Regulation of adherence and virulence by the Entamoeba histolytica lectin cytoplasmic domain, which contains a beta2 integrin motif

Killing of human cells by the parasite Entamoeba histolytica requires adherence via an amebic cell surface lectin. Lectin activity in the parasite is regulated by inside-out signaling. The lectin cytoplasmic domain has sequence identity with a region of the beta2 integrin cytoplasmic tail implicated in regulation of integrin-mediated adhesion. Intracellular expression of a fusion protein containing the cytoplasmic domain of the lectin has a dominant negative effect on extracellular lectin-mediated cell adherence. Mutation of the integrin-like sequence abrogates the dominant negative effect. Amebae expressing the dominant negative mutant are less virulent in an animal model of amebiasis. These results suggest that inside-out signaling via the lectin cytoplasmic domain may control the extracellular adhesive activity of the amebic lectin and provide in vivo demonstration of the lectin's role in virulence.     

Adenosine and other low molecular weight factors released by muscle cells inhibit tumor cell growth

In this study, we investigated the basis of the resistance of muscles to tumor metastases. We found that a low molecular weight fraction (Mr <3000) of skeletal muscle cell-conditioned medium (MCM) markedly inhibits the proliferation of carcinoma, sarcoma, or melanoma cell lines in vitro. The MCM exerts a cytostatic effect on tumor cell growth and arrests the cells in G0/G1 of the cell cycle. However, normal cell proliferation of cells such as bone marrow cells or fibroblasts was found to be refractory to the influence of the MCM. A reduction in melanoma growth was observed in mice treated with the MCM. Adenosine was identified as one of the active components in the MCM by using high-performance liquid chromatography separations, mass spectra, and nuclear magnetic resonance analyses. At a concentration of 4 microM, equal to that found in the MCM, adenosine inhibits the proliferation of tumor cell lines (Nb2 lymphoma, K-562 leukemia, and LNCaP prostate carcinoma cells) while stimulating the proliferation of normal murine bone marrow cells. By similar methods, additional inhibitory components were detected in the MCM in a molecular mass range of 600-800 Da. The ability of adenosine and other low molecular weight components to specifically inhibit tumor cell growth in vitro and in vivo may account for the resistance of muscle to tumor metastases.     

Cloning and characterization of the zebrafish (Danio rerio) aryl hydrocarbon receptor

The cell surface hyaluronan receptor CD44 promotes tumor growth and metastasis by mechanisms that remain poorly understood. We show here that CD44 associates with a proteolytic form of the matrix metalloproteinase-9 (MMP-9) on the surface of mouse mammary carcinoma and human melanoma cells. CD44-associated cell surface MMP-9 promotes cell-mediated collagen IV degradation in vitro and mediates tumor cell invasion of G8 myoblast monolayers. Several distinct CD44 isoforms coprecipitate with MMP-9 and CD44/MMP-9 coclustering is observed to be dependent on the ability of CD44 to form hyaluronan-induced aggregates. Disruption of CD44/MMP-9 cluster formation, by overexpression of soluble or truncated cell surface CD44, is shown to inhibit tumor invasiveness in vivo. Our observations indicate that CD44 serves to anchor MMP-9 on the cell surface and define a mechanism for CD44-mediated tumor invasion.     

Sequence motifs in the integrin alpha 4 cytoplasmic tail required for regulation of in vivo expansion of murine lymphoma cells

The binding of integrins to cognate ligands is tightly controlled by intracellular signals. Conversely, integrin occupancy generates biochemical signals inside the cell. The present study examined whether concepts of integrin function established by in vitro analysis apply to regulation of receptor function in complex biologic settings in vivo using a mouse model of tumor metastasis. Integrin alpha 4 subunits were truncated at amino acid Gln1014 (A4-1014), preserving the conserved GFFKR motif, and at position Glu1021 (A4-1021). In vitro adhesion assays revealed that cytoplasmic tail truncations did not affect constitutive ligand binding of alpha 4 integrins, while agonist-induced adhesion was abolished by the alpha 4-1014, but not by the alpha 4-1021, mutation. Inducible ligand binding of alpha 4 integrins was dependent on cytoskeletal function, whereas constitutive adhesion was not. In vivo metastasis formation assays demonstrated that expansion of murine T lymphoma cells in spleen is strongly inhibited by the wild-type alpha 4 subunit and the alpha 4-1021 mutant. In contrast, the in vivo phenotype of alpha 4 integrin expression in lymphoma cells was completely abrogated by the alpha 4-1014 mutation. Cross-linking of alpha 4 integrins in vitro inhibited proliferation and induced apoptosis of LB cells expressing wild-type alpha 4 subunits or the alpha 4-1021 mutant, but not of LB-A4-1014 cells. In summary, these results demonstrate that sequence motifs regulating cytoskeleton-dependent alpha 4 integrin activation in vitro are essential for the control of LB lymphoma cell expansion both in vitro and in vivo.     

Anti-epidermal growth factor receptor monoclonal antibodies affecting signal transduction

Monoclonal antibodies prepared against tyrosine phosphorylated epidermal growth factor receptor (EGFR) were tested for their effects on transmembrane signal transduction in A431 tumor cells. Monoclonal antibodies (mab) defined by SDS-sensitive epitopes, i.e., epitopes with conformational specificity, were most effective. Mab 5-125 reacting with a site of the extracellular EGFR domain blocked EGF-binding and cell proliferation in vitro, as well as tumor growth in vivo. However, this mab appeared not to be internalized upon binding to EGFR and did not trigger EGFR autophosphorylation. In contrast, mab 5-D43, also defined by an SDS-sensitive epitope and reacting with an extracellular EGFR site, did not block EGF binding but was readily internalized after binding to EGFR of untreated A431 cells. This mab induced EGFR tyrosine phosphorylation in cell lysates and tyrosine-specific autophosphorylation of insolubilized EGFR immune complexes. Cell growth in vitro was greatly stimulated in the presence of mab 5-D43. Since interaction of mab 5-D43 with EGFR induced most EGF-specific functions, although it did not bind to the EGF-specific site of EGFR, we have to assume that binding of mab 5-D43 to EGFR induced a conformational shift that activated the cytoplasmic EGFR kinase site. On the other hand, activation and/or accessibility of the EGFR kinase site could be blocked by mab 1-594, which is defined by an SDS-insensitive protein epitope of the cytoplasmic EGFR domain. Blocking of the EGFR kinase site by mab 1-594 also abolished EGF-induced tyrosine phosphorylation of endogenous cellular substrates with molecular masses of 145, 97, 85, 37, and 32 kDa, as well as of exogenous substrates such as GAT copolymer.     

Characterization of a point mutation in the hormone binding domain of the estrogen receptor from an breast tumor

It is clear that growth of the MCF-7 breast cancer cell line is stimulated by estrogen and when estrogen is removed, growth slows. We have observed a tumor derived from MCF-7 cells that grows in athymic mice in the absence of estrogen stimulation. We hypothesized that a mutation in the estrogen receptor (ER) could be responsible for this constitutive growth. Using single stranded conformational polymorphism (SSCP) and DNA sequencing analysis, we have identified an ER containing a point mutation at position 415 (gly to val) within the hormone binding domain. The functional activity of this mutant was assessed in vitro and in vivo. Using transient transfection into an ER negative breast cancer cell with an ERE luciferase reporter gene, we found that both the wild-type and mutant receptors have similar efficacy. Additionally, the estrogenic responses were blocked by antiestrogens in a concentration related manner. We also found that tumors with the mutant receptor show similar growth response in athymic mice as wild-type: stimulation with estradiol and inhibition with antiestrogens. We conclude that the point mutation at position 415 (gly to val) is not responsible for constitutive growth.     

Role of sialoglycan structures for the function of the epidermal growth factor receptor and the in vitro proliferation of head and neck cancer

Squamous cell carcinomas of the head and neck have been found to show a high expression of the receptor for epidermal growth factor (EGF). This overexpression of the receptor has been associated with malignant transformation of cells, although there is still debate as to what extent this receptor takes part in the proliferation of malignant cells and which function it fulfills. The factors which determine receptor-ligand interaction are also not clearly defined. That the extracellular domain of the EGF receptor carries carbohydrate or sialoglycan structures might be important for function of the receptor. Since tumor specific enzymes can possibly alter such structures, it was the aim of our study to investigate the role of these structures on the EGF receptor during the proliferation of head and neck carcinomas. We used the human laryngeal squamous carcinoma cell line HLaC 79 and altered, for the first time, specific glycan structures with sialidase alpha-2,3 and alpha-2,6, causing desialylation. Changes were also produced by endo-beta-galactosidase and sialyltransferase. Findings were monitored by labeling with bromo-deoxyuridine. To determine receptor affinity, 125I-labeled EGF was employed. Results showed that both cell proliferation and receptor affinity depended on the level of sialylation of the receptor carbohydrate side chains. Desialylation led to a statistically significant reduction of tumor cell proliferation to 65 +/- 33% (P < 0.01), while receptor affinity decreased to 70 +/- 26% (P < 0.01). The importance of EGF receptor for the proliferation of malignant cells seems to depend on the level of sialylation of glycan structures on receptor protein. A release of enzymes by tumor cells may then produce auto-control of tumor proliferation on its own.     

p27(kip1) acts as a downstream effector of and is coexpressed with the beta1C integrin in prostatic adenocarcinoma

Integrins are a large family of transmembrane receptors that, in addition to mediating cell adhesion, modulate cell proliferation. The beta1C integrin is an alternatively spliced variant of the beta1 subfamily that contains a unique 48-amino acid sequence in its cytoplasmic domain. We have shown previously that in vitro beta1C inhibits cell proliferation and that in vivo beta1C is expressed in nonproliferative, differentiated epithelium and is selectively downregulated in prostatic adenocarcinoma. Here we show, by immunohistochemistry and immunoblotting analysis, that beta1C is coexpressed in human prostate epithelial cells with the cell-cycle inhibitor p27(kip1), the loss of which correlates with poor prognosis in prostate cancer. In the 37 specimens analyzed, beta1C and p27(kip1) are concurrently expressed in 93% of benign and 84%-91% of tumor prostate cells. Forced expression of beta1C in vitro is accompanied by an increase in p27(kip1) levels, by inhibition of cyclin A-dependent kinase activity, and by increased association of p27(kip1) with cyclin A. beta1C inhibitory effect on cell proliferation is completely prevented by p27(kip1) antisense, but not mismatch oligonucleotides. beta1C expression does not affect either cyclin A or E levels, or cyclin E-associated kinase activity, nor the mitogen-activated protein (MAP) kinase pathway. These findings show a unique mechanism of cell growth inhibition by integrins and point to beta1C as an upstream regulator of p27(kip1) expression and, therefore, a potential target for tumor suppression in prostate cancer.     

Characterization of soluble gp130 released by melanoma cell lines: A polyvalent antagonist of cytokines from the interleukin 6 family

gp130 acts as a common transducing signal chain for all receptors belonging to the interleukin (IL)-6 receptor family. The IL-6-related cytokines [IL-6, IL-11, oncostatin M (OSM), leukemia inhibitory factor, ciliary neurotrophic factor, and cardiotrophin] often modulate tumor phenotype and control the proliferation of many tumor cell lines. We demonstrate that melanoma cell lines release, in vitro and in vivo (when transplanted in nude mice), soluble gp130 (sgp130), a potential antagonist of cytokines from the IL-6 family. Biochemical analysis revealed that sgp130 derived from melanoma patients' sera or from culture supernatants of melanoma cell lines is a Mr 104,000 protein that resolved after deglycosylation as a Mr 58,000 protein. PCR and Northern blot analysis only identified one gp130 membrane mRNA, suggesting that the soluble form of gp130 is generated by proteolytic cleavage. OSM reproducibly increases sgp130 released by melanoma cell lines, whereas leukemia inhibitory factor stimulates the production of sgp130 in only one of three cell lines tested. This tumor-derived sgp130 is functional because it binds in solution to the IL-6-soluble IL-6 receptor (gp80) complex. Recombinant sgp130 inhibits the growth inhibitory activity of the IL-6-soluble IL-6 receptor complex and OSM on some melanoma cell lines. Therefore, this soluble gp130 represents a natural antagonist of cytokines from the IL-6 family.     

Thrombin aivation of the 9E3/CEF4 chemokine involves tyrosine kinases including c-src and the epidermal growth factor receptor

The 9E3/CEF4 gene codes for a chemokine that is highly homologous to human interleukin-8 and melanoma growth-stimulating activity/groalpha. These chemokines belong to a family of molecular mediators that are importantly involved in inflammation, wound healing, tumor development, and viral entry into cells. On the chorioallantoic membrane the 9E3 protein is chemotactic for monocyte/macrophages and lymphocytes and is angiogenic. In cultured chicken embryo fibroblasts, which have many of the properties of wound fibroblasts, the gene is stimulated by a variety of agents including oncogenes, growth factors, phorbol esters, and thrombin. The strong stimulation of 9E3 by thrombin in culture correlates well with the observation that in young chicks this gene is stimulated to very high levels in fibroblasts upon wounding and remains high throughout wound repair. Activation of 9E3 by thrombin: (i) occurs very rapidly, one minute exposure to thrombin is sufficient to initiate the signals necessary for gene activation; (ii) is independent of mitogenesis; (iii) operates through the proteolytically activated receptor for thrombin; (iv) is mediated by tyrosine kinases, including c-src and the epidermal growth factor (EGF) receptor, rather than Ser/Thr kinases such as protein kinase C and protein kinase A. Inhibition of either c-src or the EGF receptor tyrosine kinase inhibits the stimulation of 9E3 by thrombin. We show here for the first time that activation of the EGF receptor through a cell-surface receptor that does not have tyrosine kinase activity can lead to expression of an immediate early response gene which encodes for a secreted protein, a chemokine. This rapidly activated tyrosine kinase pathway may be a general stress response by which in vivo a localized cell population reacts to emergency situations such as viral infection, wounding, or tumor growth.     

Immunosuppressive activity of cloned natural killer (NK1.1+) T cells established from murine tumor-infiltrating lymphocytes

To elucidate the role of NK1.1+ T cells in the antitumor immune response, we established cloned NK1.1+ T cell lines from tumor-infiltrating lymphocytes (TIL) of B16 melanoma, and examined their mode of action in generating antitumor effector T cells both in vitro and in vivo. An NK1.1+ T cell clone (TM4.2) was phenotypically CD3+ TCR-alphabeta+ CD4- CD8- NK1.1+, and CD28+. The TM4.2 cells suppressed the in vitro generation of anti-B16 melanoma CTLs, but not the effector function of CTLs. The results using a transwell membrane suggested that their suppressive activity was mediated by both soluble factors and a direct cell to cell interaction. As for the soluble factors, the suppressive activity of the culture supernatant of TM4.2 cells was neutralized by anti-TGF-beta mAb, and the TM4.2 cells actually produced a considerable amount of TGF-beta. On the other hand, the TM4.2 cells showed a high level of cytolytic activity against B cell blasts and CD80-transfected P815, and such cytolytic activity was reduced by the addition of anti-CD80 mAb. In addition, NK1.1+ T cells in the freshly isolated TIL were revealed to express CD28. Furthermore, the TM4.2 cells suppressed the in vitro generation of anti-allo CTLs irrespective of the MHC haplotype. Finally, the TM4.2 cells suppressed the in vivo antitumor immune response. Collectively, these findings demonstrate that NK1.1+ T cells in TIL show immunosuppressive activity in the antitumor immune response through the production of TGF-beta and the preferential cytolysis of B7-expressing cells.     

The type II transforming growth factor-beta receptor autophosphorylates not only on serine and threonine but also on tyrosine residues

The type I and type II receptors for transforming growth factor-beta (TGF-beta) are structurally related transmembrane serine/threonine kinases, which are able to physically interact with each other at the cell surface. To help define the initial events in TGF-beta signaling, we characterized the kinase activity of the type II TGF-beta receptor. A recombinant cytoplasmic domain of the receptor was purified from Escherichia coli and baculovirus-infected insect cells. Anti-phosphotyrosine Western blotting demonstrated that the type II receptor kinase can autophosphorylate on tyrosine. Following an in vitro kinase reaction, the autophosphorylation of the cytoplasmic domain and phosphorylation of exogenous substrate was shown by phosphoamino acid analysis to occur not only on serine and threonine but also on tyrosine. The dual kinase specificity of the receptor was also demonstrated using immunoprecipitated receptors expressed in mammalian cells and in vivo 32P labeling showed phosphorylation of the receptor on serine and tyrosine. In addition, the kinase activity of the cytoplasmic domain was inhibited by the tyrosine kinase inhibitor tyrphostin. Tryptic mapping and amino acid sequencing of in vitro autophosphorylated type II receptor cytoplasmic domain allowed the localization of the sites of tyrosine phosphorylation to positions 259, 336, and 424. Replacement of all three tyrosines with phenylalanines strongly inhibited the kinase activity of the receptor, suggesting that tyrosine autophosphorylation may play an autoregulatory role for the kinase activity of this receptor. These results demonstrate that the type II TGF-beta receptor can function as a dual specificity kinase and suggest a role for tyrosine autophosphorylation in TGF-beta receptor signaling.     

Genome instability in BVDV: an examination of the sequence and structural influences on RNA recombination

To determine the extent to which autocrine effects of acidic fibroblast growth factor (FGF)-1 overexpression contribute to an increased malignant phenotype, FGF-1-transfected MCF-7 cells were retransfected with a FGF receptor (FGFR1) vector encoding a truncated dominant-negative receptor to inhibit autocrine FGF signal transduction. This transfection eliminated FGF signaling within the breast cancer cells without interfering with their ability to produce FGF-1, thereby allowing possible paracrine effects to still be observed in vivo. Truncated FGFR1 overexpression inhibited the acquired ability of FGF-1-overexpressing cells to form colonies in soft agar in estrogen-depleted or antiestrogen-containing medium. However, soft agar colony formation was still stimulated by estrogen treatment in cells expressing up to 6 x 10(5) truncated FGFR1 sites per cell. In vivo, truncated receptor expression severely inhibited the ability of the FGF-1-overexpressing cells to form tumors without estrogen in ovariectomized mice, indicating that the mitogenic effect of FGF-1 on the breast tumor cells was important in the estrogen-independent in vivo growth of these transfectants. However, rapid formation of large tumors was still observed in estrogen-supplemented mice injected with the truncated FGFR1-expressing cells, suggesting that the paracrine effects of FGF production could act in synergy with mitogenic effects mediated by estrogen. Truncated FGFR1-overexpressing cells also continued to form tumors in tamoxifen-treated mice, raising the possibility that the paracrine effects of FGF-1 expression may allow the partial agonist properties of this antiestrogen to be more readily observed. We conclude that autocrine effects of FGF-1 increase the ability of MCF-7 breast cancer cells to grow in vitro and in vivo under estrogen-depleted conditions but that paracrine effects of FGF-1 are also involved in the enhancement of tumor growth in estrogen-supplemented or tamoxifen-treated animals.     

Antitumor effect of c-myc antisense phosphorothioate oligodeoxynucleotides on human melanoma cells in vitro and and in mice

BACKGROUND: Phosphorothioate oligodeoxynucleotides ([S]ODNs) contain a modified internucleoside phosphate backbone. Antisense [S]ODNs targeted to specific oncogenes have been used with some therapeutic success in animal models human leukemia; however, the potential for antisense [S]ODN treatment of solid tumors has only recently been explored. Purpose: We evaluated the effects of antisense [S]ODNs targeted to the c-myc oncogene on the proliferation of human melanoma cells in vitro and on the growth of human melanoma xenografts in CD-1 nude (nu/nu) mice, METHODS: The effects of 15-mer [S]ODNs containing c-myc sense, c-myc antisense, and two different scrambled sequences on the proliferation and viability of cultures of three established human melanoma cell lines (M14, JR8, and PLF2) were determined by measuring cell numbers and use of the trypan blue exclusion test. The induction of apoptosis in these cells following treatment with [S]ODNs was evaluated by fluorescence-activated cell sorter (FACS) analysis. FACS analysis was also used to determine the effects of [S]ODN treatment on the proliferation of primary cultures of a human melanoma explant (NG cells). The expression of c-Myc protein in cultured NG cells after treatment with [S]ODNs was examined by western blot analysis. The antitumor activity and the toxic effects of several [S]ODN treatment regimens were monitored by measuring differences in tumor weight (percent tumor weight inhibition), tumor growth rate (tumor growth inhibition), animal lifespan (percent increase in lifespan), the number of toxic deaths and the median number of long metastases in treated and control mice bearing NG xenografts. c-Myc protein expression in NG tumor cells following [S]ODN treatment was evaluated by FACS analysis, and the extent of apoptosis in these cells was determined by FACS analysis and morphologic examination. RESULTS: Treatment with antisense [S]ODNs, but not the others, inhibited the growth of all tested melanoma cultures in vitro; FACS analysis revealed that growth inhibition was associated with the induction of apoptosis. Antisense [S]ODN treatment also led to reduced celluLar levels of c-Myc protein. In vivo, [S]ODN antitumor activity and toxicity were dose and schedule dependent; however, only antisense [S]ODNs exhibited antitumor activity. Mice bearing NG xenografts treated with antisense [S]ODNs showed a marked inhibition of tumor growth, a reduction in the number of long metastases, and an increase in life span. Reduced levels of c-Myc protein and increased levels of apoptosis were also observed in NG tumor cells following antisense [S]ODN treatment. CONCLUSIONS: treatment of human melanoma cells and solid tumors with antisense [S]ODNs targeted to c-Myc inhibits their growth and is associated with the induction of apoptosis.     

In situ distribution of integrin alpha 2 beta 1 and alpha-actinin in melanocytic proliferations

Integrin alpha 2 beta 1 is a transmembrane protein receptor for collagen and laminin previously reported as a melanoma tumor progression antigen. alpha-Actinin is an actin-binding protein reported to interact with the cytoplasmic domain of the beta 1-integrin chain of alpha 2 beta 1. In vitro, both alpha 2 beta 1 and alpha-actinin play a role in melanoma cell motility. In turn, increased melanoma cell line motility (measured as mean migration rates), correlates with metastasis. To determine the in situ distribution of these proteins, we used monoclonal antibodies directed against the alpha 2-integrin subunit of alpha 2 beta 1 and alpha-actinin on frozen sections of 33 melanocytic proliferations, which included dermal nevi, primary melanomas, and metastatic melanomas. We found that the superficial portion of all of the melanocytic proliferations tested stained for alpha-actinin. In benign nevi and superficial spreading melanoma, there was a notable loss of staining for alpha-actinin in the cells in the deep reticular dermis. In contrast, alpha-actinin was present on almost all of the tumor cells in the nodular melanomas and the melanoma metastases. Tumors stained either uniformly positive or uniformly negative for alpha 2 beta 1; the expression of this protein correlated with the later stages of melanoma progression. Our findings suggest that alpha-actinin protein levels initially decrease and then increase during melanocytic tumor progression, whereas the alpha 2 subunit protein appears in the later stages of melanoma progression. The variable distribution of these proteins is evidence for the differential adhesive and motile properties of subpopulations of cells in melanocytic proliferations.     

Tumor-specific expression and alternate splicing of messenger ribonucleic acid encoding activin/transforming growth factor-beta receptors in human pituitary adenomas

Activin, a member of the transforming growth factor-beta (TGF beta) cytokine family, acts as a pituitary cell mitogen via a novel family of receptor-linked serine/threonine (Ser/Thr) kinases. Pituitary tumors synthesize activin subunits, and the autocrine action of these growth factors may modulate tumor proliferation. We, therefore, investigated the expression of activin/TGF beta type I receptor messenger ribonucleic acids (mRNAs), designated ALK1 through ALK5 (ALK = activin receptor-like kinase), and type II receptor mRNAs using RT-PCR in 34 human pituitary adenomas of all phenotypes and normal pituitary tissue. ALK2 and ALK5, specific mediators of activin and TGF beta signals, respectively, were found to be expressed only in tumor and not in normal pituitary cells, and ALK2 expression was found only in tumors of a mammosomatotroph cell lineage. ALK1, ALK3, and ALK4 mRNAs were found in both normal and neoplastic pituitary cells. The alternatively spliced cytoplasmic domain of ALK4 consists of 11 kinase subdomains, that are critical for modulating receptor function and intracellular signaling. Truncated forms of the ALK4 cytoplasmic domain lacking these subdomains may attenuate activin signal transduction and affect both tumor phenotype and proliferation via the formation of inactive type I/type II complexes. Three truncated ALK4 receptor mRNAs generated by alternate splicing of the cytoplasmic Ser/Thr kinase domain were found to be tumor specific. One of these truncated receptor mRNAs, ALK4-5, is a novel splice variant that has not been previously described. Expression of the ActRII and T beta RII type II receptor mRNAs, which specifically bind activin and TGF beta, respectively, was highly prevalent among all tumor subtypes and normal pituitary tissue. However, ActRIIB, an activin-specific type II receptor that displays a 3- to 4-fold higher affinity for ligand than ActRII, was expressed in 94% of tumors, but was not prevalent in normal tissue. These data are the first to demonstrate tumor-specific expression of Ser/Thr kinase receptors mRNAs and their splice variants in human pituitary adenomas.     

Cytoskeleton and motility: an immunohistological and computer simulation analysis of melanocytic skin tumors

Tumor cell motility and tumor cell proliferation are supposed to be essential for tumor invasion. The cytoskeleton, which consists of different components, is considered to be important for maintaining cell shape and facilitating cell movement. Numerous data are available about tumor cell motility in vitro, but the behavior of tumor cells in vivo is as yet poorly understood. In the present study, estimates of tumor cell motility and proliferation were statistically derived from morphological tumor patterns in human melanocytic skin tumors, and their relationship to expression of certain cytoskeletal components was evaluated. Overexpression of vimentin within tumor cells correlated with low actual tumor cell motility and proliferation, indicating a structurally stabilizing function of these filaments. An overexpression of actin was found within tumor cells of high motility and proliferation, suggesting the contribution of cytocontractile elements to active tumor cell locomotion in situ. Concerning the cytoskeleton of the stromal cells, expression of actin, myosin and tubulin correlated with a high number of motile tumor cells and high mitotic counts. Thus increased tumor cell motility seems to be associated with cytoskeletal changes not only of the tumor cells themselves but also of the surrounding stromal cells.