Loss of myosin light chain kinase induces the cellular senescence associated secretory phenotype to promote breast epithelial cell migration.

Overexpression or activation of oncogenes or loss of tumor-suppressor genes can induce cellular senescence as a defense mechanism against tumor development, thereby maintaining cellular homeostasis. However, cancer cells can circumvent this senescent state and continue to spread. Myosin light chain kinase (MLCK) is downregulated in many breast cancers.

AKT drives sustained motility following MEK inhibition via promoting SNAIL and AXL in MDA-MB-231 LM2.

The adaptive activation of alternative signaling pathways contributes to acquired resistance against targeted cancer therapies. Our previous research has shown that blocking Ras/ERK signaling promotes PI3K/AKT signaling in the lung metastatic derivative of MDA-MB-231 (LM2). Because AKT activation was required to drive sustained cell motility following MEK suppression, we extend our research to elucidate how activation of the PI3K/AKT signaling drives sustained motility following MEK inhibition.

Up-regulated fibronectin in 3D culture facilitates spreading of triple negative breast cancer cells on 2D through integrin β-5 and Src.

Using MDA-MB-231 cells as a model of triple negative breast cancer (TNBC) and its metastatic sub-cell lines that preferentially metastasize to lung, bone or brain, we found that the mRNA and protein levels of fibronectin (FN) are increased in MDA-MB-231 cells and its lung metastatic derivative, when cultivated in three-dimensional (3D) suspension cultures. The increase of FN expression in 3D was dependent on p38 mitogen-activated protein kinase (MAPK) because it was prevented by treatment of cells with SB203580, an inhibitor of p38MAPK. The up-regulated FN was converted into fibrils, and it enhanced cell spreading when cells cultured in 3D were transferred to two-dimensional (2D) culture.

Tropomyosin isoform Tpm2.1 regulates collective and amoeboid cell migration and cell aggregation in breast epithelial cells.

Metastasis dissemination is the result of various processes including cell migration and cell aggregation. These processes involve alterations in the expression and organization of cytoskeletal and adhesion proteins in tumor cells. Alterations in actin filaments and their binding partners are known to be key players in metastasis.

Loss of Tpm4.1 leads to disruption of cell-cell adhesions and invasive behavior in breast epithelial cells via increased Rac1 signaling.

Here we report the identification and characterization of a novel high molecular weight isoform of tropomyosin, Tpm4.1, expressed from the human TPM4 gene. Tpm4.

Integrin β1, myosin light chain kinase and myosin IIA are required for activation of PI3K-AKT signaling following MEK inhibition in metastatic triple negative breast cancer.

The effectiveness of targeted therapies against the Ras-ERK signaling pathway are limited due to adaptive resistance of tumor cells. Inhibition of the Ras-ERK pathway can result in activation of the PI3K-AKT pathway, thereby diminishing the therapeutic effects of targeting ERK signaling. Here we investigated the crosstalk between the Ras-ERK and PI3K-AKT pathways in MDA-MB-231 breast cancer cell lines that have a preference to metastasize to lung (LM2), brain (BrM2) or bone (BoM2).

Modeling of Menkes disease via human induced pluripotent stem cells.

Menkes disease (MD) is a copper-deficient neurodegenerative disorder that manifests severe neurologic symptoms such as seizures, lethargic states, and hypotonia. Menkes disease is due to a dysfunction of ATP7A, but the pathophysiology of neurologic manifestation is poorly understood during embryonic development. To understand the pathophysiology of neurologic symptoms, molecular and cellular phenotypes were investigated in Menkes disease-derived induced pluripotent stem cells (MD-iPSCs).

From skeletal muscle to cancer: insights learned elucidating the function of tropomyosin.

The tropomyosins (Tms) are a family of actin filament binding proteins that possess a simple dimeric α-helical coiled-coil structure along their entire length. Our knowledge of Tm structure and function has greatly expanded since they were first discovered in skeletal muscle almost 65 years ago. In multicellular organisms they exhibit extensive cell type specific isoform diversity.

Germinal center-specific protein human germinal center associated lymphoma directly interacts with both myosin and actin and increases the binding of myosin to actin.

Human germinal center associated lymphoma (HGAL) is a germinal center-specific gene whose expression correlates with a favorable prognosis in patients with diffuse large B-cell and classic Hodgkin lymphomas. HGAL is involved in negative regulation of lymphocyte motility. The movement of lymphocytes is directly driven by actin polymerization and actin-myosin interactions.

HGAL, a germinal center specific protein, decreases lymphoma cell motility by modulation of the RhoA signaling pathway.

HGAL is a germinal center (GC)-specific gene that negatively regulates lymphocyte motility and whose expression predicts improved survival of patients with diffuse large B-cell lymphoma (DLBCL) and classical Hodgkin lymphoma (cHL). We demonstrate that HGAL serves as a regulator of the RhoA signaling pathway. HGAL enhances activation of RhoA and its down-stream effectors by a novel mechanism - direct binding to the catalytic DH-domain of the RhoA-specific guanine nucleotide exchange factors (RhoGEFs) PDZ-RhoGEF and LARG that stimulate the GDP-GTP exchange rate of RhoA.

Non-muscle myosin IIB helps mediate TNF cell death signaling independent of actomyosin contractility (AMC).

Non-muscle myosin II (NM II) helps mediate survival and apoptosis in response to TNF-alpha (TNF), however, NM II's mechanism of action in these processes is not fully understood. NM II isoforms are involved in a variety of cellular processes and differences in their enzyme kinetics, localization, and activation allow NM II isoforms to have distinct functions within the same cell. The present study focused on isoform specific functions of NM IIA and IIB in mediating TNF induced apoptosis.

RSK1 drives p27Kip1 phosphorylation at T198 to promote RhoA inhibition and increase cell motility.

p90 ribosomal S6 kinase (RSK1) is an effector of both Ras/MEK/MAPK and PI3K/PDK1 pathways. We present evidence that RSK1 drives p27 phosphorylation at T198 to increase RhoA-p27 binding and cell motility. RSK1 activation and p27pT198 both increase in early G(1).

Tropomyosin as a regulator of cancer cell transformation.

Tropomyosins (Tms) are among the most studied structural proteins of the actin cytoskeleton that are implicated in neoplastic-specific alterations in actin filament organization. Decreased expression of specific nonmuscle Tm isoforms is commonly associated with the transformed phenotype. These changes in Tm expression appear to contribute to the rearrangement of microfilament bundles and morphological alterations, increased cell motility and oncogenic signaling properties of transformed cells.

HGAL, a lymphoma prognostic biomarker, interacts with the cytoskeleton and mediates the effects of IL-6 on cell migration.

HGAL is a newly identified germinal center (GC)-specific gene whose expression by the tumor cells correlates with a favorable prognosis in patients with diffuse large B-cell and classical Hodgkin lymphomas. The function of HGAL is unknown. Previous studies demonstrated that HGAL is dispensable for GC formation, immunoglobulin gene class-switch recombination, and somatic hypermutation.

Myosin light chain kinase plays a role in the regulation of epithelial cell survival.

Myosin II activation is essential for stress fiber and focal adhesion formation, and is implicated in integrin-mediated signaling events. In this study we investigated the role of acto-myosin contractility, and its main regulators, i.e.

Myosin light chain kinase and acto-myosin contractility modulate activation of the ERK cascade downstream of oncogenic Ras.

The actin cytoskeleton is recognized as an important component of both adhesion- and growth factor-dependent signaling, but its role in oncogene-dependent signaling has received much less attention. In this study, we investigated the role played by the acto-myosin cytoskeleton and its main regulators, i.e.

A critical role of tropomyosins in TGF-beta regulation of the actin cytoskeleton and cell motility in epithelial cells.

We have investigated transforming growth factor beta (TGF-beta)-mediated induction of actin stress fibers in normal and metastatic epithelial cells. We found that stress fiber formation requires de novo protein synthesis, p38Mapk and Smad signaling. We show that TGF-beta via Smad and p38Mapk up-regulates expression of actin-binding proteins including high-molecular-weight tropomyosins, alpha-actinin and calponin h2.

Modulation of acto-myosin contractility in skeletal muscle myoblasts uncouples growth arrest from differentiation.

Cell-substratum interactions trigger key signaling pathways that modulate growth control and tissue-specific gene expression. We have previously shown that abolishing adhesive interactions by suspension culture results in G(0) arrest of myoblasts. We report that blocking intracellular transmission of adhesion-dependent signals in adherent cells mimics the absence of adhesive contacts.

Alterations in tropomyosin isoform expression in human transitional cell carcinoma of the urinary bladder.

Previous studies of transformed rodent fibroblasts have suggested that specific isoforms of the actin-binding protein tropomyosin (TM) could function as suppressors of transformation, but an analysis of TM expression in patient tumor tissue is limited. The purpose of our study was to characterize expression of the different TM isoforms in human transitional cell carcinoma of the urinary bladder by immunohistochemistry and Western blot analysis. We found that TM1 and TM2 protein levels were markedly reduced and showed >60% reduction in 61% and 55% of tumor samples, respectively.

Cytoplasmic p21Cip1 is involved in Ras-induced inhibition of the ROCK/LIMK/cofilin pathway.

Accumulating evidence suggests that p21(Cip1) located in the cytoplasm might play a role in promoting transformation and tumor progression. Here we show that oncogenic H-RasV12 contributes to the loss of actin stress fibers by inducing cytoplasmic localization of p21(Cip1), which uncouples Rho-GTP from stress fiber formation by inhibiting Rho kinase (ROCK). Concomitant with the loss of stress fibers in Ras-transformed cells, there is a decrease in the phosphorylation level of cofilin, which is indicative of a compromised ROCK/LIMK/cofilin pathway.

Characterization of the metastasis-associated protein, S100A4. Roles of calcium binding and dimerization in cellular localization and interaction with myosin.

Elevated S100A4 protein expression is associated with metastatic tumor progression and appears to be a strong molecular marker for clinical prognosis. S100A4 is a calcium-binding protein that is known to form homodimers and interacts with several proteins in a calcium-dependent manner. Here we show that S100A4 localizes to lamellipodia structures in a migrating breast cancer-derived cell line and colocalizes with a known S100A4-interacting protein, myosin heavy chain IIA, at the leading edge.

Regulation of coiled-coil assembly in tropomyosins.

Tropomyosins (TMs) are a family of actin filament-binding proteins. They consist of nearly 100% alpha-helix and assemble into parallel coiled-coil dimers. In vertebrates, TMs are encoded by four genes that give rise to at least 17 distinct isoforms through the use of alternative RNA splicing and alternative promoters.

MEK mediates v-Src-induced disruption of the actin cytoskeleton via inactivation of the Rho-ROCK-LIM kinase pathway.

Cellular transformation by v-Src is believed to be caused by aberrant activation of signaling pathways that are normally regulated by cellular Src. Using normal rat kidney cells expressing a temperature-sensitive mutant of v-Src, we examined the role of the Raf/MEK/ERK, phosphatidylinositol 3-kinase/Akt, and Rho pathways in morphological transformation and cytoskeletal changes induced by v-Src. Activation of v-Src elicited a loss of actin stress fibers and focal contacts.