Reuben Kim

Bisphosphonates Induce Senescence in Normal Human Oral Keratinocytes

Bisphosphonate-related osteonecrosis of the jaw (BRONJ) commonly occurs in individuals receiving bisphosphonates (BPs) with clinical manifestations of the exposed necrotic bone. Although defective wound healing of soft tissue is frequently, if not always, observed in BRONJ, the effects of BPs on oral soft tissue or cells remain unknown. To investigate the effects of BPs on cells of oral mucosal tissue, we studied the effect of pamidronate (PAM), one of the BPs most commonly administered to cancer patients, on the phenotypes of normal human oral keratinocytes (NHOK) and fibroblasts (NHOF). When exposed to PAM at 10 µM, NHOK, not NHOF, underwent senescence: NHOK overexpressed senescence-associated β-galactosidase (SA-β-Gal), p16INK4A, IL-6, and IL-8. When exposed to a higher level (50 µM) of PAM, NHOK maintained senescent phenotypes, but NHOF underwent apoptosis. PAM-induced senescence in NHOK is mediated, in part, via geranylgeranylation of the mevalonate pathway. Our in vitro 3D oral mucosal tissue construction studies further demonstrated that PAM induced senescence and impaired re-epithelialization of oral mucosa. Analysis of these data indicates that premature senescence of oral mucosal cells and subsequent defective soft-tissue wound healing might be partly responsible for the development of BRONJ in individuals receiving PAM or other BPs.

Pulp-dentin Regeneration: Current State and Future Prospects

The goal of regenerative endodontics is to reinstate normal pulp function in necrotic and infected teeth that would result in reestablishment of protective functions, including innate pulp immunity, pulp repair through mineralization, and pulp sensibility. In the unique microenvironment of the dental pulp, the triad of tissue engineering would require infection control, biomaterials, and stem cells. Although revascularization is successful in resolving apical periodontitis, multiple studies suggest that it alone does not support pulp-dentin regeneration. More recently, cell-based approaches in endodontic regeneration based on pulpal mesenchymal stem cells (MSCs) have demonstrated promising results in terms of pulp-dentin regeneration in vivo through autologous transplantation. Although pulpal regeneration requires the cell-based approach, several challenges in clinical translation must be overcome—including aging-associated phenotypic changes in pulpal MSCs, availability of tissue sources, and safety and regulation involved with expansion of MSCs in laboratories. Allotransplantation of MSCs may alleviate some of these obstacles, although the long-term stability of MSCs and efficacy in pulp-dentin regeneration demand further investigation. For an alternative source of MSCs, our laboratory developed induced MSCs (iMSCs) from primary human keratinocytes through epithelial-mesenchymal transition by modulating the epithelial plasticity genes. Initially, we showed that overexpression of ΔNp63α, a major isoform of the p63 gene, led to epithelial-mesenchymal transition and acquisition of stem characteristics. More recently, iMSCs were generated by transient knockdown of all p63 isoforms through siRNA, further simplifying the protocol and resolving the potential safety issues of viral vectors. These cells may be useful for patients who lack tissue sources for endogenous MSCs. Further research will elucidate the level of potency of these iMSCs and assess their transdifferentiation capacities into functional odontoblasts when transplanted into the root canal microenvironment.

The Role of ORAI1 in the Odontogenic Differentiation of Human Dental Pulp Stem Cells

Pulp capping, or placing dental materials directly onto the vital pulp tissues of affected teeth, is a dental procedure that aims to regenerate reparative dentin. Several pulp capping materials are clinically being used, and calcium ion (Ca2+) released from these materials is known to mediate reparative dentin formation. ORAI1 is an essential pore subunit of store-operated Ca2+ entry (SOCE), which is a major Ca2+ influx pathway in most nonexcitable cells. Here, we evaluated the role of ORAI1 in mediating the odontogenic differentiation and mineralization of dental pulp stem cells (DPSCs). During the odontogenic differentiation of DPSCs, the expression of ORAI1 increased in a time-dependent manner. DPSCs knocked down with ORAI1 shRNA (DPSC/ORAI1sh) or overexpressed with dominant negative mutant ORAI1E106Q (DPSC/E106Q) exhibited the inhibition of Ca2+ influx and suppression of odontogenic differentiation and mineralization as demonstrated by alkaline phosphatase (ALP) activity/staining as well as alizarin red S staining when compared with DPSCs of their respective control groups (DPSC/CTLsh and DPSC/CTL). The gene expression for odontogenic differentiation markers such as osteocalcin, bone sialoprotein, and dentin matrix protein 1 (DMP1) was also suppressed. When DPSC/CTL or DPSC/E106Q cells were subcutaneously transplanted into nude mice, DPSC/CTL cells induced mineralized tissue formation with significant increases in ALP and DMP1 staining in vivo, whereas DPSC/E106Q cells did not. Collectively, our data showed that ORAI1 plays critical roles in the odontogenic differentiation and mineralization of DPSCs by regulating Ca2+ influx and that ORAI1 may be a therapeutic target to enhance reparative dentin formation.

Effects of Bioactive Compounds on Odontogenic Differentiation and Mineralization

Direct pulp capping involves the placement of dental materials directly onto vital pulp tissues after deep caries removal to stimulate the regeneration of reparative dentin. This physical barrier will serve as a “biological seal” between these materials and the pulp tissue. Although numerous direct pulp capping materials are available, the use of small bioactive compounds that can potently stimulate and expedite reparative dentin formation is still underexplored. Here, the authors compared and evaluated the pro-osteogenic and pro-odontogenic effects of 4 small bioactive compounds— phenamil (Phen), purmorphamine (Pur), genistein (Gen), and metformin (Met). The authors found that these compounds at noncytotoxic concentrations induced differentiation and mineralization of preosteoblastic MC3T3-E1 cells and preodontoblastic dental pulp stem cells (DPSCs) in a dose-dependent manner. Among them, Phen consistently and potently induced differentiation and mineralization in vitro. A single treatment with Phen was sufficient to enhance the mineralization potential of DPSCs in vitro. More importantly, Phen-treated DPSCs showed enhanced odontogenic differentiation and mineralization in vivo. Our study suggests that these small bioactive compounds merit further study for their potential clinical use as pulp capping materials.

Abstract 3715: Zoledronic acid inhibits cancer growth and cancer stem cell phenotypes in head and neck squamous cell carcinoma.

Zoledronic acid (ZA), a third generation of bisphosphonates, is known to have both anti-osteolytic and anti-tumor activities. It exerts anti-osteolytic function by interfering with mevalonate pathway and preventing protein prenylation required for growth and survival in osteoclast cells. Also, similar function has been found to induce cancer apoptosis and inhibit cancer growth in bone-related cancer, but its effect on other cancer types, including head and neck squamous cell carcinoma (HNSCC) is still unclear. In this study, we first monitored the effect of ZA on cancer growth in HNSCC cell lines in vitro. ZA significantly suppressed cancer growth, shown by decreased anchorage independent growth in soft agar assay and diminished cell growth in organotypic raft culture. Because cancer stem cell (CSC; also called tumor-initiating cell) plays a significant role in cancer growth, we further investigated the effect of ZA on CSC in HNSCC. ZA-treated HNSCC cells significantly decreased CSC phenotypes such as sphere forming ability and migratory ability. In SCC4, a tongue squamous cell carcinoma cell line, side population and expression of pluripotency marker genes were significantly decreased by ZA. Also, ZA inhibited the CSC-related Sonic Hedgehog pathway in SCC4 as demonstrated by decreased mRNA expression of transcriptional factor, Gli-1. Taken together, our data suggest that ZA targets CSC and hence inhibits cancer growth in HNSCC. Citation Format: Sung Hee Lee, Reuben Kim, Mo Kang, No-Hee Park, Ki-Hyuk Shin. Zoledronic acid inhibits cancer growth and cancer stem cell phenotypes in head and neck squamous cell carcinoma. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3715. doi:10.1158/1538-7445.AM2013-3715

Clastic cells are absent around the root surface in pulp-exposed periapical periodontitis lesions in mice

INTRODUCTION Clastic cells, originating from the monocyte-macrophage lineage, resorb mineralized tissues. In periapical periodontitis, alveolar bone around the tooth apex becomes resorbed; however, the roots of the teeth are often left intact by yet unknown mechanisms. Here, we examined the status of clastic cells in a periapical periodontitis model in mice. METHODS Periapical periodontitis was induced by performing pulp exposure on the maxillary first molar. The contralateral maxillary first molar was used as a control. The maxillae were harvested, fixed, and subjected to μCT scanning and three-dimensional volumetric analysis. TRAP staining was performed, and osteoclasts were quantified. Immunohistochemical staining was performed for RANKL, OPG, and F4/80, a marker for macrophages. RESULTS At the apex of the tooth, pulp exposure resulted in periapical radiolucency with mineralized tissues at the surrounding bone surfaces but not on the root surfaces. Histologically, clastic cells were present on the bone surfaces but absent around the root surfaces. Expression of F4/80 and RANKL was not found at close proximity to the root surfaces, but OPG was globally expressed. CONCLUSION The absence of clastic cells around the root surface of pulp-exposed teeth, in part, is associated with the lack of macrophages and RANKL expression.

Grainyhead-like 2 (GRHL2) knockout abolishes oral cancer development through reciprocal regulation of the MAP kinase and TGF-β signaling pathways

Grainyhead-Like 2 (GRHL2) is an epithelial-specific transcription factor that regulates epithelial morphogenesis and differentiation. Prior studies suggested inverse regulation between GRHL2 and TGF-β in epithelial plasticity and potential carcinogenesis. Here, we report the role of GRHL2 in oral carcinogenesis in vivo using a novel Grhl2 knockout (KO) mouse model and the underlying mechanism involving its functional interaction with TGF-β signaling. We developed epithelial-specific Grhl2 conditional KO mice by crossing Grhl2 floxed mice with those expressing CreER driven by the K14 promoter. After induction of Grhl2 KO, we confirmed the loss of GRHL2 and its target proteins, while Grhl2 KO strongly induced TGF-β signaling molecules. When exposed to 4-nitroquinoline 1-oxide (4-NQO), a strong chemical carcinogen, Grhl2 wild-type (WT) mice developed rampant oral tongue tumors, while Grhl2 KO mice completely abolished tumor development. In cultured oral squamous cell carcinoma (OSCC) cell lines, TGF-β signaling was notably induced by GRHL2 knockdown while being suppressed by GRHL2 overexpression. GRHL2 knockdown or KO in vitro and in vivo, respectively, led to loss of active p-Erk1/2 and p-JNK MAP kinase levels; moreover, ectopic overexpression of GRHL2 strongly induced the MAP kinase activation. Furthermore, the suppressive effect of GRHL2 on TGF-β signaling was diminished in cells exposed to Erk and JNK inhibitors. These data indicate that GRHL2 activates the Erk and JNK MAP kinases, which in turn suppresses the TGF -β signaling. This novel signaling represents an alternative pathway by which GRHL2 regulates carcinogenesis, and is distinct from the direct transcriptional regulation by GRHL2 binding at its target gene promoters, e.g., E-cadherin, hTERT, p63, and miR-200 family genes. Taken together, the current study provides the first genetic evidence to support the role of GRHL2 in carcinogenesis and the underlying novel mechanism that involves the functional interaction between GRHL2 and TGF-β signaling through the MAPK pathways.

Human Papillomavirus 16 E6 Induces FoxM1B in Oral Keratinocytes through GRHL2

High-risk human papillomavirus (HPV) is a major risk factor for oral and pharyngeal cancers (OPCs), yet the detailed mechanisms by which HPV promotes OPCs are not understood. Forkhead box M1B (FoxM1B) is an oncogene essential for cell cycle progression and tumorigenesis, and it is aberrantly overexpressed in many tumors. We previously showed that FoxM1B was the putative target of an epithelial-specific transcription factor, Grainyhead-like 2 (GRHL2). In the current study, we demonstrate that HPV type 16 (HPV-16) E6 induces FoxM1B in human oral keratinocytes (HOKs) and tonsillar epithelial cells (TECs) in part through GRHL2. FoxM1B was barely detectable in cultured normal human oral keratinocytes (NHOKs) and progressively increased in immortalized HOKs harboring HPV-16 genome (HOK-16B) and tumorigenic HOK-16B/BaP-T cells. Retroviral expression of HPV-16 E6 and/or E7 in NHOKs, TECs, and hypopharyngeal carcinoma cells (FaDu) revealed induction of FoxM1B and GRHL2 by the E6 protein but not E7. Both GRHL2 and FoxM1B were strongly induced in the epidermis of HPV-16 E6 transgenic mice and HPV+ oral squamous cell carcinomas. Ectopic expression of FoxM1B led to acquisition of transformed phenotype in HOK-16B cells. Loss of FoxM1B by lentiviral short hairpin RNA vector or chemical inhibitor led to elimination of tumorigenic characteristics of HOK-16B/BaP-T cells. Luciferase reporter assay revealed that GRHL2 directly bound and regulated the FoxM1B gene promoter activity. Using epithelial-specific Grhl2 conditional knockout mice, we exposed wild-type (WT) and Grhl2 KO mice to 4-nitroquinolin 1-oxide (4-NQO), which led to induction of FoxM1B in the tongue tissues and rampant oral tumor development in the WT mice. However, 4-NQO exposure failed to induce tongue tumors or induction of FoxM1B expression in Grhl2 KO mice. Collectively, these results indicate that HPV-16 induces FoxM1B in part through GRHL2 transcriptional activity and that elevated FoxM1B level is required for oropharyngeal cancer development.

Abstract 1948: Human papillomavirus enhances oral cancer stem cell phenotype by regulating microRNA-181

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA High-risk human papillomaviruses (e.g., HPV-16 and HPV-18) are closely associated with the development of human head and neck squamous cell carcinomas (HNSCC), including malignant lesions in the oral cavity. However, less is known about the possible role and the underlying mechanisms of HPV in enhancing cancer progression and promoting the virulence of cancer, including oral squamous cell carcinoma (OSCC). Cancer stem cells (CSCs) play crucial role in cancer progression, metastasis and recurrence, and are epigenetically regulated by microRNAs (miRNAs). Recent studies demonstrated that miRNA expression is affected by HPV status in HNSCC, suggesting a possible role of HPV in epigenetic regulation of CSCs. In this study, we investigated the role of high-risk HPV on malignant and CSC phenotypes as well as epigenetic regulation in OSCC. Incorporation of HPV-16 whole genome into HPV-negative OSCCs resulted in enhancement of malignant phenotypes (e.g., increased anchorage independent growth, proliferation in organotypic epithelial raft culture, and tumorigenicity in nude mice) and CSC phenotypes (e.g., increased CSC-related markers, self-renewal, and migration/invasion). High-throughput miRNA expression analysis revealed that miRNA-181 family members were significantly underexpressed in the HPV16-harboring OSCCs. HPV-16 downregulated the promoter activity of miR-181a. Furthermore, restoration of miR-181 in the presence of HPV-16 suppressed CSC-like phenotype. Taken together our data indicate that high-risk HPV enhances stemness phenotypes in OSCC by epigenetic regulation of miR-181 expression. Citation Format: Sung Hee Hee Lee, Nicole Rigas, Chang-Ryul Lee, Jiho Han, Reuben Kim, Mo Kang, No-Hee Park, Ki-Hyuk Shin. Human papillomavirus enhances oral cancer stem cell phenotype by regulating microRNA-181. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1948. doi:10.1158/1538-7445.AM2014-1948

Abstract 1598: Grainyhead-like 2 (GRHL2) regulates the expression of forkhead box transcription factor M1 (FoxM1) in human oral cancer cells and determines tumorigenicity

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA GRHL2 is a proto-oncogene that regulates epithelial proliferation and differentiation through transcriptional regulation of large number of target genes. The current study was performed to determine its role in oral carcinogenesis through regulation of forkhead box 1 (FoxM1), which is a known oncogene for many solid tumors. GRHL2 expression was highly elevated in oral squamous cell carcinoma (OSCC) tissues compared with normal oral epithelium (NHOM), and its protein expression is localized in the proliferative cells at the outer border of invasive islands of OSCC. In cultured OSCCs, GRHL2 and FoxM1 levels were both highly upregulated compared with normal human oral keratinocytes (NHOK), supporting their roles in oral carcinogenesis. When GRHL2 was knocked down in SCC4 cells by RNA interference, the cells have lost their proliferative capacity and colony formation when plated at low density. GRHL2 knockdown also resulted in marked loss of tumor spheroid formation, which is hallmark of cancer self-renewal. GRHL2 knockdown also led to loss of tumorigenic ability of cells upon xenograft transplantation in immunocompromised mice. GRHL2 appeared to determine the epithelial phenotype in OSCC cells. GRHL2 knockdown led to loss of E-cadherin and miR-200 family genes, which are epithelial markers. These data indicate that GRHL2 is required to maintain the transformed phenotype in OSCC. We also noted that GRHL2 knockdown led to drastic loss of FoxM1 expression, suggesting that GRHL2 may regulate FoxM1. To test this possibility, we performed in vivo binding assay by chromatin immunoprecipitation (ChIP), which showed GRHL2 binding at the proximal promoter of FoxM1. Luciferase reporter plasmid under FoxM1 promoter showed that GRHL2 directly regulates the gene promoter activity. FoxM1 knockdown resulted in loss of OSCC proliferation and tumor spheroid formation, while its overexpression conferred transformed phenotype in non-tumorigenic human oral keratinocytes (HOKs). Therefore, our data indicate that GRHL2 is required for the maintenance of transformed phenotype and that it plays a role in oral carcinogenesis through regulation of FoxM1. This study was supported in part by the grants from NIDCR/NIH (DE18295 and DE18959) and Jack Weichman Endowed Fund. Note: This abstract was not presented at the meeting. Citation Format: Wei Chen, Jin-Kyu Yi, Ki-Hyuk Shin, Reuben Kim, Shebli Mehrazarin, No-Hee Park, Mo K. Kang. Grainyhead-like 2 (GRHL2) regulates the expression of forkhead box transcription factor M1 (FoxM1) in human oral cancer cells and determines tumorigenicity. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1598. doi:10.1158/1538-7445.AM2014-1598