High expression of the tyrosine kinase FER is an independent prognostic factor that correlates with poor survival in breast cancer patients. To investigate whether the kinase activity is essential for FER oncogenic properties, we developed an ATP analogue-sensitive knock-in allele (FER ASKI ). Specific FER kinase inhibition in MDA-MD-231 cells reduces migration, invasion, and metastasis in a mouse model of breast cancer. Using the FER ASKI system, we identify SKI family transcriptional corepressor 1 (SKOR1) as a direct FER kinase substrate. SKOR1 loss phenocopies FER inhibition, leading to impaired proliferation, migration and invasion, and inhibition of breast cancer growth and metastasis formation in mice. We show that the candidate FER phosphorylation residue, SKOR1-Y234, is essential for FER-dependent tumor progression features. Finally, our work suggests that the SKOR1-Y234 residue promotes Smad2/3 signaling through SKOR1 binding to Smad3 attenuation. Our study thus identifies SKOR1 as a mediator of FER-dependent breast cancer progression, advocating FER kinase inhibition as a candidate strategy to treat high-grade breast cancers. h4>Summary/h4> The SKI FAMILY TRANSCRIPTIONAL COREPRESSOR 1 (SKOR1) has been mainly associated with neuronal development. Now, Sluimer et al . identify SKOR1 as a new substrate of the oncogenic tyrosine kinase FER, and a driver of TNBC progression.

The ST6Gal-I sialyltransferase is upregulated in numerous cancers, and high expression of this enzyme correlates with poor patient prognosis in various malignancies, including ovarian cancer. Through its sialylation of a select cohort of cell surface receptors, ST6Gal-I modulates cell signaling to promote tumor cell survival. The goal of the present study was to investigate the influence of ST6Gal-I on another important receptor that controls cancer cell behavior, EGFR. Additionally, the effect of ST6Gal-I on cancer cells treated with the common EGFR inhibitor, gefitinib, was evaluated.
Using the OV4 ovarian cancer cell line, which lacks endogenous ST6Gal-I expression, a kinomics assay revealed that cells with forced overexpression of ST6Gal-I exhibited increased global tyrosine kinase activity, a finding confirmed by immunoblotting whole cell lysates with an anti-phosphotyrosine antibody. Interestingly, the kinomics assay suggested that one of the most highly activated tyrosine kinases in ST6Gal-I-overexpressing OV4 cells was EGFR. Based on these findings, additional analyses were performed to investigate the effect of ST6Gal-I on EGFR activation. To this end, we utilized, in addition to OV4 cells, the SKOV3 ovarian cancer cell line, engineered with both ST6Gal-I overexpression and knockdown, as well as the BxPC3 pancreatic cancer cell line with knockdown of ST6Gal-I. In all three cell lines, we determined that EGFR is a substrate of ST6Gal-I, and that the sialylation status of EGFR directly correlates with ST6Gal-I expression. Cells with differential ST6Gal-I expression were subsequently evaluated for EGFR tyrosine phosphorylation. Cells with high ST6Gal-I expression were found to have elevated levels of basal and EGF-induced EGFR activation. Conversely, knockdown of ST6Gal-I greatly attenuated EGFR activation, both basally and post EGF treatment. Finally, to illustrate the functional importance of ST6Gal-I in regulating EGFR-dependent survival, cells were treated with gefitinib, an EGFR inhibitor widely used for cancer therapy. These studies showed that ST6Gal-I promotes resistance to gefitinib-mediated apoptosis, as measured by caspase activity assays.
Results herein indicate that ST6Gal-I promotes EGFR activation and protects against gefitinib-mediated cell death. Establishing the tumor-associated ST6Gal-I sialyltransferase as a regulator of EGFR provides novel insight into the role of glycosylation in growth factor signaling and chemoresistance.

The interaction between tumor cells and the stroma environment has crucial effects on tumor cell invasive behavior. As a major component of the stroma, collagen plays a key role on cellular adhesion and epithelial-mesenchymal transition (EMT). Recently, we found that collagen type I is significantly up-regulated in gastric cancer tissues compared with their adjacent non-neoplastic tissues. However, whether collagen type I contributes to gastric cancer invasion and metastasis is not clear. Herein we show that, collagen type I induces cell scattering and cytoskeleton rearrangement, prompts cell migration and proliferation, which indicates that collagen type I is involved in promoting gastric cancer invasion and metastasis. Collagen type I is able to reduce cell-cell adhesion and enhance migration by inducing disassembly of the E-cadherin/catenin complex in gastric carcinoma cells, which is related to tyrosine phosphorylation of beta-catenin. Tyrosine phosphorylation of beta-catenin dissociates it from E-cadherin and actin cytoskeleton and facilitates its entry into the nucleus, where beta-catenin acts as a transcriptional activator inducing genes involved in cell proliferation. In conclusion, collagen type I contributes to invasion and metastasis by regulating beta-catenin tyrosine phosphorylation and nuclear translocation to promote migration and proliferation of gastric carcinoma cells.

Ephrin (Eph) signaling via Eph receptors affects neuronal structure and function. We report here that exogenous ephrinAs (EphAs) induce outgrowth of filopodial processes from astrocytes within minutes in rat hippocampal slice cultures. Identical effects were induced by release of endogenous ephrinAs by cleavage of their glycosylphosphatidylinositol anchor. Reverse transcription-PCR and immunocytochemistry revealed the expression of multiple EphA receptors (EphARs) in astrocytes. Exogenous and endogenous ephrins did not induce process outgrowth from astrocytes transfected with a kinase-dead EphAR construct, indicating that the critical EphARs were located on glia. Concomitant with these morphological changes, ephrinA reduced the frequency of (S)-3,5-dihydroxyphenylglycine-evoked NMDA receptor-mediated inward currents in CA1 pyramidal cells, elicited by release of glutamate from glial cells. The sensitivity of CA1 cell synaptic or extrasynaptic NMDA receptors was unaffected by ephrinA, indicating that this effect was mediated by inhibition of glutamate release from glial cells. Finally, ephrinA application decreased the frequency and increased the duration of spontaneous oscillations of the intracellular [Ca2+] in astrocytes. We conclude that ephrinA-EphA signaling is a pluripotent regulator of neuron-astrocyte interactions mediating rapid structural and functional plasticity.

Pancreatic cancer is characterized by its invasiveness, early metastasis, and the production of large amounts of extracellular matrix (ECM). We analyzed the influence of type I collagen and fibronectin on the regulation of cellular adhesion in pancreatic cancer cell lines to characterize the role of ECM proteins in the development of pancreatic cancer. We show that collagen type I is able to initiate a disruption of the E-cadherin adhesion complex in pancreatic carcinoma cells. This is due to the increased tyrosine phosphorylation of the complex protein beta-catenin, which correlates with collagen type I-dependent activation of the focal adhesion kinase and its association with the E-cadherin complex. The activation and recruitment of focal adhesion kinase to the E-cadherin complex depends on the interaction of type I collagen with beta1-containing integrins and an integrin-mediated activation of the cellular kinase Src. The disassembly of the E-cadherin adhesion complex correlates with the nuclear translocation of beta-catenin, which leads to an increasing expression of the beta-catenin-Lef/Tcf target genes, cyclin D1 and c-myc. In addition to that, cells grown on collagen type I show enhanced cell proliferation. We show that components of the ECM, produced by the tumor, contribute to invasiveness and metastasis by reducing E-cadherin-mediated cell-cell adhesion and enhance proliferation in pancreatic tumor cells.