The cytoskeleton in tumor cells

Regulation of matrix metalloproteinases (MMPs) expression and secretion in MDA-MB-231 breast cancer cells by LIM and SH3 protein 1 (LASP1)

The process of tumor invasion requires degradation of extracellular matrix by proteolytic enzymes. Cancer cells form protrusive invadopodia, which produce and release matrix metalloproteinases (MMPs) to degrade the basement membrane thereby enabling metastasis. We investigated the effect of LASP1, a newly identified protein in invadopodia, on expression, secretion and activation of MMPs in invasive breast tumor cell lines.

By analyzing microarray data of in-house generated control and LASP1-depleted MDA-MB-231 breast cancer cells, we observed downregulation of MMP1, -3 and -9 upon LASP1 depletion. This was confirmed by Western blot analysis. Conversely, rescue experiments restored in part MMP expression and secretion. The regulatory effect of LASP1 on MMP expression was also observed in BT-20 breast cancer cells as well as in prostate and bladder cancer cell lines.

In line with bioinformatic FunRich analysis of our data, which mapped a high regulation of transcription factors by LASP1, public microarray data analysis detected a correlation between high LASP1 expression and enhanced c-Fos levels, a protein that is part of the transcription factor AP-1 and known to regulate MMP expression. Compatibly, in luciferase reporter assays, AP-1 showed a decreased transcriptional activity after LASP1 knockdown.

Zymography assays and Western blot analysis revealed an additional promotion of MMP secretion into the extracellular matrix by LASP1, thus, most likely, altering the microenvironment during cancer progression.

The newly identified role of LASP1 in regulating matrix degradation by affecting MMP transcription and secretion elucidated the migratory potential of LASP1 overexpressing aggressive tumor cells in earlier studies.

Emergent complexity of the cytoskeleton: from single filaments to tissue

Despite their overwhelming complexity, living cells display a high degree of internal mechanical and functional organization which can largely be attributed to the intracellular biopolymer scaffold, the cytoskeleton. Being a very complex system far from thermodynamic equilibrium, the cytoskeleton's ability to organize is at the same time challenging and fascinating. The extensive amounts of frequently interacting cellular building blocks and their inherent multifunctionality permits highly adaptive behavior and obstructs a purely reductionist approach. Nevertheless (and despite the field's relative novelty), the physics approach has already proved to be extremely successful in revealing very fundamental concepts of cytoskeleton organization and behavior. This review aims at introducing the physics of the cytoskeleton ranging from single biopolymer filaments to multicellular organisms. Throughout this wide range of phenomena, the focus is set on the intertwined nature of the different physical scales (levels of complexity) that give rise to numerous emergent properties by means of self-organization or self-assembly.

Cellular vimentin content regulates the protein level of hepatitis C virus core protein and the hepatitis C virus production in cultured cells

Hepatitis C virus (HCV) core protein is essential for virus particle formation. Using HCV core-expressing and non-expressing Huh7 cell lines, Uc39-6 and Uc321, respectively, we performed comparative proteomic studies of proteins in the 0.5% Triton X-100-insoluble fractions of cells, and found that core-expressing Uc39-6 cells had much lower vimentin content than Uc321 cells. In experiments using vimentin-overexpressing and vimentin-knocked-down cells, we demonstrated that core protein levels were affected by cellular vimentin content. When vimentin expression was knocked-down, there was no difference in mRNA level of core protein; but proteasome-dependent degradation of the core protein was strongly reduced. These findings suggest that the turnover rate of core protein is regulated by cellular vimentin content. HCV production was also affected by cellular vimentin content. Our findings together suggest that modulation of hepatic vimentin expression might enable the control of HCV production.

Use of two-dimensional gel electrophoresis in predictive toxicology: identification of potential early protein biomarkers in chemically induced hepatocarcinogenesis

Our current approach focused on the identification of potential early protein biomarker signatures which are indicative of the carcinogenic processes in rats exposed to 20 mg/kg of the liver carcinogen N-nitrosomorpholine (NNM). Treated liver was investigated at different timepoints. Therefore, proteins were separated by two-dimensional gel electrophoresis as a first step prior to identification of differentially expressed proteins by mass spectrometry. Proteomic analysis of liver samples after one day of exposure revealed significant upregulation of proteins involved in response to cellular stress induced by NNM (superoxide dismutase, heat shock protein 60, peroxiredoxin). Eighteen weeks after withdrawal of NNM, we were able to identify cancer-related proteins in rat liver bearing malignant, transformed cells (caspase-8 precursor, vimentin, Rho GDP dissociation inhibitor). Some of these proteins were already deregulated after three weeks of exposure indicating their potential usefulness as early predictive biomarkers for liver carcinogenicity (annexin A5, fructose-1,6-bisphosphatase). As regulatory toxicology approaches usually include the investigation of carcinogenicity in two-years studies in rodents, especially the detection of early protein biomarker signatures which precede the appearance of neoplasia, demonstrates the high potential of proteomics approaches to substantially reduce the time and costs of carcinogenicity testing.

Immunohistochemical investigation of chordomas: histogenetic and differential diagnostic aspects

Chordomas are rare tumors of neuroectodermal origin and often show a very heterogeneous histological picture. In a combined histochemical and immunohistochemical study of 32 chordomas collected in the Bone Tumor Registry of Westphalia we were able to show that the immunoreactivity of the cells in both chordoma and notochordal structures are in close relationship with the extracellular matrix and depends more on the metabolic activity of these cells than on the origin of the cells of the neuroectoderm. All tumor cells show a bimodal immunoreaction with cytokeratin and vimentin, as well as a strong immunoreaction with the oncofetal markers CEA and AFP. The differentiation of chordomas from other malignant tumors, mainly the myxoid variant of chondrosarcoma, may cause major difficulties, especially if only a little biopsy material is available. Here we can see that in tumors with bimodal immunoexpression of vimentin and cytokeratin, as can be found in chordomas, the further use of antibodies offers a reliable differential diagnostic tool. The positive reaction of chordomas with all epithelial tumor markers offers a clear differentiation from chondrosarcomas, which, unlike chordomas, do not express cytokeratin. The identification of a marker profile by employing common antisera is of major value in the differentiation of chordoma from other epithelial or mesenchymal tumors.

The identification of myoepithelial cells in human salivary glands. A review and comparison of light microscopical methods

Myoepithelial cells have frequently been implicated in salivary gland tumour histogenesis. A major problem has been the reliable identification of these cells at the light microscopical level, both in tumours and in normal salivary glands. Many methods have been advocated, often with comparatively little evaluation in normal human tissue and with limited comparison between techniques. This paper reviews the application of histological staining techniques, enzyme histochemistry and immunocytochemistry with antibodies to actin, myosin and keratins. The only reliable method was immunocytochemistry with an antibody to smooth muscle myosin, with immunofluorescence on frozen tissue and immunoenzyme labelling on methacarn-fixed/paraffin-processed material. Formalin fixation did not permit successful staining. Monoclonal antibodies to specific keratin polypeptides may prove to be a useful label of myoepithelial cells but at the present time the available cytokeratin antibodies preferentially stain duct cell populations.

Neurofilaments of Kultschitsky cells in human lung

The immunohistochemical localization of three triplet proteins of neurofilaments in normal Kultschitsky cells and tumourlets of the human lung has been studied using avidin-biotin-peroxidase complex (ABC) method. Kultschitsky cells and tumourlets have been stained with antisera against 68 K, 150 K and 200 K dalton components of the neurofilaments, respectively. Ultrastructural observations of human Kultschitsky cells have revealed the presence of bundles of intermediate filaments as well as microtubules and neurosecretory-type granules. In the tumourlets, similarly sized filaments were found, but were relatively scarce. Since intermediate filaments are thought to be specific to differentiated cells and neurofilament proteins are restricted to the neuronal tissues, we conclude that Kultschitsky cells of the lung are of neuronal nature.

Tumor dedifferentiation: an important step in tumor invasion

Tumor invasion in vivo was studied by light and electron microscopy as well as by immunofluorescence microscopy. Special regard was paid to the grade of tumor differentiation. Dimethylhydrazine-induced murine colonic carcinomas comprising a differentiated and an undifferentiated tumor type with low and high invasiveness respectively, were used. At the invasion front of both tumor types a striking dissociation of the organized tumor cell complexes into isolated tumor cells was found together with a loss of most of the cytological features of differentiation. It is supposed that this process mobilizes the tumor cells from the main tumor bulk enabling them to invade the host tissue by active locomotion. This view is strongly supported by the demonstration of morphological equivalents of active cell movement such as pseudopodia-like cytoplasmic extrusions, adaptive changes of the cell shape and microfilament bundles. Although the proposed mechanism of tumor invasion is essentially the same in both tumor types, the grade of differentiation is nevertheless critical, as in the undifferentiated carcinomas only subtle dedifferentiation steps (loss of basement membrane and cell junctions) are necessary to acquire an invasive status. This fact may explain the comparatively high invasiveness and poor prognosis of undifferentiated carcinomas.

The rarity of rhabdomyosarcomas in the adult. A morphologic and immunohistochemical study

An analysis was made of the rhabdomyosarcomas diagnosed in the Dept. of Pathology of the University of Groningen between 1971 and 1983. Ten cases diagnosed in patients over 30 years of age were studied in detail. After review the diagnosis was discarded on morphologic criteria in all cases. In 9 cases it was changed into malignant fibrous histiocytoma (MFH) and in one case this diagnosis was favoured, but inconclusive. In 5 cases immunohistochemical studies could be performed. In all cases staining for the muscle specific intermediate filaments desmin appeared negative and for the mesenchymal intermediate filaments vimentin positive. These cases were also positive for one or more of the histiocytic markers alpha-1-antichymotrypsin, alpha-1-antitrypsin and lysozyme. It is concluded that rhabdomyosarcoma in older patients is extremely rare and the possible relationship between MFH in the adult and rhabdomyosarcoma in childhood is discussed.

Mesenchymal and muscle-specific intermediate filaments (vimentin and desmin) in relation to differentiation in childhood rhabdomyosarcomas

Twenty-one childhood rhabdomyosarcomas were divided into three groups on the basis of cytologic composition. The tumors in group P consisted entirely of primitive mesenchymal cells, whereas those in groups M and W were characterized by the additional presence of numerous round rhabdomyoblasts and strap cells, respectively. The tumors were studied for the universal mesenchymal intermediate filament vimentin, and for the muscle-specific intermediate filament desmin. Vimentin positivity, which tended to be more prominent in primitive tumor cells, was found in all tumors, whereas desmin was found especially in round rhabdomyoblasts and strap cells. Desmin-positive primitive cells were found only in groups M and W, not in group P. It was concluded that the differentiation from primitive mesenchymal cells to morphologically recognizable myogenic tumor cells is accompanied by an increase in desmin positivity and, presumably, a decrease in vimentin positivity. Moreover, the observations suggest the existence of a group of "committed" cells that are morphologically primitive, but desmin-positive. These cells might play an important role in the observed further differentiation of rhabdomyosarcomas under chemotherapy.

Mechanisms of tumor invasion: evidence from in vivo observations

The major mechanisms of tumor invasion in vivo are discussed in the present review. A special emphasis is placed on tumor dedifferentiation which has proved to be of paramount importance for the invasion process. Based on in vivo observations obtained from various human and animal tumors a concept for the mechanism of tumor invasion is proposed which mainly comprises the following basic events: the first and essential step in tumor invasion is the tumor dedifferentiation and dissociation at the invasion front. This apparently temporary and reversible process mobilizes the tumor cells out of the main tumor bulk and enables them to invade the host tissue by active locomotion. This mechanism is essentially supported by an interstitial edema in the host tissue adjacent to the tumor periphery, which causes an 'opening and widening' of the host intercellular spaces. Enzymatic changes in the micromilieu of the extracellular matrix may contribute to this process. The tumor cell proliferation completes the invasion process in so far, as the invading tumor cells are still able to proliferate, leading this way to expanding tumor cell nests in the host tissue which have the potency to redifferentiate. The expansive growth of these tumor cell nests results in a progressive atrophy of the host tissue, mainly caused by an increasing compression and a competitive withdrawal of oxygen and other nutrients by the tumor cells. The overall picture of tumor invasion can therefore be considered as a repetitive cycle of active tumor cell locomotion followed by focal tumor cell proliferation in the host tissue.