Focal amplification and oncogene dependency of GAB2 in breast cancer

FADS2 function at the major cancer hotspot 11q13 locus alters fatty acid metabolism in cancer

Dysregulation of fatty acid metabolism and de novo lipogenesis is a key driver of several cancer types through highly unsaturated fatty acid (HUFA) signaling precursors such as arachidonic acid. The human chromosome 11q13 locus has long been established as the most frequently amplified in a variety of human cancers. The fatty acid desaturase genes (FADS1, FADS2 and FADS3) responsible for HUFA biosynthesis localize to the 11q12-13.1 region. FADS2 activity is promiscuous, catalyzing biosynthesis of several unsaturated fatty acids by Δ6, Δ8, and Δ4 desaturation. Our main aim here is to review known and putative consequences of FADS2 dysregulation due to effects on the 11q13 locus potentially driving various cancer types. FADS2 silencing causes synthesis of sciadonic acid (5Z,11Z,14Z-20:3) in MCF7 cells and breast cancer in vivo. 5Z,11Z,14Z-20:3 is structurally identical to arachidonic acid (5Z,8Z,11Z,14Z-20:4) except it lacks the internal Δ8 double bond required for prostaglandin and leukotriene synthesis, among other eicosanoids. Palmitic acid has substrate specificity for both SCD and FADS2. Melanoma, prostate, liver and lung cancer cells insensitive to SCD inhibition show increased FADS2 activity and sapienic acid biosynthesis. Elevated serum mead acid levels found in hepatocellular carcinoma patients suggest an unsatisfied demand for arachidonic acid. FADS2 circular RNAs are at high levels in colorectal and lung cancer tissues. FADS2 circular RNAs are associated with shorter overall survival in colorectal cancer patients. The evidence thusfar supports an effort for future research on the role of FADS2 as a tumor suppressor in a range of neoplastic disorders.

Setting sail: Maneuvering SHP2 activity and its effects in cancer

Since the discovery of tyrosine phosphorylation being a critical modulator of cancer signaling, proteins regulating phosphotyrosine levels in cells have fast become targets of therapeutic intervention. The nonreceptor protein tyrosine phosphatase (PTP) coded by the PTPN11 gene "SHP2" integrates phosphotyrosine signaling from growth factor receptors into the RAS/RAF/ERK pathway and is centrally positioned in processes regulating cell development and oncogenic transformation. Dysregulation of SHP2 expression or activity is linked to tumorigenesis and developmental defects. Even as a compelling anti-cancer target, SHP2 was considered "undruggable" for a long time owing to its conserved catalytic PTP domain that evaded drug development. Recently, SHP2 has risen from the "undruggable curse" with the discovery of small molecules that manipulate its intrinsic allostery for effective inhibition. SHP2's unique domain arrangement and conformation(s) allow for a truly novel paradigm of inhibitor development relying on skillful targeting of noncatalytic sites on proteins. In this review we summarize the biological functions, signaling properties, structural attributes, allostery and inhibitors of SHP2.

Systematic review and meta-analysis of genomic alterations in acral melanoma

Acral melanoma (AM) tumors arise on the palms, soles, fingers, toes, and nailbeds. A comprehensive systematic meta-analysis of AM genomic aberrations has not been conducted to date. A literature review was carried out to identify studies sequencing AM. Whole-genome/exome data from 181 samples were identified. Targeted panel sequencing data from MSK-IMPACT were included as a validation cohort (n = 92), and studies using targeted hot spot sequencing were also collated for BRAF (n = 26 studies), NRAS (n = 21), and KIT (n = 32). Statistical analysis indicated BRAF, NRAS, PTEN, TYRP1, and KIT as significantly mutated genes. Frequent copy-number aberrations were also found for important cancer genes, such as CDKN2A, KIT, MDM2, CCND1, CDK4, and PAK1, among others. Mapping genomic alterations within the context of the hallmarks of cancer identified four components frequently altered, including (i) sustained proliferative signaling and (ii) evading growth suppression, (iii) genome instability and mutation, and (iv) enabling replicative immortality. This analysis provides the largest analysis of genomic aberrations in AM in the literature to date and highlights pathways that may be therapeutically targetable.

Gab2 promotes acute myeloid leukemia growth and migration through the SHP2-Erk-CREB signaling pathway

Acute myeloid leukemia (AML) is a hematologic malignant disease largely affecting older adults with poor outcomes. Lack of effective targeted treatment is a major challenge in managing the disease in the clinic. Scaffolding adaptor Gab2 is amplified in a subset of AML. However, the causative role of Gab2 in AML remains to be explored. In this study, it was found that Gab2 was expressed at high levels in AML patient samples and AML cell lines. Experiments by knocking down Gab2 expression using shRNA showed that Gab2 promoted AML cell growth and migration in vitro and in vivo. Further studies using Gab2 mutants and pharmacological inhibitors revealed that Gab2 increased CREB phosphorylation via the SHP-2/Erk signaling pathway. CREB phosphorylation contributed to Gab2-induced cell migration by increasing MMP2 and MMP9 expression. This research indicates that high Gab2 expression promotes AML progression through the SHP2-Erk-CREB signaling pathway. CREB suppression may help treat AML with high Gab2 expression.

Discovery of novel furanylbenzamide inhibitors that target oncogenic tyrosine phosphatase SHP2 in leukemia cells

Disturbance of the dynamic balance between tyrosine phosphorylation and dephosphorylation of signaling molecules, controlled by protein tyrosine kinases and protein tyrosine phosphatases (PTPs), is known to lead to the development of cancer. While most approved targeted cancer therapies are tyrosine kinase inhibitors, PTPs have long been stigmatized as undruggable and have only recently gained renewed attention in drug discovery. One PTP target is the Src-homology 2 domain-containing phosphatase 2 (SHP2). SHP2 is implicated in tumor initiation, progression, metastasis, and treatment resistance, primarily because of its role as a signaling nexus of the extracellular signal-regulated kinase pathway, acting upstream of the small GTPase Ras. Efforts to develop small molecules that target SHP2 are ongoing, and several SHP2 allosteric inhibitors are currently in clinical trials for the treatment of solid tumors. However, while the reported allosteric inhibitors are highly effective against cells expressing WT SHP2, none have significant activity against the most frequent oncogenic SHP2 variants that drive leukemogenesis in several juvenile and acute leukemias. Here, we report the discovery of novel furanylbenzamide molecules as inhibitors of both WT and oncogenic SHP2. Importantly, these inhibitors readily cross cell membranes, bind and inhibit SHP2 under physiological conditions, and effectively decrease the growth of cancer cells, including triple-negative breast cancer cells, acute myeloid leukemia cells expressing either WT or oncogenic SHP2, and patient-derived acute myeloid leukemia cells. These novel compounds are effective chemical probes of active SHP2 and may serve as starting points for therapeutics targeting WT or mutant SHP2 in cancer.

Targeting Akt in cancer for precision therapy

Biomarkers-guided precision therapeutics has revolutionized the clinical development and administration of molecular-targeted anticancer agents. Tailored precision cancer therapy exhibits better response rate compared to unselective treatment. Protein kinases have critical roles in cell signaling, metabolism, proliferation, survival and migration. Aberrant activation of protein kinases is critical for tumor growth and progression. Hence, protein kinases are key targets for molecular targeted cancer therapy. The serine/threonine kinase Akt is frequently activated in various types of cancer. Activation of Akt promotes tumor progression and drug resistance. Since the first Akt inhibitor was reported in 2000, many Akt inhibitors have been developed and evaluated in either early or late stage of clinical trials, which take advantage of liquid biopsy and genomic or molecular profiling to realize personalized cancer therapy. Two inhibitors, capivasertib and ipatasertib, are being tested in phase III clinical trials for cancer therapy. Here, we highlight recent progress of Akt signaling pathway, review the up-to-date data from clinical studies of Akt inhibitors and discuss the potential biomarkers that may help personalized treatment of cancer with Akt inhibitors. In addition, we also discuss how Akt may confer the vulnerability of cancer cells to some kinds of anticancer agents.

The aromatase inhibitor letrozole restores FADS2 function in ER+ MCF7 human breast cancer cells

PURPOSE

Plasticity in fatty acid metabolism is increasingly recognized as a major feature influencing cancer progression and efficacy of treatments. Estrogen receptor positive MCF7 human breast cancer cells have long been known to have no FADS2-mediated Δ6-desaturase activity. Our objective was to examine the effect of estrogen and the "antiestrogen" aromatase inhibitor letrozole, on Δ5- and Δ6-desaturase synthesized fatty acids in vitro.

METHODS

Eicosa-11,14-dienoic acid (20:2n-6), a known substrate for both FADS1 and FADS2, was used as a sentinel of relative FADS2 and FADS1 activity. MCF7 cells and four additional estrogen responsive wild type cell lines (HepG2, SK-N-SH, Y79 and Caco2) were studied. FAME were quantified by GC-FID and structures identified by GCCACI-MS/MS.

RESULTS

In all five cell lines, estrogen caused a dose dependent decrease in sciadonic acid (5,11,14-20:3, ScA) via apparent inhibition of FADS1 activity, and had no effect on FADS2 catalyzed synthesis of dihomo-gamma linolenic acid (8,11,14-20:3; DGLA). In MCF7 cells, letrozole caused a dose dependent increase in FADS2-catalyzed DGLA synthesis, which plateaued in SK-N-SH cells.

CONCLUSION

Letrozole restores Δ6-desaturase mediated synthesis of the anti-inflammatory PGE1-precursor DGLA in vitro and is the first endocrine-active agent to have opposing effects on FADS1 and FADS2 catalyzed activities.

USP35, regulated by estrogen and AKT, promotes breast tumorigenesis by stabilizing and enhancing transcriptional activity of estrogen receptor α

Although endocrine therapies targeting estrogen receptor α (ERα) are effective in managing ER positive (+) breast cancer, many patients have primary resistance or develop resistance to endocrine therapies. In addition, ER+ breast cancer with PIK3CA activating mutations and 11q13-14 amplification have poor survival with unclear mechanism. We uncovered that higher expression of deubiquitinase USP35, located in 11q14.1, was associated with ER+ breast cancer and poor survival. Estrogen enhanced USP35 protein levels by downregulating USP35-targeting miRNA-140-3p and miRNA-26a-5p. USP35 promoted the growth of ER+ breast cancer in vitro and in vivo, and reduced the sensitivity of ER+ breast cancer cells to endocrine therapies such as tamoxifen and fulvestrant. Mechanistically, USP35 enhanced ERα stability by interacting and deubiquitinating ERα, and transcriptional activity of ERα by interacting with ERα in DNA regions containing estrogen response element. In addition, AKT, a key effector of PI3K, phosphorylated USP35 at Serine613, which promoted USP35 nuclear translocation, ERα transcriptional activity, and the growth of ER+ breast cancer cells. Our data indicate that USP35 and ERα form a positive feedback loop in promoting the growth of ER+ breast cancer. USP35 may be a treatment target for ER+ breast cancer with endocrine resistance or with PIK3CA mutations or hyperactivation of the PI3K pathway.

Grb2 binding induces phosphorylation-independent activation of Shp2

The regulation of phosphatase activity is fundamental to the control of intracellular signalling and in particular the tyrosine kinase-mediated mitogen-activated protein kinase (MAPK) pathway. Shp2 is a ubiquitously expressed protein tyrosine phosphatase and its kinase-induced hyperactivity is associated with many cancer types. In non-stimulated cells we find that binding of the adaptor protein Grb2, in its monomeric state, initiates Shp2 activity independent of phosphatase phosphorylation. Grb2 forms a bidentate interaction with both the N-terminal SH2 and the catalytic domains of Shp2, releasing the phosphatase from its auto-inhibited conformation. Grb2 typically exists as a dimer in the cytoplasm. However, its monomeric state prevails under basal conditions when it is expressed at low concentration, or when it is constitutively phosphorylated on a specific tyrosine residue (Y160). Thus, Grb2 can activate Shp2 and downstream signal transduction, in the absence of extracellular growth factor stimulation or kinase-activating mutations, in response to defined cellular conditions. Therefore, direct binding of Grb2 activates Shp2 phosphatase in the absence of receptor tyrosine kinase up-regulation.

microRNA-302c-3p inhibits renal cell carcinoma cell proliferation by targeting Grb2-associated binding 2 (Gab2)

The expression and biological function of Grb2-associated binding 2 (Gab2) in renal cell carcinoma (RCC) cells was tested here. We showed that Gab2 expression was significantly elevated in human RCC tissues and RCC cells. It was correlated with over-activation of Akt and downregulation of microRNA-302c-3p ("miR-302c-3p"), a putative Gab2-targeting microRNA. Knockdown of Gab2 inhibited Akt activation and 786-O RCC cell proliferation. Reversely, forced over-expression of Gab2 led to Akt hyper-activation to facilitate 786-O cell proliferation. Exogenous expression of miR-302c caused Gab2 downregulation, Akt inhibition and 786-O cell proliferation inhibition. On the other hand, miR-302c-3p depletion by expressing its anti-sense ("antagomiR-302c") led to Gab2 upregulation, Akt activation and increased 786-O cell proliferation. Significantly, miR-302c-3p failed to affect the proliferation of 786-O cells with shRNA-depleted Gab2. Together, we suggest that miR-302c-3p depletion in human RCC cells leads to Gab2 over-expression, Akt hyper-activation and cell proliferation.

Effects of Grb2-associated binding protein 2-specific siRNA on the migration and invasion of MG-63 osteosarcoma cells

To investigate the association between the expression of growth factor receptor binding protein 2-associated binding protein 2 (Gab2) in human osteosarcoma as well as the effects of Gab2 on invasion and metastasis, human MG-63 osteosarcoma cells were transfected with small interfering (si)RNA plasmid. Gab2 protein and mRNA expression levels were detected using western blotting and reverse transcription-polymerase chain reaction, respectively. The cell migration and invasion abilities were detected using in vitro chemotaxis and invasion assays, respectively, following siRNA vector expression. Gab2 was markedly expressed in MG-63 cells. The Gab2 protein and mRNA expression levels of the cells transfected with Gab2 siRNA (siGab2/MG-63) were reduced compared with those of the cells transfected with scrambled siRNA (Scr/MG-63). The chemotaxis assay demonstrated that the migration capacity of siGab2/MG-63 cells induced by 10 µg/l epidermal growth factor, was significantly reduced compared with that of the MG-63 and Scr/MG-63 cells (P<0.01). In comparison with Scr/MG-63 and MG-63 cells, a reduced number of siGab2/MG-63 cells invaded the Matrigel matrix, demonstrating that the in vitro invasion capacity was significantly decreased (P<0.01). Decreasing Gab2 expression levels using siRNA interference inhibited the migration and invasion ability of human MG-63 osteosarcoma cells.

Critical Role for GAB2 in Neuroblastoma Pathogenesis through the Promotion of SHP2/MYCN Cooperation

Growing evidence suggests a major role for Src-homology-2-domain-containing phosphatase 2 (SHP2/PTPN11) in MYCN-driven high-risk neuroblastoma, although biologic confirmation and a plausible mechanism for this contribution are lacking. Using a zebrafish model of MYCN-overexpressing neuroblastoma, we demonstrate that mutant ptpn11 expression in the adrenal gland analog of MYCN transgenic fish promotes the proliferation of hyperplastic neuroblasts, accelerates neuroblastomagenesis, and increases tumor penetrance. We identify a similar mechanism in tumors with wild-type ptpn11 and dysregulated Gab2, which encodes a Shp2 activator that is overexpressed in human neuroblastomas. In MYCN transgenic fish, Gab2 overexpression activated the Shp2-Ras-Erk pathway, enhanced neuroblastoma induction, and increased tumor penetrance. We conclude that MYCN cooperates with either GAB2-activated or mutant SHP2 in human neuroblastomagenesis. Our findings further suggest that combined inhibition of MYCN and the SHP2-RAS-ERK pathway could provide effective targeted therapy for high-risk neuroblastoma patients with MYCN amplification and aberrant SHP2 activation.

Gab2 mediates hepatocellular carcinogenesis by integrating multiple signaling pathways

Our previous studies have found that Growth factor receptor-bound protein 2-associated binding protein 2 (Gab2)-a docking protein-governs the development of fatty liver disease. Here, we further demonstrate that Gab2 mediates hepatocarcinogenesis. Compared with a faint expression in para-carcinoma tissue, Gab2 was highly expressed in ∼60-70% of human hepatocellular carcinoma (HCC) specimens. Deletion of Gab2 dramatically suppressed diethylnitrosamine-induced HCC in mice. The oncogenic effects of Gab2 in HepG2 cells were promoted by Gab2 overexpression but were rescued by Gab2 knockdown. Furthermore, Gab2 knockout in HepG2 cells restrained cell proliferation, migration and tumor growth in nude mice. Signaling pathway analysis with protein kinase inhibitors demonstrated that oncogenic regulation by Gab2 in hepatic cells involved multiple signaling molecules, including ERK, Akt, and Janus kinases (Jaks), especially those that mediate inflammatory signaling. IL-6 signaling was increased by Gab2 overexpression and impaired by Gab2 deletion via regulation of Jak2 and signal transducer and activator of transcription 3 phosphorylation and the expression of downstream genes, such as Bcl-2 (B-cell lymphoma 2), c-Myc, MMP7 (matrix metalloproteinase-7), and cyclin D1in vitro and in vivo These data indicate that Gab2 mediates the pathologic progression of HCC by integrating multiple signaling pathways and suggest that Gab2 might be a powerful therapeutic target for HCC.-Cheng, J., Zhong, Y., Chen, S., Sun, Y., Huang, L., Kang, Y., Chen, B., Chen, G., Wang, F., Tian, Y., Liu, W., Feng, G.-S., Lu, Z. Gab2 mediates hepatocellular carcinogenesis by integrating multiple signaling pathways.

Physical Confirmation and Comparative Genomics of the Rat Mammary carcinoma susceptibility 3 Quantitative Trait Locus

Human breast and rat mammary cancer susceptibility are complex phenotypes where complete sets of risk associated loci remain to be identified for both species. We tested multiple congenic rat strains to physically confirm and positionally map rat Mammary carcinoma susceptibility 3 (Mcs3)-a mammary cancer resistance allele previously predicted at Rattus norvegicus chromosome 1 (RNO1). The mammary cancer susceptible Wistar Furth (WF) strain was the recipient, and the mammary cancer resistant Copenhagen (Cop) strain was the RNO1-segment donor for congenics. Inbred WF females averaged 6.3 carcinogen-induced mammary carcinomas per rat. Two WF.Cop congenic strains averaged 2.8 and 3.4 mammary carcinomas per rat, which confirmed Mcs3 as an independently acting allele. Two other WF.Cop congenic strains averaged 6.6 and 8.1 mammary carcinomas per rat, and, thus, did not contain Mcs3 Rat Mcs3 was delimited to 27.8 Mb of RNO1 from rs8149408 to rs105131702 (RNO1:143700228-171517317 of RGSC 6.0/rn6). Human genetic variants with p values for association to breast cancer risk below 10^-7 had not been reported for Mcs3 orthologous loci; however, human variants located in Mcs3-orthologous regions with potential association to risk (10^-7 < p < 10^-3) were listed in some population-based studies. Further, rat Mcs3 contains sequence orthologous to human 11q13/14-a region frequently amplified in female breast cancer. We conclude that Mcs3 is an independently acting mammary carcinoma resistance allele. Human population-based, genome-targeted association studies interrogating Mcs3 orthologous loci may yield novel breast cancer risk associated variants and genes.

The EMSY Gene Collaborates with CCND1 in Non-Small Cell Lung Carcinogenesis

Background: Lung cancer is the leading cause of cancer deaths. The main risk factor is smoking but the risk is also associated with various genetic and epigenetic components in addition to environmental factors. Increases in the gene copy numbers due to chromosomal amplifications constitute a common mechanism for oncogene activation. A gene-dense region on chromosome 11q13 which harbors four core regions that are frequently amplified, has been associated with various types of cancer. The important cell cycle regulatory protein cyclin D1 (CCND1) is an essential driver of the first core region of the Chr11q13 amplicon. Deregulation of CCND1 has been associated with different kinds of human malignancies including lung cancer. The EMSY (c11orf30) gene has been proposed as the possible driver of the fourth core of the 11q13 amplicon and its amplification has been associated with breast and ovarian cancers. There is no report in the literature investigating the EMSY gene in lung cancer. Methods: In this study, expression levels of the EMSY and CCND1 genes were investigated in 85 patients with non small cell lung cancer by Real Time PCR. Results: Expression of the EMSY and CCND1 genes were increased in 56 (65.8%) and 50 (58.8%) of the patients, respectively. Both genes showed a higher expression in the tumors when compared to normal tissues. A strong correlation was present between the expression rates of both genes (p<0.001). Patients with adenocarcinoma had higher expression levels of both genes (p=0.02). Conclusion: We conclude that EMSY and CCND1 work in collaboration and contribute to the pathogenesis of lung cancer.

Transcriptome- and proteome-oriented identification of dysregulated eIF4G, STAT3, and Hippo pathways altered by PIK3CA H1047R in HER2/ER-positive breast cancer

PURPOSE

Phosphatidylinositol 3-kinase (PI3K)/AKT pathway aberrations are common in human breast cancer. Furthermore, PIK3CA mutations are commonly associated with resistance to anti-epidermal growth factor receptor 2 (HER2) or anti-estrogen receptor (ER) agents in HER2 or ER positive (HER2⁺/ER⁺) breast cancer. Hence, deciphering the underlying mechanisms of PIK3CA mutations in HER2⁺/ER⁺ breast cancer would provide novel insights into elucidating resistance to anti-HER2/ER therapies.

METHODS

In this study, we systematically investigated the biological consequences of PIK3CA ^H1047R in HER2⁺/ER⁺ breast cancer by uniquely incorporating mRNA transcriptomic data from The Cancer Genome Atlas and proteomic data from reverse-phase protein arrays.

RESULTS

Our integrative bioinformatics analyses revealed that several important pathways such as STAT3 and VEGF/hypoxia were selectively altered by PIK3CA ^H1047R in HER2⁺/ER⁺ breast cancer. Protein differential expression analysis indicated that an elevated eIF4G might promote tumor angiogenesis and growth via regulation of the hypoxia-activated switch in HER2⁺ PIK3CA ^H1047R breast cancer. We observed hypo-phosphorylation of EGFR in HER2⁺ PIK3CA ^H1047R breast cancer versus HER2⁺PIK3CA^wild-type (PIK3CA ^WT). In addition, ER and PIK3CA ^H1047R might cooperate to activate STAT3, MAPK, AKT, and Hippo pathways in ER⁺ PIK3CA ^H1047R breast cancer. A higher YAP_pS127 level was observed in ER⁺ PIK3CA ^H1047R patients than that in an ER⁺ PIK3CA ^WT subgroup. By examining breast cancer cell lines having both microarray gene expression and drug treatment data from the Genomics of Drug Sensitivity in Cancer and the Stand Up to Cancer datasets, we found that the elevated YAP1 mRNA expression was associated with the resistance of BCL-2 family inhibitors, but with the sensitivity to MEK/MAPK inhibitors in breast cancer cells.

CONCLUSIONS

In summary, these findings shed light on the functional consequences of PIK3CA ^H1047R-driven breast tumorigenesis and resistance to the existing therapeutic agents in HER2⁺/ER⁺ breast cancer.

GAB2 promotes cell proliferation by activating the ERK signaling pathway in hepatocellular carcinoma

Grb2-associated binding protein 2 (GAB2), a key member of the family of Gab scaffolding adaptors, is important in the phospoinositide3-kinase (PI3K) and extracellular signal-regulated kinase (ERK) signaling pathways, and is closely associated with cell proliferation, cell transformation, and tumor progression. But its role in hepatocellular carcinoma (HCC) is still unknown. In this study, we investigated the expression of GAB2 and its potential clinical and biological significances in HCC. Western bolt and immunohistochemistrical analyses revealed that GAB2 was obviously upregulated in HCC tissues. Meanwhile, GAB2 was significantly associated with histological grade, tumor size, and the proliferation marker Ki-67 through our further analysis. The Kaplan-Meier survival curves also showed that increased GAB2 expression was directly correlated with poor prognosis in HCC patients and served as an independent prognostic marker of overall survival. Moreover, serum starvation-refeeding, RNA interference, CCK-8, EDU, colony formation, and flow-cytometry analyses were all performed with the purpose of investigating GAB2's regulation of HCC cell proliferation. Our results indicated that GAB2 progressively accumulated when cells entered into S phase. Consistently, cell proliferation was distinctly hindered by small interfering RNA. More interestingly, we discovered that GAB2 promoted cell proliferation by enhancing ERK signaling and GAB2-induced cell proliferation was inhibited by the inhibition of ERK activation. Finally, GAB2 was verified to be able to confer doxorubicin resistance in HCC cells. In summary, these data demonstrated that GAB2 might promote HCC cell proliferation by enhancing ERK signaling, and all above findings provided a potential therapeutic strategy for the treatment of HCC.

RPPA-based protein profiling reveals eIF4G overexpression and 4E-BP1 serine 65 phosphorylation as molecular events that correspond with a pro-survival phenotype in chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL), the most common adult leukemia, remains incurable despite advancements in treatment regimens over the past decade. Several expression profile studies have been pursued to better understand CLL pathogenesis. However, these large-scale studies only provide information at the transcriptional level. To better comprehend the differential protein changes that take place in CLL, we performed a reverse-phase protein array (RPPA) analysis using 167 different antibodies on B-cell lysates from 18 CLL patients and 6 normal donors. From our analysis, we discovered an enrichment of protein alterations involved with mRNA translation, specifically upregulation of the translation initiator eIF4G and phosphorylation of the cap-dependent translation inhibitor 4E-BP1 at serine 65. Interestingly, 4E-BP1 phosphorylation occurred independently of AKT phosphorylation, suggesting a disconnect between PI3K/AKT pathway activation and 4E-BP1 phosphorylation. Based on these results, we treated primary CLL samples with NVP-BEZ235, a PI3K/mTOR dual inhibitor, and compared its apoptotic-inducing potential against the BTK inhibitor Ibrutinib and the PI3Kδ inhibitor Idelalisib. We demonstrated that treatment with NVP-BEZ235 caused greater apoptosis, greater apoptotic cleavage of eIF4G, and greater dephosphorylation of 4E-BP1 in primary CLL cells. Taken together, these results highlight the potential dependence of eIF4G overexpression and 4E-BP1 phosphorylation in CLL survival.

MicroRNA-197 inhibits cell proliferation by targeting GAB2 in glioblastoma

Glioblastoma is the most common type of primary brain tumor in adults, and is usually fatal in a short duration. Acquiring a better understanding of the pathogenic mechanisms of glioblastoma is essential to the design of effective therapeutic strategies. Grb2-associated binding protein 2 (GAB2) is a member of the daughter of sevenless/Gab family of scaffolding adapters, and has been reported to be important in the development and progression of human cancer. Previously, it has been reported that GAB2 is expressed at high levels in glioma, and may serve as a useful prognostic marker for glioma and a novel therapeutic target for glioma invasion intervention. Elucidating why GAB2 is overexpressed in glioma, and investigating how to downregulate it will assist in further understanding the pathogenesis and progression of the disease, and to offer novel targets for therapy. The present study used in situ hybridization to detect microRNA (miR)‑197 expression levels and Targetscan to predict that the 3'-UTR of GAB2 was targeted by miR-197. Northern blotting and reverse transcription‑quantitative polymerase chain reaction were also conducted in the current study. miR-197 is downregulated in glioblastoma tissues, compared with adjacent normal tissues, however it involvement continues to be detected in the disease. The results of the present study demonstrated that miR‑197, as a tumor suppressor gene, inhibited proliferation by regulating GAB2 in glioblastoma cells. Furthermore, GAB2 was not only upregulated in glioma, but its expression levels were also associated with the grades of glioma severity. In addition, overexpression of GAB2 suppressed the expression of miR‑197 in glioblastoma cells. Therefore, restoration of miR‑197 and targeting GAB2 may be used, in conjunction with other therapies, to prevent the progression of glioblastoma.

Structure and function of Gab2 and its role in cancer (Review)

The docking proteins of the Grb-associated binder (Gab) family transduce cellular signals between receptors and intracellular downstream effectors, and provide a platform for protein-protein interactions. Gab2, a key member of the Gab family of proteins, is involved in the amplification and integration of signal transduction, evoked by a variety of extracellular stimuli, including growth factors, cytokines and antigen receptors. Gab2 protein lacks intrinsic catalytic activity; however, when phosphorylated by protein-tyrosine kinases (PTKs), Gab2 recruits several Src homology-2 (SH2) domain-containing proteins, including the SH2-containing protein tyrosine phosphatase 2 (SHP2), the p85 subunit of phosphoinositide-3 kinase (PI3K), phospholipase C-γ (PLCγ)1, Crk, and GC-GAP. Through these interactions, the Gab2 protein triggers various downstream signal effectors, including SHP2/rat sarcoma viral oncogene/RAF/mitogen-activated protein kinase kinase/extracellular signal-regulated kinase and PI3K/AKT, involved in cell growth, differentiation, migration and apoptosis. It has been previously reported that aberrant Gab2 and/or Gab2 signaling is closely associated with human tumorigenesis, particularly in breast cancer, leukemia and melanoma. The present review aimed to focus on the structure and effector function of Gab2, its role in cancer and its potential for use as an effective therapeutic target.

Enhanced GAB2 Expression Is Associated with Improved Survival in High-Grade Serous Ovarian Cancer and Sensitivity to PI3K Inhibition

Identification of genomic alterations defining ovarian carcinoma subtypes may aid the stratification of patients to receive targeted therapies. We characterized high-grade serous ovarian carcinoma (HGSC) for the association of amplified and overexpressed genes with clinical outcome using gene expression data from 499 HGSC patients in the Ovarian Tumor Tissue Analysis cohort for 11 copy number amplified genes: ATP13A4, BMP8B, CACNA1C, CCNE1, DYRK1B, GAB2, PAK4, RAD21, TPX2, ZFP36, and URI. The Australian Ovarian Cancer Study and The Cancer Genome Atlas datasets were also used to assess the correlation between gene expression, patient survival, and tumor classification. In a multivariate analysis, high GAB2 expression was associated with improved overall and progression-free survival (P = 0.03 and 0.02), whereas high BMP8B and ATP13A4 were associated with improved progression-free survival (P = 0.004 and P = 0.02). GAB2 overexpression and copy number gain were enriched in the AOCS C4 subgroup. High GAB2 expression correlated with enhanced sensitivity in vitro to the dual PI3K/mTOR inhibitor PF-04691502 and could be used as a genomic marker for identifying patients who will respond to treatments inhibiting PI3K signaling.

MiR125a-5p acting as a novel Gab2 suppressor inhibits invasion of glioma

Poor prognosis of glioma is due to the characteristics of high invasiveness. Recently, it was demonstrated that Gab2 was over-expressed and related to cellular migration and invasion in glioma, however, the mechanisms of regulation are still unknown. A better understanding of molecular events key to the carcinogenesis and tumor progression may facilitate development of new therapeutic targets and anti-glioma strategies. This study is the first to focus on miR125a-5p, which was predicted to regulate Gab2 with directly targeting the 3' un-translated region (3'UTR) of Gab2 and could inhibit migration and invasion of glioma cells by mediating Gab2 to affect cytoskeleton rearrangement and matrix metalloproteinases expression. Interestingly, further evaluation revealed that the miR125a-5p promoter was hypermethylated and that attenuating promoter methylation was sufficient to up-regulate miR125a-5p expression in glioma cells. Additionally, we reported that miR125a-5p was down-regulated in glioma as well as statistical analysis suggested that its expression level correlated with the World Health Organization grades of glioma (P < 0.05) and that patients with a low miR125a-5p level exhibited shorter survival time (P < 0.05). Taken together, these results reveal that miR125a-5p represents potential therapeutic targets in glioma by modulating Gab2.

Targeting protein tyrosine phosphatase SHP2 for therapeutic intervention

Protein tyrosine phosphatases have been the focus of considerable research efforts aimed at developing novel therapeutics; however, these targets are often characterized as being ‘undruggable’ due to the challenge of achieving selectivity, potency and cell permeability. More recently, there has been renewed interest in developing inhibitors of the tyrosine phosphatase SHP2 (PTPN11) in the light of its broad role in cancer, specifically juvenile myelomonocytic leukemia, and recent studies that implicate SHP2 as a key factor in breast cancer progression. Recent significant advances in the field of SHP2 inhibitor development raise the question: are we on the verge of a new era of protein tyrosine phosphatase-directed therapeutics? This article critically appraises recent developments, assesses ongoing challenges and presents a perspective on possible future directions.

Clinical significance of GAB2, a scaffolding/docking protein acting downstream of EGFR in human colorectal cancer

PURPOSE

Recent studies indicated that the scaffolding adaptor protein GAB2 (GRB2-associated binding protein 2) plays a critical role in the proliferation and migration of various cancers. This study aimed to determine the role of aberrant GAB2 expression in human colorectal cancer (CRC).

METHODS

Quantitative real-time reverse transcription polymerase chain reaction was used to evaluate GAB2 mRNA expression in 152 CRC tissues samples to determine the clinicopathological significance of GAB2 expression. We also performed in vitro proliferation assays using siGAB2-transfected CRC cells.

RESULTS

GAB2 expression in tumor colorectal tissues was significantly higher than in normal colorectal tissues (p = 0.0212). High GAB2 expression levels were associated with malignant clinicopathologic potential factors, including lymphatic invasion (p = 0.0003), venous invasion (p = 0.0170), and liver metastasis (p = 0.0144). The survival rate of patients with high GAB2 expression levels was significantly lower than that of patients with low GAB2 expression (p = 0.0074). Multivariate analysis indicated that GAB2 expression was a factor affecting lymph node metastasis. Cell proliferation was significantly suppressed by siGAB2 expression in CRC cells in vitro.

CONCLUSIONS

GAB2 expression was associated with lymph node metastasis and may play a role in the growth and metastasis of CRC. These results suggest that GAB2 is a potential therapeutic target in CRC.

Combined detection of Gab1 and Gab2 expression predicts clinical outcome of patients with glioma

Grb2-associated binder 1 (Gab1) and Gab2 play important roles in cancer cell signaling. In particular, it has been demonstrated that the upregulation of Gab2 may be correlated with the World Health Organization (WHO) grade of gliomas and that patients with high Gab2 expression levels exhibited shorter survival time. However, the prognostic value of combined expression of Gab1 and Gab2 has not been explored. Gab1 and Gab2 expression in human gliomas and non-neoplastic brain tissues was measured by immunohistochemistry. Both the expression levels of Gab1 and Gab2 proteins in glioma tissues were significantly higher than those in non-neoplastic brain tissues (both P < 0.001). In addition, the overexpression of Gab1 and Gab2 proteins were both significantly associated with advanced WHO grades (both P < 0.001) and low KPS (both P = 0.01). Moreover, the overall survival of patients with high Gab1 protein expression or high Gab2 protein expression was obviously lower than those with low expressions (both P < 0.001). Notably, glioma patients with combined overexpression of Gab1 and Gab2 proteins (Gab1-high/Gab2-high) had shortest overall survival (P < 0.001). Furthermore, multivariate analysis showed that Gab1 expression (P = 0.01), Gab2 expression (P = 0.02), and combined expression of Gab1 and Gab2 (Gab1/Gab2, P = 0.006) were all independent prognostic factors for overall survival in glioma patients. Gab1 and Gab2 proteins are differentially expressed in glioma patients and closely correlated with the biological behavior of this malignancy. Combination of Gab1 and Gab2 expression may represent a promising biomarker for prognostication of human gliomas.

Src-homology 2 domain-containing tyrosine phosphatase 2 promotes oral cancer invasion and metastasis

Background

Tumor invasion and metastasis represent a major unsolved problem in cancer pathogenesis. Recent studies have indicated the involvement of Src-homology 2 domain-containing tyrosine phosphatase 2 (SHP2) in multiple malignancies; however, the role of SHP2 in oral cancer progression has yet to be elucidated. We propose that SHP2 is involved in the progression of oral cancer toward metastasis.

Methods

SHP2 expression was evaluated in paired oral cancer tissues by using immunohistochemical staining and real-time reverse transcription polymerase chain reaction. Isogenic highly invasive oral cancer cell lines from their respective low invasive parental lines were established using a Boyden chamber assay, and changes in the hallmarks of the epithelial-mesenchymal transition (EMT) were assessed to evaluate SHP2 function. SHP2 activity in oral cancer cells was reduced using si-RNA knockdown or enforced expression of a catalytically deficient mutant to analyze migratory and invasive ability in vitro and metastasis toward the lung in mice in vivo.

Results

We observed the significant upregulation of SHP2 in oral cancer tissues and cell lines. Following SHP2 knockdown, the oral cancer cells markedly attenuated migratory and invasion ability. We observed similar results in phosphatase-dead SHP2 C459S mutant expressing cells. Enhanced invasiveness was associated with significant upregulation of E-cadherin, vimentin, Snail/Twist1, and matrix metalloproteinase-2 in the highly invasive clones. In addition, we determined that SHP2 activity is required for the downregulation of phosphorylated ERK1/2, which modulates the downstream effectors, Snail and Twist1 at a transcript level. In lung tissue sections of mice, we observed that HSC3 tumors with SHP2 deletion exhibited significantly reduced metastatic capacity, compared with tumors administered control si-RNA.

Conclusions

Our data suggest that SHP2 promotes the invasion and metastasis of oral cancer cells. These results provide a rationale for further investigating the effects of small-molecule SHP2 inhibitors on the progression of oral cancer, and indicate a previously unrecognized SHP2-ERK1/2-Snail/Twist1 pathway that is likely to play a crucial role in oral cancer invasion and metastasis.

In vivo multiplexed interrogation of amplified genes identifies GAB2 as an ovarian cancer oncogene

High-grade serous ovarian cancers are characterized by widespread recurrent copy number alterations. Although some regions of copy number change harbor known oncogenes and tumor suppressor genes, the genes targeted by the majority of amplified or deleted regions in ovarian cancer remain undefined. Here we systematically tested amplified genes for their ability to promote tumor formation using an in vivo multiplexed transformation assay. We identified the GRB2-associated binding protein 2 (GAB2) as a recurrently amplified gene that potently transforms immortalized ovarian and fallopian tube secretory epithelial cells. Cancer cell lines overexpressing GAB2 require GAB2 for survival and show evidence of phosphatidylinositol 3-kinase (PI3K) pathway activation, which was required for GAB2-induced transformation. Cell lines overexpressing GAB2 were as sensitive to PI3K inhibition as cell lines harboring mutant PIK3CA. Together, these observations nominate GAB2 as an ovarian cancer oncogene, identify an alternative mechanism to activate PI3K signaling, and underscore the importance of PI3K signaling in this cancer.

Gab2 expression in glioma and its implications for tumor invasion

Gliomas are characterized by high invasiveness and poor prognosis. Better understanding of the mechanism of invasion in glioma cells is essential to the design of effective therapy. Recently Grb2-associated binder 2 (Gab2), a member of the DOS/Gab family of scaffolding adapters, has been reported to play important roles in the development and progression of human cancers. However, it is not known whether Gab2 has any role in the migration and invasion of gliomas. This study attempts to investigate the association between Gab2 expression and progression of gliomas and the molecular mechanism of Gab2 in the glioma cell invasion. Methods. The expression of Gab2 in pairs of matched glioma tissues and their normal brain tissues was detected by Western blot. Immunohistochemistry was applied to evaluate the expression of Gab2 in 163 cases of histologically diagnosed gliomas. The invasive character of Gab2 decreased glioma cells and control glioma cells were investigated in vitro and in vivo in SCID mice brain. Results. Gab2 is found to be high expressed in gliomas and a subset of cancer cell lines. Statistical analysis suggested that the up-regulation of Gab2 correlated with the WHO grade of gliomas (p < 0.01) and that patients with high Gab2 expression levels exhibited shorter survival time (p < 0.01). In an animal experiment, knockdown of Gab2 through siRNA inhibited invasive ability of glioma cells into the brain of SCID mice. In cell research, reduction of Gab2 by siRNA inhibits the migration and invasion of glioma cells by mediating cytoskeleton rearrangement and MMPs expression. Additionally, IGF-1-induced pAkt and pmTOR phosphorylation was suppressed by the knockdown of Gab2. Conclusion. Gab2 may be a useful prognostic marker for gliomas and a novel therapeutic target for glioma invasion intervention.

Src homology phosphotyrosyl phosphatase-2 expression is an independent negative prognostic factor in human breast cancer

AIMS

Src homology phosphotyrosyl phosphatase-2 (SHP2) is a ubiquitously expressed phosphatase that plays an essential role in the downstream signalling pathways of multiple growth factor receptors, thus representing a potential target for cancer therapy. Recent studies suggest that SHP2 contributes to tumour initiation, progression and metastasis in breast cancer, yet the impact of SHP2 expression on prognosis in human breast cancer has not been evaluated.

METHODS AND RESULTS

To explore further the role of SHP2 in breast cancer, we conducted an immunohistochemical study using a tissue microarray encompassing 1401 formalin-fixed breast cancer specimens with detailed clinical annotation and outcome data. Of 1401 evaluable breast cancers, 651 (46%) were positive for SHP2. SHP2 expression was associated positively with tumour grade, lymph node status and tumour stage. In univariate survival analysis, cases with SHP2 expression had a significantly worse overall survival (OS). In multivariate analysis, SHP2 remained an independent negative prognostic factor for OS. SHP2 expression was a negative prognostic factor for OS in the luminal A and the luminal B HER2(-) intrinsic subtypes.

CONCLUSIONS

Our data demonstrate for the first time that SHP2 is an independent predictor of survival in breast cancer, suggesting that SHP2 may be a potential target for therapy.

The role of endosomal signaling triggered by metastatic growth factors in tumor progression

Within tumor microenvironment, a lot of growth factors such as hepatocyte growth factor and epidermal growth factor may induce similar signal cascade downstream of receptor tyrosine kinase (RTK) and trigger tumor metastasis synergistically. In the past decades, the intimate relationship of RTK-mediated receptor endocytosis with signal transduction was well established. In general, most RTK undergoes clathrin-dependent endocytosis and/or clathrin-independent endocytosis. The internalized receptors may sustain the signaling within early endosome, recycling to plasma membrane for subsequent ligand engagement or sorting to late endosomes/lysosome for receptor degradation. Moreover, receptor endocytosis influences signal transduction in a temporal and spatial manner for periodical and polarized cellular processes such as cell migration. The endosomal signalings triggered by various metastatic factors are quite similar in some critical points, which are essential for triggering cell migration and tumor progression. There are common regulators for receptor endocytosis including dynamin, Rab4, Rab5, Rab11 and Cbl. Moreover, many critical regulators within the RTK signal pathway such as Grb2, p38, PKC and Src were also modulators of endocytosis. In the future, these may constitute a new category of targets for prevention of tumor metastasis.

Gab2 phosphorylation by RSK inhibits Shp2 recruitment and cell motility

The scaffolding adapter protein Gab2 (Grb2-associated binder) participates in the signaling response evoked by various growth factors and cytokines. Gab2 is overexpressed in several human malignancies, including breast cancer, and was shown to promote mammary epithelial cell migration. The role of Gab2 in the activation of different signaling pathways is well documented, but less is known regarding the feedback mechanisms responsible for its inactivation. We now demonstrate that activation of the Ras/mitogen-activated protein kinase (MAPK) pathway promotes Gab2 phosphorylation on basic consensus motifs. More specifically, we show that RSK (p90 ribosomal S6 kinase) phosphorylates Gab2 on three conserved residues, both in vivo and in vitro. Mutation of these phosphorylation sites does not alter Gab2 binding to Grb2, but instead, we show that Gab2 phosphorylation inhibits the recruitment of the tyrosine phosphatase Shp2 in response to growth factors. Expression of an unphosphorylatable Gab2 mutant in mammary epithelial cells promotes an invasion-like phenotype and increases cell motility. Taken together, these results suggest that RSK is part of a negative-feedback loop that restricts Gab2-dependent epithelial cell motility. On the basis of the widespread role of Gab2 in receptor signaling, these findings also suggest that RSK plays a regulatory function in diverse receptor systems.

New insights into signalling networks regulating breast cancer stem cells

In a recent paper, Aceto and colleagues report that Src homology 2 domain-containing protein tyrosine phosphatase 2 (Shp2) plays a critical role in maintenance of breast tumour-initiating cells, and they define novel effectors downstream of Shp2 that regulate cellular invasion and self-renewal, including the transcription factors c-Myc and zinc finger E-box binding homeobox 1 and the suppressor of miRNA biogenesis lin-28 homolog B. These findings provide important mechanistic insights into breast tumourigenesis and highlight Shp2 as a potential therapeutic target.

GAB2 induces tumor angiogenesis in NRAS-driven melanoma

GAB2 is a scaffold protein with diverse upstream and downstream effectors. MAPK and PI3K signaling pathways are known effectors of GAB2. It is amplified and overexpressed in a variety of human tumors including melanoma. Here we show a previously undescribed role for GAB2 in NRAS-driven melanoma. Specifically, we found that GAB2 is co-expressed with mutant NRAS in melanoma cell lines and tumor samples and its expression correlated with metastatic potential. Co-expression of GAB2(WT) and NRAS(G12D) in melanocytes and in melanoma cells increased anchorage-independent growth by providing GAB2-expressing cells a survival advantage through upregulation of BCL-2 family of anti-apoptotic factors. Of note, collaboration of GAB2 with mutant NRAS enhanced tumorigenesis in vivo and led to an increased vessel density with strong CD34 and VEGFR2 activity. We found that GAB2 facilitiated an angiogenic switch by upregulating HIF-1α and VEGF levels. This angiogenic response was significantly suppressed with the MEK inhibitor PD325901. These data suggest that GAB2-mediated signaling cascades collaborate with NRAS-driven downstream activation for conferring an aggressive phenotype in melanoma. Second, we show that GAB2/NRAS signaling axis is non-linear and non-redundant in melanocytes and melanoma, and thus are acting independent of each other. Finally, we establish a link between GAB2 and angiogenesis in melanoma for the first time. In conclusion, our findings provide evidence that GAB2 is a novel regulator of tumor angiogenesis in NRAS-driven melanoma through regulation of HIF-1α and VEGF expressions mediated by RAS-RAF-MEK-ERK signaling.

GAB2--a scaffolding protein in cancer

Adaptor or scaffolding proteins mediate protein-protein interactions that drive the formation of protein complexes. Grb2-associated binding protein 2 (GAB2) scaffolding protein is an intermediary molecule that links plasma membrane receptor signaling including receptor tyrosine kinases with the downstream effectors, such as protein tyrosine phosphatase, nonreceptor type 11 (SHP2), p85 subunit of phosphoinositide-3 kinase (PI3-K), phospholipase C-gamma 1 (PLC-γ), v-crk sarcoma virus CT10 (CRK), Src homology 2 domain containing transforming protein 1 (SHC), and SH2 containing inositol phosphatase (SHIP). Although, well described in signal transduction, its role in cancer has recently been emerging especially in leukemia, breast and ovarian cancer, and melanoma. GAB2 is essential for two major signal transduction pathways in cancer, the PI3-K-AKT and extracellular signal-regulated kinase (ERK) signaling pathways, and thus regulates a number of key cellular processes. This review focuses on structure and function of GAB2, its regulatory proteins, emerging role in cancer, and potential as a therapeutic target.

Functional characterization of cancer-associated Gab1 mutations

Grb2-associated binder 1 (Gab1) is a docking protein that transduces signals from a variety of tyrosine kinases, including Met and the epidermal growth factor receptor (EGFR). Although the related protein Gab2 is strongly implicated in human cancer, a role for Gab1 has been less clear. However, a screen for gene mutations in breast cancer identified two somatic mutations in Gab1, Y83C and T387N. In this paper we describe the functional characterization of these Gab1 mutants. MCF-10A immortalized mammary epithelial cells overexpressing Gab1 Y83C and T387N exhibited a more elongated, fibroblastic phenotype compared with wild-type Gab1 controls. Expression of Gab1 or the mutants promoted epidermal growth factor (EGF)-independent proliferation in monolayer culture to a similar degree. However, in Matrigel culture, both mutants enhanced the formation of acini exhibiting an aberrant, branched morphology. In addition, expression of the mutants modestly increased Erk activation. The two mutants also enhanced branching morphogenesis in a different mammary epithelial cell line, HC11. To gain further insights into the mechanism of action of these mutations, we mapped Gab1 phosphorylation sites by mass spectrometry. This detected phosphorylation of T387 but ;not Y83. Cellular stimulation with EGF or hepatocyte growth factor (HGF) led to a transient, or sustained, induction of T387 phosphorylation, respectively. As T387 corresponds in position to Gab2 T391, which suppresses Gab2 signaling in a phosphorylation-dependent manner, these data support a model in which the T387N mutation abrogates negative-feedback regulation of Gab1. Interrogation of publically-available databases revealed additional cancer-associated mutations at, or in close proximity to, identified serine/threonine phosphorylation sites in other docking proteins. These data indicate that aberrant Gab1 signaling can directly contribute to breast cancer progression, and that negative feedback sites in docking proteins can be targeted by oncogenic mutations.

Functional characterization of the 19q12 amplicon in grade III breast cancers

INTRODUCTION

The 19q12 locus is amplified in a subgroup of oestrogen receptor (ER)-negative grade III breast cancers. This amplicon comprises nine genes, including cyclin E1 (CCNE1), which has been proposed as its 'driver'. The aim of this study was to identify the genes within the 19q12 amplicon whose expression is required for the survival of cancer cells harbouring their amplification.

METHODS

We investigated the presence of 19q12 amplification in a series of 313 frozen primary breast cancers and 56 breast cancer cell lines using microarray comparative genomic hybridisation (aCGH). The nine genes mapping to the smallest region of amplification on 19q12 were silenced using RNA interference in phenotypically matched breast cancer cell lines with (MDA-MB-157 and HCC1569) and without (Hs578T, MCF7, MDA-MB-231, ZR75.1, JIMT1 and BT474) amplification of this locus. Genes whose silencing was selectively lethal in amplified cells were taken forward for further validation. The effects of cyclin-dependent kinase 2 (CDK2) silencing and chemical inhibition were tested in cancer cells with and without CCNE1 amplification.

RESULTS

19q12 amplification was identified in 7.8% of ER-negative grade III breast cancer. Of the nine genes mapping to this amplicon, UQCRFS1, POP4, PLEKHF1, C19ORF12, CCNE1 and C19ORF2 were significantly over-expressed when amplified in primary breast cancers and/or breast cancer cell lines. Silencing of POP4, PLEKHF1, CCNE1 and TSZH3 selectively reduced cell viability in cancer cells harbouring their amplification. Cancer cells with CCNE1 amplification were shown to be dependent on CDK2 expression and kinase activity for their survival.

CONCLUSIONS

The 19q12 amplicon may harbour more than a single 'driver', given that expression of POP4, PLEKHF1, CCNE1 and TSZH3 is required for the survival of cancer cells displaying their amplification. The observation that cancer cells harbouring CCNE1 gene amplification are sensitive to CDK2 inhibitors provides a rationale for the testing of these chemical inhibitors in a subgroup of patients with ER-negative grade III breast cancers.

Tyrosine phosphatase SHP2 promotes breast cancer progression and maintains tumor-initiating cells via activation of key transcription factors and a positive feedback signaling loop

New cancer therapies are likely to arise from an in-depth understanding of the signaling networks influencing tumor initiation, progression and metastasis. We show a fundamental role for Src-homology 2 domain-containing phosphatase 2 (SHP2) in these processes in human epidermal growth factor receptor 2 (HER2)-positive and triple-negative breast cancers. Knockdown of SHP2 eradicated breast tumor-initiating cells in xenograft models, and SHP2 depletion also prevented invasion in three-dimensional cultures and in a transductal invasion assay in vivo. Notably, SHP2 knockdown in established breast tumors blocked their growth and reduced metastasis. Mechanistically, SHP2 activated stemness-associated transcription factors, including v-myc myelocytomatosis viral oncogene homolog (c-Myc) and zinc finger E-box binding homeobox 1 (ZEB1), which resulted in the repression of let-7 microRNA and the expression of a set of 'SHP2 signature' genes. We found these genes to be simultaneously activated in a large subset of human primary breast tumors that are associated with invasive behavior and poor prognosis. These results provide new insights into the signaling cascades influencing tumor-initiating cells as well as a rationale for targeting SHP2 in breast cancer.

Gab2 regulates the migratory behaviors and E-cadherin expression via activation of the PI3K pathway in ovarian cancer cells

Ovarian cancer, the most deadly gynecologic malignancy, is often diagnosed late and at the advanced stage when the cancer cells have already migrated and invaded into other tissues and organs. Better understanding of the mechanism of metastasis in ovarian cancer cells is essential to the design of effective therapy. In this study, we investigated the function of scaffolding adaptor protein Gab2 in ovarian cancer cells. Gab2 is found to be overexpressed in a subset of ovarian tumors and cancer cell lines. Gab2 expression mainly regulates the migratory behaviors of ovarian cancer cells. Overexpression of Gab2 promotes the migration and invasion, and down-regulates E-cadherin expression in ovarian cancer cells with low-Gab2 expression. Conversely, knockdown of Gab2 expression inhibits the migration and invasion, and promotes E-cadherin expression in ovarian cancer cells with high-Gab2 expression. By expressing Gab2 wild type and Gab2 mutants that are defective in activation the PI3K and Shp2-Erk pathways, we find that Gab2 inhibits E-cadherin expression and enhances the expression of Zeb1, a transcription factor involved in epithelial-to-mesenchymal transition (EMT), and cell migration and invasion through the activation of the PI3K pathway. Knockdown of Zeb1 expression blocks Gab2-induced suppression of E-cadherin expression and increase in cell invasion. LY294002 and GDC-0941, inhibitors of PI3K, or Rapamycin, an inhibitor of PI3K downstream target mTOR, can reverse the effects of Gab2 on migration and invasion. Overall, our studies reveal that Gab2 overexpression, via activation of the PI3K-Zeb1 pathway, promotes characteristics of EMT in ovarian cancer cells.

Characterization of the DNA copy-number genome in the blood of cutaneous T-cell lymphoma patients

Cutaneous T-cell lymphoma (CTCL) is a heterogeneous non-Hodgkin's lymphoma that may variably involve the skin, lymph nodes, and peripheral blood. Malignant burden ranges from cutaneous patches and plaques with little evidence of blood involvement to erythroderma often in association with frank leukemia, as in Sézary syndrome. Toward a better understanding of the pathogenesis of this CD4+ T-cell malignancy, we conducted a high-resolution genomic analysis combining DNA (23 samples) and mRNA (12 samples) data of peripheral blood isolates from CTCL patients across a spectrum of stages. Strikingly, even patients with limited involvement, e.g., normal CD4 counts, contained significant copy-number alterations. Defining genomic characteristics of CTCL blood involvement included gains on 8q and 17q, and deletions on 17p and chromosome 10. A consensus analysis of 108 leukemic CTCL samples demonstrated global similarities among patients with varied blood involvement, narrowing 38 of 62 loci. Toward an annotated framework for in vitro testing, we also characterized genomic alterations in five CTCL cell lines (HH, HUT78, PNO, SeAx, and Sez4), revealing intact core features of leukemic CTCL. Together, these studies produce the most comprehensive view of the leukemic CTCL genome to date, with implications for pathogenesis, molecular classification, and potential future therapeutic developments.

Pivotal role of reduced let-7g expression in breast cancer invasion and metastasis

Screening of the entire let-7 family of microRNAs (miRNA) by in situ hybridization identified let-7g as the only member, the diminished expression of which was significantly associated with lymph node metastasis and poor survival in breast cancer patients. Abrogation of let-7g expression in otherwise nonmetastatic mammary carcinoma cells elicited rapid metastasis from the orthotopic location, through preferential targets, Grb2-associated binding protein 2 (GAB2) and fibronectin 1 (FN1), and consequent activation of p44/42 mitogen-activated protein kinase (MAPK) and specific matrix metalloproteinases. Treatment with estrogen or epidermal growth factor specifically reduced the expression of mature let-7g through activation of p44/42 MAPK and subsequently stimulated expression of GAB2 and FN1, which, in turn, promoted tumor invasion. We thus identify let-7g as a unique member of the let-7 miRNA family that can serve as a prognostic biomarker in breast cancer and also propose a paradigm used by specific signaling molecules via let-7g to cooperatively promote breast cancer invasion and metastasis. Thus, let-7 family members neither possess equivalent clinicopathologic correlation nor function in breast cancer.

High-resolution genomic analysis of the 11q13 amplicon in breast cancers identifies synergy with 8p12 amplification, involving the mTOR targets S6K2 and 4EBP1

The chromosomal region 11q13 is amplified in 15-20% of breast cancers; an event not only associated with estrogen receptor (ER) expression but also implicated in resistance to endocrine therapy. Coamplifications of the 11q13 and 8p12 regions are common, suggesting synergy between the amplicons. The aim was to identify candidate oncogenes in the 11q13 region based on recurrent amplification patterns and correlations to mRNA expression levels. Furthermore, the 11q13/8p12 coamplification and its prognostic value, was evaluated at the DNA and the mRNA levels. Affymetrix 250K NspI arrays were used for whole-genome screening of DNA copy number changes in 29 breast tumors. To identify amplicon cores at 11q13 and 8p12, genomic identification of significant targets in cancer (GISTIC) was applied. The mRNA expression levels of candidate oncogenes in the amplicons [RAD9A, RPS6KB2 (S6K2), CCND1, FGF19, FGF4, FGF3, PAK1, GAB2 (11q13); EIF4EBP1 (4EBP1), PPAPDC1B, and FGFR1 (8p12)] were evaluated using real-time PCR. Resulting data revealed three main amplification cores at 11q13. ER expression was associated with the central 11q13 amplification core, encompassing CCND1, whereas 8p12 amplification/gene expression correlated to S6K2 in a proximal 11q13 core. Amplification of 8p12 and high expression of 4EBP1 or FGFR1 was associated with a poor outcome in the group. In conclusion, single nucleotide polymorphism arrays have enabled mapping of the 11q13 amplicon in breast tumors with high resolution. A proximal 11q13 core including S6K2 was identified as involved in the coamplification/coexpression with 8p12, suggesting synergy between the mTOR targets S6K2 and 4EBP1 in breast cancer development and progression.

Overexpression of Grb2-associated binder 2 in human lung cancer

Objective: Grb2-associated binder 2 (Gab2), a member of the family of Gab scaffolding adaptors, transmits and amplifies the signals from receptor tyrosine kinases. A recent study demonstrated that Gab2 was over-expressed in breast cancers and metastatic melanomas, and Gab2 was an oncogenic protein. However, the roles of Gab2 in lung cancers are largely unknown.

Method: In this study, to investigate whether Gab2 expression could be a characteristic of lung cancers, we analyzed the expression of Gab2 in 88 lung frozen tissue samples and 122 paraffin-embedded tissue specimens, using quantitative real-time-PCR, immunohistochemistry and western blot.

Results: We found that the positive expression rate of Gab2 in the tumor tissues, as detected by immunohistochemistry, 62.5% in squamous cell cancers, 51.35% in adenocarcinomas, and 75% in other types of lung cancers, was significantly higher than that (12%) in normal lung tissues. The mRNA expression detected by quantitative real-time-PCR and protein expression detected by western blotting in different groups were consistent with the immunohistochemical results.

Conclusion: Our data indicate that Gab2 is over-expressed in malignant lung tissues compared with that in normal lung tissues, and suggest that Gab2 expression may play a role in lung cancer development.

Gab2 regulates cytoskeletal organization and migration of mammary epithelial cells by modulating RhoA activation

The oncogenic signal transducer Gab2 mediates altered cytoskeletal organization and enhanced cell migration of mammary epithelial cells via down-regulation of RhoA activity. This sheds new light on the role of Gab2 in cancer cell metastasis.

The docking protein Gab2 is overexpressed in several human malignancies, including breast cancer, and is associated with increased metastatic potential. Here we report that Gab2 overexpression in MCF-10A mammary epithelial cells led to delayed cell spreading, a decrease in stress fibers and mature focal adhesions, and enhanced cell migration. Expression of a Gab2 mutant uncoupled from 14-3-3-mediated negative feedback (Gab2^2×A) led to a more mesenchymal morphology and acquisition of invasive potential. Expression of either Gab2 or Gab2^2×A led to decreased activation of RhoA, but only the latter increased levels of Rac-GTP. Expression of constitutively active RhoA in MCF-10A/Gab2 cells restored stress fibers and focal adhesions, indicating that Gab2 signals upstream of RhoA to suppress these structures. Mutation of the two Shp2-binding sites to phenylalanine (Gab2^ΔShp2) markedly reduced the effects of Gab2 on cellular phenotype and RhoA activation. Expression of Gab2 or Gab2^2×A, but not Gab2^ΔShp2, promoted Vav2 phosphorylation and plasma membrane recruitment of p190A RhoGAP. Knockdown of p190A RhoGAP reversed Gab2-mediated effects on stress fibers and focal adhesions. The identification of a novel pathway downstream of Gab2 involving negative regulation of RhoA by p190A RhoGAP sheds new light on the role of Gab2 in cancer progression.

Docking proteins

Docking proteins comprise a distinct category of intracellular, noncatalytic signalling protein, that function downstream of a variety of receptor and receptor-associated tyrosine kinases and regulate diverse physiological and pathological processes. The growth factor receptor bound 2-associated binder/Daughter of Sevenless, insulin receptor substrate, fibroblast growth factor receptor substrate 2 and downstream of tyrosine kinases protein families fall into this category. This minireview focuses on the structure, function and regulation of these proteins.