[Show abstract][Hide abstract] ABSTRACT: Homeoproteins, a family of transcription factors that have conserved homeobox domains, play critical roles in embryonic development in a wide range of species. Accumulating studies have revealed that homeoproteins are aberrantly expressed in multiple tumors and function as either tumor promoters or suppressors. In this study, we show that two homeoproteins, HOXB13 and ALX4, are associated with epithelial to mesenchymal transition (EMT) and invasion of ovarian cancer cells. HOXB13 and ALX4 formed a complex in cells, and exogenous expression of either protein promoted EMT and invasion. Conversely, depletion of either protein suppressed invasion and induced reversion of EMT. SLUG is a C2H2-type zinc-finger transcription factor that promotes EMT in various cell lines. Knockdown of HOXB13 or ALX4 suppressed SLUG expression, and exogenous expression of either protein promoted SLUG expression. Finally, we showed that SLUG expression was essential for the HOXB13- or ALX4-mediated EMT and invasion. Our results show that HOXB13/SLUG and ALX4/SLUG axes are novel pathways that promote EMT and invasion of ovarian cancer cells.
[Show abstract][Hide abstract] ABSTRACT: Echinoderm microtubule-associated protein (EMAP)-like (EML) family proteins are microtubule-associated proteins that have a conserved hydrophobic EMAP-like protein (HELP) domain and multiple WD40 domains. In this study, we examined the role of EML4, which is a member of the EML family, in cell division. Time-lapse microscopy analysis demonstrated that EML4 depletion induced chromosome misalignment during metaphase and delayed anaphase initiation. Further analysis by immunofluorescence showed that EML4 was required for the organization of the mitotic spindle and for the proper attachment of kinetochores to microtubules. We searched for EML4-associating proteins by mass spectrometry analysis and found that the nuclear distribution gene C (NUDC) protein, which is a critical factor for the progression of mitosis, was associated with EML4. This interaction was mediated by the WD40 repeat of EML4 and by the C-terminus of NUDC. In the absence of EML4, NUDC was no longer able to localize to the mitotic spindle, whereas NUDC was dispensable for EML4 localization. Our results show that EML4 is critical for the loading of NUDC onto the mitotic spindle for mitotic progression.
No preview · Article · Mar 2015 · Cell cycle (Georgetown, Tex.)
[Show abstract][Hide abstract] ABSTRACT: The TGFbeta-mediated alteration of the tumor microenvironment plays a crucial role in tumor progression. Mesothelial cells are the primary components of the tumor microenvironment for ovarian cancer cells; however, the exact role of TGFbeta-stimulated mesothelial cells in ovarian cancer progression remains uncertain. In this report, we examined the effects of TGFbeta-treated mesothelial cells on ovarian cancer progression. We show that TGFbeta-stimulated human primary mesothelial cells (HPMCs) are able to promote cancer cell attachment and proliferation and the activation of the promoter activities of MMP-2 and MMP-9, which are metalloproteinases necessary for tumor invasion. Expression of the miR-200 family was down-regulated in HPMCs by TGFbeta stimulation, and restoration of the expression of miR-200 family members in HPMCs suppressed cancer cell attachment and proliferation. Down-regulation of the miR-200 family by TGFbeta induced fibronectin 1 production, which promoted cancer cell attachment to HPMCs. Finally, we demonstrated that the delivery of the miR-200s to mesothelial cells in mice inhibited ovarian cancer cell implantation and dissemination. Our results suggest that alteration of the tumor microenvironment by the miR-200 family could be a novel therapeutic strategy for ovarian cancer treatment.
No preview · Article · Jun 2014 · Molecular Cancer Therapeutics
[Show abstract][Hide abstract] ABSTRACT: Pleomorphic adenoma gene like-2 (PLAGL2), a member of the PLAG gene family, is a C2H2 zinc finger transcriptional factor that
is involved in cellular transformation and apoptosis. In this report, we show that PLAGL2 is associated with the organization
of stress fibers and with small guanosine triphosphatase (GTPase) activity. Depletion of PLAGL2 in two different ovarian cancer
cell lines, ES-2 and HEY, induced activation of RhoA, whereas activity of Rac1 was suppressed. Organization of actin stress
fibers and focal adhesions was significantly promoted by PLAGL2 knockdown in a RhoA-dependent manner. Conversely, exogenous
expression of PLAGL2 in MDA-MB-231 cells, a breast cancer cell line, resulted in the activation of Rac1 and the inactivation
of RhoA. In addition, PLAGL2 expression induced lamellipodia formation and disruption of stress fiber formation. Finally,
we show that CHN1 expression is essential for Rac1 inactivation in PLAGL2-depleted cells. Our results demonstrate a crucial
role of PLAGL2 in actin dynamics and give further insight into the role of PLAGL2 in cellular transformation and apoptosis.
[Show abstract][Hide abstract] ABSTRACT: Ovarian cancer is a highly invasive and metastatic disease with a poor prognosis if diagnosed at an advanced stage, which is often the case. Recent studies argue that ovarian cancer cells that have undergone epithelial to mesenchymal transition (EMT) acquire aggressive malignant properties, but the relevant molecular mechanisms in this setting are not well understood. Here we report findings from an siRNA screen that identified the homeobox transcription factor ALX1 as a novel regulator of EMT. RNAi-mediated attenuation of ALX1 expression restored E-cadherin expression and cell-cell junction formation in ovarian cancer cells, suppressing cell invasion, anchorage-independent growth and tumor formation. Conversely, enforced expression of ALX1 in ovarian cancer cells or non-tumorigenic epithelial cells induced EMT. We found that ALX1 upregulated expression of the key EMT regulator Snail (SNAI1) and that it mediated EMT activation and cell invasion by ALX1. Our results define the ALX1/Snail axis as a novel EMT pathway that mediates cancer invasion.
[Show abstract][Hide abstract] ABSTRACT: Phosphorylation of actin-binding proteins plays a pivotal role in the remodeling of the actin cytoskeleton to regulate cell migration. Palladin is an actin-binding protein that is phosphorylated by growth factor stimulation; however, the identity of the involved protein kinases remains elusive. In this study, we report that palladin is a novel substrate of extracellular signal-regulated kinase (ERK). Suppression of ERK activation by a chemical inhibitor reduced palladin phosphorylation, and expression of active MEK alone was sufficient for phosphorylation. In addition, an in vitro kinase assay demonstrated direct palladin phosphorylation by ERK. We found that Ser77 and Ser197 are essential residues for phosphorylation. Although the phosphorylation of these residues was not required for actin cytoskeletal organization, we found that expression of non-phosphorylated palladin enhanced cell migration. Finally, we show that phosphorylation inhibits the palladin association with Abl tyrosine kinase. Taken together, our results indicate that palladin phosphorylation by ERK has an anti-migratory function, possibly by modulating interactions with molecules that regulate cell migration.
[Show abstract][Hide abstract] ABSTRACT: Expression of endogenous and exogenous palladin in each cell line. (A) Expression of endogenous palladin and exogenously expressed proteins in the indicated cell lines were examined by western blotting. An arrow indicates exogenously expressed palladin, and an arrowhead indicates endogenous palladin. (B) Endogenous palladin expression and exogenously expressed proteins in the indicated cell lines were examined by western blotting.
[Show abstract][Hide abstract] ABSTRACT: Gap junctional communication, which is mediated by the connexin protein family, is essential for the maintenance of normal tissue function and homeostasis. Loss of intercellular communication results in a failure to coordinately regulate cellular functions, and it can facilitate tumorigenesis. Expression of oncogenes and stimulation with cytokines has been shown to suppress intercellular communication; however, the exact mechanism by which intercellular communication is disrupted by these factors remains uncertain. In this report, we show that Akt is essential for the disruption of gap junctional communication in v-Src-transformed cells. In addition, inhibition of Akt restores gap junctional communication after it is suppressed by TNF-α signaling. Furthermore, we demonstrate that the expression of a constitutively active form of Akt1, but not of Akt2 or Akt3, is sufficient to suppress gap junctional communication. Our results clearly define Akt1 as one of the critical regulators of gap junctional communication.
No preview · Article · Sep 2010 · Biochemical and Biophysical Research Communications
[Show abstract][Hide abstract] ABSTRACT: Human papillomaviruses (HPV) are the main etiological factor for cervical carcinoma. HPV-16 is the most prevalent high-risk HPV-genotype found in HPV-associated cancers. We studied the effect of HPV-16 E7 oncoprotein on cadherin-mediated cell adhesion. The expression of E7 strongly suppressed the cadherin-mediated cell adhesion in the rat fibroblast cell line 3Y1. This suppression was associated with the decreased expression of N-cadherin at the transcriptional level. The treatment of 3Y1 cells that express E7 (E7-3Y1) with MEK inhibitor recovered the cadherin-mediated cell adhesion together with the accumulation of N-cadherin at the cell-cell contact site. Moreover, the suppression of c-Jun, which is the element of AP-1 transcriptional factor, leads to the recovery of N-cadherin expression and cadherin-mediated cell adhesion in E7-3Y1 cells. Taken together, our results demonstrate that E7 regulates cadherin-mediated cell adhesion through the modulation of cadherin expression via the MEK-ERK and AP-1 signaling pathway.
No preview · Article · Sep 2009 · International Journal of Oncology