Transcriptomic and functional studies reveal miR-431-5p as a tumour suppressor in pancreatic ductal adenocarcinoma cells

The lactate receptor HCAR1 (hydroxycarboxylic acid receptor 1) is highly expressed in pancreatic ductal adenocarcinoma (PDAC), where it regulates lactate transport between the cancer cells. Little is known about the underlying cause of high HCAR1 expression in PDAC, and in the present study, we investigated whether HCAR1 could be a target of miRNA regulation. By searching for predicted miRNA candidates in silico, we identified miR-431-5p as a possible regulator of HCAR1. We found miR-431-5p to repress HCAR1 expression through direct binding to the 3' UTR. The endogenous expression of miR-431-5p and HCAR1 was found to be negatively related in the PDAC cell lines BxPC-3, Capan-2, and PANC-1. Overexpression of miR-431-5p inhibited cell proliferation in all the cell lines, and a shift in cell cycle progression and induction of apoptosis were found in the BxPC-3 cells. Transcriptomic analysis of mRNA from BxPC-3 cells revealed numerous differentially expressed genes (DEGs), including HCAR1, in response to miR-431-5p overexpression. A significant proportion of these DEGs was enriched in cancer-related processes and signalling pathways. Among the most significantly repressed DEGs was ATP6V0E1, encoding the integral subunit e of vacuolar ATPase (V-ATPase), an enzyme that is important for cancer cell survival. Small interfering RNA (siRNA)-mediated knockdown of HCAR1 and ATP6V0E1 showed that only knockdown of ATP6V0E1 mimicked the effect of miR-431-5p overexpression on cell viability. Our findings indicate that miR-431-5p acts as a tumour suppressor in PDAC cells, with BxPC-3 cells being most responsive.

Dental erosion in mice with impaired salivary gland function

Objective: Salivary flow rate exerts an essential impact on the development and progression of dental erosion. In this work, the experimental dental erosion in non-obese diabetic (NOD) mice with reduced salivary flow rate was induced, and the erosive effect of acidic drinks on their dentition was studied.Material and methods: Three acidic drinks (sports drink, cola light drink and sugar containing cola drink) were given to adult NOD mice (groups: N = 11) as the only drink for 6 weeks. Two control groups were included; wild type and NOD control (groups: N = 9). Experimental and control (water) teeth were dissected out and observed by scanning electron microscopy (SEM). Mandibular first molars were subsequently embedded in Epon, ground transversely, observed again by SEM, and the enamel thickness and tooth height were measured.Results: Mandibular molars were considerably more eroded than maxillary molars. The erosive process started at the top of the cusps and subsequently extended in the cervical, mesio-distal, and pulpal direction. Erosive lesions were evident in increased succession from sports drink, cola light to cola drink exposed mandibular molars, with the lingual tooth height being approximately 23%, 26%, and 37% lower, respectively, compared to the control. The lingual enamel was approximately 48% thinner in sports drink molars and 62% thinner in cola light molars. In cola drink molars, the lingual enamel was totally eroded, and significant erosion of dentine was evident.Conclusion: Reduced salivary flow, together with a high consumption of acidic drinks, results in severe erosion of NOD mice molars.

Transcriptomic analysis of MicroRNA expression in enamel-producing cells

There is little evidence for the involvement of microRNAs (miRNAs) in the regulation of circadian rhythms during enamel development. Few studies have used ameloblast-like cell line LS8 to study the circadian rhythm of gene activities related to enamel formation. However, the transcriptomic analysis of miRNA expression in LS8 cells has not been established yet. In this study, we analyze the oscillations of miRNAs in LS8 cells during one-day cycle of 24 h by next generation deep sequencing. After removal of low quality reads, contaminants, and ligation products, we obtained a high number of clean reads in all 12 samples from four different time points. The length distribution analysis indicated that 77.5% of clean reads were between 21 and 24 nucleotides (nt), of which 35.81% reads exhibited a length of 22 nt. In total, we identified 1471 miRNAs in LS8 cells throughout all four time-points. 1330 (90.41%) miRNAs were identified as known miRNA sequences, whereas 139 (9.59%) were unannotated and classified as novel miRNA sequences. The differential expression analysis showed that 191 known miRNAs exhibited significantly (P-value < 0.01) different levels of expression across three time-points investigated (T6, T12, and T18) compared to T0. Verification of sequencing data using qRT-PCR on six selected miRNAs suggested good correlation between the two methods. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed significant enrichment of predicted target genes of differentially expressed miRNAs. The present study shows that miRNAs are highly expressed in LS8 cells and that a significant number of them oscillate during one-day cycle of 24 h. This is the first transcriptomic analysis of miRNAs in ameloblast-like cell line LS8 that can be potentially used to further characterize the epigenetic regulation of miRNAs during enamel formation.

New animal model of extrinsic dental erosion-Erosive effect on the mouse molar teeth

OBJECTIVE

Consumption of acidic food and drinks is considered as important risk factor for development of dental erosion. There are several in vitro and in situ studies focusing on the risk indicators and preventive treatment, however, the need for a standardized animal model has been emphasised for many years. The aim was to establish an animal model of extrinsic dental erosion, which may serve as a standard for future studies to improve our understanding of the erosion.

DESIGN

Two acidic drinks, sports drink and cola drink, were given to young mice for six weeks. Experimental and control (water) molars and incisors were dissected out and observed by scanning electron microscopy (SEM). Mandibular first molars were subsequently ground transversely and observed again by SEM. The tooth height and enamel thickness were measured on the SEM images.

RESULTS

The lingual surface of the mandibular molars was most eroded after consumption of acidic drinks. The cola drink exhibited higher erosive effect on mandibular molars compared to sports drink. The lingual tooth height, compared to control, was about 34% and 18% lower in the cola drink and sports drink molars, respectively. Compared to the control molars, the lingual enamel was about 23% thinner in the sports drink molars and totally eroded on the certain lingual areas of the cola drink molars.

CONCLUSIONS

This new animal model of extrinsic dental erosion and the presented method with ground molars observed in SEM are suitable for further studies, which will gain deeper insights into the erosive disease.

Circadian clock and oral cancer

The circadian clock is comprised of a master component situated in the hypothalamic suprachiasmatic nucleus and subordinate clock genes in almost every cell of the body. The circadian clock genes and their encoded proteins govern the organism to follow the natural signals of time, and adapt to external changes in the environment. The majority of physiological processes in mammals exhibit variable circadian rhythms, which are generated and coordinated by an oscillation in the expression of the clock genes. A number of studies have reported that alteration in the expression level of clock genes is correlated with several pathological conditions, including cancer. However, little is known about the role of clock genes in homeostasis of the oral epithelium and their disturbances in oral carcinogenesis. The present review summarizes the current state of knowledge of the implications of clock genes in oral cancer. It has been demonstrated that the development of oral squamous cell carcinoma undergoes circadian oscillation in relation to tumor volume and proliferation rate. The circadian clock gene period (PER)1 has been associated with oral cancer pathogenesis and it is suggested that changes in the expression of PER1 may exhibit an important role in the development, invasion, and metastasis of oral squamous cell carcinoma. However, its role remains elusive and there is a need for further research in order to understand the underlying mechanisms of the clock genes in oral cancer pathogenesis.

MicroRNAs: Modulators of Tooth Development

MicroRNAs (miRNAs) are non-coding RNAs that are involved in various biological pathways by regulating gene expression. Teeth develop via reciprocal and sequential interactions between the epithelium and the ectomesenchyme. The speci.c functions of several genes during tooth development are known, and the involvement of their mutations in the pathogenesis of congenital dental defects has been widely studied. The miRNA pathway is considered to have a significant role in embryogenesis including tooth development. It has been shown that miRNAs regulate morphogenesis of tooth by fine-tuning the signalling networks, however, their precise role in tooth differentiation and morphogenesis is still elusive. The present review focuses on the studies that have used animal models to explore the function of miRNAs in tooth development. Major findings with special emphasis on the miRNA involvement in .ne-tuning and network regulation are presented and discussed. Disturbances in tooth development in the global miRNA processing knockouts mirror the essential fine-tuning guiding appropriate formation of dental hard tissues. However, further investigation of single miRNA function and mutation, including deletion and overexpression, may lead to improved knowledge on development of particular dental defects in humans. In the light of similarities between tooth development and other organs originating from the epithelium, further understanding of miRNAs` function during tooth development may have wide biological relevance.

Anti-proliferative Properties of miR-20b and miR-363 from the miR-106a-363 Cluster on Human Carcinoma Cells

BACKGROUND

The miR-106a-363 cluster, encoding six miRNAs (miR- 106a, miR-18b, miR-20b, miR-19b-2, miR-92-2 and miR-363), has been shown to be overexpressed in various tumours. In oral carcinoma cells, however only miR- 106a was detectable from this cluster. We have investigated how effects of transfection of oral carcinoma cells with a non-expressed member of this cluster affect mRNA transcriptomes and cellular selected functions.

METHODS

Investigate effects of miR-20b and miR-363 mimics on cellular respiration, glycolysis and mobility. Effects on mRNA transcriptomes were monitored using microarrays.

RESULTS

The studies show that in oral carcinoma cells transfected with miR-20b -, or miR-363-3p or miR-363-5p mimic different mRNAs were differentially expressed. Nevertheless, bioinformatics analysis suggested significant associations of differentially expressed genes to inhibition of cellular proliferation, cell cycle and cellular migration. These results were also experimentally confirmed.

CONCLUSIONS

Transfection of miRNA mimics for unexpressed members of the miR-106a-363 cluster (miR20b, miR-363-3p and miR-363-5p) exhibit an anti-proliferative effect on oral carcinoma cells, although likely mediated by different regulatory mechanisms.

Circadian rhythms and gene expression during mouse molar tooth development

OBJECTIVES

Incremental markings in dental enamel suggest that the circadian clock may influence the molecular underpinnings orchestrating enamel formation. The aim of this study was to investigate whether the genes and microRNAs (miRNAs) oscillate in a circadian pattern during tooth and enamel development.

MATERIAL AND METHODS

Comparative gene and miRNA expression profiling of the first mandibular molar tooth germ isolated at different time-points during the light and night period was performed using microarrays and validated using real-time RT-PCR. Bioinformatic analysis was carried out using Ingenuity Pathway Analysis (IPA), and TargetScan software was used in order to identify computationally predicted miRNA-mRNA target relationships.

RESULTS

In total, 439 genes and 32 miRNAs exhibited significantly different (p < 0.05) levels of expression in the light phase compared with the night phase tooth germs. Genes involved in enamel formation, i.e. Amelx, Ambn, Amtn, and Odam, oscillated in a circadian pattern. Furthermore, the circadian clock genes, in particular Clock and Bmal1, oscillated in mouse molar tooth germ during 24-h intervals. The expression of Clock and Bmal1 was inversely correlated with the expression of miR-182 and miR-141, respectively.

CONCLUSIONS

MiRNAs, including miR-182 and miR-141, are involved in the control of peripheral circadian rhythms in the developing tooth by regulating the expression of genes coding for circadian transcription factors such as CLOCK and BMAL1. Regulation of circadian rhythms may be important for enamel phenotype, and the morphology of dental enamel may vary between individuals due to differences in circadian profiles.

The Three Paralogous MicroRNA Clusters in Development and Disease, miR-17-92, miR-106a-363, and miR-106b-25

MicroRNAs (miRNAs) form a class of noncoding RNA genes whose products are small single-stranded RNAs that are involved in the regulation of translation and degradation of mRNAs. There is a fine balance between deregulation of normal developmental programs and tumor genesis. An increasing body of evidence suggests that altered expression of miRNAs is entailed in the pathogenesis of human cancers. Studies in mouse and human cells have identified the miR-17-92 cluster as a potential oncogene. The miR-17-92 cluster is often amplified or overexpressed in human cancers and has recently emerged as the prototypical oncogenic polycistron miRNA. The functional analysis of miR-17-92 is intricate by the existence of two paralogues: miR-106a-363 and miR-106b-25. During early evolution of vertebrates, it is likely that the three clusters commenced via a series of duplication and deletion occurrences. As miR-106a-363 and miR-106b-25 contain miRNAs that are very similar, and in some cases identical, to those encoded by miR-17-92, it is feasible that they regulate a similar set of genes and have overlapping functions. Further understanding of these three clusters and their functions will increase our knowledge about cancer progression. The present review discusses the characteristics and functions of these three miRNA clusters.

An investigation into anti-proliferative effects of microRNAs encoded by the miR-106a-363 cluster on human carcinoma cells and keratinocytes using microarray profiling of miRNA transcriptomes

Transfection of human oral squamous carcinoma cells (clone E10) with mimics for unexpressed miR-20b or miR-363-5p, encoded by the miR-106a-363 cluster (miR-20b, miR-106a, miR-363-3p, or miR-363-5p), caused 40–50% decrease in proliferation. Transfection with mimics for miR-18a or miR-92a, encoded by the miR-17-92 cluster (all members being expressed in E10 cells), had no effect on proliferation. In contrast, mimic for the sibling miRNA-19a yielded about 20% inhibition of proliferation. To investigate miRNA involvement profiling of miRNA transcriptomes were carried out using deoxyoligonucleotide microarrays. In transfectants for miR-19a, or miR-20b or miR-363-5p most differentially expressed miRNAs exhibited decreased expression, including some miRNAs encoded in paralogous miR-17-92—or miR-106b-25 cluster. Only in cells transfected with miR-19a mimic significantly increased expression of miR-20b observed—about 50-fold as judged by qRT-PCR. Further studies using qRT-PCR showed that transfection of E10 cells with mimic for miRNAs encoded by miR-17-92 - or miR-106a-363 - or the miR-106b-25 cluster confirmed selective effect on expression on sibling miRNAs. We conclude that high levels of miRNAs encoded by the miR-106a-363 cluster may contribute to inhibition of proliferation by decreasing expression of several sibling miRNAs encoded by miR-17-92 or by the miR-106b-25 cluster. The inhibition of proliferation observed in miR-19a-mimic transfectants is likely caused by the miR-19a-dependent increase in the levels of miR-20b and miR-106a. Bioinformatic analysis of differentially expressed miRNAs from miR-106a, miR-20b and miR-363-5p transfectants, but not miR-92a transfectants, yielded significant associations to “Cellular Growth and Proliferation” and “Cell Cycle.” Western blotting results showed that levels of affected proteins to differ between transfectants, suggesting that different anti-proliferative mechanisms may operate in these transfectants.

Expression of Clu and Tgfb1 during murine tooth development: effects of in-vivo transfection with anti-miR-214

Expression of clusterin (Clu) in the murine first molar tooth germ was markedly increased at postnatal developmental stages. The time-course of expression of this gene paralleled those of other genes encoding proteins involved during the secretory phase of odontogenesis, as described previously. Immunohistochemical studies of clusterin in murine molar tooth germs suggested this protein to be located in outer enamel epithelium, regressing enamel organ, secretory ameloblasts, and the dental epithelium connecting the tooth to the oral epithelium at an early eruptive stage. Immunolabelling of transforming growth factor beta-1 (TGF-β1) revealed it to be located close to clusterin. The levels of expression of Clu and Tgfb1 were markedly decreased following in-vivo transfection with anti-miR-214. In contrast, the expression of several genes associated with regulation of growth and development were increased by this treatment. We suggest that clusterin has functions during secretory odontogenesis and the early eruptive phase. Bioinformatic analysis after treatment with anti-miR-214 suggested that, whilst cellular activities associated with tooth mineralization and eruption were inhibited, activities associated with an alternative developmental activity (i.e. biosynthesis of contractile proteins) appeared to be stimulated. These changes probably occur through regulation mediated by a common cluster of transcription factors and support suggestions that microRNAs (miRNAs) are highly significant as regulators of differentiation during odontogenesis.

Expression of delta-like 1 homologue and insulin-like growth factor 2 through epigenetic regulation of the genes during development of mouse molar

Delta-like 1 homolog (Dlk1) and insulin-like growth factor 2 (Igf2) are two of six well-studied mouse imprinted gene clusters that are paternally expressed. Their expression is also linked to their maternally expressed non-coding RNAs, encoded by Gene trap locus 2 (Gtl2) and Imprinted maternally expressed transcript (H19), co-located as imprinted gene clusters. Using deoxyoligonucleotide microarrays and real-time RT-PCR analysis we showed Dlk1 and Gtl2 to exhibit a time-course of expression during tooth development that was similar to that of Igf2 and H19. Western blot analysis of proteins encoded by Dlk1 and Igf2 suggested that the levels of these proteins reflected those of the corresponding mRNAs. Immunohistochemical studies of DLK1 in murine molars detected the protein in both epithelial and mesenchymal regions, in developing cusp mesenchyme, and in newly synthesized enamel and dentin tubules. IGF2 protein was detected primarily at prenatal stages, suggesting that it may be active before birth. Analysis of methylation of cytosine-phosphate-guanine (CpG) islands in both Dlk1 and Igf2 suggested the presence of an increasing fraction of hypermethylated bases with increasing time of development. The increased levels of hypermethylation coincided both with the diminished levels of expression of Dlk1 and Igf2 and with decreased levels of DLK1 and IGF2 proteins in the tooth germ, suggesting that their expression is regulated via methylation of CpG islands present in these genes.

Effects of in vivo transfection with anti-miR-214 on gene expression in murine molar tooth germ

MicroRNAs (miRNAs) are an abundant class of noncoding RNAs that are believed to be important in many biological processes through regulation of gene expression. Little is known of their function in tooth morphogenesis and differentiation. MicroRNA-214 (miR-214), encoded by the polycistronic Dnm30os gene, is highly expressed during development of molar tooth germ and was selected as a target for silencing with anti-miR-214. Mandibular injection of 1–100 pmol of anti-miR-214 close to the developing first molar in newborn mice resulted in significant decrease in expression of miR-214, miR-466h, and miR-574-5p in the tooth germ. Furthermore, levels of miR-199a-3p, miR-199a-5p, miR-690, miR-720, and miR-1224 were significantly increased. Additionally, the expression of 863 genes was significantly increased and the expression of 305 genes was significantly decreased. Among the genes with increased expression was Twist-1 and Ezh2, suggested to regulate expression of miR-214. Microarray results were validated using real-time RT-PCR and Western blotting. Among genes with decreased expression were Amelx, Calb1, Enam, and Prnp; these changes also being reflected in levels of corresponding encoded proteins in the tooth germ. In the anti-miR-214-treated molars the enamel exhibited evidence of hypomineralization with remnants of organic material and reduced surface roughness after acid etching, possibly due to the transiently decreased expression of Amelx and Enam. In contrast, several genes encoding contractile proteins exhibited significantly increased expression. mRNAs involved in amelogenesis ( Ambn, Amelx, Enam) were not found among targets of miRNAs that were differentially expressed following treatment with anti-miR-214. It is therefore suggested that effects of miR-214 on amelogenesis are indirect, perhaps mediated by the observed miR-214-dependent changes in levels of expression of numerous transcription factors.

PGE2 production in oral cancer cell lines is COX-2-dependent

It has been suggested that epithelial cyclooxygenase-2 (COX-2) promotes oral carcinogenesis and carcinoma malignancy through increased prostaglandin E(2) (PGE(2)) production. Although oral squamous cell carcinomas (OSCC) often express COX-2, they may also produce PGE(2) in a COX-1-dependent manner. We used 6 isolated cell lines to investigate which COX isoforms OSCC may use for PGE(2) production. COX-1 and -2 expression patterns divided the 6 OSCC cell lines into 3 distinct groups: both COX isoforms low, only COX-1 high, or both COX isoforms high. Multicolor immunohistofluorescence staining confirmed the COX-expression profiles in organotypic 3D cultures and the COX-2 dominance in OSCC tumors. Epidermal growth factor (EGF) stimulation induced COX-2 (but not COX-1) expression and increased PGE(2) production, which was attenuated by COX-2 (but not COX-1) specific inhibition or siRNA-mediated COX-2 gene knockdown. Thus, PGE(2) production in OSCC cell lines was COX-2-dependent.

Nerve growth factor beta/pro-nerve growth factor and their receptors in normal human oral mucosa

Nerve growth factor beta (NGF-beta) and its precursor proNGF are important for the differentiation and survival of neurons and dermal keratinocytes. The aim of this study was to determine the role that NGF might play in the differentiation and wound healing of oral mucosa. Cultured normal human oral mucosal keratinocytes expressed mRNA for NGF-beta/proNGF and for their receptors TrkA and p75(NTR). Lysates from cultured oral mucosal keratinocytes did not contain detectable amounts of mature 14-kDa NGF-beta but did contain several NGF proforms with molecular weights between 32 and 114 kDa. Culture medium from oral mucosal keratinocytes contained 75 kDa proNGF. The addition of NGF-beta significantly enhanced the proliferation of oral mucosal keratinocyte cultures and in vitro scratch closure. Immunostaining of biopsies from normal oral mucosa showed the presence of proNGF in all epithelial layers. NGF staining was observed in the granular and upper spinous cell layers. TrkA immunoreactivity was detected in basal and parabasal cells, with weak to moderate staining in spinous and granular cell layers. p75(NTR) staining was seen in basal cell layers. These findings indicate that NGF-beta/proNGF have mitogenic and motogenic effects on oral mucosal keratinocytes and therefore may aid in the healing of oral wounds. Differential expression of NGF and NGF receptors throughout the epithelium suggests a role in epithelial differentiation.

The gene for human transcription factor TCF11 is located telomeric to D17S1827, BTR and HP1Hsbeta on chromosome 17q22

We report the screening of thirty-one YACs with a number of markers using polymerase chain reaction (PCR) to construct a physical map of part of human chromosome 17q21.3-q22. A contig of YACs covering about 4 Mb was constructed around the TCF11 gene at 68 cM from the most telomeric marker on the p arm, localizing TCF11 telomeric to genetic marker D17S1827. Both human and mouse P1-derived artificial chromosomes (PACs) containing TCF11 were isolated and characterized. The human heterochromatin protein 1 gene, HP1Hsbeta, and its homologue in mouse, MoMOD1, were identified centromeric to TCF11.