Myosin light chain kinase inhibitors can block invasion and adhesion of human pancreatic cancer cell lines

Increased expression of myosin light chain kinase mRNA is related to metastasis in non-small cell lung cancer

BACKGROUND

The invasiveness of tumor cells depends in large part on their motility, which in turn depends on cytoskeletal function. A major cytoskeletal component involved in cell motility is myosin II, the classical form of myosin first identified in muscle but also expressed in nonmuscle cells. Myosin II is activated by myosin light chain kinase (MLCK), which phosphorylates it on its regulatory light chain. In this context, the contribution made by MLCK to tumor cell motility and invasiveness has been investigated extensively in vitro, but clinical evidence of such a contribution has been lacking. In the present study, therefore, we examined the role of MLCK in the metastasis of non-small cell lung cancer (NSCLC) in a clinical setting.

METHODS

We measured MLCK mRNA expression in tumor samples from 39 NSCLC patients using real-time semiquantitative reverse transcription polymerase chain reaction carried out in a LightCycler. We then correlated MLCK mRNA expression with known clinicopathological factors.

RESULTS

We found that levels of MLCK mRNA expression were higher in patients who showed disease recurrence and distant metastasis than in those who did not. Moreover, the 3-year disease-free survival rate among patients showing lower levels of MLCK mRNA expression [log10(MLCK/GAPDH) <1.4] was significantly greater than among those showing higher MLCK mRNA expression [log10(MLCK/GAPDH) > or =1.4] (87.5 vs. 50.0%; log-rank test, p = 0.021).

CONCLUSION

These findings are the first clinical evidence that expression of MLCK is correlated with disease recurrence and distant metastasis in NSCLC.

Enhancement of T cell localization in mammary tumors through transient inhibition of T cell myosin function

Adoptive immunotherapy is hampered by poor lymphocyte localization in tumors. The polarized, adhesive phenotype of activated lymphocytes may contribute to this problem by making the cells prone to trapping and damage in pulmonary microvasculature. We found that transient inhibition of T cell polarization prior to i.v. infusion reduces trapping and improves tumor localization. Activated T cells were rendered nonpolar and nonadhesive by treatment with myosin light-chain kinase inhibitor ML-7. Polarity, adhesiveness, and motility recovered by 6 h after treatment, cytotoxicity, and proliferation by 24 h. ErbB2-specific T cells were infused i.v. into mice bearing ErbB2-expressing mammary tumors. ML-7 pre-treatment reduced T cell arrest in lungs by a factor of eight, improved tumor localization by 4-fold, and increased lymph node homing. Although this improvement alone proved insufficient to alter outcome in an immunotherapy experiment, this study indicates that cytoskeletal modification is a promising strategy for altering the trafficking of infused lymphocytes.

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Abstract

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Myosin phosphatase targeting subunit 1 affects cell migration by regulating myosin phosphorylation and actin assembly

Myosin II plays important roles in many contractile-like cell functions, including cell migration, adhesion, and retraction. Myosin II is activated by regulatory light chain (RLC) phosphorylation whereas RLC dephosphorylation by myosin light chain phosphatase containing a myosin phosphatase targeting subunit (MYPT1) leads to myosin inactivation. HeLa cells contain MYPT1 in addition to a newly identified human variant 2 containing an internal deletion. RLC dephosphorylation, cell migration, and adhesion were inhibited when either or both MYPT1 isoforms were knocked down by RNA interference. RLC was highly phosphorylated (60%) when both isoforms were suppressed by siRNA treatment relative to control cells (10%) with serum-starvation and ROCK inhibition. Prominent stress fibers and focal adhesions were associated with the enhanced RLC phosphorylation. The reintroduction of MYPT1 or variant 2 in siRNA-treated cells decreased stress fibers and focal adhesions. MYPT1 knockdown also led to an increase of F-actin relative to G-actin in HeLa cells. The myosin inhibitor blebbistatin did not inhibit this effect, indicating MYPT1 likely affects actin assembly independent of RLC phosphorylation. Proper expression of MYPT1 or variant 2 is critical for RLC phosphorylation and actin assembly, thus maintaining normal cellular functions by simultaneously controlling cytoskeletal architecture and actomyosin activation.

Slipping or gripping? Fluorescent speckle microscopy in fish keratocytes reveals two different mechanisms for generating a retrograde flow of actin

Fish keratocytes can generate rearward directed traction forces within front portions of the lamellipodium, suggesting that a retrograde flow of actin may also occur here but this was not detected by previous photoactivation experiments. To investigate the relationship between retrograde flow and traction force generation, we have transfected keratocytes with GFP-actin and used fluorescent speckle microscopy, to observe speckle flow. We detected a retrograde flow of actin within the leading lamellipodium that is inversely proportional to both protrusion rate and cell speed. To observe the effect of reducing contractility, we treated transfected cells with ML7, a potent inhibitor of myosin II. Surprisingly, ML7 treatment led to an increase in retrograde flow rate, together with a decrease in protrusion and cell speed, but only in rapidly moving cells. In slower moving cells, retrograde flow decreased, whereas protrusion rate and cell speed increased. These results suggest that there are two mechanisms for producing retrograde flow. One involves slippage between the cytoskeleton and adhesions, that decreases traction force production. The other involves slippage between adhesions and the substratum, which increases traction force production. We conclude that a biphasic relationship exists between retrograde actin flow and adhesiveness in moving keratocytes.

Evaluation of gene expression profile of keratinocytes in response to JP-8 jet fuel

The skin is the principal barrier against any environmental insult. Therefore, there is a high risk for a large number of military and civilian personnel exposed to jet fuel JP-8 to suffer percutaneous absorption of this fuel. This paper reports the use of cDNA microarray to identify the gene expression profile in normal human epidermal keratinocytes exposed to JP-8 for 24-h and 7-day periods. The effects of JP-8 exposure on keratinocytes at these two different periods induced a set of genes with altered expression in response to this type of insult. Microarray data were visualized using a novel algorithm based on simple statistical analyses to reduce data dimensionality and identify subsets of discriminant genes. Predictive neural networks were built using a multiplayer perceptron to carry out a proper classification task in microarray data in the untreated versus JP-8-treated samples. The pattern of expressions in response to JP-8 provides evidences that detoxificant-related and cell growth regulator genes with the most variability in the level of expression may be useful genetic markers in adverse health effects of personnel exposed to JP-8. The approaches in our analysis provide a simple, safe, novel, and effective method that is reliable in identifying and analyzing gene expression in samples treated with JP-8 or over potential toxic agents. Gene expression data from these studies can be used to build accurate predictive models that separate different molecular profiles. The data establish the use and effectiveness of these approaches for future prospective studies.

Inhibition of pancreatic adenocarcinoma cellular invasiveness by blebbistatin: a novel myosin II inhibitor

Blebbistatin is a novel 1-phenyl-2-pyrrolidinone derivative capable of inhibiting non-muscle myosin II activity with a high degree of specificity. We examined the effects of blebbistatin on pancreatic adenocarcinoma cellular migration, invasion, adhesion, and spreading. Blebbistatin dose-dependently inhibited cellular migration and invasiveness, quantified by modified Boyden chamber assay. Matrix metalloproteinase 2 and 9 activities were unaffected by blebbistatin and cellular proliferation was inhibited only by concentrations of blebbistatin exceeding those required to inhibit myosin II activity and to interfere with migration and invasion. While blebbistatin treatment did not affect cell adhesion to the extracellular matrix component fibronectin, it markedly impaired cell spreading on this substrate. Cell surface expression of the archetypal fibronectin receptor (alpha(5)beta(1) integrin) was unaffected by blebbistatin. Our observations illustrate the critical role of non-muscle myosin II in pancreatic adenocarcinoma cellular invasiveness and extracellular matrix interaction and suggest that therapeutic strategies targeting myosin II warrant further investigation.

Regulation of MDCK cell-substratum adhesion by RhoA and myosin light chain kinase after ATP depletion

The attachment of epithelial cells to the extracellular matrix substratum is essential for their differentiation and polarization. Despite this, the precise adhesion mechanism and its regulation are poorly understood. In the kidney, an ischemic insult causes renal tubular epithelial cells to detach from the basement membrane, even though they remain viable. To understand this phenomenon, and to probe the regulation of epithelial cell attachment, we used a model system consisting of newly adherent Madin-Darby canine kidney (MDCK) cells subjected to ATP depletion to mimic ischemic injury. We found that MDCK cells detach from collagen I after 60 min of ATP depletion but reattach when resupplied with glucose. Detachment is not caused by degradation or endocytosis of beta(1)-integrins, which mediate attachment to collagen I. Basal actin filaments and paxillin-containing adhesion complexes are disrupted by ATP depletion and quickly reform on glucose repletion. However, partial preservation of basal actin by overexpression of constitutively active RhoA does not significantly affect cell detachment. Furthermore, Y-27632, an inhibitor of the RhoA effector Rho-kinase, does not prevent reattachment of cells on glucose addition, even though reformation of central stress fibers and large adhesion complexes is blocked. In contrast, reattachment of ATP-depleted cells and detachment of cells not previously subjected to ATP depletion are prevented by ML-7, an inhibitor of myosin light chain kinase (MLCK). We conclude that initial adherence of MDCK cells to a collagen I substratum is mediated by peripheral actin filaments and adhesion complexes regulated by MLCK but not by stress fibers and adhesion complexes controlled by RhoA.

Rho kinase inhibitors block activation of pancreatic stellate cells

1. In response to pancreatic injury and in cell culture, pancreatic stellate cells (PSCs) are transformed ('activated') into highly proliferative myofibroblast-like cells, which express alpha-smooth muscle actin (alpha-SMA), and produce type I collagen and other extracellular matrix components. There is accumulating evidence that activated PSCs play important roles in pancreatic fibrosis and inflammation. 2. The small GTP-binding protein Rho has emerged as an important regulator of the actin cytoskeleton and cell morphology through the downstream effector Rho kinase (ROCK). But, the roles of Rho-ROCK pathway in PSCs are unknown. Here, we examined the effects of (+)-(R)-trans-4-(1-aminoethyl)-N-(4-pyridyl) cyclohexanecarboxamide (Y-27632) and HA-1077 (fasudil), specific inhibitors of ROCK, on the activation of PSCs. 3. PSCs were isolated from the pancreas of male Wistar rats after perfusion with collagenase P. The actin cytoskeleton was analyzed by phalloidin staining. Expression of RhoA and ROCK was examined by immunostaining and Western blotting. Effects of Y-27632 and HA-1077 on alpha-SMA expression, platelet-derived growth factor-induced proliferation and chemotaxis, and collagen production were assessed. 4. Culture-activated PSCs developed a well-spread cell shape, with extended stress fiber formation. PSCs expressed RhoA, ROCK-1, and ROCK-2. 5. Y-27632 caused disassembly of stress fibers. Y-27632 and HA-1077 inhibited alpha-SMA expression, proliferation, chemotaxis, and type I collagen production in culture-activated PSCs. 6. In addition, Y-27632 and HA-1077 inhibited spontaneous activation of freshly isolated PSCs in culture on plastic. 7. These findings suggest a role of Rho-ROCK pathway in the activation process of PSCs by regulating the actin cytoskeleton, and a potential application of Rho-ROCK pathway inhibitors for the treatment of pancreatic inflammation and fibrosis.

Tumour-cell invasion and migration: diversity and escape mechanisms

Cancer cells possess a broad spectrum of migration and invasion mechanisms. These include both individual and collective cell-migration strategies. Cancer therapeutics that are designed to target adhesion receptors or proteases have not proven to be effective in slowing tumour progression in clinical trials--this might be due to the fact that cancer cells can modify their migration mechanisms in response to different conditions. Learning more about the cellular and molecular basis of these different migration/invasion programmes will help us to understand how cancer cells disseminate and lead to new treatment strategies.

Single-cell epithelial defects close rapidly by an actinomyosin purse string mechanism with functional tight junctions

Restitution of single-cell defects, a frequent event in epithelia with high turnover, is poorly understood. Morphological and functional changes were recorded, using intravital time-lapse video microscopy, confocal fluorescence microscopy, and conductance scanning techniques. After artificial single-cell loss from an HT-29/B6 colonic cell monolayer, the basal ends of adjacent cells extended. Concurrently, the local conductive leak associated with the defect sealed with an exponential time course (from 0.48 +/- 0.05 microS 2 min post lesion to 0.17 +/- 0.02 microS 8 min post lesion, n = 17). Between 3 and 10 min post lesion, a band of actin arose around the gap, which colocalized with a ring of ZO-1 and occludin. Hence, tight junction proteins bound to the actin band facing the gap, and competent tight junctions assembled in the adjoining cell membranes. Closure and sealing were inhibited when actin polymerization was blocked by cytochalasin D, delayed following decrease of myosin-ATPase activity by butanedione monoxime, and blocked after myosin light chain kinase inhibition by ML-7. The Rho-associated protein kinase inhibitor Y-27632 did not affect restitution. After loosening of intercellular contacts in low Ca(2+) Ringer solution, the time course of restitution was not significantly altered. Albeit epithelial conductivity was 12-fold higher in low Ca(2+) Ringer solution than in controls, under both conditions the repaired epithelium assumed the same conductivity as distant intact epithelium. In conclusion, epithelial restitution of single-cell defects comprises rapid closure by an actinomyosin 'purse-string' mechanism and simultaneous formation of a functional barrier from tight junction proteins also associated with the purse string.

Rho-kinase contributes to diphosphorylation of myosin II regulatory light chain in nonmuscle cells

Phosphorylation of myosin II regulatory light chain (MRLC) is important for cell motility and cytokinesis in nonmuscle cells. Although the regulation of monophosphorylated MRLC at serine 19 throughout the cell cycle was examined in detail, MRLC diphosphorylation at both threonine 18 and serine 19 is still unclear. Here we found that Rho-kinase has an activity for MRLC diphosphorylation in nonmuscle cells using sequential column chromatographies. Transfection of Rho-kinase-EGFP induced the excess diphosphorylated MRLC and the bundling of the actin filaments. Conversely, the treatment of cells with a specific inhibitor of Rho-kinase, Y-27632, resulted in the decrease of endogenous diphosphorylated MRLC and actin stress fibers. Immunolocalization studies showed that both diphosphorylated MRLC and Rho-kinase accumulated and colocalized at the contractile ring and the midbody in dividing cells. Taken together, it is suggested that Rho-kinase contributes to MRLC diphosphorylation and reorganization of actin filaments in nonmuscle cells.

Differential display of expressed genes in pancreatic cancer cells

Activating K-ras mutations occur in 80-95% of pancreatic cancers. The purpose of this study was to conduct an open, panoramic survey of gene expression, using K-ras status as the axis over which to sub-classify pancreatic cancers. Differential display was used to contrast mRNA purified from exponentially growing PANC-1 and Capan-2 cells (mutated K-ras) with Hs766T and BxPC-3 cells (wild-type). Differences were confirmed by Northern analysis. Twenty-five transcripts were differentially expressed by a factor of two or more. Four transcripts were over-expressed and twelve were under-expressed in the mutants relative to the wild-types. The transcripts most strikingly over-expressed by the mutant cell lines were MARCKS, DKFZp547C244, and RPLP2. The transcripts over-expressed by the wild-types were CEACAM6, cDNA AK026924, and myosin light chain-6. Profiling of gene expression with respect to K-ras mutation status may lead to new insights into pancreatic cancer pathogenesis, as well as to the identification of novel therapeutic targets.