Co-regulation of p16INK4A and migratory genes in culture conditions that lead to premature senescence in human keratinocytes

Regulation of cell function and identity by cellular senescence

During aging and in some contexts, like embryonic development, wound healing, and diseases such as cancer, senescent cells accumulate and play a key role in different pathophysiological functions. A long-held belief was that cellular senescence decreased normal cell functions, given the loss of proliferation of senescent cells. This view radically changed following the discovery of the senescence-associated secretory phenotype (SASP), factors released by senescent cells into their microenvironment. There is now accumulating evidence that cellular senescence also promotes gain-of-function effects by establishing, reinforcing, or changing cell identity, which can have a beneficial or deleterious impact on pathophysiology. These effects may involve both proliferation arrest and autocrine SASP production, although they largely remain to be defined. Here, we provide a historical overview of the first studies on senescence and an insight into emerging trends regarding the effects of senescence on cell identity.

Genomic Engineering of Oral Keratinocytes to Establish In Vitro Oral Potentially Malignant Disease Models as a Platform for Treatment Investigation

Precancerous cells in the oral cavity may appear as oral potentially malignant disorders, but they may also present as dysplasia without visual manifestation in tumor-adjacent tissue. As it is currently not possible to prevent the malignant transformation of these oral precancers, new treatments are urgently awaited. Here, we generated precancer culture models using a previously established method for the generation of oral keratinocyte cultures and incorporated CRISPR/Cas9 editing. The generated cell lines were used to investigate the efficacy of a set of small molecule inhibitors. Tumor-adjacent mucosa and oral leukoplakia biopsies were cultured and genetically characterized. Mutations were introduced in CDKN2A and TP53 using CRISPR/Cas9 and combined with the ectopic activation of telomerase to generate cell lines with prolonged proliferation. The method was tested in normal oral keratinocytes and tumor-adjacent biopsies and subsequently applied to a large set of oral leukoplakia biopsies. Finally, a subset of the immortalized cell lines was used to assess the efficacy of a set of small molecule inhibitors. Culturing and genomic engineering was highly efficient for normal and tumor-adjacent oral keratinocytes, but success rates in oral leukoplakia were remarkably low. Knock-out of CDKN2A in combination with either the activation of telomerase or knock-out of TP53 seemed a prerequisite for immortalization. Prolonged culturing was accompanied by additional genetic aberrations in these cultures. The generated cell lines were more sensitive than normal keratinocytes to small molecule inhibitors of previously identified targets. In conclusion, while very effective for normal keratinocytes and tumor-adjacent biopsies, the success rate of oral leukoplakia cell culturing methods was very low. Genomic engineering enabled the prolonged culturing of OL-derived keratinocytes but was associated with acquired genetic changes. Further studies are required to assess to what extent the immortalized cultures faithfully represent characteristics of the cells in vivo.

A Protocol to Produce Genetically Edited Primary Oral Keratinocytes Using the CRISPR-Cas9 System

The Nobel Prize awarded gene editing system, CRISPR-Cas9, is probably one of the greatest achievements of the last decades. CRISPR-Cas9 can introduce irreversible genomic changes in its target DNA by simple specifying a 20-nucleotide sequence within its RNA guide. Due to its simplicity, efficacy, and relative low cost in comparison with other genome editing systems, it has become the most common gene editing system used in research laboratories. Here we describe a step-by-step protocol to produce genetically edited primary oral keratinocytes using the CRISPR-Cas9 system.

MED1 Ablation Promotes Oral Mucosal Wound Healing via JNK Signaling Pathway

Mediator complex subunit 1 (MED1) is a coactivator of multiple transcription factors and plays a key role in regulating epidermal homeostasis as well as skin wound healing. It is unknown, however, whether it plays a role in healing oral mucosal wounds. In this study, we investigate MED1's functional effects on oral mucosal wound healing and its underlying mechanism. The epithelial-specific MED1 null (Med1epi-/-) mice were established using the Cre-loxP system with C57/BL6 background. A 3 mm diameter wound was made in the cheek mucosa of the 8-week-old mice. In vivo experiments were conducted using HE staining and immunostaining with Ki67 and uPAR antibodies. The in vitro study used lentiviral transduction, scratch assays, qRT-PCR, and Western blotting to reveal the underlying mechanisms. The results showed that ablation of MED1 accelerated oral mucosal wound healing in 8-week-old mice. As a result of ablation of MED1, Activin A/Follistatin expression was altered, resulting in an activation of the JNK/c-Jun pathway. Similarly, knockdown of MED1 enhanced the proliferation and migration of keratinocytes in vitro, promoting re-epithelialization, which accelerates the healing of oral mucosal wounds. Our study reveals a novel role for MED1 in oral keratinocytes, providing a new molecular therapeutic target for accelerated wound healing.

Unraveling Potential Candidate Targets Associated with Expression of p16INK4a or p16 Truncated Fragment by Comparative Proteomics Analysis

Background:

p16 is a tumor suppressor protein that is significantly involved in cycle regulation through the reduction of cell progression from the G1 phase to the S phase via CDK-cyclin D/p16INK4a/pRb/E2F cascade. The minimum functional domain of p16 has been uncovered that may function comparable to wild type p16.

Objective:

To expand the knowledge on molecules and mechanisms by which p16 or p1666-156 fragment suppresses human fibrosarcoma cell line growth, differential proteome profiles of fibrosarcoma cells following p16 full length or the functional domain overexpression, were analyzed.

Methods:

Following transfecting HT-1080 fibrosarcoma cells with p16 full length, p1666-156 truncated form, and pcDNA3.1 empty vector, protein extract of each sample was harvested and clarified by centrifugation, and then the protein content was determined via Bradford assay. All protein extract of each sample was analyzed by two-dimensional gel electrophoresis. Immunoblot analysis was performed as further validation of the expression status of identified proteins.

Results:

Expression of p16 or p1666-156 fragment could induce mostly the common alterations (up/- down-regulation) of proteome profile of HT-1080 cells. Mass spectrometry identification of the differentially expressed protein spots revealed several proteins that were grouped in functional clusters, including cell cycle regulation and proliferation, cell migration and structure, oxidative stress, protein metabolism, epigenetic regulation, and signal transduction.

Conclusion:

The minimum functional domain of p16 could act in the same way as p16 full length. Also, these new findings can significantly enrich the understanding of p16 growth-suppressive function at the molecular level by the introduction of potential candidate targets for new treatment strategies. Furthermore, the present study provides strong evidence on the functional efficacy of the identified fragment of p16 for further attempts toward peptidomimetic drug design or gene transfer to block cancer cell proliferation.

IRF6 Regulates the Delivery of E-Cadherin to the Plasma Membrane

IRF6 is a transcription factor that is required for craniofacial development and epidermal morphogenesis. Specifically, Irf6-deficient mice lack the terminally differentiated epidermal layers, leading to an absence of barrier function. This phenotype also includes intraoral adhesions due to the absence of the oral periderm, leading to the mislocalization of E-cadherin and other cell‒cell adhesion proteins of the oral epithelium. However, the mechanisms by which IRF6 controls the localization of cell adhesion proteins are not understood. In this study, we show that in human and murine keratinocytes, loss of IRF6 leads to a breakdown of epidermal sheets after mechanical stress. This defect is due to a reduction of adhesion proteins at the plasma membrane. Dynamin inhibitors rescued the IRF6-dependent resistance of epidermal sheets to mechanical stress, but only inhibition of clathrin-mediated endocytosis rescued the localization of junctional proteins at the membrane. Our data show that E-cadherin recycling but not its endocytosis is affected by loss of IRF6. Overall, we demonstrate a role for IRF6 in the delivery of adhesion proteins to the cell membrane.

Ultraviolet B irradiation-induced keratinocyte senescence and impaired development of 3D epidermal reconstruct

Ultraviolet B (UVB) induces morphological and functional changes of the skin. This study investigated the effect of UVB on keratinocyte senescence and the development of reconstructed human epidermis (RHE). Primary normal human keratinocytes (NHK) from juvenile foreskin were irradiated with UVB (30 mJ cm-2) and these effects were compared to NHK that underwent senescence in the late passage. UVB enhanced the accumulation of reactive oxygen species (ROS) and halted cell replication as detected by BrdU cell proliferation assay. The senescence phenotype was evaluated by beta-galactosidase (β-gal) staining and qPCR of genes related to senescent regulation, i.e. p16INK4a, cyclin D2, and IFI27. Senescence induced by high dose UVB resulted in morphological changes, enhanced β-gal activity, elevated cellular ROS levels and reduced DNA synthesis. qPCR revealed differential expression of the genes regulated senescence. p16INK4a expression was significantly increased in NHK exposed to UVB whereas enhanced IFI27 expression was observed only in cultural senescence. The levels of cyclin D2 expression were not significantly altered either by UVB or long culturing conditions. UVB significantly induced the aging phenotype in keratinocytes and impaired epidermal development. RHE generated from UVB-irradiated keratinocytes showed a thinner cross-sectional structure and the majority of keratinocytes in the lower epidermis were degenerated. The 3D epidermis model is useful in studying the skin aging process.

Extracellular vesicles produced by primary human keratinocytes in response to TLR agonists induce stimulus-specific responses in antigen-presenting cells

Cells can communicate through the extracellular vesicles (EVs) they secrete. Pathogen associated molecular patterns (PAMPs), alter the biophysical and communicative properties of EVs released from cells, but the functional consequences of these changes are unknown. Characterization of keratinocyte-derived EVs after poly(I:C) treatment (poly(I:C)-EVs) showed slight differences in levels of EV markers TSG101 and Alix, a loss of CD63 and were positive for autophagosome marker LC3b-II and the cytokine IL36γ compared to EVs from unstimulated keratinocytes (control-EVs). Flagellin treatment (flagellin-EVs) led to an EV marker profile like control-EVs but lacked LC3b-II. Flagellin-EVs also lacked IL-36γ despite nearly identical intracellular levels. While poly(I:C) treatment led to the clear emergence of a > 200 nm diameter EV sub-population, these were not found in flagellin-EVs. EV associated IL-36γ colocalized with LC3b-II in density gradient analysis, equilibrating to 1.10 g/mL, indicating a common EV species. Poly(I:C), but not flagellin, induced intracellular vesicles positive for IL-36γ, LC3b-II, Alix and TSG101, consistent with fusion of autophagosomes and multivesicular bodies. Simultaneous rapamycin and flagellin treatment induced similar intracellular vesicles but was insufficient for the release of IL-36γ⁺/LC3b-II⁺ EVs. Finally, a qRT-PCR array screen showed eight cytokine/chemokine transcripts were altered (p < 0.05) in monocyte-derived Langerhans cells (LCs) when stimulated with poly(I:C)-EVs while three were altered when LCs were stimulated with flagellin-EVs compared to control-EVs. After independent confirmation, poly(I:C)-EVs upregulated BMP6 (p = 0.035) and flagellin-EVs upregulated CXCL8 (p = 0.005), VEGFA (p = 0.018) and PTGS2 (p = 0.020) compared to control-EVs. We conclude that exogenous signals derived from pathogens can alter keratinocyte-mediated modulation of the local immune responses by inducing changes in the types of EVs secreted and responses in antigen presenting cells.

Prostaglandin E2 receptor 3 (EP3) signaling promotes migration of cervical cancer via urokinase-type plasminogen activator receptor (uPAR)

Purpose

Cervical cancer metastasis results in poor prognosis and increased mortality, which is not separated from inflammatory reactions accumulated by prostaglandin E2 (PGE2). As a specific G-protein coupled PGE2 receptor, EP3 is demonstrated as a negative prognosticator of cervical malignancy. Now, we aimed to investigate the pathological mechanism of EP3 in modulating cervical cancer carcinogenesis.

Methods

Bioinformatics analysis was used to identify PAI-1 and uPAR correlations with EP3 expression, as well as the prognosis of cervical cancer patients. In vitro analyses were carried out to investigate the role of EP3 on cervical cancer proliferation and migration.

Results

In vitro studies showed that sulprostone (an EP3 agonist) enhanced the proliferation and migration of cervical cancer cells, whereas silencing of EP3 inhibited their proliferation and migration. Furthermore, EP3 knockdown increased the expression of plasminogen activator inhibitor type 1 (PAI-1), urokinase-type plasminogen activator receptor (uPAR), and phosphorylated extracellular signal-regulated kinases 1/2 (p-ERK1/2), but decreased p53 expression. Bioinformatics analysis showed that both PAI-1 and uPAR were correlated with EP3 expression, as well as the prognosis of cervical cancer patients. The survival analysis further showed that uPAR overexpression (IRS≥2) was correlated with a lower overall survival rate of cervical cancer patients with advanced stages (FIGO III-IV).

Conclusion

These results indicated that EP3 signaling pathway might facilitate the migration of cervical cancer cells through modulating uPAR expression. Therefore, EP3 and uPAR could represent novel therapeutic targets in the treatment of cervical cancer in advantaged stages.

Electronic supplementary material

The online version of this article (10.1007/s00432-020-03272-0) contains supplementary material, which is available to authorized users.

Effects of ionizing radiation on telomere length and telomerase activity in cultured human lens epithelium cells

PURPOSE

To investigate the effects of ionizing radiation on telomere length and telomerase activity in human lens epithelial cells. There are studies suggesting evidence of telomere length in association with opacity of the lens; however, these studies have been conducted on Canine Lens cells. Our study was designed to understand further the effects of different doses of ionizing radiation on telomere length and telomerase activity in cultured human lens epithelium cells from three Donors.

MATERIALS AND METHODS

For this study, embryonic human lens epithelial (HLE) cells from three donors, obtained commercially were cultured. Telomere length and telomerase activity were measured after each passage until cells stopped growing in culture. This was repeated on irradiated (0.001 Gy, 0.01 Gy, 0.02 Gy, 0.1 Gy, 1 Gy and 2 Gy) cells. DNA damage response using the H2AX and telomere dysfunction foci assays were also examined at 30 mins, 24 hours, 48 hours and 72 hours postirradiation.

RESULTS AND CONCLUSION

We have demonstrated genetic changes in telomere length and oxidative stress, which may be relevant to cataractogenesis. Our study shows that in control cells telomere length increases as passage increases. We have also demonstrated that telomere length increases at higher doses of 1.0 Gy and 2.0 Gy. However, telomerase activity decreases dose dependently and as passages increase. These results are not conclusive and further studies ex vivo measuring lens opacity and telomere length in the model would be beneficial in a bigger cohort, hence confirming a link between telomere length, cataractogenesis and genetic factors.

DEK associates with tumor stage and outcome in HPV16 positive oropharyngeal squamous cell carcinoma

Oropharyngeal squamous cell carcinomas (OPSCC) are common, have poor outcomes, and comprise two biologically and clinically distinct diseases. While OPSCC that arise from human papillomavirus infections (HPV+) have better overall survival than their HPV- counterparts, the incidence of HPV+ OPSCC is increasing dramatically, affecting younger individuals which are often left with life-long co-morbidities from aggressive treatment. To identify patients which do poorly versus those who might benefit from milder regimens, risk-stratifying biomarkers are now needed within this population. One potential marker is the DEK oncoprotein, whose transcriptional upregulation in most malignancies is associated with chemotherapy resistance, advanced tumor stage, and worse outcomes. Herein, a retrospective case study was performed on DEK protein expression in therapy-naïve surgical resections from 194 OPSCC patients. We found that DEK was associated with advanced tumor stage, increased hazard of death, and interleukin IL6 expression in HPV16+ disease. Surprisingly, DEK levels in HPV16- OPSCC were not associated with advanced tumor stage or increased hazard of death. Overall, these findings mark HPV16- OPSCC as an exceptional malignancy were DEK expression does not correlate with outcome, and support the potential prognostic utility of DEK to identify aggressive HPV16+ disease.

Therapeutic targeting of replicative immortality

One of the hallmarks of malignant cell populations is the ability to undergo continuous proliferation. This property allows clonal lineages to acquire sequential aberrations that can fuel increasingly autonomous growth, invasiveness, and therapeutic resistance. Innate cellular mechanisms have evolved to regulate replicative potential as a hedge against malignant progression. When activated in the absence of normal terminal differentiation cues, these mechanisms can result in a state of persistent cytostasis. This state, termed “senescence,” can be triggered by intrinsic cellular processes such as telomere dysfunction and oncogene expression, and by exogenous factors such as DNA damaging agents or oxidative environments. Despite differences in upstream signaling, senescence often involves convergent interdependent activation of tumor suppressors p53 and p16/pRB, but can be induced, albeit with reduced sensitivity, when these suppressors are compromised. Doses of conventional genotoxic drugs required to achieve cancer cell senescence are often much lower than doses required to achieve outright cell death. Additional therapies, such as those targeting cyclin dependent kinases or components of the PI3K signaling pathway, may induce senescence specifically in cancer cells by circumventing defects in tumor suppressor pathways or exploiting cancer cells’ heightened requirements for telomerase. Such treatments sufficient to induce cancer cell senescence could provide increased patient survival with fewer and less severe side effects than conventional cytotoxic regimens. This positive aspect is countered by important caveats regarding senescence reversibility, genomic instability, and paracrine effects that may increase heterogeneity and adaptive resistance of surviving cancer cells. Nevertheless, agents that effectively disrupt replicative immortality will likely be valuable components of new combinatorial approaches to cancer therapy.

Foxo1 inhibits diabetic mucosal wound healing but enhances healing of normoglycemic wounds

Re-epithelialization is an important part in mucosal wound healing. Surprisingly little is known about the impact of diabetes on the molecular events of mucosal healing. We examined the role of the transcription factor forkhead box O1 (Foxo1) in oral wounds of diabetic and normoglycemic mice with keratinocyte-specific Foxo1 deletion. Diabetic mucosal wounds had significantly delayed healing with reduced cell migration and proliferation. Foxo1 deletion rescued the negative impact of diabetes on healing but had the opposite effect in normoglycemic mice. Diabetes in vivo and in high glucose conditions in vitro enhanced expression of chemokine (C-C motif) ligand 20 (CCL20) and interleukin-36γ (IL-36γ) in a Foxo1-dependent manner. High glucose-stimulated Foxo1 binding to CCL20 and IL-36γ promoters and CCL20 and IL-36γ significantly inhibited migration of these cells in high glucose conditions. In normal healing, Foxo1 was needed for transforming growth factor-β1 (TGF-β1) expression, and in standard glucose conditions, TGF-β1 rescued the negative effect of Foxo1 silencing on migration in vitro. We propose that Foxo1 under diabetic or high glucose conditions impairs healing by promoting high levels of CCL20 and IL-36γ expression but under normal conditions, enhances it by inducing TGF-β1. This finding provides mechanistic insight into how Foxo1 mediates the impact of diabetes on mucosal wound healing.

Identification of RNA aptamers that internalize into HPV-16 E6/E7 transformed tonsillar epithelial cells

Human papillomavirus type 16 (HPV-16) associated oropharyngeal cancers are on a significant increase and better therapeutic strategies are needed. The HPV-16 oncogenes E6 and E7 are expressed in HPV-associated cancers and are able to transform human tonsillar epithelial cells (HTECs). We used cell-Systematic Evolution of Ligands by Exponential Enrichment (SELEX) to select for RNA aptamers that entered into HPV-16 E6/E7-HTECs. After 12 rounds of cell-SELEX, a pool of aptamers was obtained that had significantly greater internalization capacity (~5-fold) into E6/E7-HTECs as compared to primary HTECs or fibroblasts. Analysis of individual aptamers from the pool indicated variable internalization into E6/E7-HTECs (1-8-fold as compared to a negative control). Most of the individual aptamers internalized into E6/E7 and primary HTECs with similar efficiency, while one aptamer exhibited ~3-fold better internalization into E6/E7-HTECs. Aptamers that internalize into cells may be useful for delivering therapeutic agents to HPV-16 associated malignancies.

Markers of cellular senescence

Cellular senescence is a tumor suppression mechanism that evolved to limit duplication in somatic cells. Senescence is imposed by natural replicative boundaries or stress-induced signals, such as oncogenic transformation. Neoplastic cells can be forced to undergo senescence through genetic manipulations and epigenetic factors, including anticancer drugs, radiation, and differentiating agents. Senescent cells show distinct phenotypic and molecular characteristics, both in vitro or in vivo. These biomarkers might either cause or result from senescence induction, but could also be the byproducts of physiological changes in these non-replicating cells.

Dyskeratosis Congenita Dermal Fibroblasts are Defective in Supporting the Clonogenic Growth of Epidermal Keratinocytes

Telomere shortening is associated with cellular senescence and aging. Dyskeratosis congenita (DC) is a premature aging syndrome caused by mutations in genes for telomerase components or telomere proteins. DC patients have very short telomeres and exhibit aging-associated pathologies including epidermal abnormalities and bone marrow failure. Here, we show that DC skin fibroblasts are defective in their ability to support the clonogenic growth of epidermal keratinocytes. Conditioned media transfer experiments demonstrated that this defect was largely due to lack of a factor or factors secreted from the DC fibroblasts. Compared to early passage normal fibroblasts, DC fibroblasts express significantly lower transcript levels of several genes that code for secreted proteins, including Insulin-like Growth Factor 1 (IGF1) and Hepatocyte Growth Factor (HGF). Aged normal fibroblasts with short telomeres also had reduced levels of IGF1 and HGF, similar to early passage DC fibroblasts. Knockdown of IGF1 or HGF in normal fibroblasts caused a reduction in the capacity of conditioned media from these fibroblasts to support keratinocyte clonogenic growth. Surprisingly, reconstitution of telomerase in DC fibroblasts did not significantly increase transcript levels of IGF1 or HGF or substantially increase the ability of the fibroblasts to support keratinocyte growth, indicating that the gene expression defect is not readily reversible. Our results suggest that telomere shortening in dermal fibroblasts leads to reduction in expression of genes such as IGF1 and HGF and that this may cause a defect in supporting normal epidermal proliferation.

Capturing epidermal stemness for regenerative medicine

The skin is privileged because several skin-derived stem cells (epithelial stem cells from epidermis and its appendages, mesenchymal stem cells from dermis and subcutis, melanocyte stem cells) can be efficiently captured for therapeutic use. Main indications remain the permanent coverage of extensive third degree burns and healing of chronic cutaneous wounds, but recent advances in gene therapy technology open the door to the treatment of disabling inherited skin diseases with genetically corrected keratinocyte stem cells. Therapeutic skin stem cells that were initially cultured in research or hospital laboratories must be produced according strict regulatory guidelines, which ensure patients and medical teams that the medicinal cell products are safe, of constant quality and manufactured according to state-of-the art technology. Nonetheless, it does not warrant clinical efficacy and permanent engraftment of autologous stem cells remains variable. There are many challenges ahead to improve efficacy among which to keep telomere-dependent senescence and telomere-independent senescence (clonal conversion) to a minimum in cell culture and to understand the cellular and molecular mechanisms implicated in engraftment. Finally, medicinal stem cells are expansive to produce and reimbursement of costs by health insurances is a major concern in many countries.

Regulation of senescence in cancer and aging

Senescence is regarded as a physiological response of cells to stress, including telomere dysfunction, aberrant oncogenic activation, DNA damage, and oxidative stress. This stress response has an antagonistically pleiotropic effect to organisms: beneficial as a tumor suppressor, but detrimental by contributing to aging. The emergence of senescence as an effective tumor suppression mechanism is highlighted by recent demonstration that senescence prevents proliferation of cells at risk of neoplastic transformation. Consequently, induction of senescence is recognized as a potential treatment of cancer. Substantial evidence also suggests that senescence plays an important role in aging, particularly in aging of stem cells. In this paper, we will discuss the molecular regulation of senescence its role in cancer and aging. The potential utility of senescence in cancer therapeutics will also be discussed.

Epigenetic alterations of the SERPINE1 gene in oral squamous cell carcinomas and normal oral mucosa

A high level of plasminogen activator inhibitor-1 (PAI-1 or SERPINE1) in tumor extracts is a marker of a poor prognosis in human cancers, including oral carcinomas. However, the mechanisms responsible for the upregulation of PAI-1 in cancers remain unclear. Investigating specific PAI-1 expressing cells in oral carcinomas by immunohistochemistry, we found that PAI-1 was expressed in 18 of the 20 patients, mainly by cancer cells. Two showed PAI-1 positive stromal cells surrounding the tumor areas and five showed PAI-1 positive cells in tumor-adjacent normal epithelium. By real-time RT-PCR analysis, 17 of 20 patients with oral carcinoma were found to have between 2.5- and 50-fold increased tumor PAI-1 mRNA level, as compared with the matched tumor-adjacent normal tissues. The PAI-1 mRNA level in connective tissues from 15 healthy volunteers was similar to the level in tumor-adjacent normal tissues, but the level in epithelium was 5- to 10-fold lower. Analyzing DNA methylation of 25 CpG sites within 960 bp around the transcription initiation site of the SERPINE1 gene by bisulfite sequencing, we did the surprising observation that both tumors and tumor-adjacent normal tissue had a significant level of methylation, whereas there was very little methylation in tissue from healthy volunteers, suggesting that tumor-adjacent normal tissue already contains transformation-associated epigenetic changes. However, there was no general inverse correlation between PAI-1 mRNA levels and SERPINE1 gene methylation in all tissues, showing that CpG methylation is not the main determinant of the PAI-1 expression level in oral tissue.

Aberrant heterodimerization of keratin 16 with keratin 6A in HaCaT keratinocytes results in diminished cellular migration

Keratin filaments form obligatory heterodimers consisting of one type I and one type II keratin that build the intermediate filaments. In keratinocytes, type II keratin 6 (K6) interacts with type I keratin 16 (K16). We previously showed that the intermediate filament protein K16 is up-regulated in aged human skin. Here, we report that there is an obvious imbalance of K16 to K6 mRNA in in vivo and in vitro aging, which possibly leads to cellular effects. To unveil a possible biological function of K16 overexpression we investigated the migration potential of keratinocytes having up-regulated K16 expression in vitro. Two cell lines were established by transfection of human keratinocytes (HaCaT cells) with K16 or control vectors and subsequent fluorescence-activated cell sorting. By performing migration assays we were able to show a 90% reduction in the migration ability of the K16-overexpressing keratinocytes. In addition, a delay in wound closure associated with K16-overexpressing cells was shown by scratch assays. Transient overexpression of K6A in K16-overexpressing keratinocytes partially corrected the cell-migration defect. By real-time PCR we excluded co-regulation of the annotated interaction partner, K6, in the K16 cell line. Finally, we observed a decreased level of tyrosine phosphorylation in K16-overexpressing cells. Taken together, these data highlight the possibility of a physiological role for K6/K16 heterodimers in keratinocyte cell migration, in addition to the heterodimer's known functions in cell differentiation and mechanical resilience.

Senescence-associated oxidative DNA damage promotes the generation of neoplastic cells

Studies on human fibroblasts have led to viewing senescence as a barrier against tumorigenesis. Using keratinocytes, we show here that partially transformed and tumorigenic cells systematically and spontaneously emerge from senescent cultures. We show that these emerging cells are generated from senescent cells, which are still competent for replication, by an unusual budding-mitosis mechanism. We further present data implicating reactive oxygen species that accumulate during senescence as a potential mutagenic motor of this post-senescence emergence. We conclude that senescence and its associated oxidative stress could be a tumor-promoting state for epithelial cells, potentially explaining why the incidence of carcinogenesis dramatically increases with advanced age.

Proliferative defects in dyskeratosis congenita skin keratinocytes are corrected by expression of the telomerase reverse transcriptase, TERT, or by activation of endogenous telomerase through expression of papillomavirus E6/E7 or the telomerase RNA component, TERC

Dyskeratosis congenita (DC) is characterized by the triad of reticulate skin pigmentation, nail dystrophy and leukoplakia. Epidermal atrophy, hair growth defects, bone marrow failure and increased risk of cancer are also common in DC patients. DC is caused by mutations in genes encoding for telomerase complex factors. Although there is an association of epidermal abnormalities with DC, epidermal cells from DC donors have not been previously characterized. We have isolated skin keratinocytes from affected members of a family with an autosomal dominant form of DC that is caused by a mutation in the RNA component of telomerase, TERC. Here, we demonstrate that, similar to DC fibroblasts from these donors, DC keratinocytes have short telomeres and a short lifespan. DC keratinocytes also exhibited impaired colony forming efficiency (CFE) and migration capacity. Exogenous expression of the reverse transcriptase (RT) component of telomerase, TERT, activated telomerase levels to half that of TERT expressing normal cells and maintained telomeres at a short length with concomitant extension of lifespan. Unlike fibroblasts, transduction of human papillomavirus type 16 E6/E7 genes into DC keratinocytes activated telomerase to half that of E6/E7 expressing normal cells, and robust proliferation was observed. While expression of TERC has no measurable effect on telomerase in fibroblasts, expression of TERC in keratinocytes upregulated telomerase activity and, rarely, allowed rescue of proliferative defects. Our results point to important differences between DC fibroblasts and keratinocytes and show, for the first time, that expression of TERC can increase the lifespan of primary human epithelial cells.

Hypertrophy and fibrosis in the cardiomyopathy of uremia--beyond coronary heart disease

Cardiac disease is the leading cause of death in uremic patients. In contrast to previous opinion, coronary events account for a relatively small proportion of cardiac deaths, the most common causes being sudden death and heart failure. Against this background the current text will discuss noncoronary cardiac pathology, specifically the pathogenesis and the morphological findings caused by (pathological) cardiac hypertrophy, cardiac interstitial fibrosis and microvascular disease.

DNA microarrays in dermatology and skin biology

Because of its accessibility, skin has been among the first organs analyzed using DNA microarrays. Skin cancers, melanomas, and basal and squamous cell carcinomas have been intensely investigated because they are very frequent and can be fatal. Psoriasis, one of the most common human inflammatory diseases, has been studied comprehensively using DNA microarrays. In addition, epidermal keratinocytes have been the target of many studies because they respond to a rich variety of inflammatory and immunomodulating cytokines, hormones, vitamins, ultraviolet (UV) light, toxins, and physical injury. Because of the ethical considerations, the effects of harmful or dangerous agents on skin have been studied using artificial skin substitutes. Transcriptional mechanisms that regulate epidermal differentiation and cornification have begun to yield their mysteries, and very exciting recent studies identified the genes specifically expressed in epidermal stem cells. Thus, skin has everything: stem cells, differentiation, signaling, inflammation, diseases, and cancer. All these exciting facets of skin have been explored using DNA microarrays. Researchers in skin biology and dermatology were among the first to implement this technology and we expect that they will continue to generate exciting and useful new knowledge.

Methylation of the p16(INK4a) promoter region in telomerase immortalized human keratinocytes co-cultured with feeder cells

Human keratinocytes grown in co-culture with fibroblast feeder cells have an extended in vitro lifespan and delayed accumulation of the tumor suppressor protein p16(INK4a) when compared to the same cells grown on tissue culture plastic alone. Previous studies have indicated that human keratinocytes can be immortalized by telomerase activity alone when grown in co-culture with feeder cells, suggesting that loss of the p16(INK4a)/Rb pathway is not required for immortalization. Using two independent human keratinocyte cell strains, we found that exogenous telomerase expression and co-culture with feeder cells results in efficient extension of lifespan without an apparent crisis. However, when these cells were transferred from the co-culture environment to plastic alone they experienced only a brief period of slowed growth before continuing to proliferate indefinitely. Examination of immortal cell lines demonstrated p16(INK4a) promoter methylation had occurred in both the absence and presence of feeder cells. Reintroduction of p16(INK4a) into immortal cell lines resulted in rapid growth arrest. Our results suggest that p16(INK4a)/Rb-induced telomere-independent senescence, although delayed in the presence of feeders, still provides a proliferation barrier to human keratinocytes in this culture system and that extended culture of telomerase-transduced keratinocytes on feeders can lead to the methylation of p16(INK4a).

A keratinocyte hypermotility/growth-arrest response involving laminin 5 and p16INK4A activated in wound healing and senescence

Keratinocytes become migratory to heal wounds, during early neoplastic invasion, and when undergoing telomere-unrelated senescence in culture. All three settings are associated with expression of the cell cycle inhibitor p16INK4A (p16) and of the basement membrane protein laminin 5 (LN5). We have investigated cause-and-effect relationships among laminin 5, p16, hypermotility, and growth arrest. Plating primary human keratinocytes on the gamma2 precursor form of laminin 5 (LN5') immediately induced directional hypermotility at approximately 125 microm/hour, followed by p16 expression and growth arrest. Cells deficient in p16 and either p14ARF or p53 became hypermotile in response to LN5' but did not arrest growth. Plating on LN5' triggered smad nuclear translocation, and all LN5' effects were blocked by a transforming growth factor (TGF) beta receptor I (TGFbetaRI) kinase inhibitor. In contrast, plating cells on collagen I triggered a TGFbetaRI kinase-independent hypermotility unaccompanied by smad translocation or growth arrest. Plating on control surfaces with TGFbeta induced hypermotility after a 1-day lag time and growth arrest by a p16-independent mechanism. Keratinocytes serially cultured with TGFbetaRI kinase inhibitor exhibited an extended lifespan, and immortalization was facilitated following transduction to express the catalytic subunit of telomerase (TERT). These results reveal fundamental features of a keratinocyte hyper-motility/growth-arrest response that is activated in wound healing, tumor suppression, and during serial culture.

Molecular signaling and genetic pathways of senescence: Its role in tumorigenesis and aging

In response to progressive telomere shortening in successive cell divisions, normal somatic cells enter senescence, during which they cease to proliferate irreversibly and undergo dramatic changes in gene expression. Senescence can also be activated by various types of stressful stimuli, including aberrant oncogenic signaling, oxidative stress, and DNA damage. Because of the limited proliferative capacity imposed by senescence, as well as the ability of senescent cells to influence neighboring non-senescent cells, senescence has been proposed to play an important role in tumorigenesis and to contribute to aging. Considerable effort has been put into elucidating the molecular mechanisms of senescence, including the signals that trigger senescence, the molecular pathways by which cells enter senescence, and evidence that supports its role in tumorigenesis and aging.