Switch from p53 to MDM2 as differentiating human keratinocytes lose their proliferative potential and increase in cellular size

DNA damage signalling histone H2AX is required for tumour growth

Cancer most frequently develops in self-renewal tissues that are the target of genetic alterations due to mutagens or intrinsic DNA replication errors. Histone γH2AX has a critical role in the cellular DNA repair pathway cascade and contributes to genomic stability. However, the role of γH2AX in the ontology of cancer is unclear. We have investigated this issue in the epidermis, a self-renewal epithelium continuously exposed to genetic hazard and replication stress. Silencing H2AX caused cell cycle hyperactivation, impaired DNA repair and epidermal hyperplasia in the skin. However, mutagen-induced carcinogenesis was strikingly reduced in the absence of H2AX. KO tumours appeared significantly later than controls and were fewer, smaller and more benign. The stem cell marker Δp63 drastically diminished in the KO epidermis. We conclude that H2AX is required for tissue-making during both homoeostasis and tumourigenesis, possibly by contributing to the control and repair of stem cells. Therefore, although H2AX is thought to act as a tumour suppressor and our results show that it contributes to homeostasis, they also indicate that it is required for the development of cancer.

ZetaSuite: computational analysis of two-dimensional high-throughput data from multi-target screens and single-cell transcriptomics

Two-dimensional high-throughput data have become increasingly common in functional genomics studies, which raises new challenges in data analysis. Here, we introduce a new statistic called Zeta, initially developed to identify global splicing regulators from a two-dimensional RNAi screen, a high-throughput screen coupled with high-throughput functional readouts, and ZetaSuite, a software package to facilitate general application of the Zeta statistics. We compare our approach with existing methods using multiple benchmarked datasets and then demonstrate the broad utility of ZetaSuite in processing public data from large-scale cancer dependency screens and single-cell transcriptomics studies to elucidate novel biological insights.

Molecular mapping of interstitial lung disease reveals a phenotypically distinct senescent basal epithelial cell population

Compromised regenerative capacity of lung epithelial cells can lead to cellular senescence, which may precipitate fibrosis. While increased markers of senescence have been reported in idiopathic pulmonary fibrosis (IPF), the origin and identity of these senescent cells remain unclear, and tools to characterize context-specific cellular senescence in human lung are lacking. We observed that the senescent marker p16 is predominantly localized to bronchiolized epithelial structures in scarred regions of IPF and systemic sclerosis-associated interstitial lung disease (SSc-ILD) lung tissue, overlapping with the basal epithelial markers Keratin 5 and Keratin 17. Using in vitro models, we derived transcriptional signatures of senescence programming specific to different types of lung epithelial cells and interrogated these signatures in a single-cell RNA-Seq data set derived from control, IPF, and SSc-ILD lung tissue. We identified a population of basal epithelial cells defined by, and enriched for, markers of cellular senescence and identified candidate markers specific to senescent basal epithelial cells in ILD that can enable future functional studies. Notably, gene expression of these cells significantly overlaps with terminally differentiating cells in stratified epithelia, where it is driven by p53 activation as part of the senescence program.

Impact of p53 modulation on interactions between p53 family members during HaCaT keratinocytes differentiation

HaCaT cell line is a widely used model for studying normal human keratinocytes. However, mutations of TP53 gene are typical for this cell line, which have a substantial impact on functions of the encoded protein. The features of this regulatory circuit should be considered when using HaСaT cells for assessment of human skin physiology and pathology in vitro. The study was aimed to assess the features of differentiation realization in HaCaT cells with modulated activity of p53 protein. The expression of p53 was reduced by knockdown of TP53 gene by shRNA (by 2.2 times, p < 0.05), and the elevated concentration of the p53 active forms was achieved via exposure of cells to Nutlin-3a, the MDM2 inhibitor and the major negative regulator of p53. It has been found that regulation of at least three differentiation markers, СASP14, IVL (expression increase by 3.9 and 3.7 times respectively in the p53-knockdown cells, p < 0.05) and TGM1 (twofold expression decrease in the p53-knockdown cells, and 1.7-fold expression increase under exposure to Nutlin-3a, p < 0.05) in HaCaT cells is p53-mediated. The positive correlation has been revealed for expression of TGM1 and p53 that might be realized indirectly via ΔNp63 expression alteration. At the same time, modulation of p53 does not result in significant alterations in expression of cytokeratins.

The DNA damage response links human squamous proliferation with differentiation

How rapid cell multiplication leads to cell differentiation in developing tissues is still enigmatic. This question is central to morphogenesis, cell number control, and homeostasis. Self-renewal epidermoid epithelia are continuously exposed to mutagens and are the most common target of cancer. Unknown mechanisms commit rapidly proliferating cells to post-mitotic terminal differentiation. We have over-activated or inhibited the endogenous DNA damage response (DDR) pathways by combinations of activating TopBP1 protein, specific shRNAs, or chemical inhibitors for ATR, ATM, and/or DNA-PK. The results dissect and demonstrate that these signals control keratinocyte differentiation in proliferating cells independently of actual DNA damage. The DDR limits keratinocyte multiplication upon hyperproliferative stimuli. Moreover, knocking down H2AX, a common target of the DDR pathways, inhibits the epidermoid phenotype. The results altogether show that the DDR is required to maintain the balance proliferation differentiation and suggest that is part of the squamous program. We propose a homeostatic model where genetic damage is automatically and continuously cleansed by cell-autonomous mechanisms.

p21CIP1 controls the squamous differentiation response to replication stress

The control of cell fate is critical to homeostasis and cancer. Cell cycle cdk inhibitor p21CIP1 has a central and paradoxical role in the regulatory crossroads leading to senescence, apoptosis, or differentiation. p21 is an essential target of tumor suppressor p53, but it also is regulated independently. In squamous self-renewal epithelia continuously exposed to mutagenesis, p21 controls cell fate by mechanisms still intriguing. We previously identified a novel epidermoid DNA damage-differentiation response. We here show that p21 intervenes in the mitosis block that is required for the squamous differentiation response to cell cycle deregulation and replication stress. The inactivation of endogenous p21 in human primary keratinocytes alleviated the differentiation response to oncogenic loss of p53 or overexpression of the DNA replication major regulator Cyclin E. The bypass of p21-induced mitotic block involving upregulation of Cyclin B allowed DNA damaged cells to escape differentiation and continue to proliferate. In addition, loss of p21 drove keratinocytes from differentiation to apoptosis upon moderate UV irradiation. The results show that p21 is required to drive keratinocytes towards differentiation in response to genomic stress and shed light into its dual and paradoxical role in carcinogenesis.

Sublethal UV irradiation induces squamous differentiation via a p53-independent, DNA damage-mitosis checkpoint

The epidermis is a self-renewal epithelium continuously exposed to the genotoxic effects of ultraviolet (UV) light, the main cause of skin cancer. Therefore, it needs robust self-protective mechanisms facing genomic damage. p53 has been shown to mediate apoptosis in sunburn cells of the epidermis. However, epidermal cells daily receive sublethal mutagenic doses of UV and massive apoptosis would be deleterious. We have recently unravelled an anti-oncogenic keratinocyte DNA damage-differentiation response to cell cycle stress. We now have studied this response to high or moderate single doses of UV irradiation. Whereas, as expected, high levels of UV induced p53-dependent apoptosis, moderate levels triggered squamous differentiation. UV-induced differentiation was not mediated by endogenous p53. Overexpression of the mitosis global regulator FOXM1 alleviated the proliferative loss caused by UV. Conversely, knocking-down the mitotic checkpoint protein Wee1 drove UV-induced differentiation into apoptosis. Therefore, the results indicate that mitosis checkpoints determine the response to UV irradiation. The differentiation response was also found in cells of head and neck epithelia thus uncovering a common regulation in squamous tissues upon chronic exposure to mutagens, with implications into homeostasis and disease.

FoxO1 enhances differentiation and apoptosis in human primary keratinocytes

Forkhead box-O1 (FoxO1) is a key nutrient- and growth factor-dependent regulator of metabolism, but its functional role in human primary keratinocytes (HPKs) is less known. To investigate the role of FoxO1 in HPKs and effect of insulin-like growth factor 1 (IGF-1) and isotretinoin on FoxO1 expression, HPKs were treated with 1.2 mmol/L calcium chloride, 1-20 ng/mL IGF-1 and 0.1-10 μmol/L isotretinoin. Recombinant adenovirus expressing FoxO1 or FKHR shRNA lentivirus transfection was introduced to upregulate or silence FoxO1 expression. Epidermal FoxO1 immunostaining was lower in acne lesion than in normal skin. FoxO1 overexpression induced involucrin expression, G2/M arrest and apoptosis but suppressed proliferation, while FoxO1 silencing decreased involucrin expression but increased proliferation, S phase and viable cells in HPKs. IGF-1 downregulated FoxO1 and involucrin but upregulated p-Akt expression in HPKs, which was blocked by pretreatment with LY294002. Isotretinoin enhanced FoxO1, p53 and p21 but inhibited p-FoxO1 and involucrin expression in HPKs. These results demonstrate that FoxO1 promotes differentiation and apoptosis in HPKs. IGF-1 may reduce keratinocyte differentiation through PI3K/Akt/FoxO1 pathway, while isotretinoin can reinforce FoxO1 expression. FoxO1 may be involved in acne pathogenesis and could serve as a potential therapeutic target.

Rapid Decrease in KRT14 and TP53 mRNA Expression in the Buccal Mucosa of Patients Receiving Total-Body Irradiation for Allogeneic Stem Cell Transplantation

The only curative treatment option for relapsed patients with acute myeloid leukemia (AML) is allogeneic stem cell transplantation. Depletion of hematopoietic stem cells and leukemic blast cells is achieved through the systemic administration of DNA damaging agents, including total-body irradiation (TBI) prior to transplantation. Since other tissues are radiosensitive, the identification of biomarkers could facilitate the management of additional toxicities. Buccal keratinocytes are readily accessible and could provide a source of cells for RNA analysis. In this study, we obtained miRNAs and mRNAs from daily buccal swabs collected from patients undergoing allogeneic stem cell transplantation. Unexpectedly, there was no prominent p53-induced mRNA or miRNA response in these samples, despite the fact that the p53 pathway is a well-characterized radiation-inducible response. Instead, the expression of mRNAs encoding p53 and cytokeratin 14 (TP53 and KRT14, respectively) decreased precipitously within hours of the first radiation treatment. These patients went on to develop oral mucositis, however, it is unclear whether TP53 and/or KRT14 expression are predictive of this adverse event. Larger scale analysis of buccal epithelial samples from patients undergoing allogeneic stem cell transplantation appears to be warranted.

Full-Length Isoforms of Kaposi's Sarcoma-Associated Herpesvirus Latency-Associated Nuclear Antigen Accumulate in the Cytoplasm of Cells Undergoing the Lytic Cycle of Replication

The latency-associated nuclear antigen (LANA) of the Kaposi's sarcoma-associated herpesvirus (KSHV) performs a variety of functions to establish and maintain KSHV latency. During latency, LANA localizes to discrete punctate spots in the nucleus, where it tethers viral episomes to cellular chromatin and interacts with nuclear components to regulate cellular and viral gene expression. Using highly sensitive tyramide signal amplification, we determined that LANA localizes to the cytoplasm in different cell types undergoing the lytic cycle of replication after de novo primary infection and after spontaneous, tetradecanoyl phorbol acetate-, or open reading frame 50 (ORF50)/replication transactivator (RTA)-induced activation. We confirmed the presence of cytoplasmic LANA in a subset of cells in lytically active multicentric Castleman disease lesions. The induction of cellular migration by scratch-wounding confluent cell cultures, culturing under subconfluent conditions, or induction of cell differentiation in primary cultures upregulated the number of cells permissive for primary lytic KSHV infection. The induction of lytic replication was characterized by high-level expression of cytoplasmic LANA and nuclear ORF59, a marker of lytic replication. Subcellular fractionation studies revealed the presence of multiple isoforms of LANA in the cytoplasm of ORF50/RTA-activated Vero cells undergoing primary infection. Mass spectrometry analysis demonstrated that cytoplasmic LANA isoforms were full length, containing the N-terminal nuclear localization signal. These results suggest that trafficking of LANA to different subcellular locations is a regulated phenomenon, which allows LANA to interact with cellular components in different compartments during both the latent and the replicative stages of the KSHV life cycle.IMPORTANCE Kaposi's sarcoma-associated herpesvirus (KSHV) causes AIDS-related malignancies, including lymphomas and Kaposi's sarcoma. KSHV establishes lifelong infections using its latency-associated nuclear antigen (LANA). During latency, LANA localizes to the nucleus, where it connects viral and cellular DNA complexes and regulates gene expression, allowing the virus to maintain long-term infections. Our research shows that intact LANA traffics to the cytoplasm of cells undergoing permissive lytic infections and latently infected cells in which the virus is induced to replicate. This suggests that LANA plays important roles in the cytoplasm and nuclear compartments of the cell during different stages of the KSHV life cycle. Determining cytoplasmic function and mechanism for regulation of the nuclear localization of LANA will enhance our understanding of the biology of this virus, leading to therapeutic approaches to eliminate infection and block its pathological effects.

Nucleus Morphometry in Cultured Epithelial Cells Correlates with Phenotype

Phenotype of cultured ocular epithelial transplants has been shown to affect clinical success rates following transplantation to the cornea. The purpose of this study was to evaluate the relationship between cell nucleus morphometry and phenotype in three types of cultured epithelial cells. This study provides knowledge for the development of a non-invasive method of determining the phenotype of cultured epithelium before transplantation. Cultured human conjunctival epithelial cells (HCjE), human epidermal keratinocytes (HEK), and human retinal pigment epithelial cells (HRPE) were analyzed by quantitative immunofluorescence. Assessments of nucleus morphometry and nucleus-to-cytoplasm ratio (N/C ratio) were performed using ImageJ. Spearman's correlation coefficient was employed for statistical analysis. Levels of the proliferation marker PCNA in HCjE, HEK, and HRPE correlated positively with nuclear area. Nuclear area correlated significantly with levels of the undifferentiated cell marker ABCG2 in HCjE. Bmi1 levels, but not p63α levels, correlated significantly with nuclear area in HEK. The N/C ratio did not correlate significantly with any of the immunomarkers in HCjE (ABCG2, CK7, and PCNA) and HRPE (PCNA). In HEK, however, the N/C ratio was negatively correlated with levels of the undifferentiated cell marker CK14 and positively correlated with Bmi1 expression. The size of the nuclear area correlated positively with proliferation markers in all three epithelia. Morphometric indicators of phenotype in cultured epithelia can be identified using ImageJ. Conversely, the N/C ratio did not show a uniform relationship with phenotype in HCjE, HEK, or HRPE. N/C ratio therefore, may not be a useful morphometric marker for in vitro assessment of phenotype in these three epithelia.

Asymmetric stem-cell division ensures sustained keratinocyte hyperproliferation in psoriatic skin lesions

Excessive expansion of the transit-amplifying (TA) cell compartment is a distinct morphological characteristic of psoriatic epidermal hyperplasia. In order to examine the activation of basal stem cells and how they replenish such an enlarged compartment of TA cells in psoriatic epidermis, we utilized a BrdU labeling method to monitor mitotic stem cells in a mouse model of psoriasiform dermatitis, which was induced by imiquimod. Our results showed that perpendicular and parallel cell division characteristics of dividing stem cells existed in the inflamed epidermis. When we analyzed template‑DNA strand segregation in trypsin-dissociated human psoriatic keratinocytes using BrdU pulse-chase labeling, we found that the percentage of asymmetric segregation of BrdU was significantly increased in the cell pairs of psoriatic epidermal cells compared with normal epidermal cells. Furthermore, we also examined the effects of both interleukin (IL)-17A and IL-22 cytokines on the differentiation status of cultured human keratinocytes. The results indicated that both cytokines had synergistic effects on passage-one epidermal cell sheets derived from skin explants and also on cultured keratinocytes, were involved in the maintenance of the undifferentiated stem cell phenotype, and these results suggest an efficient mechanism for preventing the premature loss of basal stem-cell pools in the pro-inflammatory cytokine-enriched milieu of the psoriatic epidermis. Our findings suggest that inhibition of hyperactive stem cells represents a potential therapeutic target to combat recalcitrant epidermal hyperplasia in psoriasis.

Cancer stem cells and cell size: A causal link?

The majority of normal animal cells are 10-20 μm in diameter. Many signaling mechanisms, notably PI3K/Akt/mTOR, Myc, and Hippo pathways, tightly control and coordinate cell growth, cell size, cell division, and cell number during homeostasis. These regulatory mechanisms are frequently deregulated during tumorigenesis resulting in wide variations in cell sizes and increased proliferation in cancer cells. Here, we first review the evidence that primitive stem cells in adult tissues are quiescent and generally smaller than their differentiated progeny, suggesting a correlation between small cell sizes with the stemness. Conversely, increased cell size positively correlates with differentiation phenotypes. We then discuss cancer stem cells (CSCs) and present some evidence that correlates cell sizes with CSC activity. Overall, a causal link between CSCs and cell size is relatively weak and remains to be rigorously assessed. In the future, optimizing methods for isolating cells based on size should help elucidate the connection between cancer cell size and CSC characteristics.

Electrical stimulation enhances epidermal proliferation in human cutaneous wounds by modulating p53-SIVA1 interaction

Cutaneous wounds establish endogenous "wound current" upon injury until re-epithelialization is complete. Keratinocyte proliferation, regulated partly by p53, is required for epidermal closure. SIVA1 promotes human double minute 2 homolog (HDM2)-mediated p53 regulation. However, the role of SIVA1 in wound healing is obscure. Here, we report that electrical stimulation (ES) accelerates wound healing by upregulating SIVA1 and its subsequent ability to modulate p53 activities. Cultured donut-shaped human skin explants, subjected to ES, exhibited better epidermal stratification, increased proliferation, and upregulation of gene and protein expression of HDM2/SIVA1, compared with non-ES-treated explants. ES significantly increased in vitro keratinocyte proliferation and phospho-p53-SIVA1 interaction; however, this showed stable expression of phospho-p53, which increased significantly in the absence of SIVA1. Here, HDM2 alone was unable to downregulate nuclear-accumulated phospho-p53, which was evident from decreased proliferation and increased sub-G1 population seen by flow cytometry. Further examination of the epidermis of human cutaneous wounds showed higher p53-SIVA1 coexpression and proliferation 7 days after injury in ES-treated wounds compared with control wounds. In summary, ES-inducible SIVA1 modulates p53 activities in proliferating keratinocytes, and exogenous ES affects p53/HDM2/SIVA1 axis leading to increased proliferation during re-epithelialization. This highlights ES as a potential strategy for enhancing cutaneous repair.

Inactivation of p53 in Human Keratinocytes Leads to Squamous Differentiation and Shedding via Replication Stress and Mitotic Slippage

Tumor suppressor p53 is a major cellular guardian of genome integrity, and its inactivation is the most frequent genetic alteration in cancer, rising up to 80% in squamous cell carcinoma (SCC). By adapting the small hairpin RNA (shRNA) technology, we inactivated endogenous p53 in primary epithelial cells from the epidermis of human skin. We show that either loss of endogenous p53 or overexpression of a temperature-sensitive dominant-negative conformation triggers a self-protective differentiation response, resulting in cell stratification and expulsion. These effects follow DNA damage and exit from mitosis without cell division. p53 preserves the proliferative potential of the stem cell compartment and limits the power of proto-oncogene MYC to drive cell cycle stress and differentiation. The results provide insight into the role of p53 in self-renewal homeostasis and help explain why p53 mutations do not initiate skin cancer but increase the likelihood that cancer cells will appear.

Cycling up the epidermis: reconciling 100 years of debate

There is likely general consensus within the skin research community that cell cycle control is critical to epidermal homeostasis and disease. The current predominant model proposes that keratinocytes switch off DNA replication and undergo cell cycle and cell growth arrest as they initiate terminal differentiation. However, this model cannot explain key physiological features of the skin, mainly why squamous differentiation prevails over proliferation in benign hyperproliferative disorders. In recent years, we have proposed an alternative model that involves mitotic slippage and endoreplication. This new model is controversial and has encountered resistance within the field. However, looking back at history, the epidermal cell cycle has been a matter of controversy and debate for around 100 years now. The accumulated data are confusing and contradictory. Our present model can explain and reconcile both old and new paradoxical observations. Here, we explain and discuss the endoreplicative cell cycle, the evidence for and against its existence in human epidermis and the important implications for skin homeostasis and disease. We show that regardless of the strengths or weaknesses of the Endoreplication Model, the existing evidence in support of the Cell Cycle Arrest Model is very weak.

Mathematical modeling of the impact of actin and keratin filaments on keratinocyte cell spreading

Keratin intermediate filaments (IFs) form cross-linked arrays to fulfill their structural support function in epithelial cells and tissues subjected to external stress. How the cross-linking of keratin IFs impacts the morphology and differentiation of keratinocytes in the epidermis and related surface epithelia remains an open question. Experimental measurements have established that keratinocyte spreading area is inversely correlated to the extent of keratin IF bundling in two-dimensional culture. In an effort to quantitatively explain this relationship, we developed a mathematical model in which isotropic cell spreading is considered as a first approximation. Relevant physical properties such as actin protrusion, adhesion events, and the corresponding response of lamellum formation at the cell periphery are included in this model. Through optimization with experimental data that relate time-dependent changes in keratinocyte surface area during spreading, our simulation results confirm the notion that the organization and mechanical properties of cross-linked keratin filaments affect cell spreading; in addition, our results provide details of the kinetics of this effect. These in silico findings provide further support for the notion that differentiation-related changes in the density and intracellular organization of keratin IFs affect tissue architecture in epidermis and related stratified epithelia.

Cyclin E drives human keratinocyte growth into differentiation

Human epidermis is continuously exposed to environmental mutagenic hazard and is the most frequent target of human cancer. How the epidermis coordinates proliferation with differentiation to maintain homeostasis, even in hyperproliferative conditions, is unclear. For instance, overactivation of the proto-oncogene MYC in keratinocytes stimulates differentiation. Here we explore the cell cycle regulation as proliferating human keratinocytes commit to terminal differentiation upon loss of anchorage or overactivation of MYC. The S-phase of the cell cycle is deregulated as mitotic regulators are inhibited in the onset of differentiation. Experimental inhibition of mitotic kinase cdk1 or kinases of the mitosis spindle checkpoint Aurora B or Polo-like Kinase, triggered keratinocyte terminal differentiation. Furthermore, hyperactivation of the cell cycle by overexpressing the DNA replication regulator Cyclin E induced mitosis failure and differentiation. Inhibition of Cyclin E by shRNAs attenuated the induction of differentiation by MYC. In addition, we present evidence that Cyclin E induces DNA damage and the p53 pathway. The results provide novel clues for the mechanisms committing proliferative keratinocytes to differentiate, with implications for tissue homeostasis maintenance, HPV amplification and tumorigenesis.

It Takes 15 to Tango: Making Sense of the Many Ubiquitin Ligases of p53

The transcription factor p53 regulates numerous cellular processes to guard against tumorigenesis. Cell-cycle inhibition, apoptosis, and autophagy are all regulated by p53 in a cell- and context-specific manner, underscoring the need for p53 activity to be kept low in most circumstances. p53 is kept in check primarily through its regulated ubiquitination and degradation by a number of different factors, whose contributions may reflect complex context-specific needs to restrain p53 activity. Chief among these E3 ubiquitin ligases in p53 homeostasis is the ubiquitously expressed proto-oncogene MDM2, whose loss renders vertebrates unable to limit p53 activity, resulting in early embryonic lethality. MDM2 has been validated as a critical, universal E3 ubiquitin ligase for p53 in numerous tissues and organisms to date, but additional E3 ligases have also been identified for p53 whose contribution to p53 activity is unclear. In this review, we summarize the recent advances in our knowledge regarding how p53 activity is apparently controlled by a multitude of ubiquitin ligases beyond MDM2.

The mysterious human epidermal cell cycle, or an oncogene-induced differentiation checkpoint

Fifteen years ago, we reported that proto-oncogene MYC promoted differentiation of human epidermal stem cells, a finding that was surprising to the MYC and the skin research communities. MYC was one of the first human oncogenes identified, and it had been strongly associated with proliferation. However, it was later shown that MYC could induce apoptosis under low survival conditions. Currently, the notion that MYC promotes epidermal differentiation is widely accepted, but the cell cycle mechanisms that elicit this function remain unresolved. We have recently reported that keratinocytes respond to cell cycle deregulation and DNA damage by triggering terminal differentiation. This mechanism might constitute a homeostatic protection face to cell cycle insults. Here, I discuss recent and not-so-recent evidence suggesting the existence of a largely unexplored oncogene-induced differentiation response (OID) analogous to oncogene-induced apoptosis (OIA) or senescence (OIS). In addition, I propose a model for the role of the cell cycle in skin homeostasis maintenance and for the dual role of MYC in differentiation.

hTERT, MYC and TP53 deregulation in gastric preneoplastic lesions

Background

Gastric cancer is a serious public health problem in Northern Brazil and in the world due to its high incidence and mortality. Despite the severity of the disease, more research is needed to better understand the molecular events involved in this intestinal-type gastric carcinogenesis process. Since precancerous lesions precede intestinal-type gastric cancer, here, we evaluated the hTERT, MYC, and TP53 mRNA and protein expression, as well as TP33 copy number, in gastric preneoplastic lesions.

Methods

We evaluated 19 superficial gastritis, 18 atrophic gastritis, and 18 intestinal metaplasia from cancer-free individuals of Northern Brazil. Quantitative reverse transcription PCR was used to analyze the mRNA expression and immunohistochemical methods were used to assess protein immunoreactivity in tissue samples. The number of TP53 gene copies was investigated in gastric diseases by quantitative PCR.

Results

We observed hTERT, MYC, and p53 immunoreactivity only in intestinal metaplasia samples. The immunoreactivity of these proteins was strongly associated with each other. A significantly higher MYC mRNA expression was observed in intestinal metaplasia compared to gastritis samples. Loss of TP53 was also only detected in intestinal metaplasia specimens.

Conclusions

We demonstrated that hTERT, MYC, and TP53 are deregulated in intestinal metaplasia of individuals from Northern Brazil and these alterations may facilitate tumor initiation.

A cell cycle role for the epigenetic factor CTCF-L/BORIS

CTCF is a ubiquitous epigenetic regulator that has been proposed as a master keeper of chromatin organisation. CTCF-like, or BORIS, is thought to antagonise CTCF and has been found in normal testis, ovary and a large variety of tumour cells. The cellular function of BORIS remains intriguing although it might be involved in developmental reprogramming of gene expression patterns. We here unravel the expression of CTCF and BORIS proteins throughout human epidermis. While CTCF is widely distributed within the nucleus, BORIS is confined to the nucleolus and other euchromatin domains. Nascent RNA experiments in primary keratinocytes revealed that endogenous BORIS is present in active transcription sites. Interestingly, BORIS also localises to interphase centrosomes suggesting a role in the cell cycle. Blocking the cell cycle at S phase or mitosis, or causing DNA damage, produced a striking accumulation of BORIS. Consistently, ectopic expression of wild type or GFP- BORIS provoked a higher rate of S phase cells as well as genomic instability by mitosis failure. Furthermore, down-regulation of endogenous BORIS by specific shRNAs inhibited both RNA transcription and cell cycle progression. The results altogether suggest a role for BORIS in coordinating S phase events with mitosis.

The histone methyltransferase Setd8 acts in concert with c-Myc and is required to maintain skin

Keratinocyte-specific ablation of the histone H4K20 methyltransferase Setd8 reveals its essential role in embryonic and postnatal skin homeostasis. Molecularly, the c-myc target gene Setd8 regulates proliferation/differentiation by controlling p63 function.

Setd8/PR-Set7/KMT5a-dependent mono-methylation of histone H4 at lysine 20 is essential for mitosis of cultured cells; yet, the functional roles of Setd8 in complex mammalian tissues are unknown. We use skin as a model system to explore how Setd8 may regulate cell division in vivo. Deletion of Setd8 in undifferentiated layers of the mouse epidermis impaired both proliferation and differentiation processes. Long-lived epidermal progenitor cells are lost in the absence of Setd8, leading to an irreversible loss of sebaceous glands and interfollicular epidermis. We show that Setd8 is a transcriptional target of c-Myc and an essential mediator of Myc-induced epidermal differentiation. Deletion of Setd8 in c-Myc-overexpressing skin blocks proliferation and differentiation and causes apoptosis. Increased apoptosis may be explained by our discovery that p63, an essential transcription factor for epidermal commitment is lost, while p53 is gained upon removal of Setd8. Both overexpression of p63 and deletion of p53 rescue Setd8-induced apoptosis. Thus, Setd8 is a crucial inhibitor of apoptosis in skin and its activity is essential for epidermal stem cell survival, proliferation and differentiation.

IRF6 is a mediator of Notch pro-differentiation and tumour suppressive function in keratinocytes

While the pro-differentiation and tumour suppressive functions of Notch signalling in keratinocytes are well established, the underlying mechanisms remain poorly understood. We report here that interferon regulatory factor 6 (IRF6), an IRF family member with an essential role in epidermal development, is induced in differentiation through a Notch-dependent mechanism and is a primary Notch target in keratinocytes and keratinocyte-derived SCC cells. Increased IRF6 expression contributes to the impact of Notch activation on growth/differentiation-related genes, while it is not required for induction of 'canonical' Notch targets like p21(WAF1/Cip1), Hes1 and Hey1. Down-modulation of IRF6 counteracts differentiation of primary human keratinocytes in vitro and in vivo, promoting ras-induced tumour formation. The clinical relevance of these findings is illustrated by the strikingly opposite pattern of expression of Notch1 and IRF6 versus epidermal growth factor receptor in a cohort of clinical SCCs, as a function of their grade of differentiation. Thus, IRF6 is a primary Notch target in keratinocytes, which contributes to the role of this pathway in differentiation and tumour suppression.

Dental follicle stem cells and tissue engineering

Adult stem cells are multipotent and can be induced experimentally to differentiate into various cell lineages. Such cells are therefore a key part of achieving the promise of tissue regeneration. The most studied stem cells are those of the hematopoietic and mesenchymal lineages. Recently, mesenchymal stem cells were demonstrated in dental tissues, including dental pulp, periodontal ligament, and dental follicle. The dental follicle is a loose connective tissue that surrounds the developing tooth. Dental follicle stem cells could therefore be a cell source for mesenchymal stem cells. Indeed, dental follicle is present in impacted teeth, which are commonly extracted and disposed of as medical waste in dental practice. Dental follicle stem cells can be isolated and grown under defined tissue culture conditions, and recent characterization of these stem cells has increased their potential for use in tissue engineering applications, including periodontal and bone regeneration. This review describes current knowledge and recent developments in dental follicle stem cells and their application.

A mitosis block links active cell cycle with human epidermal differentiation and results in endoreplication

How human self-renewal tissues co-ordinate proliferation with differentiation is unclear. Human epidermis undergoes continuous cell growth and differentiation and is permanently exposed to mutagenic hazard. Keratinocytes are thought to arrest cell growth and cell cycle prior to terminal differentiation. However, a growing body of evidence does not satisfy this model. For instance, it does not explain how skin maintains tissue structure in hyperproliferative benign lesions. We have developed and applied novel cell cycle techniques to human skin in situ and determined the dynamics of key cell cycle regulators of DNA replication or mitosis, such as cyclins E, A and B, or members of the anaphase promoting complex pathway: cdc14A, Ndc80/Hec1 and Aurora kinase B. The results show that actively cycling keratinocytes initiate terminal differentiation, arrest in mitosis, continue DNA replication in a special G2/M state, and become polyploid by mitotic slippage. They unambiguously demonstrate that cell cycle progression coexists with terminal differentiation, thus explaining how differentiating cells increase in size. Epidermal differentiating cells arrest in mitosis and a genotoxic-induced mitosis block rapidly pushes epidermal basal cells into differentiation and polyploidy. These observations unravel a novel mitosis-differentiation link that provides new insight into skin homeostasis and cancer. It might constitute a self-defence mechanism against oncogenic alterations such as Myc deregulation.

Stem cells isolated from human dental follicles have osteogenic potential

OBJECTIVE

Stem cells isolated from human dental follicles as a potential cell source for bone-tissue engineering were examined for correcting a critical bone defect.

STUDY DESIGN

Impacted third molars were collected and single cell-derived cell populations were cultivated in growth medium. Single cell-derived cell lines were examined in terms of cell shape, gene expression patterns, differentiation capacity in vitro, and osteogenic potential in vivo.

RESULTS

Three distinct cell populations were identified with different morphologies, patterns of gene expression, and differentiation capacity. All 3 cell populations promoted bone formation when transplanted into surgically created critical-size defects in immunodeficient rat calvaria, compared with control animals without cell transplantation, although one of these populations showed a weak capacity for osteogenetic differentiation in vitro.

CONCLUSIONS

Human dental follicle can derive at least 3 unique cell populations in culture, all of which promote bone formation in vivo.

Câncer de pele: uso de medidas preventivas e perfil demográfico de um grupo de risco na cidade de Botucatu

Buscou-se junto a um grupo de risco para o câncer de pele seu o perfil demográfico e analisou-se o uso de medidas preventivas utilizadas pelos mesmos e pela empresa. Estudo quantitativo com 33 carteiros da Empresa Brasileira de Correios e Telégrafos em Botucatu, Brasil. Dados obtidos por meio de um formulário que investigava perfil demográfico, tempo de trabalho na empresa, horário de exposição ao sol, história de queimaduras solares, história de câncer na família e formas de prevenção do câncer de pele utilizadas. Na análise dos dados, utilizou-se estatística descritiva segundo Teste Exato de Fisher ao nível de 5% de probabilidade. Os resultados mostraram que a faixa etária predominante foi de 26 a 30 e de 31 a 35 anos, correspondendo a 42,42% da amostra, a cor da pele foi à branca com 93,94% e 81,82% trabalham há mais de cinco anos na empresa. O hábito de usar filtro solar foi encontrado em 63,63% dos entrevistados, sendo a não aderência a este justificada em 75% por falta de costume. Em relação aos equipamentos protetores do sol a empresa fornece para 100% deles. Os achados permitem a caracterização da população estudada, identificada como de risco para o câncer de pele, propiciando a profilaxia através de ações em saúde, visando à sensibilização dos mesmos para com as medidas preventivas que podem ser adotadas.

Enrichment of putative human epidermal stem cells based on cell size and collagen type IV adhesiveness

The enrichment and identification of human epidermal stem cells (EpSCs) are of paramount importance for both basic research and clinical application. Although several approaches for the enrichment of EpSCs have been established, enriching a pure population of viable EpSCs is still a challenging task. An improved approach is worth developing to enhance the purity and viability of EpSCs. Here we report that cell size combined with collagen type IV adhesiveness can be used in an improved approach to enrich pure and viable human EpSCs. We separated the rapidly adherent keratinocytes into three populations that range in size from 5-7 microm (population A), to 7-9 microm (population B), to > or =9 microm (population C) in diameter, and found that human putative EpSCs could be further enriched in population A with the smallest size. Among the three populations, population A displayed the highest density of beta1-integrin receptor, contained the highest percentage of cells in G0/G1 phase, showed the highest nucleus to cytoplasm ratio, and possessed the highest colony formation efficiency (CFE). When injected into murine blastocysts, these cells participated in multi-tissue formation. More significantly, compared with a previous approach that sorted putative EpSCs according to beta1-integrin antibody staining, the viability of the EpSCs enriched by the improved approach was significantly enhanced. Our results provide a putative strategy for the enrichment of human EpSCs, and encourage further study into the role of cell size in stem cell biology.

Combined effects of MDM2 SNP 309 and p53 mutation on oral squamous cell carcinomas associated with areca quid chewing

The recently identified single nucleotide polymorphism in the MDM2 promoter (SNP 309) may contribute to the early onset of both sporadic and hereditary malignancies in patients with defective p53. We tested this hypothesis by examining the effects of combined MDM2 polymorphisms and somatic p53 mutations on 351 oral squamous cell carcinomas (OSCCs) associated with areca quid chewing. We found that the G allele of MDM2 SNP 309 was associated with early age of onset (p=0.02) and poor differentiation of OSCC tumors (p=0.01). The frequency of lymph node extracapsular spread (LNECS) was increased in individuals having both the MDM2 SNP 309 GG genotype and p53 mutation (chi(2) for trend p=0.04). MDM2 GG genotype and p53 mutations were associated with poor disease-free survival in both early and lymph node positive advanced stage OSCC patients (Hazard ratio=2.77 and 1.93, respectively). Taken together, an interaction between MDM2 SNP 309 and p53 with respect to tumor behaviors (including disease onset, tumor differentiation, LNECS and disease-free survival) was observed in sporadic Taiwanese OSCCs.

KGF suppresses α2β1 integrin function and promotes differentiation of the transient amplifying population in human prostatic epithelium

Prostate epithelial stem cells are self-renewing cells capable of differentiation into prostate epithelium, and are thought to contribute towards both benign and malignant conditions in the human prostate. We have previously demonstrated that prostate epithelial basal cells express high levels of integrin α2β1 and this population can be subdivided into stem (α2β1hi CD133+) and transient-amplifying population (TAP) cells (α2β1hi CD133-). However, the molecular mechanism(s) controlling the commitment and regulation of these cells towards differentiated epithelium remains unclear. Here, we demonstrate that β1 integrin function is required for the maintenance of basal prostatic epithelial cells and suppression of its function by either methylcellulose or, more specifically, β1-blocking antibody (80 μg/ml) induces differentiation, with associated expression of the differentiation-specific markers prostate acid phosphatase (PAP) and cytokeratin 18 (CK18). Keratinocyte growth factor (KGF), a stromal-derived growth factor, has previously been implicated in prostate organogenesis using in vitro tissue recombination experiments. We show that treatment with KGF (10 ng/ml) potently induces epithelial differentiation with concomitant suppression of α2β1 integrin expression as well as the induction of androgen receptor expression. Specifically, p38-MAPK appears to be involved and the presence of SB202190, a p38 inhibitor, significantly blocks KGF-induced differentiation. Furthermore, the expression of the high-affinity receptor tyrosine kinase to KGF (FGFR2) is predominantly detectable in α2β1hi CD133- TAP cells when compared with stem cells (α2β1hi CD133+), which would therefore be relatively unresponsive to the differentiating effect of KGF. Taken together, using a human primary culture model, we have demonstrated key roles for interactions between KGF and integrin-mediated function in the regulation of prostate epithelial differentiation.

Cell size correlates with phenotype and proliferative capacity in human corneal epithelial cells

This study investigated whether cell size correlates with phenotype and proliferative capacity in human corneal epithelial cells. Primary cultured human corneal epithelial cells were sorted by flow cytometry based on forward scatter profile in comparison with the profile of beads of known size. Four fractions (A, B, C, and D) of cells ranging in size from 10 to 16, 17 to 23, 24 to 30, and >or=31 microm in diameter, respectively, were collected to evaluate their 5-bromo-2-deoxyuridine (BrdU) label retention properties, cell phenotype, and clonal growth capacity on a 3T3 fibroblast feeder layer. Among these four populations, cell size was shown to positively correlate with the expression of the differentiation markers keratin (K) 3, K12, and involucrin and inversely with the levels of stem cell-associated markers DeltaNp63 and ABCG2 and with colony-forming efficiency (CFE) and growth capacity. Population A with the smallest size, accounting for 11.0%+/-4.5% of the entire population, contained the greatest number of BrdU label-retaining slow-cycling cells, displayed the highest percentage of cells immunopositive to p63 and ABCG2 and negative to K3 and involucrin, expressed the highest levels of DeltaNp63 and ABCG2 mRNA and the lowest levels of K3, K12, and involucrin, and possessed the highest CFE and growth capacity. These findings suggest that cell size correlates with cell differentiation phenotypes and proliferative capacity in human corneal epithelial cells. The smallest cells in population A seem to be enriched for putative stem cells, and small cell size may represent one of the important properties of adult corneal epithelial stem cells.

Development and characterization of a canine oral mucosa equivalent in a serum-free environment

The objectives of this study were to develop a serum-free system for culturing canine oral keratinocytes, the construction and characterization of a canine ex vivo produced oral mucosa equivalent (EVPOME), and transduction green fluorescent protein (GFP) into keratinocytes as a post-grafting tracking marker. Dissociated canine buccal mucosa keratinocytes were cultured in a chemically defined serum-free medium, Epilife trade mark. First-passage keratinocytes were transfected with the GFP gene using a lentiviral vector, sorted by flow cytometer and seeded onto a dermal equivalent, AlloDerm(R) to form EVPOMEs. The EVPOME was characterized by histology and immunohistochemistry, for p63, Ki-67, and involucrin. Laser confocal microscopy was used to locate GFP-transfected keratinocytes within the EVPOME. Cultured canine oral keratinocytes grew rapidly over the first three passages and then the proliferative rate decreased. The canine EVPOME formed a well-stratified epithelial layer. The majority of p63 and Ki-67 immunopositive cells were located in the basal layer whereas cytoplasmic involucrin expression was seen in the suprabasal layers, similar to native canine buccal mucosa. Under laser confocal microscopy, significant green fluorescence was observed throughout the EVPOME. In conclusion, canine EVPOMEs were successfully fabricated in a defined serum-free system with similar characteristics to native buccal mucosa. GFP-transfected canine oral keratinocytes could be identified within the EVPOME.

p53 deficiency exacerbates pleiotropic mitotic defects, changes in nuclearity and polyploidy in transdifferentiating pancreatic acinar cells

In a primary culture model for pancreatic acinar-ductal transdifferentiation, cells exhibited increased proliferation, changes in nuclearity and polyploidy. We identify the 'nucleus to centrosome' ratio of the progenitor cell, the dissemination of centrosomes at spindle poles and cytokinesis failure as critical determinants of mitosis outcome and centrosome inheritance. Abortive cytokinesis of mononuclear cells contributes to the binuclear cell pool, whereas enclosure of entire mitotic formations, within a single nuclear envelope, perpetuates polyploidization. Binuclear cell nuclei combine their genomes on a single metaphase plate, doubling descendant ploidy. Moreover, approximately 42% of binuclear and tetraploid cells assemble aberrant spindles with up to 8 centrosomes/poles. These phenotypes were exacerbated in p53-deficient cultures exhibiting increased S-phase entry, giant nuclei, multinucleation, multipolar mitoses and centrosome hyperamplification. The tendency of p53-proficient cells to spontaneously evade the tetraploidy checkpoint degenerates to uncontrolled polyploid progression in p53-deficient cultures, explaining why p53 abrogation alone rapidly descends to aneuploidy in this system. We detected constitutively nuclear mdm2, which may circumvent endogenous cell-cycle checkpoints, and pronounced accumulation of p21 and p27 in multinuclear cells and giant nuclei, consistent with roles in polyploidization. This in vitro model may recapitulate the processes underlying genomic instability in pancreatic tumours in vivo, and attests to the existence of a p53-dependent polyploidy checkpoint acting to limit the degree of polyploidization.

Arsenite maintains germinative state in cultured human epidermal cells

Arsenic is a well-known carcinogen for human skin, but its mechanism of action and proximal macromolecular targets remain to be elucidated. In the present study, low micromolar concentrations of sodium arsenite maintained the proliferative potential of epidermal keratinocytes, decreasing their exit from the germinative compartment under conditions that promote differentiation of untreated cells. This effect was observed in suspension and in post-confluent surface cultures as measured by colony-forming ability and by proportion of rapidly adhering colony-forming cells. Arsenite-treated cultures exhibited elevated levels of beta1-integrin and beta-catenin, two proteins enriched in cells with high proliferative potential. Levels of phosphorylated (inactive) glycogen synthase kinase 3beta were higher in the treated cultures, likely accounting for the increased levels of transcriptionally available beta-catenin. These findings suggest that arsenic could have co-carcinogenic and tumor co-promoting activities in the epidermis as a result of increasing the population and persistence of germinative cells targeted by tumor initiators and promoters. These findings also identify a critical signal transduction pathway meriting further exploration in pursuit of this phenomenon.

Inhibition of p63 transcriptional activity by p14ARF: functional and physical link between human ARF tumor suppressor and a member of the p53 family

The ARF/MDM2/p53 pathway is a principal defense mechanism to protect the organism from uncontrolled effects of deregulated oncogenes. Oncogenes activate ARF, which interacts with and inhibits the ubiquitin ligase MDM2, resulting in p53 stabilization and activation. Once stabilized and activated, p53 can either induce or repress a wide array of different gene targets, which in turn can regulate cell cycle, DNA repair, and a number of apoptosis-related genes. Here we show that, unlike p53, p63, a member of the p53 family, directly interacts with p14(ARF). Through this interaction ARF inhibits p63-mediated transactivation and transrepression. In p63-transfected cells, ARF, which normally localizes into nucleoli, accumulates in the nucleoplasm. Based on these observations, we suggest that stimuli inducing p14(ARF) expression can, at the same time, activate p53 and impair p63 transcriptional activity, altering the pattern of p53 target gene expression. Here we show, for the first time, a physical and functional link between the p14(ARF) tumor suppressor protein and p63, a member of the p53 family.

Design principle of gene expression used by human stem cells: implication for pluripotency

Human embryonic stem cells (ESC) are undifferentiated and are endowed with the capacities of self-renewal and pluripotential differentiation. Adult stem cells renew their own tissue, but whether they can transdifferentiate to other tissues is still controversial. To understand the genetic program that underlies the pluripotency of stem cells, we compared the transcription profile of ESC with that of progenitor/stem cells of human hematopoietic and keratinocytic origins, along with their mature cells to be viewed as snapshots along tissue differentiation. ESC gene profiles show higher complexity with significantly more highly expressed genes than adult cells. We hypothesize that ESC use a strategy of expressing genes that represent various differentiation pathways and selection of only a few for continuous expression upon differentiation to a particular target. Such a strategy may be necessary for the pluripotency of ESC. The progenitors of either hematopoietic or keratinocytic cells also follow the same design principle. Using advanced clustering, we show that many of the ESC expressed genes are turned off in the progenitors/stem cells followed by a further down-regulation in adult tissues. Concomitantly, genes specific to the target tissue are up-regulated toward mature cells of skin or blood.

Limited tumor growth (HT29) in vivo under RO205-2349 is due to increased apoptosis and reduced cell volume but not to decreased proliferation rate

The peroxisome proliferator-activated receptor (PPARgamma) is a nuclear receptor that plays a regulatory role in cell differentiation and proliferation. PPARgamma was first detected in adipocytes, however, it has been shown that this receptor is also expressed in normal as well as tumor cells including malignant colonic epithelial cells. In this study, the effect of the PPARgamma agonist RO205-2349, a recently developed thiazolidinedione, on tumor growth was evaluated. For this purpose, human colon cancer cells (HT29) were grown in severe combined immunodeficient mice. Under daily RO205-2349 treatment (50 mg/kg/day) a significantly reduced tumor weight became evident after 3 weeks. In the control (n = 10) and treatment (n = 10) groups the mean tumor weights were 0.45 and 0.16 g, respectively. The mean percentages of apoptotic cells were 0.8 and 2.7% in the control and treatment groups, respectively, and the cell diameter measured on average 11.4 and 9.4 microm. In contrast, cell proliferation and differentiation, which are considered to be influenced by the PPARgamma, remained unaffected as could be seen by Ki-67 and carcinoembryonic antigen immunoreactivity indicating that increased rate of apoptosis and cell shrinkage are responsible for the differences in tumor growth. Hence, in this human/mouse xenograft model, mechanisms other than the classical activation of PPARgamma are likely reasons causing limited tumor growth.

Genome-wide comparison of human keratinocyte and squamous cell carcinoma responses to UVB irradiation: implications for skin and epithelial cancer

To gain insight into the transformation of epidermal cells into squamous carcinoma cells (SCC), we compared the response to ultraviolet B radiation (UVB) of normal human epidermal keratinocytes (NHEK) versus their transformed counterpart, SCC, using biological and molecular profiling. DNA microarray analyses (Affymetrix), approximately 12000 genes) indicated that the major group of upregulated genes in keratinocytes fall into three categories: (i). antiapoptotic and cell survival factors, including chemokines of the CXC/CC subfamilies (e.g. IL-8, GRO-1, -2, -3, SCYA20), growth factors (e.g. HB-EGF, CTGF, INSL-4), and proinflammatory mediators (e.g. COX-2, S100A9), (ii). DNA repair-related genes (e.g. GADD45, ERCC, BTG-1, Histones), and (iii). ECM proteases (MMP-1, -10). The major downregulated genes are DeltaNp63 and PUMILIO, two potential markers for the maintenance of keratinocyte stem cells. NHEK were found to be more resistant than SCC to UVB-induced apoptosis and this resistance was mainly because of the protection from cell death by secreted survival factors, since it can be transferred from NHEK to SCC cultures by the conditioned medium. Whereas the response of keratinocytes to UVB involved regulation of key checkpoint genes (p53, MDM2, p21(Cip1), DeltaNp63), as well as antiapoptotic and DNA repair-related genes - no or little regulation of these genes was observed in SCC. The effect of UVB on NHEK and SCC resulted in upregulation of 251 and 127 genes, respectively, and downregulation of 322 genes in NHEK and 117 genes in SCC. To further analyse these changes, we used a novel unsupervised coupled two-way clustering method that allowed the identification of groups of genes that clearly partitioned keratinocytes from SCC, including a group of genes whose constitutive expression levels were similar before UVB. This allowed the identification of discriminating genes not otherwise revealed by simple static comparison in the absence of UVB irradiation. The implication of the changes in gene profile in keratinocytes for epithelial cancer is discussed.

Helicobacter pylori infection generated gastric cancer through p53-Rb tumor-suppressor system mutation and telomerase reactivation

AIM

To investigate the relationship between Helicobacter pylori (H.pylori) infection and the expressions of the p53, Rb, c-myc, bcl-2 and hTERT mRNA in a series of diseases from chronic gastritis (CG), intestinal metaplasia type I or II(IMI-II), intestinal metaplasia type III (IMIII), mild or modest dysplasia (DysI-II), severe dysplasia (DysIII) to gastric cancer(GC) and to elucidate the mechanism of gastric carcinogenesis relating to H.pylori infection.

METHODS

272 cases between 1998 and 2001 were available for the study including 42 cases of CG, 46 cases of IMI-II, 25 cases of IMIII, 48 cases of DysI-II, 27 cases of DysIII, 84 cases of GC. H.pylori infection and the expressions of p53, Rb, c-myc, bcl-2 were detected by means of streptavidin-peroxidase (SP) immunohistochemical method. HTERT mRNA was detected by in situ hybridization (ISH).

RESULTS

The expressions of p53, Rb, c-myc, hTERT mRNA and bcl-2 were higher in the GC than in CG, IM, Dys. The expression of c-myc was higher in IMIII with H.pylori infection (10/16) than that without infection (1/9) and the positive rate in DysI-II and DysIII with H.pylori infection was 18/30 and 13/17, respectively, higher than that without infection (4/18 and 3/10, respectively). In our experiment mutated p53 had no association with H.pylori infection, the expression of Rb was associated with H.pylori infection in GC, but the p53-Rb tumor-suppressor system abnormal in DysI-II cases, DysIII and GC cases with H.pylori infection was 21/30, 15/17 and 48/48 respectively, higher than non-infection groups (4/18, 3/10, 28/36). Furthermore the level of hTERT mRNA in GC with H.pylori infection (47/48) was higher than that without infection (30/36), however the relationship between bcl-2 and H.pylori was only in IMIII. C-myc had a close association with hTERT mRNA in DysIII and GC (P=0.0 253,0.0 305 respectively).

CONCLUSION

In the gastric carcinogenesis, H.pylori might cause the severe imbalance of proliferation and apoptosis in the precancerous lesions (IMIII and GysIII) first, leading to p53-Rb tumor-suppressor system mutation and telomerase reactivation, and finally causes gastric cancer.

Regulation of apoptosis by p53 in UV-irradiated human epidermis, psoriatic plaques and senescent keratinocytes

The carcinogenic effects of sunlight in human epidermis may be thwarted by either: transient growth arrest and repair of DNA photodamage in keratinocytes (KCs); elimination of KCs with damaged DNA via apoptosis; or by stimulating a senescence switch whereby KCs become irreversibly growth arrested. Using normal human skin organ cultures and living epidermal equivalents, we demonstrate that in the proliferative basal layer, removal of KCs via apoptosis had a rapid onset (beginning within 2 h) following UV-light exposure generating progressively greater numbers of KCs with thymine dimers as the dose of UV-light was increased; involved induction of Apaf-1, activation of caspase-3, and was dependent on p53 activation as addition of a p53 chemical inhibitor blocked the apoptotic response. Suprabasal layer KCs underwent apoptosis at much later time points (>8 h). KCs in the basal layer repaired DNA damage more rapidly than KCs in suprabasal layers. Steady state levels of p53 increased in irradiated cells, and the increase was accompanied by phosphorylation of serine 9 and serine 15, but not serine 6 residues. By contrast, cultured KCs undergoing spontaneous replicative senescence were resistant to UV-induced apoptosis. Senescent KCs constitutively contained low levels of p53, which were neither increased nor phosphorylated or acetylated after UV-exposure and possessed minimal DNA binding activity, indicative of functional inactivation. Furthermore, treatment of senescent KCs with DNA damaging agent adriamycin did not result in activation of latent p53 or apoptosis. When KCs within psoriatic plaques were examined, they resembled senescent KCs in that they expressed p53, which was not phosphorylated or acetylated. Thus, UV-light induces DNA damage in human epidermal KCs triggering p53 activation, and subsequent apoptosis involving distinct cell layers and kinetics. However, the lack of p53 activation as seen in senescent KCs and psoriatic plaques, is associated with a relative resistance of KCs to UV-induced apoptosis. In conclusion, the sensitivity and resistance of KCs to apoptosis depends not only on the location within various layers of epidermis and levels of p53, but may also involve p53 activation via post-translational modifications.

Making decisions through Myc

c-Myc is a transcriptional regulator involved in carcinogenesis through its role in growth control and cell cycle progression. Here we attempt to relate its role in stimulating the G1-S transition to the ability to affect functioning of key cell cycle regulators, and we focus on how its property of modulating transcription of a wide range of target genes could explain its capacity to affect multiple pathways leading to proliferation, apoptosis, growth, and transformation.