Osmotic Regulation Is Required for Cancer Cell Survival under Solid Stress.

For a solid tumor to grow, it must be able to support the compressive stress that is generated as it presses against the surrounding tissue. Although the literature suggests a role for the cytoskeleton in counteracting these stresses, there has been no systematic evaluation of which filaments are responsible or to what degree. Here, using a three-dimensional spheroid model, we show that cytoskeletal filaments do not actively support compressive loads in breast, ovarian, and prostate cancer. However, modulation of tonicity can induce alterations in spheroid size. We find that under compression, tumor cells actively efflux sodium to decrease their intracellular tonicity, and that this is reversible by blockade of sodium channel NHE1. Moreover, although polymerized actin does not actively support the compressive load, it is required for sodium efflux. Compression-induced cell death is increased by both sodium blockade and actin depolymerization, whereas increased actin polymerization offers protective effects and increases sodium efflux. Taken together, these results demonstrate that cancer cells modulate their tonicity to survive under compressive solid stress.

Transcription factor ID1 is involved in decidualization of stromal cells: Implications in preeclampsia.

Decidual stromal cells (DSC) from women with preeclampsia (PE) show defective decidualization upon in vitro treatment with cAMP. Decidualization is associated with a multitude of gene expression changes and is a prerequisite for embryo implantation. We reason that the process of decidualization involves a cascade of changes in transcriptional regulators. Our prior studies have found defective decidualization of PE-DSCs as reflected by low prolactin (PRL) levels and other decidualization markers. Transcription factor array analysis identified inhibitor of DNA binding (ID1) and FOXO1 as top differentially expressed genes during decidualization. Unlike ID1, FOXO1 involvement in decidualization has been established. We hypothesized that ID1 plays a major role in regulating stromal cell decidualization. Our data shows basal ID1 mRNA expression is significantly higher in PE DSCs. Cyclic AMP-mediated decidualization significantly upregulates ID1 mRNA expression in DSCs and siRNA-mediated knockdown of ID1 significantly interferes with decidualization as shown by a reduction in PRL and FOXO1 expression, and morphologic criteria. Thus ID1 may serve as a master regulator of stromal cell differentiation and defects in ID1 expression may affect decidualization as seen in PE-DSCs.

Transcription factor AP2A affects sFLT1 expression and decidualization in decidual stromal cells: Implications to preeclampsia pathology.

Preeclampsia (PE) yields a spectrum of phenotypic expression, leading to varying degrees of hypertension, maternal renal dysfunction and placental insufficiency with resultant maternal and neonatal morbidity. Increased sFLT1 expression contributing to angiogenic factor imbalance, placental hypoxia, failed immune adaptation to the fetus and defective decidualization are among the commonly proposed theories of PE pathogenesis. Recently researchers have focused their attention on the events that occur at the maternal fetal interface as potential contributors to PE pathogenesis. Decidual stromal cells (DSC) isolated from preeclamptic women show diminished ability to decidualize upon stimulation and reduced capacity to downregulate sFlt-1 levels. In this study, we sought to gain insight into the molecular mechanism(s) involved in the aberrant decidualization capacity of PE DSC. Our findings using qRT-PCR show that PE DSCs have 6-fold higher basal levels of transcription factor AP2A (TFAP2A) RNA compared to women without PE and that expression of TFAP2A increases during decidualization but only in DSCs of normotensive (NT) women. Silencing of TFAP2A using Trilencer siRNA upregulated sFLT1 expression only in NT-DSCs but suppressed the expression of decidualization markers PRL, IGFBP1 and their regulator FOXO1 in cells from both groups. Collectively, our observations suggest that TFAP2A acts as a repressor of sFLT1 and plays a necessary role in decidualization possibly through interacting with another factor that is aberrantly expressed in PE DSCs.

Mesenchymal Stem Cells Induce Directional Migration of Invasive Breast Cancer Cells through TGF-ß.

Mesenchymal stem cells (MSCs) are recruited to the tumor microenvironment and influence tumor progression; however, how MSCs induce the invasion of cancer cells is not completely understood. Here, we used a 3D coculture model to determine how MSCs affect the migration of invasive breast cancer cells. Coculture with MSCs increases the elongation, directional migration, and traction generation of breast cancer cells. MSC-induced directional migration directly correlates with traction generation and is mediated by transforming growth factor ß (TGF-ß) and the migratory proteins rho-associated kinase, focal adhesion kinase, and matrix metalloproteinases. Treatment with MSC conditioned media or recombinant TGF-ß1 elicits a similar migration response to coculture. Taken together, this work suggests TGF-ß is secreted by MSCs, leading to force-dependent directional migration of invasive breast cancer cells. These pathways may be potential targets for blocking cancer cell invasion and subsequent metastasis.

Alterations in ovarian cancer cell adhesion drive taxol resistance by increasing microtubule dynamics in a FAK-dependent manner.

Chemorefractory ovarian cancer patients show extremely poor prognosis. Microtubule-stabilizing Taxol (paclitaxel) is a first-line treatment against ovarian cancer. Despite the close interplay between microtubules and cell adhesion, it remains unknown if chemoresistance alters the way cells adhere to their extracellular environment, a process critical for cancer metastasis. To investigate this, we isolated Taxol-resistant populations of OVCAR3 and SKOV3 ovarian cancer cell lines. Though Taxol-resistant cells neither effluxed more drug nor gained resistance to other chemotherapeutics, they did display increased microtubule dynamics. These changes in microtubule dynamics coincided with faster attachment rates and decreased adhesion strength, which correlated with increased surface ß1-integrin expression and decreased focal adhesion formation, respectively. Adhesion strength correlated best with Taxol-sensitivity, and was found to be independent of microtubule polymerization but dependent on focal adhesion kinase (FAK), which was up-regulated in Taxol-resistant cells. FAK inhibition also decreased microtubule dynamics to equal levels in both populations, indicating alterations in adhesive signaling are up-stream of microtubule dynamics. Taken together, this work demonstrates that Taxol-resistance dramatically alters how ovarian cancer cells adhere to their extracellular environment causing down-stream increases in microtubule dynamics, providing a therapeutic target that may improve prognosis by not only recovering drug sensitivity, but also decreasing metastasis.