Dysfunctional clock signaling is observed in a variety of pathological conditions. Many members of the clock gene family are upregulated in tumor cells. Here, we explored the consequences of a commonly disrupted signaling pathway in head and neck cancer on the regulation of circadian clock genes. PTEN is a key molecular controller of the PI3K signaling, and loss of PTEN function is often observed in a variety of cancers. Our main goal was to determine whether PTEN regulates circadian clock signaling. We found that oxidation-driven loss of PTEN function resulted in the activation of mTOR signaling and activation of the core clock protein BMAL1 (also known as ARNTL). The PTEN-induced BMAL1 upregulation was further confirmed using small interference RNA targeting PTEN, and in vivo conditional depletion of PTEN from the epidermis. We observed that PTEN-driven accumulation of BMAL1 was mTOR-mediated and that administration of Rapamycin, a specific mTOR inhibitor, resulted in in vivo rescue of normal levels of BMAL1. Accumulation of BMAL1 by deletion of PER2, a Period family gene, was also rescued upon in vivo administration of mTOR inhibitor. Notably, BMAL1 regulation requires mTOR regulatory protein Raptor and Rictor. These findings indicate that mTORC1 and mTORC2 complex plays a critical role in controlling BMAL1, establishing a connection between PI3K signaling and the regulation of circadian rhythm, ultimately resulting in deregulated BMAL1 in tumor cells with disrupted PI3K signaling.
head and neck cancer; oral cancer
Kallikrein-related-peptidase-4 (KLK4), a serine protease originally discovered in developing tooth with broad target sequence specificity, serves vital functions in dental enamel formation. KLK4 is involved in degradation of extracellular matrix proteins and it is thought that this proteolytic activity could also promote tumor invasion and metastasis. Recent studies have associated KLK4 expression with tumor progression and clinical outcome, particularly in prostate and ovarian cancers. Very little is known in regard with KLK4 involvement in oral squamous cell carcinomas (OSCCs). Our objective was to investigate KLK4 expression in OSCC pathogenesis and disease progression. KLK4 expression was evaluated by immunohistochemistry, Western blots and zymograms in OSCC lines. Invasion assays using high versus low/undetectable KLK4-expressing OSCC cell lines were performed jointly with KLK4 siRNA inhibition. A large collection of OSCC specimens was evaluated for KLK4 expression and correlation with patients’ characteristics and outcomes were determined. Our data indicates that KLK4 is differentially expressed in oral carcinomas. OSCC cell lines with high invasive and metastatic potential show the highest levels of KLK4 expression. KLK4 mRNA and protein expression is correlated with enzyme activity detected by zymograms. Inhibition of KLK4 expression results in diminished invasive potential in OSCC cell lines. Consistently, KLK4 expression is stronger in primary tumors that later either recurred or developed metastases suggesting that its preferential expression in OSCC might contribute to the individual tumor biology. Therefore, this study provides supportive evidence in favor of a prognostic value for KLK4 in OSCC and suggests that KLK4 could serve as a potential therapeutic target in oral cancer patients.
Oral squamous cell carcinoma (OSCC); cell lines; Kallikrein-related-peptidase-4 (KLK4); clinical outcome; invasion; metastasis
Although a big deal of dental research is being focused to the understanding of early stages of tooth development, a huge gap exist on our knowledge on how the dental hard tissues are formed and how this process is controlled daily in order to produce very complex and diverse tooth shapes adapted for specific functions. Emerging evidence suggests that clock genes, a family of genes that controls circadian functions within our bodies, regulate also dental mineralized tissues formation. Enamel formation, for example, is subjected to rhythmical molecular signals that occur on short (24 hour) periods and control the secretion and maturation of the enamel matrix. Accordingly, gene expression and ameloblast functions are also tightly modulated in regular daily intervals. This review summarizes the current knowledge on the circadian controls of dental mineralized tissues development with a special emphasis on amelogenesis.
Ameloblasts; Odontoblasts; Circadian Rhythms; Clock Genes; Cementum; Bone
Oral squamous cell carcinoma (OSCC) is an aggressive malignancy with high mortality rates. Major challenges for OSCC management include development of resistance to therapy and early formation of distant metastases. Cancer stem cells (CSCs) have emerged as important players in both pathologic mechanisms. Increased fucosylation activity and increased expression of fucosylated polysaccharides, such as Sialyl Lewis X (SLex), are associated with invasion and metastasis. However, the role of fucosylation in CSCs has not been elucidated yet. We used the spheroid culture technique to obtain a CSC-enriched population and compared orospheres with adherent cells. We found that orospheres expressed markers of CSCs and metastasis at higher levels, were more invasive and tumorigenic, and were more resistant to cisplatin/radiation than adherent counterparts. We found fucosyltransferases FUT3 and FUT6 highly up-regulated, increased SLex expression and increased adhesion by shear flow assays in orospheres. Inhibition of fucosylation negatively affected orospheres formation and invasion of oral CSCs. These results confirm that orospheres are enriched in CSCs and that fucosylation is of paramount importance for CSC invasion. In addition, SLex may play a key role in CSC metastasis. Thus, inhibition of fucosylation may be used to block CSCs and metastatic spread.
cancer stem cells; oral cancer; fucosylation; radiation; cisplatin
Amelogenin is the major enamel matrix protein with key roles in amelogenesis. Although for many decades amelogenin was considered to be exclusively expressed by ameloblasts, more recent studies have shown that amelogenin is also expressed in other dental and no-dental cells. However, amelogenin expression in human tissues remains unclear. Here, we show that amelogenin protein is not only expressed during human embryonic development but also in pathological conditions such as carious lesions and injuries after dental cavity preparation. In developing embryonic teeth, amelogenin stage-specific expression is found in all dental epithelia cell populations but with different intensities. In the different layers of enamel matrix, waves of positive vs. negative immunostaining for amelogenin are detected suggesting that the secretion of amelogenin protein is orchestrated by a biological clock. Amelogenin is also expressed transiently in differentiating odontoblasts during predentin formation, but was absent in mature functional odontoblasts. In intact adult teeth, amelogenin was not present in dental pulp, odontoblasts, and dentin. However, in injured and carious adult human teeth amelogenin is strongly re-expressed in newly differentiated odontoblasts and is distributed in the dentinal tubuli under the lesion site. In an in vitro culture system, amelogenin is expressed preferentially in human dental pulp cells that start differentiating into odontoblast-like cells and form mineralization nodules. These data suggest that amelogenin plays important roles not only during cytodifferentiation, but also during tooth repair processes in humans.
amelogenin; ameloblasts; tooth; odontoblast; enamel; carious; dental injury; dental pulp
Oral mucosa is continuously exposed to environmental forces and has to be constantly renewed. Accordingly, the oral mucosa epithelium contains a large reservoir of epithelial stem cells necessary for tissue homeostasis. Despite considerable scientific advances in stem cell behavior in a number of tissues, fewer studies have been devoted to the stem cells in the oral epithelium. Most of oral mucosa stem cells studies are focused on identifying cancer stem cells (CSC) in oral squamous cell carcinomas (OSCCs) among other head and neck cancers. OSCCs are the most prevalent epithelial tumors of the head and neck region, marked by their aggressiveness and invasiveness. Due to their highly tumorigenic properties, it has been suggested that CSC may be the critical population of cancer cells in the development of OSCC metastasis. This review presents a brief overview of epithelium stem cells with implications in oral health, and the clinical implications of the CSC concept in OSCC metastatic dissemination.
Oral squamous cell carcinoma; epithelial stem cells; invasion; metastasis; cancer stem cells; oral mucosa
Head and neck squamous carcinomas (HNSCC) have devastating morbidity rates with mortality mainly because of metastasis.
Multiplex Enzyme-linked-immunosorbent-assay (ELISA) to assay a variety of cytokine levels secreted by a panel of stage- and anatomic site-specific primary, recurrent and metastatic University of Michigan-HNSCC cell lines over a 72-hour time-course.
Conditioned medium from metastatic or recurrent HNSCC showed significantly higher amounts of interleukin (IL)-6, IL-6 receptor, Tumor Growth Factor-beta (TGF-β) and Vascular Endothelial Growth Factor (VEGF) than nonmetastatic cells or normal oral keratinocytes. Tumor Necrosis Factor was only secreted by the stage IV, metastatic, or recurrence-derived cell lines.
The cytokine profile of cultured HNSCC cells suggests that high levels of IL-6 and IL-6R, TGF-β, and VEGF are significantly related with their metastatogenic potential and provide rationale for determining if serum testing for a combination of these four soluble factors could be of predictive value for the HNSCC tumor progression and clinical outcome.
Head and neck squamous carcinoma (HNSCC); cell lines; cytokines profiling; multiplex analysis; clinical outcome; metastasis
To evaluate in vitro the potential links between sialyl Lewis X (sLeX) and cancer stem cells (CSC) in head and neck squamous cell carcinoma (HNSCC). HNSCC is an aggressive malignancy with high mortality mainly due to metastasis. CSC have emerged as important players in HNSCC metastasis. sLeX is a tetrasaccharide carbohydrate known to play a key-role in metastatic dissemination by promoting binding of the tumor cells to the endothelium.
Experimental, in vitro.
Laboratory of Head and Neck Cancer Metastasis, University of Michigan.
Subjects and Methods
A panel of stage- and anatomic-site specific primary and metastatic HNSCC cell lines was assessed by flow cytometry to quantify sLeX relative expression levels. Serum-free conditioned media from the same HNSCC lines was collected over a time-course of 72 hours and assessed by Western-blot for secreted sLeX expression. Representative HNSCC cell lines were cultured as floating orospheres (condition that enhance CSC growth) or under normal adherent conditions and characterized by flow cytometry for CSC markers (CD44, aldehyde dehydrogenase [ALDH]) comparatively with sLeX expression.
sLeX is predominantly expressed in carcinomas originating from the oral cavity. Secreted sLeX is also found to be high in oral carcinomas and increased over the analyzed time course. Floating orospheres were strongly positive for CD44 and ALDH confirming CSC enrichment of the orospheres. Tumor cells grown as orospheres are 95-100% positive for sLeX compared to 10-40% of adherent counterpart.
These studies provide the first evidence of sLeX relationship with CSC in HNSCC.
head and neck squamous cell carcinomas; sLeX (sialyl Lewis X); CD44; stem cells; in vitro analysis
Ameloblasts, the cells responsible for making enamel, modify their morphological features in response to specialized functions necessary for synchronized ameloblast differentiation and enamel formation. Secretory and maturation ameloblasts are characterized by the expression of stage-specific genes which follows strictly controlled repetitive patterns. Circadian rhythms are recognized as key regulators of development and diseases of many tissues including bone. Our aim was to gain novel insights on the role of clock genes in enamel formation and to explore the potential links between circadian rhythms and amelogenesis. Our data shows definitive evidence that the main clock genes (Bmal1, Clock, Per1 and Per2) oscillate in ameloblasts at regular circadian (24h) intervals both at RNA and protein levels. This study also reveals that two markers of ameloblast differentiation i.e. amelogenin (Amelx; a marker of secretory ameloblasts) and kallikrein-related peptidase 4 (Klk4, a marker of maturation ameloblasts) are downstream targets of clock genes. Both, Amelx and Klk4 show 24h oscillatory expression patterns and their expression levels are up-regulated after Bmal1 over-expression in HAT-7 ameloblast cells. Taken together, these data suggest that both the secretory and the maturation stage of amelogenesis might be under circadian control. Changes in clock genes expression patterns might result in significant alterations of enamel apposition and mineralization.
Clock genes; enamel; amelogenin; kallikrein-related peptidase 4; odontoblasts
Stage-specific expression of ameloblast-specific genes is controlled by differential expression of transcription factors. In addition, ameloblasts follow daily rhythms in their main activities i.e. enamel protein secretion and enamel mineralization. This time related control is orchestrated by oscillations of clock proteins involved in circadian rhythms regulation. Our aim was to identify the potential links between daily rhythms and developmental controls of ameloblast differentiation. The effects of selected transcriptional factors Distal-less homeobox 3 (Dlx3) and Runt related transcription factor 2 (Runx2) and clock gene Nuclear receptor subfamily 1, group D, member 1 (Nr1d1) on secretory and maturation ameloblasts [using stage-specific markers amelogenin (Amel), enamelin (Enam) and kallikrein related-peptidase 4 (Klk4)] were evaluated in HAT-7 ameloblast cell line. Amel and Enam steady-state RNA expression levels were down-regulated in Runx2 over-expressing cells and up-regulated in Dlx3 over-expressing cells. In contrast, Klk4 was up-regulated by both Dlx3 and Runx2. Furthermore, a temporal and spatial relationship between clock genes and ameloblast differentiation markers was detected. Of interest, clock genes not only affected rhythmic expression of ameloblast specific genes but also influenced the expression of Runx2. Multi-scale mathematical modeling is being explored to further understand the temporal and developmental controls of ameloblast differentiation. Our study provides novel insights into the regulatory mechanisms sustaining ameloblast differentiation.
Ameloblast gene regulation; circadian rhythms; clock genes; multi-scale modeling; enamel
The process of tooth mineralization and the role of molecular control of cellular behavior during embryonic tooth development have attracted much attention the last few years. The knowledge gained from the research in these fields has improved the general understanding about the formation of dental tissues and the entire tooth and set the basis for teeth regeneration. Tissue engineering using scaffold and cell aggregate methods has been considered to produce bioengineered dental tissues, while dental stem/progenitor cells, which can differentiate into dental cell lineages, have been also introduced into the field of tooth mineralization and regeneration. Some of the main strategies for making enamel, dentin, and complex tooth-like structures are presented in this paper. However, there are still significant barriers that obstruct such strategies to move into the regular clinic practice, and these should be overcome in order to have the regenerative dentistry as the important mean that can treat the consequences of tooth-related diseases.
Morphological and functional changes during ameloblast and odontoblast differentiation suggest that enamel and dentin formation is under circadian control. Circadian rhythms are endogenous self-sustained oscillations with periods of 24 hours that control diverse physiological and metabolic processes. Mammalian clock genes play a key role in synchronizing circadian functions in many organs. However, close to nothing is known on clock genes expression during tooth development. In this work, we investigated the expression of four clock genes during tooth development. Our results showed that circadian clock genes Bmal1, clock, per1, and per2 mRNAs were detected in teeth by RT-PCR. Immunohistochemistry showed that clock protein expression was first detected in teeth at the bell stage (E17), being expressed in EOE and dental papilla cells. At post-natal day four (PN4), all four clock proteins continued to be expressed in teeth but with different intensities, being strongly expressed within the nucleus of ameloblasts and odontoblasts and down-regulated in dental pulp cells. Interestingly, at PN21 incisor, expression of clock proteins was down-regulated in odontoblasts of the crown-analogue side but expression was persisting in root-analogue side odontoblasts. In contrast, both crown and root odontoblasts were strongly stained for all four clock proteins in first molars at PN21. Within the periodontal ligament (PDL) space, epithelial rests of Malassez (ERM) showed the strongest expression among other PDL cells. Our data suggests that clock genes might be involved in the regulation of ameloblast and odontoblast functions, such as enamel and dentin protein secretion and matrix mineralization.
Clock genes; Tooth development; Bmal1; Clock; Per1; Per2; expression pattern; immunohistochemistry
Epithelial-mesenchymal interactions guide tooth development through its early stages and establish the morphology of the dentin surface upon which enamel will be deposited. Starting with the onset of amelogenesis beneath the future cusp tip, the shape of the enamel layer covering the crown is determined by five growth parameters. Appositional growth occurs at a mineralization front along the ameloblast distal membrane in which amorphous calcium phosphate (ACP) ribbons form and lengthen. The ACP ribbons convert to calcium hydroxyapatite as the ribbons elongate. Appositional growth involves a secretory cycle that leaves an imprint of incremental lines. A potentially important function of enamel proteins is to ensure alignment of successive mineral increments on the tips of enamel ribbons deposited in the previous cycle so the crystallites lengthen with each cycle. Enamel crystallites harden in a maturation process that involves mineral deposition on the sides of existing crystallites until they interlock with adjacent crystallites. Neutralization of acidity generated by hydroxyapatite formation is a key part of the mechanism. Here we review the growth parameters that determine the shape of the enamel crown as well as the mechanisms of enamel appositional growth and maturation.
appositional growth; amelogenin; enamelin; ameloblastin; tooth
Enamel development requires the strictly regulated spatiotemporal expression of genes encoding enamel matrix proteins. The mechanisms orchestrating the initiation and termination of gene transcription at each specific stage of amelogenesis are unknown. In this study, we identify cis-regulatory regions necessary for normal enamelin (Enam) expression. Sequence analysis of the Enam promoter 5′-noncoding region identified potentially important cis-regulatory elements located within 5.2 kb upstream of the Enam translation initiation site. DNA constructs containing 5.2 or 3.9 kb upstream of the Enam translation initiation site were linked to an LacZ reporter gene and used to generate transgenic mice. The 3.9-kb Enam-LacZ transgenic lines showed no expression in ameloblasts, but ectopic LacZ staining was detected in osteoblasts. In contrast, the 5.2-kb Enam-LacZ construct was sufficient to mimic the endogenous Enam ameloblast-specific expression pattern. Our study provides new insights into the molecular control of Enam cell- and stage-specific expression.
Enam; cis-regulatory elements; Ameloblasts; Enamel proteins; Osteoblasts; Tissue-specific expression
Enamel formation is orchestrated by the sequential expression of genes encoding enamel matrix proteins; however, the mechanisms sustaining the spatio–temporal order of gene transcription during amelogenesis are poorly understood. The aim of this study was to characterize the cis-regulatory sequences necessary for normal expression of enamelin (Enam). Several enamelin transcription regulatory regions, showing high sequence homology among species, were identified. DNA constructs containing 5.2 or 3.9 kb regions upstream of the enamelin translation initiation site were linked to a LacZ reporter and used to generate transgenic mice. Only the 5.2-Enam–LacZ construct was sufficient to recapitulate the endogenous pattern of enamelin tooth-specific expression. The 3.9-Enam–LacZ transgenic lines showed no expression in dental cells, but ectopic β-galactosidase activity was detected in osteoblasts. Potential transcription factor-binding sites were identified that may be important in controlling enamelin basal promoter activity and in conferring enamelin tissue-specific expression. Our study provides new insights into regulatory mechanisms governing enamelin expression.
ameloblasts; enamel proteins; enamelin; osteoblasts; tissue-specific expression
Two proteases are secreted into the enamel matrix of developing teeth. The early protease is enamelysin (MMP-20). The late protease is kallikrein 4 (KLK4). Mutations in MMP20 and KLK4 both cause autosomal recessive amelogenesis imperfecta, a condition featuring soft, porous enamel containing residual protein. MMP-20 is secreted along with enamel proteins by secretory stage ameloblasts. Enamel protein cleavage products accumulate in the space between the crystal ribbons, helping to support them. MMP-20 steadily cleaves accumulated enamel proteins, so their concentration decreases with depth. Kallikrein 4 is secreted by transition and maturation stage ameloblasts. KLK4 aggressively degrades the retained organic matrix following the termination of enamel protein secretion. The principle functions of MMP-20 and KLK4 in dental enamel formation are to facilitate the orderly replacement of organic matrix with mineral, generating an enamel layer that is harder, less porous, and unstained by retained enamel proteins.
amelogenesis imperfecta; EMSP1; enamelysin; kallikrein; matrix metalloproteinase; tooth enamel
Enamel development requires the strictly regulated spatiotemporal expression of genes encoding enamel matrix proteins. The mechanisms orchestrating the initiation and termination of gene transcription at each specific stage of amelogenesis are unknown. In this study, we identify cis- regulatory regions necessary for normal enamelin (Enam) expression. Sequence analysis of the Enam promoter 5′-noncoding region identified potentially important cis-regulatory elements located within 5.2 kb upstream of the Enam translation initiation site. DNA constructs containing 5.2 or 3.9 kb upstream of the Enam translation initiation site were linked to an LacZ reporter gene and used to generate transgenic mice. The 3.9-kb Enam-LacZ transgenic lines showed no expression in ameloblasts, but ectopic LacZ staining was detected in osteoblasts. In contrast, the 5.2-kb Enam-LacZ construct was sufficient to mimic the endogenous Enam ameloblast-specific expression pattern. Our study provides new insights into the molecular control of Enam cell- and stage-specific expression.
Enam; cis-regulatory elements; Ameloblasts; Enamel proteins; Osteoblasts; Tissue-specific expression