Stimulation of β1-Integrin Function by Epidermal Growth Factor and Heregulin-β Has Distinct Requirements for erbB2 but a Similar Dependence on Phosphoinositide 3-OH Kinase

Integrins and growth factor receptors are important participants in cellular adhesion and migration. The EGF receptor (EGFR) family of tyrosine kinases and the β1-integrin adhesion receptors are of particular interest, given the implication for their involvement in the initiation and progression of tumorigenesis. We used adhesion and chemotaxis assays to further elucidate the relationship between these two families of transmembrane signaling molecules. Specifically, we examined integrin-mediated adhesive and migratory characteristics of the metastatic breast carcinoma cell line MDA-MB-435 in response to stimulation with growth factors that bind to and activate the EGFR or erbB3 in these cells. Although ligand engagement of the EGFR stimulated modest β1-dependent increases in cell adhesion and motility, heregulin-β (HRGβ) binding to the erbB3 receptor initiated rapid and potent induction of breast carcinoma cell adhesion and migration and required dimerization of erbB3 with erbB2. Pharmacologic inhibitors of phosphoinositide 3-OH kinase (PI 3-K) or transient expression of dominant negative forms of PI 3-K inhibited both EGF- and HRGβ-mediated adhesion and potently blocked HRGβ- and EGF-induced cell motility. Our results illustrate the critical role of PI 3-K activity in signaling pathways initiated by the EGFR or erbB3 to up-regulate β1-integrin function.     

DGKZ promotes TGFβ signaling pathway and metastasis in triple-negative breast cancer by suppressing lipid raft-dependent endocytosis of TGFβR2

Diacylglycerol kinase ζ (DGKZ) is a diacylglycerol kinase that metabolizes diacylglycerol to yield phosphatidic acid, and its function in breast cancer progression remains unclear. In this study, via screening of a CRISPR-Cas9 knockout library containing lipid metabolic genes, DGKZ was identified as a potential prometastatic gene. We first confirmed that high DGKZ expression correlated with tumor progression and poor prognosis in patients. Next, knockout of DGKZ in triple-negative breast cancer cell lines were found to significantly inhibit metastatic behaviors in vitro and in vivo, whereas its overexpression increased the metastatic potential of cell lines. Mechanistic studies based on RNA sequencing and bioinformatic analysis indicated that DGKZ might regulate cell metastasis by promoting epithelial–mesenchymal transition via the transforming growth factor β (TGFβ) signaling pathway. Furthermore, we found that overexpression of DGKZ activated the TGFβ/TGFβR2/Smad3 signaling pathway by inhibiting the degradation of TGFβR2 through suppression of caveolin/lipid raft-dependent endocytosis. Moreover, the caveolin/lipid raft-dependent endocytosis of TGFβR2 was regulated by the metabolite phosphatidic acid, which might alter TGFβR2 partitioning in lipid rafts and nonlipid rafts by affecting the fluidity of the plasma membrane. These findings suggested that DGKZ is a novel promoter of metastasis and that it could be a potential prognostic indicator in patients with triple-negative breast cancer.Subject terms: Breast cancer, Cell migration     

Diacylglycerol Kinase ζ Regulates Actin Cytoskeleton Reorganization through Dissociation of Rac1 from RhoGDI

Activation of Rac1 GTPase signaling is stimulated by phosphorylation and release of RhoGDI by the effector p21-activated kinase 1 (PAK1), but it is unclear what initiates this potential feed-forward mechanism for regulation of Rac activity. Phosphatidic acid (PA), which is produced from the lipid second messenger diacylglycerol (DAG) by the action of DAG kinases (DGKs), is known to activate PAK1. Here, we investigated whether PA produced by DGKζ initiates RhoGDI release and Rac1 activation. In DGKζ-deficient fibroblasts PAK1 phosphorylation and Rac1–RhoGDI dissociation were attenuated, leading to reduced Rac1 activation after platelet-derived growth factor stimulation. The cells were defective in Rac1-regulated behaviors, including lamellipodia formation, membrane ruffling, migration, and spreading. Wild-type DGKζ, but not a kinase-dead mutant, or addition of exogenous PA rescued Rac activation. DGKζ stably associated with PAK1 and RhoGDI, suggesting these proteins form a complex that functions as a Rac1-selective RhoGDI dissociation factor. These results define a pathway that links diacylglycerol, DGKζ, and PA to the activation of Rac1: the PA generated by DGKζ activates PAK1, which dissociates RhoGDI from Rac1 leading to changes in actin dynamics that facilitate the changes necessary for cell motility.     

Intracellular nanovesicles mediate α5β1 integrin trafficking during cell migration

Membrane traffic is an important regulator of cell migration through the endocytosis and recycling of cell surface receptors such as integrin heterodimers. Intracellular nanovesicles (INVs) are transport vesicles that are involved in multiple membrane trafficking steps, including the recycling pathway. The only known marker for INVs is tumor protein D54 (TPD54/TPD52L2), a member of the TPD52-like protein family. Overexpression of TPD52-like family proteins in cancer has been linked to poor prognosis and an aggressive metastatic phenotype, which suggests cell migration may be altered under these conditions. Here, we show that TPD54 directly binds membrane and associates with INVs via a conserved positively charged motif in its C terminus. We describe how other TPD52-like proteins are also associated with INVs, and we document the Rab GTPase complement of all INVs. Depletion of TPD52-like proteins inhibits cell migration and invasion, while their overexpression boosts motility. We show that inhibition of migration is likely due to altered recycling of α5β1 integrins in INVs.     

Thymic function affects breast cancer development and metastasis by regulating expression of thymus secretions PTMα and Tβ15b1

Breast cancer is currently one of the most common malignant tumors in women. Our previous research found that thymic dysfunction has a certain relationship with the occurrence and development of breast cancer. In order to explore whether the functional status of thymus is related to the development and metastasis of breast cancer, we use BALB/c wild type mice (BALB wt), BALB/c nude mice (BALB nu), BALB wt mice implanted with 4T1 cells (wt 4T1), BALB nu with 4T1 (nu 4T1), D-galactose treatment wt 4T1 mice (D-Gal), Thymalfasin treatment wt 4T1 mice (Tα1), Cyclophosphamide treatment wt 4T1 mice (CTX), Doxorubicin treatment wt 4T1 mice (Dox) in the research. As a result, nu 4T1, D-Gal and DOX had earlier lung metastases. Gene chip results showed that PTMα and Tβ15b1 were the most up-regulated and down-regulated genes in thymosin-related genes, respectively. Overexpression or silencing of PTMα and Tβ15b1 genes did not affect the proliferation of 4T1 cells. PTMα gene silenced, cell migration and invasion ability enhanced, while PTMα gene overexpression, the cell invasion ability weaken. In vivo, PTMα gene overexpression promotes tumor growth and lung metastasis in the early stage, but has no significant effect in the later stage. Tβ15b1 overexpression also promotes tumor growth in the early stage, but suppresses in the later stage. Tβ15b1 gene silencing inhibits tumor lung metastasis. Thus, our findings demonstrated that thymic function affects breast cancer development and metastasis by regulating expression of thymus secretions PTMα and Tβ15b1. Our study provided new directions for breast cancer therapy.     

Naa10p and IKKα interaction regulates EMT in oral squamous cell carcinoma via TGF‐β1/Smad pathway

Epithelial‐mesenchymal transition (EMT) has been contributed to increase migration and invasion of cancer cells. However, the correlate of Naa10p and IKKα with EMT in oral squamous cell carcinoma (OSCC) is not yet fully understood. In our present study, we found N‐α‐acetyltransferase 10 protein (Naa10p) and IκB kinase α (IKKα) were abnormally abundant in oral squamous cell carcinoma (OSCC). Bioinformatic results indicate that the expression of Naa10p and IKKα is correlated with TGF‐β1/Smad and EMT‐related molecules. The Transwell migration, invasion, qRT‐PCR and Western blot assay indicated that Naa10p repressed OSCC cell migration, invasion and EMT, whereas IKKα promoted TGF‐β1–mediated OSCC cell migration, invasion and EMT. Mechanistically, Naa10p inhibited IKKα activation of Smad3 through the interaction with IKKα directly in OSCC cells after TGF‐β1 stimulation. Notably, knockdown of Naa10p reversed the IKKα‐induced change in the migration, invasion and EMT‐related molecules in OSCC cells after TGF‐β1 stimulation. These findings suggest that Naa10p interacted with IKKα mediates EMT in OSCC cells through TGF‐β1/Smad, a novel pathway for preventing OSCC.     

RNF12 is regulated by AKT phosphorylation and promotes TGF-β driven breast cancer metastasis

Transforming growth factor-β (TGF-β) acts as a pro-metastatic factor in advanced breast cancer. RNF12, an E3 ubiquitin ligase, stimulates TGF-β signaling by binding to the inhibitory SMAD7 and inducing its proteasomal degradation. How RNF12 activity is regulated and its exact role in cancer is incompletely understood. Here we report that RNF12 was overexpressed in invasive breast cancers and its high expression correlated with poor prognosis. RNF12 promoted breast cancer cell migration, invasion, and experimental metastasis in zebrafish and murine xenograft models. RNF12 levels were positively associated with the phosphorylated AKT/protein kinase B (PKB) levels, and both displayed significant higher levels in the basal-like subtype compared with the levels in luminal-like subtype of breast cancer cells. Mechanistically, AKT-mediated phosphorylation induced the nuclear localization of RNF12, maintained its stability, and accelerated the degradation of SMAD7 mediated by RNF12. Furthermore, we demonstrated that RNF12 and AKT cooperated functionally in breast cancer cell migration. Notably, RNF12 expression strongly correlated with both phosphorylated AKT and phosphorylated SMAD2 levels in breast cancer tissues. Thus, our results uncovered RNF12 as an important determinant in the crosstalk between the TGF-β and AKT signaling pathways during breast cancer progression.Subject terms: Cancer, Cell biology     

OTUD7B stabilizes estrogen receptor α and promotes breast cancer cell proliferation

Breast cancer is the most common malignancy in women worldwide. Estrogen receptor α (ERα) is expressed in ∼70% of breast cancer cases and promotes estrogen-dependent cancer progression. In the present study, we identified OTU domain-containing 7B (OTUD7B), a deubiquitylase belonging to A20 subgroup of ovarian tumor protein superfamily, as a bona fide deubiquitylase of ERα in breast cancer. OTUD7B expression was found to be positively correlated with ERα in breast cancer and associated with poor prognosis. OTUD7B could interact with, deubiquitylate, and stabilize ERα in a deubiquitylation activity-dependent manner. Depletion of OTUD7B decreased ERα protein level, the expression of ERα target genes, and the activity of estrogen response element in breast cancer cells. In addition, OTUD7B depletion significantly decreased ERα-positive breast cancer cell proliferation and migration. Finally, overexpression of ERα could rescue the suppressive effect induced by OTUD7B depletion, suggesting that the ERα status was essential to the function of OTUD7B in breast carcinogenesis. In conclusion, our study revealed an interesting post-translational mechanism between ERα and OTUD7B in ERα-positive breast cancer. Targeting the OTUD7B–ERα complex may prove to be a potential approach to treat patients with ERα-positive breast cancer.Subject terms: Breast cancer, Cell growth     

Integrin αvβ3 Requirement for Sustained Mitogen-activated Protein Kinase Activity during Angiogenesis

Angiogenesis depends on growth factors and vascular cell adhesion events. Integrins and growth factors are capable of activating the ras/MAP kinase pathway in vitro, yet how these signals influence endothelial cells during angiogenesis is unknown. Upon initiation of angiogenesis with basic fibroblast growth factor (bFGF) on the chick chorioallantoic membrane (CAM), endothelial cell mitogen-activated protein (MAP) kinase (ERK) activity was detected as early as 5 min yet was sustained for at least 20 h. The initial wave of ERK activity (5–120 min) was refractory to integrin antagonists, whereas the sustained activity (4–20 h) depended on integrin αvβ3, but not β1 integrins. Inhibition of MAP kinase kinase (MEK) during this sustained αvβ3-dependent ERK signal blocked the formation of new blood vessels while not influencing preexisting blood vessels on the CAM. Inhibition of MEK also blocked growth factor induced migration but not adhesion of endothelial cells in vitro. Therefore, angiogenesis depends on sustained ERK activity regulated by the ligation state of both a growth factor receptor and integrin αvβ3.     

NOP14 regulates the growth,migration, and invasion of colorectal cancer cells by modulating the NRIP1/GSK-3β/β-catenin signaling pathway

Colorectal cancer (CRC) is the third most common cancer diagnosed worldwide. Recently, nucleolar complex protein 14 (NOP14) has been discovered to play a critical role in cancer development and progression, but the mechanisms of action of NOP14 in colorectal cancer remain to be elucidated. In this study, we used collected colorectal cancer tissues and cultured colorectal cancer cell lines (SW480, HT29, HCT116, DLD1, Lovo), and measured the mRNA and protein expression levels of NOP14 in colorectal cancer cells using qPCR and Western blotting. GFP-NOP14 was constructed and siRNA fragments against NOP14 were synthesized to investigate the importance of NOP14 for the development of colorectal cells. Transwell migration assays were used to measure cell invasion and migration, CCK-8 kits were used to measure cell activity, and flow cytometry was applied to the observation of apoptosis. We found that both the mRNA and protein levels of NOP14 were significantly upregulated in CRC tissues and cell lines. Overexpression of GFP-NOP14 markedly promoted the growth, migration, and invasion of the CRC cells HT19 and SW480, while genetic knockdown of NOP14 inhibited these behaviors. Overexpression of NOP14 promoted the expression of NRIP1 and phosphorylated inactivation of GSK-3β, leading to the upregulation of β-catenin. Genetic knockdown of NOP14 had the opposite effect on NRIP1/GSK-3/β-catenin signals. NOP14 therefore appears to be overexpressed in clinical samples and cell lines of colorectal cancer, and promotes the proliferation, growth, and metastasis of colorectal cancer cells by modulating the NRIP1/GSK-3β/β-catenin signaling pathway.Key words: Colorectal cancer, NOP14, proliferation, migration, invasion     

TGF-β induces GBM mesenchymal transition through upregulation of CLDN4 and nuclear translocation to activate TNF-α/NF-κB signal pathway

Glioblastoma (GBM) is the most common and aggressive primary malignant brain tumor. The unregulated expression of Claudin-4 (CLDN4) plays an important role in tumor progression. However, the biological role of CLDN4 in GBM is still unknown. This study aimed to determine whether CLDN4 mediates glioma malignant progression, if so, it would further explore the molecular mechanisms of carcinogenesis. Our results revealed that CLDN4 was significantly upregulated in glioma specimens and cells. The inhibition of CLND4 expression could inhibit mesenchymal transformation, cell invasion, cell migration and tumor growth in vitro and in vivo. Moreover, combined with in vitro analysis, we found that CLDN4 can modulate tumor necrosis factor-α (TNF-α) signal pathway. Meanwhile, we also validated that the transforming growth factor-β (TGF-β) signal pathway can upregulate the expression of CLDN4, and promote the invasion ability of GBM cells. Conversely, TGF-β signal pathway inhibitor ITD-1 can downregulate the expression of CLDN4, and inhibit the invasion ability of GBM cells. Furthermore, we found that TGF-β can promote the nuclear translocation of CLDN4. In summary, our findings indicated that the TGF-β/CLDN4/TNF-α/NF-κB signal axis plays a key role in the biological progression of glioma. Disrupting the function of this signal axis may represent a new treatment strategy for patients with GBM.Subject terms: CNS cancer, Epithelial-mesenchymal transition     

Integrin α6Aβ1 Induces CD81-dependent Cell Motility without Engaging the Extracellular Matrix Migration Substrate

It is well established that integrins and extracellular matrix (ECM) play key roles in cell migration, but the underlying mechanisms are poorly defined. We describe a novel mechanism whereby the integrin α6β1, a laminin receptor, can affect cell motility and induce migration onto ECM substrates with which it is not engaged. By using DNA-mediated gene transfer, we expressed the human integrin subunit α6A in murine embryonic stem (ES) cells. ES cells expressing α6A (ES6A) at the surface dimerized with endogenous β1, extended numerous filopodia and lamellipodia, and were intensely migratory in haptotactic assays on laminin (LN)-1. Transfected α6A was responsible for these effects, because cells transfected with control vector or α6B, a cytoplasmic domain α6 isoform, displayed compact morphology and no migration, like wild-type ES cells. The ES6A migratory phenotype persisted on fibronectin (Fn) and Ln-5. Adhesion inhibition assays indicated that α6β1 did not contribute detectably to adhesion to these substrates in ES cells. However, anti-α6 antibodies completely blocked migration of ES6A cells on Fn or Ln-5. Control experiments with monensin and anti-ECM antibodies indicated that this inhibition could not be explained by deposition of an α6β1 ligand (e.g., Ln-1) by ES cells. Cross-linking with secondary antibody overcame the inhibitory effect of anti-α6 antibodies, restoring migration or filopodia extension on Fn and Ln-5. Thus, to induce migration in ES cells, α6Aβ1 did not have to engage with an ECM ligand but likely participated in molecular interactions sensitive to anti-α6β1 antibody and mimicked by cross-linking. Antibodies to the tetraspanin CD81 inhibited α6Aβ1-induced migration but had no effect on ES cell adhesion. It is known that CD81 is physically associated with α6β1, therefore our results suggest a mechanism by which interactions between α6Aβ1 and CD81 may up-regulate cell motility, affecting migration mediated by other integrins.     

Regulation of Mammary Stem/Progenitor Cells by PTEN/Akt/β-Catenin Signaling

Recent evidence suggests that many malignancies, including breast cancer, are driven by a cellular subcomponent that displays stem cell-like properties. The protein phosphatase and tensin homolog (PTEN) is inactivated in a wide range of human cancers, an alteration that is associated with a poor prognosis. Because PTEN has been reported to play a role in the maintenance of embryonic and tissue-specific stem cells, we investigated the role of the PTEN/Akt pathway in the regulation of normal and malignant mammary stem/progenitor cell populations. We demonstrate that activation of this pathway, via PTEN knockdown, enriches for normal and malignant human mammary stem/progenitor cells in vitro and in vivo. Knockdown of PTEN in normal human mammary epithelial cells enriches for the stem/progenitor cell compartment, generating atypical hyperplastic lesions in humanized NOD/SCID mice. Akt-driven stem/progenitor cell enrichment is mediated by activation of the Wnt/β-catenin pathway through the phosphorylation of GSK3-β. In contrast to chemotherapy, the Akt inhibitor perifosine is able to target the tumorigenic cell population in breast tumor xenografts. These studies demonstrate an important role for the PTEN/PI3-K/Akt/β-catenin pathway in the regulation of normal and malignant stem/progenitor cell populations and suggest that agents that inhibit this pathway are able to effectively target tumorigenic breast cancer cells.     

ASIC1a stimulates the resistance of human hepatocellular carcinoma by promoting EMT via the AKT/GSK3β/Snail pathway driven by TGFβ/Smad signals

Multidrug resistance is the main obstacle to curing hepatocellular carcinoma (HCC). Acid‐sensing ion channel 1a (ASIC1a) has critical roles in all stages of cancer progression, especially invasion and metastasis, and in resistance to therapy. Epithelial to mesenchymal transition (EMT) transforms epithelial cells into mesenchymal cells after being stimulated by extracellular factors and is closely related to tumour infiltration and resistance. We used Western blotting, immunofluorescence, qRT‐PCR, immunohistochemical staining, MTT, colony formation and scratch healing assay to determine ASIC1a levels and its relationship to cell proliferation, migration and invasion. ASIC1a is overexpressed in HCC tissues, and the amount increased in resistant HCC cells. EMT occurred more frequently in drug‐resistant cells than in parental cells. Inactivation of ASIC1a inhibited cell migration and invasion and increased the chemosensitivity of cells through EMT. Overexpression of ASIC1a upregulated EMT and increased the cells’ proliferation, migration and invasion and induced drug resistance; knocking down ASIC1a with shRNA had the opposite effects. ASIC1a increased cell migration and invasion through EMT by regulating α and β‐catenin, vimentin and fibronectin expression via the AKT/GSK‐3β/Snail pathway driven by TGFβ/Smad signals. ASIC1a mediates drug resistance of HCC through EMT via the AKT/GSK‐3β/Snail pathway.     

Phosphorylation of PKCδ by FER tips the balance from EGFR degradation to recycling

Receptor degradation terminates signaling by activated receptor tyrosine kinases. Degradation of EGFR occurs in lysosomes and requires the switching of RAB5 for RAB7 on late endosomes to enable their fusion with the lysosome, but what controls this critical switching is poorly understood. We show that the tyrosine kinase FER alters PKCδ function by phosphorylating it on Y374, and that phospho-Y374-PKCδ prevents RAB5 release from nascent late endosomes, thereby inhibiting EGFR degradation and promoting the recycling of endosomal EGFR to the cell surface. The rapid association of phospho-Y374-PKCδ with EGFR-containing endosomes is diminished by PTPN14, which dephosphorylates phospho-Y374-PKCδ. In triple-negative breast cancer cells, the FER-dependent phosphorylation of PKCδ enhances EGFR signaling and promotes anchorage-independent cell growth. Importantly, increased Y374-PKCδ phosphorylation correlating with arrested late endosome maturation was identified in ∼25% of triple-negative breast cancer patients, suggesting that dysregulation of this pathway may contribute to their pathology.