Using these cells, we confirmed tumor associated ability of DDX6 in vitro and in vivo. Although proliferation improvement was not found, decreased DDX6 influenced upregulated clonogenic ability and resistant response against radiation treatment in vivo and in vitro. Taken together, we suggest that DDX6 discovered by using whole genome screening was responsible for radio- and chemoresistance in GBM.

Human somatostatin receptor-3 distinctively induces apoptosis in MCF-7 and cell cycle arrest in MDA-MB-231 breast cancer cells

Somatostatin (SST) mediates cytostatic and pro-apoptotic effects through five somatostatin receptors (SSTR1-5). The modest clinical benefits of SST analogs in cancers of different origin such as breast cancer are attributed to diminished SSTRs expression at tumor sites. In the present study, SSTR3 was overexpressed in MCF-7 and MDA-MB-231, and analyzed for downstream signaling molecules associated with cytostatic and cytotoxic effect. Cells overexpressing SSTR3 displayed inhibition of EGF induced proliferation and enhanced antiproliferative effect of SSTR3-specific agonist in comparison to non-transfected cells. SSTR3 overexpression in MCF-7 cells (R3-MCF-7) constitutively enhanced TUNEL staining, PARP-1 and p27(Kip1) expression suggesting apoptosis and cell-cycle arrest. Conversely, R3-MB-231 cells with SSTR3 overexpression exerted cytostatic and were devoid of any cytotoxic effects. The expression of PTP-1C and the status of ERK1/2, p38 and PI3K phosphorylation was modulated in a cell-specific manner. These findings provide new insights in understanding the antiproliferative role of SSTR3 in breast tumor biology.

Increased SHP-1 expression results in radioresistance, inhibition of cellular senescence, and cell cycle redistribution in nasopharyngeal carcinoma cells

Background

Radioresistance is the main limit to the efficacy of radiotherapy in nasopharyngeal carcinoma (NPC). SHP-1 is involved in cancer progression, but its role in radioresistance and senescence of NPC is not well understood. This study aimed to assess the role of SHP-1 in the radioresistance and senescence of NPC cells.

Methods

SHP-1 was knocked-down and overexpressed in CNE-1 and CNE-2 cells using lentiviruses. Cells were irradiated to observe their radiosensitivity by colony forming assay. BrdU incorporation assay and flow cytometry were used to monitor cell cycle. A β-galactosidase assay was used to assess senescence. Western blot was used to assess SHP-1, p21, p53, pRb, Rb, H3K9Me3, HP1γ, CDK4, cyclin D1, cyclin E, and p16 protein expressions.

Results

Compared with CNE-1-scramble shRNA cells, SHP-1 downregulation resulted in increased senescence (+107 %, P < 0.001), increased radiosensitivity, higher proportion of cells in G0/G1 (+33 %, P < 0.001), decreased expressions of CDK4 (−44 %, P < 0.001), cyclin D1 (−41 %, P = 0.001), cyclin E (−97 %, P < 0.001), Rb (−79 %, P < 0.001), and pRb (−76 %, P = 0.001), and increased expression of p16 (+120 %, P = 0.02). Furthermore, SHP-1 overexpression resulted in radioresistance, inhibition of cellular senescence, and cell cycle arrest in the S phase. Levels of p53 and p21 were unchanged in both cell lines (all P > 0.05).

Conclusion

SHP-1 has a critical role in radioresistance, cell cycle progression, and senescence of NPC cells. Down-regulating SHP-1 may be a promising therapeutic approach for treating patients with NPC.

Insulin-like growth factor and epidermal growth factor signaling in breast cancer cell growth: focus on endocrine resistant disease

Breast cancer is the most common type of cancer for women worldwide with a lifetime risk amounting to a staggering total of 10%. It is well established that the endogenous synthesis of insulin-like growth factor (IGF) and epidermal growth factor (EGF) polypeptide growth factors are closely correlated to malignant transformation and all the steps of the breast cancer metastatic cascade. Numerous studies have demonstrated that both estrogens and growth factors stimulate the proliferation of steroid-dependent tumor cells, and that the interaction between these signaling pathways occurs at several levels. Importantly, the majority of breast cancer cases are estrogen receptor- (ER-) positive which have a more favorable prognosis and pattern of recurrence with endocrine therapy being the backbone of treatment. Unfortunately, the majority of patients progress to endocrine therapy resistant disease (acquired resistance) whereas a proportion of patients may fail to respond to initial therapy (de novo resistance). The IGF-I and EGF downstream signaling pathways are closely involved in the process of progression to therapy resistant disease. Modifications in the bioavailability of these growth factors contribute critically to disease progression. In the present review therefore, we will discuss in depth how IGF and EGF signaling participate in breast cancer pathogenesis and progression to endocrine resistant disease.

AP4 activates cell migration and EMT mediated by p53 in MDA-MB-231 breast carcinoma cells

Tumor metastasis is the primary cause of mortality in most cancer patients. Before disassociation from the tumors, most of malignant tumor cells undergo the epithelial-mesenchymal transition to break away from the adhesions between the cells and the surrounding extracellular matrix. Recently, activating enhancer-binding protein (AP4) has been shown to be a mediator of EMT in colorectal cancer and high level of AP4 correlates with poor prognosis in cancer patients. It has been found that AP4 upregulates the genes involved in EMT and cell proliferation in colorectal cancer cells and that the aggressive human breast cancer cells MDA-MB-231 are highly metastatic. Therefore, we tested the hypothesis that AP4 may also affect cell migration and EMT in this cell type. Three different assays, including the wound-healing assay, the Boyden chamber assay, and the cell tracking assay, were employed to confirm that AP4 activated both cell migration and invasion. Immunofluorescence staining and Western blot analysis revealed that the cells underwent EMT when AP4 was upregulated. In contrast, overexpression of dominant-negative AP4, lacking the DNA-binding domain, inactivated the DNA-binding ability of endogenous AP4 and led to lower cell motility. Furthermore, we found that AP4 enhanced p53 expression at both transcriptional and translational levels. Knockdown of p53 by siRNA significantly diminished the activation of cell migration by AP4, indicating that AP4 can regulate cell migration via the activity of p53.

RFX1-dependent activation of SHP-1 induces autophagy by a novel obatoclax derivative in hepatocellular carcinoma cells

Obatoclax is a small molecule which targets the Bcl-2 family, and is to treat leukemia, lymphoma and lung carcinoma. Previously, an obatoclax analogue, SC-2001, was found to disrupt the protein-protein interactions of the Bcl-2 family and also repress Bcl-XL and Mcl-1 expression via STAT3 inactivation. Here, we report a novel mechanism of autophagy induction by SC-2001 in liver cancer cells. The findings indicate that SC-2001 induced the autophagy marker LC3-II in four hepatocellular carcinoma (HCC) cells. Autophagosomes induced by SC-2001-treated cells were confirmed by electron microscopy. SC-2001 activated SHP-1, dephosphorylated STAT3 and Mcl-1, and subsequently released free beclin 1. Overexpression of STAT3 and Mcl-1 in PLC5 cells attenuated the induction of SC-2001 on autophagy. Abolishment of SHP-1 by a specific inhibitor aboragated the autophagic effects induced by SC-2001. In addition, it was further revealed that RFX-1, a transcription factor of SHP-1, is a critical regulator in SC-2001-mediated autophagy. Downregulation of RFX-1 by si-RNA protected cells from SC-2001-induced autophagy. Importantly, Huh7 tumor-bearing nude mice treated with SC-2001 showed downregulation of Mcl-1 and p-STAT3 protein expression and upregulation of SHP-1, LC3II, and RFX-1 protein expression. In summary, our data suggest that SC-2001 induces autophagic cell death in a RFX1/SHP-1/STAT3/Mcl-1 signaling cascade.

SC-2001 overcomes STAT3-mediated sorafenib resistance through RFX-1/SHP-1 activation in hepatocellular carcinoma

Hepatocellular carcinoma is the fifth most common solid cancer worldwide. Sorafenib, a small multikinase inhibitor, is the only approved therapy for advanced HCC. The clinical benefit of sorafenib is offset by the acquisition of sorafenib resistance. Understanding of the molecular mechanism of STAT3 overexpression in sorafenib resistance is critical if the clinical benefits of this drug are to be improved. In this study, we explored our hypothesis that loss of RFX-1/SHP-1 and further increase of p-STAT3 as a result of sorafenib treatment induces sorafenib resistance as a cytoprotective response effect, thereby, limiting sorafenib sensitivity and efficiency. We found that knockdown of RFX-1 protected HCC cells against sorafenib-induced cell apoptosis and SHP-1 activity was required for the process. SC-2001, a molecule with similar structure to obatoclax, synergistically suppressed tumor growth when used in combination with sorafenib in vitro and overcame sorafenib resistance through up-regulating RFX-1 and SHP-1 resulting in tumor suppression and mediation of dephosphorylation of STAT3. In addition, sustained sorafenib treatment in HCC led to increased p-STAT3 which was a key mediator of sorafenib sensitivity. The combination of SC-2001 and sorafenib strongly inhibited tumor growth in both wild-type and sorafenib-resistant HCC cell bearing xenograft models. These results demonstrate that inactivation of RFX/SHP-1 induced by sustained sorafenib treatment confers sorafenib resistance to HCC through p-STAT3 up-regulation. These effects can be overcome by SC-2001 through RFX-1/SHP-1 dependent p-STAT3 suppression. In conclusion, the use of SC-2001 in combination with sorafenib may constitute a new strategy for HCC therapy.

Obatoclax analog SC-2001 inhibits STAT3 phosphorylation through enhancing SHP-1 expression and induces apoptosis in human breast cancer cells

Interfering oncogenic STAT3 signaling is a promising anti-cancer strategy. We examined the efficacy and drug mechanism of an obatoclax analog SC-2001, a novel STAT3 inhibitor, in human breast cancer cells. Human breast cancer cell lines were used for in vitro studies. Apoptosis was examined by both flow cytometry and western blot. Signaling pathways were assessed by western blot. In vivo efficacy of SC-2001 was tested in xenograft nude mice. SC-2001 inhibited cell growth and induced apoptosis in association with downregulation of p-STAT3 (Tyr 705) in breast cancer cells. STAT3-regulated proteins, including Mcl-1, survivin, and cyclin D1, were repressed by SC-2001. Over-expression of STAT3 in MDA-MB-468 cells protected cells from SC-2001-induced apoptosis. Moreover, SC-2001 enhanced the expression of protein tyrosine phosphatase SHP-1, a negative regulator of STAT3. Furthermore, the enhanced SHP-1 expression, in conjunction with increased SHP-1 phosphatase activity, was mediated by upregulated transcription by RFX-1. Chromatin immunoprecipitation assay revealed that SC-2001 increased the binding capacity of RFX-1 to the SHP-1 promoter. Knockdown of either RFX-1 or SHP-1 reduced SC-2001-induced apoptosis, whereas ectopic expression of RFX-1 increased SHP-1 expression and enhanced the apoptotic effect of SC-2001. Importantly, SC-2001 suppressed tumor growth in association with enhanced RFX-1 and SHP-1 expression and p-STAT3 downregulation in MDA-MB-468 xenograft tumors. SC-2001 induced apoptosis in breast cancer cells, an effect that was mediated by RFX-1 upregulated SHP-1 expression and SHP-1-dependent STAT3 inactivation. Our study indicates targeting STAT3 signaling pathway may be a useful approach for the development of targeted agents for anti-breast cancer.

SHP-1-Pyk2-Src protein complex and p38 MAPK pathways independently regulate IL-10 production in lipopolysaccharide-stimulated macrophages

The role of tyrosine phosphatase Src homology region 2 domain-containing phosphatase (SHP)-1 in LPS-activated cytokine production and inflammation was investigated by determining TNF-α and IL-10 production in splenic macrophages employing SHP-1-null (me/me) mouse model. LPS-stimulated me/me splenic macrophages secreted significantly less IL-10 with concomitantly elevated levels of TNF-α compared with wild-type (WT) macrophages irrespective of LPS dose and duration of stimulation. IL-10 significantly inhibited LPS-induced TNF-α production in both me/me and WT macrophages. The critical requirement for SHP-1 in regulating LPS-induced IL-10 and TNF-α production was confirmed by interfering with SHP-1 expression in WT macrophages and by reconstituting me/me macrophages with the SHP-1 gene. To delineate the role of SHP-1 in positive regulation of LPS-induced IL-10 production, signaling proteins representing SHP-1 targets were examined. The results reveal that tyrosine kinases Src and proline-rich tyrosine kinase 2 (Pyk2) regulate SHP-1-dependent LPS-induced IL-10 production and infer that optimal LPS-induced IL-10 production requires an assembly of a protein complex consisting of SHP-1-Pyk2-Src proteins. Moreover, LPS-induced IL-10 production also requires activation of the p38 MAPK independent of SHP-1 function. Overall, to our knowledge our results show for the first time that SHP-1 acts as a positive regulator of LPS-induced IL-10 production in splenic macrophages through two distinct and independent SHP-1-Pyk2-Src and p38 MAPK pathways.

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.

Inhibition of proliferation of estrogen receptor‑positive MCF‑7 human breast cancer cells by tamoxifen through c‑Jun transcription factors

Activator of protein 1 (AP-1) is a heterodimeric transcription factor composed of various members of the Jun and Fos families and binds to DNA at specific AP-1 binding sites. AP-1 transcriptional activity is increased by phosphorylation at serine residues in the c‑Jun component of AP-1. In the present study, the proliferation of MCF-7 breast cancer cells was found to be suppressed by tamoxifen (TAM)-activated c-Jun through the protein kinase C (PKC) pathway. The molecular mechanism by which c‑Jun activation induces antiproliferative signals in estrogen receptor (ER)-positive MCF-7 human breast cancer cells remains unknown. TAM inhibited the proliferation of ER-positive MCF-7 human breast cancer cells and ER-negative MDA-MB-435 human breast cancer cells and 48 h incubation with 10 µM TAM led to inhibition of 80% of proliferation. In addition, no significant difference in c-Jun mRNA and protein levels was detected in MCF-7 and MDA-MB-435 cells stimulated by TAM for 48 h. TAM treatment of MCF-7 cells activated the transcriptional activity of AP-1, which responds specifically to phorbol ester. To determine the role of c-Jun in the antiproliferation of MCF-7 cells stimulated by TAM, the inhibition rates of MCF‑7 cells were correlated with c‑Jun expression and stimulation of TAM. Results showed that the inhibition rate of TAM-stimulated MCF-7 cells was positively regulated by overexpression of c-Jun and negatively regulated by underexpression of c-Jun. Overall, these results indicate that the TAM-stimulated antiproliferation of MCF-7 cells is positively regulated by c-Jun through activation of the PKC pathway.

The tyrosine phosphatase SHP-1 negatively regulates cytotrophoblast proliferation in first-trimester human placenta by modulating EGFR activation

Insulin-like growth factors (IGFs) influence placental cell (cytotrophoblast) kinetics. We recently reported that the protein tyrosine phosphatase (PTP) SHP-2 positively regulates IGF actions in the placenta. In other systems, the closely related PTP, SHP-1, functions as a negative regulator of signaling events but its role in the placenta is still unknown. We examined the hypothesis that SHP-1 negatively regulates IGF actions in the human placenta. Immunohistochemical (IHC) analysis demonstrated that SHP-1 is abundant in cytotrophoblast. SHP-1 expression was decreased in first-trimester placental explants using siRNA; knockdown did not alter IGF-induced proliferation but it significantly enhanced proliferation in serum-free conditions, revealing that placental growth is endogenously regulated. Candidate regulators were determined by using antibody arrays, Western blotting, and IHC to examine the activation status of multiple receptor tyrosine kinases (RTKs) in SHP-1-depleted explants; amongst the alterations observed was enhanced activation of EGFR, suggesting that SHP-1 may interact with EGFR to inhibit proliferation. The EGFR tyrosine kinase inhibitor PD153035 reversed the elevated proliferation seen in the absence of SHP-1. This study demonstrates a role for SHP-1 in human trophoblast turnover and establishes SHP-1 as a negative regulator of EGFR activation. Targeting placental SHP-1 expression may provide therapeutic benefits in common pregnancy conditions with abnormal trophoblast proliferation.