Immortalization of ameloblastoma cells via reactivation of telomerase function: Phenotypic and molecular characteristics

Histopathologic and Molecular Insights Following the Management of Ameloblastomas via Targeted Therapies - Pathological and Clinical Perspectives

PURPOSE

Current standard of care for ameloblastoma (conventional/unicystic - mural type) usually mandates extensive bone resection that frequently necessitates immediate reconstruction with serious sequelae, especially among young patients. BRAF-mutated ameloblastomas can be targeted by BRAF inhibitors to markedly reduce their size, enabling conservative removal of residual tumor. We aimed to characterize the effect of post-treatment histomorphologic changes.

METHODS

Study included 14 patients, 11 mandibular and three maxillary tumors. Cases with very minimal residual tumor were defined as near-complete response, while those with mostly vital residual tumor as partial response. The epithelium component was scored for architectural and cellular changes, stroma - for fibrosis, inflammation and new bone formation, on a 3-tired score system: 0-no, 1-focal and 3-frequent changes. The mean scores of each parameter, total epithelium and total stroma were calculated and related to duration of treatment. Differences in the mean scores were investigated for mandibular tumors with near-complete response (n = 3) and partial response (n = 8).

RESULTS

There were no significant differences in mean epithelium or stroma scores between tumors with near-complete and those with partial response (2.22 ± 0.68 versus 2.08 ± 0.43, p = 0.55; 1.41 ± 1.04 versus 1.43 ± 0.44, p = 0.27), suggesting that ameloblastomas have potential to undergo complete response to targeted treatment. This is probably dependent upon tumor/patient/treatment-related factors. Response to treatment appears to be predictable with neoplastic epithelium being first, while the stromal response increases during treatment, the entire process expanding over weeks-to-months.

CONCLUSION

Albeit preliminary, these are the first comprehensive histomorphologic findings on BRAF-treated ameloblastomas. Analyzing the suggested parameters in tumors with partial response, should highlight which tumor component has responded/failed to respond. This could serve as a basis for decision-taking toward subsequent steps in adjuvant treatment (e.g., follow-up, conservative surgery, modifications/changes in treatment regimen, combinations of approaches), with a prime aim of jaw preservation and minimal risk of sequelae.

Targeting BRD4 attenuates the stemness and aggressiveness of ameloblastoma

BACKGROUND

BRD4, belonging to the bromodomain extra-terminal (BET) protein family, plays a unique role in tumor progression. However, the potential impact of BRD4 in ameloblastoma (AM) remains largely unknown. Herein, we aimed to assess the expression and functional role of BRD4 in AM.

METHODS

The expression level of BRD4 was assessed by immunohistochemistry. The proliferation, migration, invasion, and tumorigenic abilities of AM cells were assessed by a series of assays. To explore the molecular expression profile of BRD4-depleted AM cells, RNA sequencing (RNA-seq) was performed. Bioinformatic analysis was performed on AM expression matrices obtained from the Gene Expression Omnibus (GEO). The therapeutic efficacy of BET-inhibitors (BETi) was assessed with AM patient-derived organoids.

RESULTS

Upregulation of BRD4 was observed in conventional AMs, recurrent AMs, and ameloblastic carcinomas. Depletion of BRD4 inhibited proliferation, invasion, migration, and tumorigenesis in AM. Administration of BETi attenuated the aggressiveness of AM and the growth of AM patient-derived organoids. Bioinformatic analysis indicated that BRD4 may promote AM progression by regulating the Wnt pathway and stemness-associated pathways.

CONCLUSION

BRD4 increases the aggressiveness and promotes the recurrence of ameloblastoma by regulating the Wnt pathway and stemness-associated pathways. These findings highlight BRD4 as a promising therapeutic target in AM management.

Single-cell transcriptomics reveals cell atlas and identifies cycling tumor cells responsible for recurrence in ameloblastoma

Ameloblastoma is a benign tumor characterized by locally invasive phenotypes, leading to facial bone destruction and a high recurrence rate. However, the mechanisms governing tumor initiation and recurrence are poorly understood. Here, we uncovered cellular landscapes and mechanisms that underlie tumor recurrence in ameloblastoma at single-cell resolution. Our results revealed that ameloblastoma exhibits five tumor subpopulations varying with respect to immune response (IR), bone remodeling (BR), tooth development (TD), epithelial development (ED), and cell cycle (CC) signatures. Of note, we found that CC ameloblastoma cells were endowed with stemness and contributed to tumor recurrence, which was dominated by the EZH2-mediated program. Targeting EZH2 effectively eliminated CC ameloblastoma cells and inhibited tumor growth in ameloblastoma patient-derived organoids. These data described the tumor subpopulation and clarified the identity, function, and regulatory mechanism of CC ameloblastoma cells, providing a potential therapeutic target for ameloblastoma.

Interrogation of TERT promoter hotspot mutations in ameloblastoma and ameloblastic carcinoma

BACKGROUND

TERT promoter mutations increase telomerase activity, conferring cell immortality. The coexistence of TERT promoter mutations with BRAFV600E is associated with aggressiveness. Ameloblastoma and ameloblastic carcinoma are infiltrative neoplasms that harbor BRAFV600E; however, it remains unknown if these odontogenic tumors also show TERT promoter mutations.

METHODS

Genomic DNA of paraffin-embedded ameloblastomas (n = 6) and ameloblastic carcinomas (n = 3) were Sanger-sequenced to assess the hotspot TERT promoter mutations C228T and C250T. BRAFV600E status was screened by TaqMan allele-specific quantitative polymerase chain reaction.

RESULTS

None of the samples harbored TERT promoter mutations. The BRAFV600E mutation was positive in 3 of 6 of ameloblastomas and in 1 of 3 of ameloblastic carcinomas.

CONCLUSION

The absence of TERT promoter mutation in the samples indicates that this molecular event is not relevant to the tumors' pathogenesis. Further studies are necessary to explore undefined genetic or epigenetic mechanisms related to TERT-upregulation in ameloblastoma, and the telomerase activity in ameloblastic carcinoma.

FOSL1 promotes tumor growth and invasion in ameloblastoma

Background

FOSL1, a key component of the Activating protein-1 (AP-1) transcriptional complex, plays an important role in cancer cell migration, invasion, and proliferation. However, the impact of FOSL1 in ameloblastoma (AM) has not been clarified. Herein, we aimed to assess the expression of FOSL1 and investigate its functional role in AM.

Methods

The expression of FOSL1 was examined based on an immunohistochemistry analysis of 96 AM samples. Cell proliferation, migration, invasion, and tumorigenesis were assessed using Cell Counting Kit-8 (CCK-8), colony formation, Transwell, and sphere formation assays. RNA sequencing (RNA-seq) was employed to investigate the molecular alterations of AM cells upon FOSL depletion. Microarrays of AMs were downloaded from the Gene Expression Omnibus (GEO) database for bioinformatics analysis. In addition, patient-derived AM organoids were used to evaluate the therapeutic value of the AP-1 inhibitor.

Results

FOSL1 was detected in the nuclei of AMs and upregulated in conventional AMs compared to unicystic AMs and normal oral epithelium. Compared with primary AM, FOSL1 expression was significantly increased in recurrent AM. Genetic knockdown of FOSL1 suppressed the proliferation, migration, invasion, and sphere formation of AMs. Similar results were also observed by pharmacological inhibition of AP-1 activity. Moreover, the AP-1 inhibitor T5224 impeded the growth of organoids derived from AM patients. Mechanistically, our Ingenuity Pathway Analysis (IPA) and gene set enrichment analysis (GSEA) results revealed that depletion of FOSL1 inactivated kinetochore metaphase signaling and the epithelial–mesenchymal transition pathway and then impaired the aggressiveness of AM cells accordingly.

Conclusion

FOSL1 promotes tumor recurrence and invasive growth in AM by modulating kinetochore metaphase signaling and the epithelial–mesenchymal transition pathway; thus, it represents a promising therapeutic target for AM treatment.

DNA damage and repair scenario in ameloblastoma

Ameloblastoma is a rare human disease of benign neoplasm odontogenic tumor with a lower prevalence but higher recurrence rate. Etiology of ameloblastoma is not fully understood thus lacks implementation of curative treatments. One of the proposed models of evolution of ameloblastoma is related to alteration in DNA damage and repair effects. Growing body of literature has associated defect in DNA damage and repair mechanisms with cancer risk and various adverse health outcomes in humans. Persistent defect of repair and escape of these genomic unstable cells from cell death mechanisms can contribute towards accumulation of oncogene driver or tumor suppressor mutations selective for malignant transformations. In addition, growth, progression and survival of tumor depends upon its DNA repair mechanisms too, thus identifying a DNA repair biomarker can be of advantageous to eliminate the tumor. Understanding the interconnection of oral lesion and role of various DNA repair mechanisms in context to ameloblastoma will assist to build up a platform for translational based research. This study is a literature review of research work published up to date in the field of ameloblastoma in regard to DNA damage and repair effects.

Upregulation of interleukin-8 and activin A induces osteoclastogenesis in ameloblastoma

Ameloblastoma is a common odontogenic benign tumor located in the jaws and is characterized by severe local bone destruction. The current study aimed to investigate the effect of interactions between tumor cells and bone marrow stromal cells (BMSCs) on osteoclast formation in ameloblastoma. The impact of ameloblastoma/BMSC interactions on cytokine production, gene expression and osteoclastogenesis was examined using an immortalized ameloblastoma cell line that the authors' previously established. The results demonstrated that interactions between ameloblastoma cells and BMSCs increased interleukin (IL)‑8 and activin A secretion by BMSCs. IL‑8 expression in BMSCs was modulated by tumor‑derived tumor necrosis factor‑α and IL‑8 contributed to osteoclast formation not only directly but also by stimulating receptor activator of NF‑κB ligand (RANKL) expression in BMSCs. Activin A secretion in BMSCs was stimulated by ameloblastoma cells via cell‑to‑cell‑mediated activation of c‑Jun N‑terminal kinase activation, acting as a cofactor of RANKL to induce osteoclast formation and function. The present study highlights the critical role of communication between BMSCs and ameloblastoma cells in bone resorption in ameloblastoma.

TNF-α-induced IL-6 and MMP-9 expression in immortalized ameloblastoma cell line established by hTERT

OBJECTIVE

Ameloblastoma (AM) shows locally invasive behaviour. However, biological investigations regarding regulation of gene expression associated with AM pathological features are difficult to perform, because AM cells can be passaged for a few generations due to senescence. We report a newly established immortalized AM cell line, AMB cells, by transfection with human telomerase reverse transcriptase (hTERT). Furthermore, we examined whether TNF-α modulates bone resorption-related genes, IL-6 and MMP-9 in cooperation with TGF-β or IFN-γ.

MATERIALS AND METHODS

Following transfection of an hTERT expression vector into AM cells using a non-viral method, the effects of cytokines on the expressions of IL-6 and MMP-9 mRNA were examined using real-time PCR. TNF-α-induced NF-κB activity was examined by western blotting and transcription factor assays.

RESULTS

AMB cells continued to grow for more than 100 population doublings. Stimulation with TNF-α increased IL-6 and MMP-9 mRNA expressions, as well as NF-κB activation. Furthermore, TGF-β and IFN-γ dramatically increased TNF-α-mediated expressions of MMP-9 and IL-6 mRNA, respectively, while those responses were suppressed by NF-κB inhibitor.

CONCLUSION

We established an immortalized AM cell line by hTERT transfection. TNF-α-mediated regulation of MMP-9 and IL-6 via NF-κB may play an important role in the pathological behaviour of AMs, such as bone resorption.

Proliferation and differentiation of rat osteoporosis mesenchymal stem cells (MSCs) after telomerase reverse transcriptase (TERT) transfection

Background

The aim of this study was to determine whether MSC are excellent materials for MSCs transplantation in the treatment of osteoporosis.

Material/Methods

We studied normal, osteoporosis, and TERT-transfected MSC from normal and osteoporosis rats to compare the proliferation and osteogenic differentiation using RT-PCR and Western blot by constructing an ovariectomized rat model of osteoporosis (OVX). The primary MSC from model rats were extracted and cultured to evaluate the proliferation and differentiation characteristics.

Results

MSCs of osteoporosis rats obviously decreased in proliferation ability and osteogenic differentiation compared to that of normal rats. In contrast, in TERT-transfected MSC, the proliferation and differentiation ability, and especially the ability of osteogenic differentiation, were significantly higher than in osteoporosis MSC.

Conclusions

TERT-transfected MSCs can help osteoporosis patients in whom MSC proliferation and osteogenic differentiation ability are weak, with an increase in both bone mass and bone density, becoming an effective material for autologous transplantation of MSCs in further treatment of osteoporosis. However, studies are still needed to prove the in vivo effect, biological safety, and molecular mechanism of TERT-osteoporosis treatment. Additionally, because the results are from an animal model, more research is needed in generalizing rat model findings to human osteoporosis patients.

Altered expression of genes associated with telomere maintenance and cell function of human vascular endothelial cell at elevated temperature

The pathophysiological alterations of vascular endothelial cells induced by heat were studied. Human umbilical venous endothelial cells were cultured for 1 day at three different temperatures (37, 39, and 42 °C). The telomere lengths, the expressions of proteins associated with telomere length maintenance, apoptosis, heat shock, and vascular function were analyzed. The cell growth was not suppressed at 39 °C but suppressed at 42 °C. The mean telomere length did not change, whereas the telomere length distribution altered at 42 °C. Long telomere decreased and middle-sized telomere increased in the telomere length distribution at 42 °C. The telomerase activity did not show any heat-associated alterations. However, of the components of telomerase, telomerase reverse transcriptase was up-regulated along temperature elevation. In contrast, the expression level of RNA component TERC did not altered. Among the analyzed apoptosis-associated proteins, p21 was down-regulated and phosphorylated p53 was up-regulated. Heat shock proteins and NO synthase were up-regulated at 42 °C. These results suggested that induced growth suppression or cell senescence was induced by strong heat stress rather than mild one predominantly in cells bearing long telomeres with p53 activation, and simultaneously activated some telomere-associated factors, heat shock proteins, and NO synthesis probably for heat-resistant cell survival.

Telomerase expression in amyotrophic lateral sclerosis (ALS) patients

Telomerase and telomeric complex have been linked to a variety of disease states related to neurological dysfunction. In amyotrophic lateral sclerosis (ALS) patients, telomerase activity, as human telomerase reverse transcriptase (hTERT) expression, has not been characterized yet. Here, for the first time, we characterized telomerase and related pathway in blood sample and spinal cord from ALS patients compared with healthy controls. We found that hTERT expression level was significantly lower in ALS patients and was correlated either to p53 mRNA expression or p21 expression, pointing out the hypothesis that telomerase inhibition could be a pathogenetic contributor to neurodegeneration in ALS. As a consequence of the reduced telomerase activity, we identified shorter telomeres in leukocytes from sporadic ALS patients compared with healthy control group.

hTERT- and hCTLA4Ig-expressing human bone marrow-derived mesenchymal stem cells: in vitro and in vivo characterization and osteogenic differentiation

Multipotent mesenchymal stem cells (MSCs) are commonly used as seed cells in studies of tissue engineering and regenerative medicine but their clinical application is limited, due to insufficient numbers of autogeneic MSCs, immune rejection of allogeneic MSCs and replicative senescence. We constructed two gene expression vectors for transfection of the human telomerase reverse transcriptase (hTERT) and cytotoxic T lymphocyte-associated antigen 4-Ig (CTLA4Ig) genes into human bone marrow-derived stem cells (hBMSCs). Successful transfection of both genes generated hTERT-CTLA4Ig hBMSCs that expressed both telomerase (shown by immunohistochemistry and a TRAPeze assay) and CTLA4Ig (demonstrated by immunocytochemistry and western blotting) without apparent mutual interference. Both hTERT BMSCs (92 population doublings) and hTERT-CTLA4Ig hBMSCs (60 population doublings) had an extended lifespan compared with hBMSCs (18 population doublings). Cell cycle analysis revealed that, compared with hBMSCs, a lower proportion of hTERT hBMSCs were in G₀ /G₁ phase but a higher proportion were in S phase; compared with hTERT hBMSCs, a higher proportion of hTERT-CTLA4Ig hBMSCs were in G₀ /G₁ phase, while a lower proportion were in S and G₂ /M phases. hTERT-CTLA4Ig hBMSCs retained their capacity for osteogenic differentiation in vitro, shown by the detection of hydroxyapatite mineral deposition (labelled tetracycline fluorescence staining), calcareous nodules (alizarin red S staining), alkaline phosphatase (calcium-cobalt method) and osteocalcin (immunocytochemistry). Furthermore, subcutaneous transplantation of hTERT-CTLA4Ig hBMSCs in a rat xenotransplantation model resulted in the successful generation of bone-like tissue, confirmed using radiography and histological assessment. We propose that allogeneic hTERT-CTLA4Ig hBMSCs may be ideal seed cells for bone tissue engineering. Copyright © 2014 John Wiley & Sons, Ltd.

Phenotype-independent effects of retroviral transduction in human dental pulp stem cells

An immortalized human dental pulp stem cell (DPSC) line of an odontoblastic phenotype is established to circumvent the normal programmed senescence and to maintain the cell line's usefulness as a tool for further study of cellular activity. DPSCs are isolated from human dental pulp tissues and transfected using hTERT. The influence of this process on the DPSC phenotype and the mRNA expression of oncogenes involved in cellular senescence is investigated. The results reveal an absence of altered DPSC morphology and phenotype following the exogenous introduction of the hTERT gene, which is coupled with a significant reduction in p16 mRNA expression. This provides insight into how to circumvent in vitro dental pulp stem cell death following the exogenous introduction of hTERT.

Alterations in the telomere length distribution and the subtelomeric methylation status in human vascular endothelial cells under elevated temperature in culture condition

Temperature-associated alteration in the telomere lengths of vascular endothelial cells has not been well investigated. Telomere length of human umbilical vein endothelial cells (HUVECs) cultured at a high temperature (42 °C) was analyzed. Here described are heat-associated phenotypical alterations of human vascular endothelial cell under prolonged heat stress in terms of telomere length, telomerase activity, and the expression of telomere associated proteins and heat shock proteins. The genomic DNA extracted from HUVECs cultured for 3 days under 42 °C was digested with methylation-sensitive and -insensitive isoschizomers and was subjected to genomic Southern blot probed with a telomere DNA fragment. Their telomere lengths and telomere length distributions were analyzed. Telomerase activity and the expressions of telomere-associated RNA, telomere-associated proteins (TERC, TERT, TRF1, and TRF2), and heat shock proteins (Hsp60, Hsp70, and Hsp90) were also analyzed. At 42 °C, cell growth was suppressed and the cell senescence rate was transiently elevated. A proportional decrease in the number of long telomeres was observed transiently at 42 °C. A trend of subtelomeric hypomethylation and lowered telomerase activity were observed at 42 °C after 3-day culture. The altered phenotypes on day 1 seemed reactive responses for cell protection to heat, and those on day 3 seemed exhausted reactions after 3-day culture. Maintained expression was observed in Hsps, TRF2, and TERC. These altered phenotypes might contribute to cell-survival under prolonged heat stress.

BMI-1 activation is crucial in hTERT-induced epithelial-mesenchymal transition of oral epithelial cells

BMI-1 (B lymphoma Mo-MLV insertion region 1 homolog) has been reported to be over-expressed in cell immortalisation and the epithelial-mesenchymal transition (EMT) of cancer cells. The aim of this study is to study the roles of BMI-1 in the human telomerase reverse transcriptase (hTERT)-induced immortalisation and EMT. In this study, hTERT(+)-OME cells and hTERT(+)-HaCaT cells were acquired by viral transduction of hTERT to primary cultured oral keratinocytes and HaCaT cells (skin epidermal cells). siRNA transduction was used for the inhibition of BMI-1 expression. RT-PCR and Western blots were performed to detect the expressions of twist, vimentin, BMI-1, hTERT and p16INK4a in these cell lines. EMT was assessed by immunohistochemistry (expressions of cytokertin & vimentin), Western blots (expressions of Twist, vimentin & E-cadherin) and RT-PCR (expression of Twist). The results indicated that hTERT(+)-OME cells and hTERT(+)-HaCaT cells underwent EMT spontaneously with high expression of Twist. p16INK4a was silenced in both hTERT-transduced cells but could be detected in HaCaT cells. Moreover, BMI-1 was highly expressed in hTERT(+)-OME and hTERT(+)-HaCaT cells but was negative in HaCaT cells. When the expression of BMI-1 was blocked by siRNA transduction, the proliferations of hTERT(+)-OME and hTERT(+)-HaCaT cells were inhibited and the mono-spheroid colony formation of these hTERT-transduced cells was decreased. In addition, the expression of p16INK4a was regained while the expressions of EMT markers (twist and vimentin) were down-regulated in these two BMI-1 blocking cell lines. To conclude, this study suggests BMI-1 expression plays a role in hTERT-induced immortalisation and EMT.

A new oncolytic adenoviral vector carrying dual tumour suppressor genes shows potent anti-tumour effect

Cancer Targeting Gene-Viro-Therapy (CTGVT) is a promising cancer therapeutical strategy that strengthens the anti-tumour effect of oncolytic virus by expressing inserted foreign anti-tumour genes. In this work, we constructed a novel adenoviral vector controlled by the tumour-specific survivin promoter on the basis of the ZD55 vector, which is an E1B55KD gene deleted vector we previously constructed. Compared with the original ZD55 vector, this new adenoviral vector (ZD55SP/E1A) showed much better ability of replication and reporter gene expression. We then combined anti-tumour gene interleukine-24 (IL-24) with an RNA polymerase III-dependent U6 promoter driving short hairpin RNA (shRNA) that targets M-phase phosphoprotein 1 (MPHOSPH1, a newly identified oncogene) by inserting the IL-24 and the shRNA of MPHOSPH1 (shMPP1) expression cassettes into the new ZD55SP/E1A vector. Our results demonstrated excellent anti-tumour effect of ZD55SP/E1A-IL-24-shMPP1 in vitro on multiple cancer cell lines such as lung cancer, liver cancer and ovarian caner. At high multiplicity-of-infection (MOI), ZD55SP/E1A-IL-24-shMPP1 triggered post-mitotic apoptosis in cancer cells by inducing prolonged mitotic arrest; while at low MOI, senescence was induced. More importantly, ZD55SP/E1A-IL-24-shMPP1 also showed excellent anti-tumour effects in vivo on SW620 xenograft nude mice. In conclusion, our strategy of constructing an IL-24 and shMPP1 dual gene expressing oncolytic adenoviral vector, which is regulated by the survivin promoter and E1B55KD deletion, could be a promising method of cancer gene therapy.

Telomerase activity and telomere length distribution in vascular endothelial cells in a short-term culture under the presence of hydrogen peroxide

AIM

The aim of this study was to assess the biological effects of oxidative stress on human vascular endothelial cells.

METHODS

The telomeric changes and the alterations of the expression of telomere-associated proteins in human umbilical venous endothelial cells (HUVEC) cultured in the presence of hydrogen peroxide (H2 O2 ) were analyzed.

RESULTS

During the culture, the cell growth rate decreased, whereas the telomerase activity of the surviving cells increased. As the H2 O2 level increased, long telomeres decreased proportionally, thus resulting in a telomere length distribution that was rich in short telomeres. These observations suggested that H2 O2 -affected endothelial cells bear telomeric features similar to those of aged cells. In contrast, the expression of telomere-associated proteins, TRF1 and TRF2, showed different changes. TRF1 increased in relation to H2 O2 concentration, whereas TRF2 showed no significant change. The surviving cells exposed to H2 O2 showed a H2 O2 -dose dependent increase in telomerase activity, whereas the telomere protein and RNA components were only elevated in low concentrations of H2 O2 .

CONCLUSIONS

The increase in telomerase activity and TRF1 protein expression of vascular endothelial cell might show an aspect of cellular protective reaction against oxygen stress.

P16/p53 expression and telomerase activity in immortalized human dental pulp cells

INTRODUCTION

Residing within human dental pulp are cells of an ectomesenchymal origin which have the potential to differentiate into odontoblast-like cells. These cells have a limited growth potential owing to the effects of cell senescence. This study examines the effects of immortalizing odontoblast-like cells on cell proliferation and mineralization by comparing transformed dental pulp stem cells (tDPSCs) and non-transformed dental pulp stem cells (nDPSCs).

RESULTS

With the exogenous expression of hTERT, tDPSCs maintained a continued expression of odontogenic markers for cell proliferation and mineralization (ALP, COL-1, DMP-1, DSPP, OCN amd OPN)as did nDPScs. Oncoprotein expression was seen in both groups except for a noted absence of p16 in the tDPSCs. nDPSCs also showed lower levels of total ALP and DNA activity in comparison to tDPSCs when assayed as well as low telomerase activity readings.

METHODS

Using a retroviral vector, exogenous human telomerase reverse transcriptase (hTERT) was expressed in tDPSCs. Both cell groups were cultured and their telomerase activities is determined using a telomerase quantification assay. Also examined were the expression of genes involved in proliferation and mineralization such as human alkaline phosphatase (ALP), β-actin, collagen 1 (col-1), core binding factor (cbfa-1), dentin matrix protein (DMP-1), dentin sialophosphoprotein (DSPP), GAPDH, hTERT, osteocalcin (OCN), osteopontin (OPN) as well as oncoproteins involved in senescence (p16, p21 and p53) using RT-PCR. DNA and alkaline phosphatase activity was assayed in both cell groups.

CONCLUSIONS

These results indicate maintainance of odontoblast-like differentiation characteristics after retroviral transformation with hTERT and suggest a possible link with a reduced p16 expression.

Review article: Current concepts of ameloblastoma pathogenesis

Ameloblastoma is a locally destructive and invasive tumour that can recur despite adequate surgical removal. Molecular studies have offered interesting findings regarding ameloblastoma pathogenesis. In the present review, the following topics are discussed regarding its molecular nature: clonality, cell cycle proliferation, apoptosis, tumour suppressor genes, ameloblastin and other enamel matrix proteins, osteoclastic mechanism and matrix metalloproteinases and other signalling molecules. It is clear from the literature reviewed that translational studies are necessary to identify prognostic markers of ameloblastoma behaviour and to establish new diagnostic tools to the differential diagnosis of unicystic from multicystic ameloblastoma. Finally, molecular biology studies are also important to develop more effective alternative approaches to the treatment of this aggressive odontogenic tumour.