Heterogeneous tumor stromal microenvironments of oral squamous cell carcinoma cells in tongue and nodal metastatic lesions in a xenograft mouse model

BACKGROUND

Oral squamous cell carcinoma exhibits a poor prognosis, caused by aggressive progression and early-stage metastasis to cervical lymph nodes. Here, we developed a xenograft mouse model to explore the heterogeneity of the tumor microenvironment that may govern local invasion and nodal metastasis of tumor cells.

METHODS

We transplanted five oral carcinoma cell lines into the tongues of nude mice and determined tongue tumor growth and micrometastatic dissemination by serially sectioning the tongue and lymph node lesions in combination with immunohistochemistry and computer-assisted image analysis. Our morphometric analysis enabled a quantitative assessment of blood and lymphatic endothelial densities in the intratumoral and host stromal regions.

RESULTS

All cell lines tested were tumorigenic in mouse tongue. The metastatic lesion-derived carcinoma cell lines (OSC19, OSC20, and HSC2) yielded a 100% nodal metastasis rate, whereas the primary tumor-derived cell lines (KOSC2 and HO-1-u-1) showed <40% metastatic potential. Immunohistochemistry showed that the individual cell lines gave rise to heterogeneous tumor architecture and phenotypes and that their micrometastatic lesions assimilated the immunophenotypic properties of the corresponding tongue tumors. Notably, OSC19 and OSC20 cells shared similar aggressive tumorigenicity in both the tongue and lymph node environments but displayed markedly diverse immunophenotypes and gene expression profiles.

CONCLUSIONS

Our model facilitated comparing the tumor microenvironments in tongue and lymph node lesions. The results support that tumorigenicity and tumor architecture in the host tongue environment depend on the origin and properties of the carcinoma cell lines and that metastatic progression may take place through heterogeneous tumor-host interactions.

Molecular contribution to cleft palate production in cleft lip mice

Cleft palate following cleft lip may include a developmental disorder during palatogenesis. CL/Fr mice fetuses, which develop cleft lip and palate spontaneously, have less capability for in vivo cell proliferation in palatal mesenchyme compared with CL/Fr normal fetuses. In order to know the changes of signaling molecules contributing to cleft palate morphogenesis following cleft lip, the mRNA expression profiles were compared in palatal shelves oriented vertically (before elevation) in CL/Fr fetuses with or without cleft lip. The changes in mRNA profile of cleft palate morphogenesis were presented in a microarray analysis, and genes were restricted to lists contributing to cleft palate development in CL/Fr fetuses with cleft lip. Four candidate genes (Ywhab, Nek2, Tacc1 and Frk) were linked in a gene network that associates with cell proliferation (cell cycle, MAPK, Wnt and Tgf beta pathways). Quantitative real-time RT-PCR highlighted the candidate genes that significantly changed in CL/Fr fetuses with cleft lip (Ywhab, Nek2 and Tacc1). The results of these molecular contributions will provide useful information for a better understanding of palatogenesis in cleft palate following cleft lip. Our data indicated the genetic contribution to cleft palate morphogenesis following cleft lip.

Generation of a mouse model with down-regulated U50 snoRNA (SNORD50) expression and its organ-specific phenotypic modulation

Box C/D-type small nucleolar RNAs (snoRNAs) are functional RNAs responsible for mediating 2'-O-ribose methylation of ribosomal RNAs (rRNAs) within the nucleolus. In the past years, evidence for the involvement of human U50 snoRNA in tumorigenesis has been accumulating. We previously identified U50HG, a non-protein-coding gene that hosted a box C/D-type U50 snoRNA, in a chromosomal breakpoint in a human B-cell lymphoma. Mouse genome analysis revealed four mouse U50 (mU50) host-genes: three mU50HG-a gene variants that were clustered in the genome and an mU50HG-b gene that we supposed to be the U50HG ortholog. In this study, to investigate the physiological importance of mU50 snoRNA and its involvement in tumorigenesis, we eliminated mU50 snoRNA sequences from the mU50HG-b gene. The established mouse line (ΔmU50(HG-b)) showed a significant reduction of mU50 snoRNA expression without alteration of the host-gene length and exon-intron structure, and the corresponding target rRNA methylation in various organs was reduced. Lifelong phenotypic monitoring showed that the ΔmU50(HG-b) mice looked almost normal without accelerated tumorigenicity; however, a notable difference was the propensity for anomalies in the lymphoid organs. Transcriptome analysis showed that dozens of genes, including heat shock proteins, were differentially expressed in ΔmU50(HG-b) mouse lymphocytes. This unique model of a single snoRNA knockdown with intact host-gene expression revealed further new insights into the discrete transcriptional regulation of multiple mU50 host-genes and the complicated dynamics involved in organ-specific processing and maintenance of snoRNAs.

Progression of oral squamous cell carcinoma accompanied with reduced E-cadherin expression but not cadherin switch

The cadherin switch from E-cadherin to N-cadherin is considered as a hallmark of the epithelial-mesenchymal transition and progression of carcinomas. Although it enhances aggressive behaviors of adenocarcinoma cells, the significance and role of cadherin switch in squamous cell carcinomas (SCCs) are largely controversial. In the present study, we immunohistochemically examined expression of E-cadherin and N-cadherin in oral SCCs (n = 63) and its implications for the disease progression. The E-cadherin-positive carcinoma cells were rapidly decreased at the invasive front. The percentage of carcinoma cells stained E-cadherin at the cell membrane was reduced in parallel with tumor dedifferentiation (P<0.01) and enhanced invasion (P<0.01). In contrast, N-cadherin-positive cells were very limited and did not correlate with the clinicopathological parameters. Mouse tongue tumors xenotransplantated oral SCC cell lines expressing both cadherins in vitro reproduced the reduction of E-cadherin-positive carcinoma cells at the invasive front and the negligible expression of N-cadherin. These results demonstrate that the reduction of E-cadherin-mediated carcinoma cell-cell adhesion at the invasive front, but not the cadherin switch, is an important determinant for oral SCC progression, and suggest that the environments surrounding carcinoma cells largely affect the cadherin expression.

Identification of novel ribonucleo-protein complexes from the brain-specific snoRNA MBII-52

Small nucleolar RNAs (snoRNAs) guide nucleotide modifications within ribosomal RNAs or spliceosomal RNAs by base-pairing to complementary regions within their RNA targets. The brain-specific snoRNA MBII-52 lacks such a complementarity to rRNAs or snRNAs, but instead has been reported to target the serotonin receptor 2C pre-mRNA, thereby regulating pre-mRNA editing and/or alternative splicing. To understand how the MBII-52 snoRNA might be involved in these regulatory processes, we isolated the MBII-52 snoRNP from total mouse brain by an antisense RNA affinity purification approach. Surprisingly, by mass spectrometry we identified 17 novel candidates for MBII-52 snoRNA binding proteins, which previously had not been reported to be associated with canonical snoRNAs. Among these, Nucleolin and ELAVL1 proteins were confirmed to independently and directly interact with the MBII-52 snoRNA by coimmunoprecipitation. Our findings suggest that the MBII-52 snoRNA assembles into novel RNA-protein complexes, distinct from canonical snoRNPs.

Identification of mesenchymal stem cell (MSC)-transcription factors by microarray and knockdown analyses, and signature molecule-marked MSC in bone marrow by immunohistochemistry

Although ex vivo expanded mesenchymal stem cells (MSC) have been used in numerous studies, the molecular signature and in vivo distribution status of MSC remain unknown. To address this matter, we identified numerous human MSC-characteristic genes--including nine transcription factor genes--using DNA microarray and real-time RT-PCR analyses: Most of the MSC-characteristic genes were down-regulated 24 h after incubation with osteogenesis-, chondrogenesis- or adipogenesis-induction medium, or 48-72 h after knockdown of the nine transcription factors. Furthermore, knockdowns of ETV1, ETV5, FOXP1, GATA6, HMGA2, SIM2 or SOX11 suppressed the self-renewal capacity of MSC, whereas those of FOXP1, SOX11, ETV1, SIM2 or PRDM16 reduced the osteogenic- and/or adipogenic potential. In addition, immunohistochemistry using antibodies for the MSC characteristic molecules--including GATA6, TRPC4, FLG and TGM2--revealed that MSC-like cells were present near the endosteum and in the interior of bone marrow of adult mice. These findings indicate that MSC synthesize a set of MSC markers in vitro and in vivo, and that MSC-characteristic transcription factors are involved in MSC stemness regulation.

Expression of SIP1 in oral squamous cell carcinomas: implications for E-cadherin expression and tumor progression

Loss of E-cadherin expression allows carcinoma cells to liberate from the primary site and enhances invasion and metastasis. The genetic aberration of E-cadherin is a rare event in sporadic carcinomas, and transcription repressors are considered to take a central role in E-cadherin loss. However, expression of E-cadherin repressors is largely dependent on tissue and cell type. To identify the repressor expressed in oral squamous carcinomas, we compared the expression levels of E-cadherin and repressors by real-time RT-PCR. Among the repressors including SNAIL, SLUG, SIP1, E12 and E47, SIP1 was inversely correlated to E-cadherin (P < 0.05). Chromatin immunoprecipitation showed that SIP1 specifically bound to the E-cadherin promoter region. SIP1 expression was immuno-histochemically detected in 27.7% of 47 oral carcinomas, and SIP1-positive carcinomas did not express E-cadherin (P < 0.01). Thirteen patients with SIP1 staining showed a lower disease-specific survival rate (P < 0.05). Multivariate risk factor analysis demonstrated that SIP1 expression was an independent prognostic value for disease-specific overall survival (P < 0.05). These results suggest that SIP1 contributes to the loss of E-cadherin expression and that detection of SIP1 expression is a predictive and prognostic tool in clinical management of oral carcinomas.

Fluoride and apatite formation in vivo and in vitro

In recent years, the biomineralization process has attracted much interest from academics and industries for potential technological application. The rule in biomineralization is to have a variety of interfaces and surfaces which can act as nucleators. The ultimate step in any biomineralization process, i.e. the deposition of mineral, must conform to the driving forces operating on the system. A new paradigm in the assessment of the driving force for biomineralization is that a variety of ions existing in the mineralizing milieu are not a bystander, but are instead an active player that directly regulates the precipitation process and nature of biogenic apatites. Thus, the most putative stoichiometric model of a biomineral is (Ca)(5-x)(Mg)q(Na)u(HPO4)v(CO3)w(PO4)(3-y)(OH,F)(1-z). Fluoride participates in many aspects of calcium phosphate formation in vivo and has enormous effects on its process and on the nature and properties of the final products. In the development of biogenic apatites, fluoride ion in the mineralizing media is supposed to accelerate the hydrolysis of acidic precursor(s) and increase the growth rates by augmenting the driving force for precipitation. Inhibitory activities of ions and molecules are related to their adsorption onto the apatite surfaces. From theoretical and practical points of view, it is of paramount importance to elucidate and predict the effect and outcome of fluoride (accelerator) and inhibitors of biological relevance, because of their use in combination for healthcare in dentistry and medicine, e.g. prevention of dental caries and calculus deposition and in the formulation of antiosteoporosis treatments.

Influence of hyperbaric environment on physiological tremor

The effect of pressured environment from 1 to 24 ATA (Atmosphere Absolute) on total power spectrum (TP) of physiological tremor, whose value was the sum of power spectra for frequency range in 0.5-50 Hz, was investigated. The main effects obtained were as follows. (1) In the case of 3 ATA, TP during the pressure holding period denoted a similar value as the value in 1 ATA. In the latter half of the period, the TP increased. When the pressured environment is 4 ATA, in which the partial pressure of the nitrogen gas was 3.6 ATA, the TP decreased during the pressure holding period compared with the value in 1 ATA. Nitrogen narcosis was recognized at the partial pressure of 3.6 ATA, thus the effect denoted a decrease of TP. (2) In the cases of 16 and 19 ATA using heliox gas, during the pressure holding period, TP decreased compared with the value in 1 ATA, but in the case of 24 ATA the value increased. The partial pressure of helium gas of 23.6 ATA indicated a high pressure nervous syndrome, therefore, the influence of high pressure on TP was recognized as one of the causes of the increase of TP. (3) The influence of inhibitors of the autonomic nervous system on TP during the pressure holding period of 3 ATA was recognized. After intake of the inhibitor for the parasympathetic nerve (atropine) during the pressure period, TP increased, while for the intake of the inhibitor for the sympathetic nerve (propanol), TP decreased.

Sexual dimorphism of porcine amelogenins: male-specific amelogenins have strong adsorption properties onto apatite crystals

The present studies were undertaken to investigate the sexual dimorphism of porcine amelogenins and to gain information as to whether excesses of male amelogenins, if any, possess functional significance in protein-crystal interactions. Enamel proteins, including the intact full-length amelogenins and their degraded polypeptides, were isolated from the secretory enamel of male and female pigs. To identify the amelogenins among the separated pools of male- and female-matrix proteins, rabbit anti-C13 and C25 peptide sera were used, which reacted specifically with the conserved C-terminal domain. Immunoblotting showed that a few extra members of the amelogenins, sharing common epitopes at the C-terminus, were recognized in male products. The apparent yield of the male amelogenins was only marginal, on the basis of their stained intensities on the gel, but the secreted male amelogenins demonstrated selective (probably the strongest among the amelogenins) adsorption properties onto apatite crystals. Reflecting the general symmetric electrophoretic profiles of the male- and female-enamel proteins in toto, there were no sex-linked differences in the protein-crystal interaction and the resulting regulatory function of crystal precipitation.

Osmotic shock induces G1 arrest through p53 phosphorylation at Ser33 by activated p38MAPK without phosphorylation at Ser15 and Ser20

Osmotic shock induced transient stabilization of p53, possibly due to increased degradation of Mdm2. Stabilized p53 was activated by p38(MAPK), resulting in G(1) arrest through induction of p21(WAF1). Among the postulated phosphorylation sites involved in p53 stabilization or activation (Ser(15), Ser(20), Ser(33), and Ser(46)), only Ser(33) was phosphorylated. Furthermore, interaction of p53 with the transcriptional coactivator p300 was induced, and Lys(382) of p53 was acetylated. Although inhibition of p38(MAPK) did not prevent nuclear accumulation of p53, phosphorylation of Ser(33) was markedly suppressed by SB203580, a specific inhibitor of p38(MAPK). Under these conditions, acetylation of Lys(382) and induction of p21(WAF1) were also inhibited, and cells with elevated levels of p53 showed normal cell cycle progression. Activated p38(MAPK) phosphorylated endogenous p53 at Ser(33) in living cells. In stable transformants expressing dominant negative MKK6, an upstream protein kinase of p38(MAPK), p53 stabilization was induced normally following osmotic shock, but phosphorylation of Ser(33), acetylation of Lys(382), and induction of p21(WAF1) were almost completely inhibited. These results suggest that phosphorylation at Ser(33) by p38(MAPK) is critical for activation of p53 following osmotic shock. Phosphorylation of neither Ser(15) nor Ser(20) was needed in this activation.

UV-radiation induces dose-dependent regulation of p53 response and modulates p53-HDM2 interaction in human fibroblasts

We address here the effects of increasing fluencies of UV-radiation on stability, modifications, activity and HDM2-interactions of endogenous p53 tumor suppressor and on cellular damage response of human diploid fibroblasts. Low amounts of UVB/C-radiation induced a transient cell cycle arrest of the cells which correlated with rapid but transient increase in p53 levels. In contrast, high UV-fluency caused cell apoptosis and a slower but sustained increase in p53. Regulation of p53 target genes was highly dependent on the radiation dose used. Whereas low doses induced p21/Cip1/Waf1 and HDM2, high doses induced only GADD45 and BAX increasing the BAX:BCL-2 ratio. The levels of HDM2, a negative regulator of p53, increased only by the low dose of UVC and p53-HDM2 association was promoted. In the absence of HDM2-induction after the high dose of UV-radiation p53-HDM2-interaction was promoted, but HDM2 failed to downregulate p53. p53 site-specific modifications (Ser15, Ser33, Ser37, Lys382) varied kinetically and were dependent on the fluency of the radiation used. Maximal phosphorylation of p53 on Ser15 and Ser33 correlated with increased levels of HDM2-free p53. The results suggest that regulation of p53 and HDM2 by UV-radiation is highly dose-dependent and contributes to the outcome of the cellular response.

The secretion of amelogenins is associated with the induction of enamel and dentinoid in an ameloblastic fibro-odontoma

Ameloblastic fibro-odontoma is the unique entity of epithelial-ectomesenchymal odontogenic tumors, which is characterized by enamel formation in addition to dentine. We examined immunohistochemically a case of this tumor in which enamel having prism structures was developed in the absence of odontoblast differentiation but was in contact with mesenchymal matrices. Histological examination showed diverse morphological features of epithelial tumor cells, e.g., cuboidal cells comprising tooth bud-like projections, ameloblast- and stellate reticulum-like cells, and residual cells in forms of extended cords or islands of odontogenic epithelium. Immunostaining with anti-amelogenin sera proved that the intracellular production of amelogenins was initiated at the tooth bud-like stage. The secreted amelogenins were detected almost exclusively in the induced enamel and dentinoid areas, as well as in the core region of cementicle-like spheres deposited in the encapsulating stroma. The results obtained indicate that the odontogenic tumor epithelia and its products, i.e., amelogenins, participate in multifaceted aspects of dental hard tissue formation that takes place during oncogenesis.

Human SMG-1, a novel phosphatidylinositol 3-kinase-related protein kinase, associates with components of the mRNA surveillance complex and is involved in the regulation of nonsense-mediated mRNA decay

Nonsense-mediated mRNA decay (NMD) is a conserved surveillance mechanism that eliminates imperfect mRNAs that contain premature translation termination codons (PTCs) and code for nonfunctional or potentially harmful polypeptides. We show that a novel phosphatidylinositol 3-kinase-related protein kinase, hSMG-1, is a human ortholog of a product of Caenorhabditis elegans smg-1, one of seven smg genes involved in NMD. hSMG-1 phosphorylates hUPF1/SMG-2 in vivo and in vitro at specific serine residues in SQ motifs. hSMG-1 can associate with hUPF1/SMG-2 and other components of the surveillance complex. In particular, overexpression of a kinase-deficient point mutant of hSMG-1, hSMG-1-DA, results in a marked suppression of the PTC-dependent beta-globin mRNA degradation; whereas that of wild-type hSMG-1 enhances it. We also show that inhibitors of hSMG-1 induce the accumulation of truncated p53 proteins in human cancer cell lines with p53 PTC mutation. Taken together, we conclude that hSMG-1 plays a critical role in NMD through the direct phosphorylation of hUPF1/SMG-2 in the evolutionally conserved mRNA surveillance complex.

p53DINP1, a p53-inducible gene, regulates p53-dependent apoptosis

Using the differential display method combined with a cell line that carries a well-controlled expression system for wild-type p53, we isolated a p53-inducible gene, termed p53DINP1 (p53-dependent damage-inducible nuclear protein 1). Cell death induced by DNA double-strand breaks (DSBs), as well as Ser46 phosphorylation of p53 and induction of p53AIP1, were blocked when we inhibited expression of p53DINP1 by means of an antisense oligonucleotide. Overexpression of p53DINP1 and DNA damage by DSBs synergistically enhanced Ser46 phosphorylation of p53, induction of p53AIP1 expression, and apoptotic cell death. Furthermore, the protein complex interacting with p53DINP1 was shown to phosphorylate Ser46 of p53. Our results suggest that p53DINP1 may regulate p53-dependent apoptosis through phosphorylation of p53 at Ser46, serving as a cofactor for the putative p53-Ser46 kinase.

Inhibition of human breast cancer cell growth by blockade of the mevalonate-protein prenylation pathway is not prevented by overexpression of cyclin D1

Overexpression of the cyclin D1 (CCND1) gene, encoding a downstream effector of mitogenic signals that plays a central role in G1 phase progression, is often found in cancerous cells. In sporadic breast cancer (BC), this is one of the most frequent and early genetic lesions identified so far, found in more than 50% of the tumors. Inhibitors of the mevalonate/protein prenylation pathway belong to a new family of cancer therapeutic agents that act by blocking intracellular mitogenic signal transduction pathways, thereby preventing expansion of pre-cancerous foci and inhibiting growth of transformed cells. It is not known at present whether constitutively high intracellular levels of cyclin D1 might interfere with the cytostatic actions of mevalonate/protein prenylation inhibitors. This possibility was investigated here by assessing the cell cycle effects of Simvastatin, a non-toxic upstream inhibitor of the mevalonate pathway, on human BC MCF-7 cells expressing either normal or enhanced levels of cyclin D1 from of a stably transfected, tet-inducible expression vector. Results show that constitutive overexpression of this protein, such as that found in sporadic BCs, does not influence the growth inhibitory effects of Simvastatin in vitro. In addition, D1-overexpressing embryo fibroblasts were also found to be responsive to the cell cycle effects of mevalonate/protein prenylation pathway blockade, further suggesting that high intracellular levels of cyclin D1 do not prevent the cytostatic actions of compounds targeting this metabolic pathway.

Stimulation of DNA Polymerase α Activity by Cdk2-Phosphorylated Rb Protein

We propose a new role of retinoblastoma protein as a cell growth activator in its phosphorylated form. The hyper-phosphorylated retinoblastoma protein generated by the action of cdk2/cyclin E strongly stimulated the activity of DNA polymerase alpha, but did not stimulate DNA polymerases delta, epsilon, or primase. But, cdk4/cyclin D-phosphorylated retinoblastoma protein showed little stimulation. Hyper-phosphorylated retinoblastoma protein interacted with the catalytic subunit of DNA polymerase alpha, and stabilised DNA polymerase alpha from heat inactivation at 45 degrees C. These results suggest that in G1 phase, hypo-phosphorylated retinoblastoma protein suppresses the progression of cell cycle as a transcription inhibitor, but that after phosphorylation by cdk2/cyclin E at the G1/S boundary, hyper-phosphorylated retinoblastoma protein acts as a cell-cycle promoter by optimising the DNA polymerase alpha reaction.