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

General Semi-Solid Freeze Casting for Uniform Large-Scale Isotropic Porous Scaffolds: An Application for Extensive Oral Mucosal Reconstruction

Ice-templated porous biomaterials possess transformative potential in regenerative medicine; yet, scaling up ice-templating processes for broader applications-owing to inconsistent pore formation-remains challenging. This study reports an innovative semi-solid freeze-casting technique that draws inspiration from semi-solid metal processing (SSMP) combined with ice cream-production routines. This versatile approach allows for the large-scale assembly of various materials, from polymers to inorganic particles, into isotropic 3D scaffolds featuring uniformly equiaxed pores throughout the centimeter scale. Through (cryo-)electron microscopy, X-ray tomography, and finite element modeling, the structural evolution of ice grains/pores is elucidated, demonstrating how the method increases the initial ice nucleus density by pre-fabricating a semi-frozen slurry, which facilitates a transition from columnar to equiaxed grain structures. For a practical demonstration, as-prepared scaffolds are integrated into a bilayer tissue patch using biodegradable waterborne polyurethane (WPU) for large-scale oral mucosal reconstruction in minipigs. Systematic analyses, including histology and RNA sequencing, prove that the patch modulates the healing process toward near-scarless mucosal remodeling via innate and adaptive immunomodulation and activation of pro-healing genes converging on matrix synthesis and epithelialization. This study not only advances the field of ice-templating fabrication but sets a promising precedent for scaffold-based large-scale tissue regeneration.

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.

Childhood hematopoietic stem cells constitute the permissive window for RUNX1-ETO leukemogenesis

Cancer is a very rare event at the cellular level, although it is a common disease at the body level as one third of humans die of cancer. A small subset of cells in the body harbor the cellular features that constitute a permissive window for a particular genetic change to induce cancer. The significance of a permissive window is ironically best shown by a large number of failures in generating the animal model for acute myeloid leukemia (AML) with t(8;21). Over the decades, the RUNX1-ETO fusion gene created by t(8;21) has been introduced into various types of hematopoietic cells, largely at adult stage, in mice; however, all the previous attempts failed to generate tractable AML models. In stark contrast, we recently succeeded in inducing AML with the clinical features seen in human patients by specifically introducing RUNX1-ETO in childhood hematopoietic stem cells (HSCs). This result in mice is consistent with adolescent and young adult (AYA) onset in human t(8;21) patients, and suggests that childhood HSCs constitute the permissive window for RUNX1-ETO leukemogenesis. If loss of a permissive window is induced pharmacologically, cancer cells might be selectively targeted. Such a permissive window modifier may serve as a novel therapeutic drug.

DNA damage triggers squamous metaplasia in human lung and mammary cells via mitotic checkpoints

Epithelial transdifferentiation is frequent in tissue hyperplasia and contributes to disease in various degrees. Squamous metaplasia (SQM) precedes epidermoid lung cancer, an aggressive and frequent malignancy, but it is rare in the epithelium of the mammary gland. The mechanisms leading to SQM in the lung have been very poorly investigated. We have studied this issue on human freshly isolated cells and organoids. Here we show that human lung or mammary cells strikingly undergo SQM with polyploidisation when they are exposed to genotoxic or mitotic drugs, such as Doxorubicin or the cigarette carcinogen DMBA, Nocodazole, Taxol or inhibitors of Aurora-B kinase or Polo-like kinase. To note, the epidermoid response was attenuated when DNA repair was enhanced by Enoxacin or when mitotic checkpoints where abrogated by inhibition of Chk1 and Chk2. The results show that DNA damage has the potential to drive SQM via mitotic checkpoints, thus providing novel molecular candidate targets to tackle lung SCC. Our findings might also explain why SCC is frequent in the lung, but not in the mammary gland and why chemotherapy often causes complicating skin toxicity.

Construction of a three commitment points for S phase entry cell cycle model and immune-related ceRNA network to explore novel therapeutic options for psoriasis

While competing endogenous RNAs (ceRNAs) play pivotal roles in various diseases, the proliferation and differentiation of keratinocytes are becoming a research focus in psoriasis. Therefore, the three commitment points for S phase entry (CP1-3) cell cycle model has pointed to a new research direction in these areas. However, it is unclear what role ceRNA regulatory mechanisms play in the interaction between keratinocytes and the immune system in psoriasis. In addition, the ceRNA network-based screening of potential therapeutic agents for psoriasis has not been explored. Therefore, we used multiple bioinformatics approaches to construct a ceRNA network for psoriasis, identified CTGF as the hub gene, and constructed a ceRNA subnetwork, after which validation datasets authenticated the results' accuracy. Subsequently, we used multiple online databases and the single-sample gene-set enrichment analysis algorithm, including the CP1-3 cell cycle model, to explore the mechanisms accounting for the increased proliferation and differentiation of keratinocytes and the possible roles of the ceRNA subnetwork in psoriasis. Next, we performed cell cycle and cell trajectory analyses based on a single-cell RNA-seq dataset of psoriatic skin biopsies. We also used weighted gene co-expression network analysis and single-gene batch correlation analysis-based gene set enrichment analysis to explore the functions of CTGF. Finally, we used the Connectivity Map to identify MS-275 (entinostat) as a novel treatment for psoriasis, SwissTargetPrediction to predict drug targets, and molecular docking to investigate the minimum binding energy and binding sites of the drug to target proteins.

A novel loss-of-function mutation of the voltage-gated potassium channel Kv10.2 involved in epilepsy and autism

Background

Novel developmental mutations associated with disease are a continuous challenge in medicine. Clinical consequences caused by these mutations include neuron and cognitive alterations that can lead to epilepsy or autism spectrum disorders. Often, it is difficult to identify the physiological defects and the appropriate treatments.

Results

We have isolated and cultured primary cells from the skin of a patient with combined epilepsy and autism syndrome. A mutation in the potassium channel protein Kv10.2 was identified. We have characterised the alteration of the mutant channel and found that it causes loss of function (LOF). Primary cells from the skin displayed a very striking growth defect and increased differentiation. In vitro treatment with various carbonic anhydrase inhibitors with various degrees of specificity for potassium channels, (Brinzolamide, Acetazolamide, Retigabine) restored the activation capacity of the mutated channel. Interestingly, the drugs also recovered in vitro the expansion capacity of the mutated skin cells. Furthermore, treatment with Acetazolamide clearly improved the patient regarding epilepsy and cognitive skills. When the treatment was temporarily halted the syndrome worsened again.

Conclusions

By in vitro studying primary cells from the patient and the activation capacity of the mutated protein, we could first, find a readout for the cellular defects and second, test pharmaceutical treatments that proved to be beneficial. The results show the involvement of a novel LOF mutation of a Potassium channel in autism syndrome with epilepsy and the great potential of in vitro cultures of primary cells in personalised medicine of rare diseases.

Protooncogene MYC drives human melanocyte melanogenesis and senescence

In spite of extensive research and advances on the molecular biology of melanoma, the process of melanocytic differentiation or its relationship with proliferation is poorly understood. The role of proto-oncogenes in normal melanocyte biology is also intriguing. Proto-oncogene MYC is overexpressed in 40% of melanomas. It has been suggested that MYC can mediate senescence bypass in malignant melanocytes, an important event in melanoma development, likely in cooperation with other oncogenic pathways. However, despite the apparent importance of MYC in melanoma, its functions in normal melanocytes are unknown. We have overexpressed MYC in freshly isolated human primary melanocytes and studied the effects on melanocytic proliferation and differentiation. MYC promoted a transient activation of melanocytes including cell cycle entry, DNA damage and cell migration. Subsequently, MYC induced melanogenesis, increased cellular size and complexity and senescence. Interestingly, we also found strong expression of MYC in regions of human nevi displaying high pigmentation and high expression of senescence marker p16. The results altogether show that MYC drives melanocytic differentiation and suggest that senescence is associated with differentiation. We discuss the implications into the mechanisms governing melanocytic differentiation and the development of melanoma.

The tumor suppression theory of aging

Despite continued increases in human life expectancy, the factors determining the rate of human biological aging remain unknown. Without understanding the molecular mechanisms underlying aging, efforts to prevent aging are unlikely to succeed. The tumor suppression theory of aging introduced here proposes somatic mutation as the proximal cause of aging, but postulates that oncogenic transformation and clonal expansion, not functional impairment, are the relevant consequences of somatic mutation. Obesity and caloric restriction accelerate and decelerate aging due to their effect on cell proliferation, during which most mutations arise. Most phenotypes of aging are merely tumor-suppressive mechanisms that evolved to limit malignant growth, the dominant age-related cause of death in early and middle life. Cancer limits life span for most long-lived mammals, a phenomenon known as Peto's paradox. Its conservation across species demonstrates that mutation is a fundamental but hard limit on mammalian longevity. Cell senescence and apoptosis and differentiation induced by oncogenes, telomere shortening or DNA damage evolved as a second line of defense to limit the tumorigenic potential of clonally expanding cells, but accumulating senescent cells, senescence-associated secretory phenotypes and stem cell exhaustion eventually cause tissue dysfunction and the majority, if not most, phenotypes of aging.

Functional cooperation between ASK1 and p21Waf1/Cip1 in the balance of cell-cycle arrest, cell death and tumorigenesis of stressed keratinocytes

Both CDKN1A (p21 ^Waf1/Cip1) and Apoptosis signal-regulating kinase 1 (ASK1) play important roles in tumorigenesis. The role of p21 ^Waf1/Cip1 in attenuating ASK1-induced apoptosis by various stress conditions is well established. However, how ASK1 and p21 ^Waf1/Cip1 functionally interact during tumorigenesis is still unclear. To address this aspect, we crossed ASK1 knockout (ASK1KO) mice with p21 ^Waf1/Cip1 knockout (p21KO) mice to compare single and double-mutant mice. We observed that deletion of p21 ^Waf1/Cip1 leads to increased keratinocyte proliferation but also increased cell death. This is mechanistically linked to the ASK1 axis-induced apoptosis, including p38 and PARP. Indeed, deletion of ASK1 does not alter the proliferation but decreases the apoptosis of p21KO keratinocytes. To analyze as this interaction might affect skin carcinogenesis, we investigated the response of ASK1KO and p21KO mice to DMBA/TPA-induced tumorigenesis. Here we show that while endogenous ASK1 is dispensable for skin homeostasis, ASK1KO mice are resistant to DMBA/TPA-induced tumorigenesis. However, we found that epidermis lacking both p21 and ASK1 reacquires increased sensitivity to DMBA/TPA-induced tumorigenesis. We demonstrate that apoptosis and cell-cycle progression in p21KO keratinocytes are uncoupled in the absence of ASK1. These data support the model that a critical event ensuring the balance between cell death, cell-cycle arrest, and successful divisions in keratinocytes during stress conditions is the p21-dependent ASK1 inactivation.

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.

Squamous differentiation requires G2/mitosis slippage to avoid apoptosis

The cellular mechanisms controlling cell fate in self-renewal tissues remain unclear. Cell cycle failure often leads to an apoptosis anti-oncogenic response. We have inactivated Cdk1 or Polo-like-1 kinases, essential targets of the mitotic checkpoints, in the epithelia of skin and oral mucosa. Here, we show that inactivation of the mitotic kinases leading to polyploidy in vivo, produces a fully differentiated epithelium. Cells within the basal layer aberrantly differentiate and contain large or various nuclei. Freshly isolated KO cells were also differentiated and polyploid. However, sustained metaphase arrest downstream of the spindle anaphase checkpoint (SAC) due to abrogation of CDC20 (essential cofactor of anaphase-promoting complex), impaired squamous differentiation and resulted in apoptosis. Therefore, upon prolonged arrest keratinocytes need to slip beyond G2 or mitosis in order to initiate differentiation. The results altogether demonstrate that mitotic checkpoints drive squamous cell fate towards differentiation or apoptosis in response to genetic damage.

Protective Effects of Salicornia europaea on UVB-Induced Misoriented Cell Divisions in Skin Epithelium

Correct orientation of cell division is extremely important in the maintenance, regeneration, and repair of continuously proliferating tissues, such as the epidermis. Regulation of the axis of division of epidermal cells prevents the apoptosis-induced compensatory proliferation, and eventually the cancer. Thus, the orientation of cell division is critical for maintaining the tissue architecture. In this study, we investigated the effects of S. europaea extract on the texture of human skin and the behavior of these cells during skin morphogenesis. In sun-exposed skin, S. europaea improved the texture. A multilayered, highly differentiated in vitro skin model indicated that, S. europaea extract suppressed the UVB-induced changes in the morphology of basal keratinocytes. Orientation of cell division was determined by measuring the axis of mitosis in the vertical sections of our experimental model. Analyses of the digital images revealed that S. europaea preserved the axis of division of basal keratinocytes from UVB-induced perturbations. Our findings uncover a new mechanism by which S. europaea responds to the spindle misorientation induced by UVB.

Inhibition of sphingosine 1-phosphate lyase activates human keratinocyte differentiation and attenuates psoriasis in mice

Sphingosine 1-phosphate (S1P) lyase is an intracellular enzyme that catalyzes the irreversible degradation of S1P and has been suggested as a therapeutic target for the treatment of psoriasis vulgaris. Because S1P induces differentiation of keratinocytes, we examined whether modulation of S1P lyase and altered intracellular S1P levels regulate proliferation and differentiation of human neonatal epidermal keratinocyte (HEKn) cells. To identify the physiological functions of S1P lyase in skin, we inhibited S1P lyase in HEKn cells with an S1P lyase-specific inhibitor (SLI) and with S1P lyase 1 (SGPL1)-specific siRNA (siSGPL1). In HEKn cells, pharmacological treatment with the SLI caused G1 arrest by upregulation of p21 and p27 and induced keratin 1, an early differentiation marker. Similarly, genetic suppression by siSGPL1 arrested the cell cycle at the G1 phase and activated differentiation. In addition, enzyme suppression by siSGPL1 upregulated keratin 1 and differentiation markers including involucrin and loricrin. When hyperproliferation of HEKn cells was induced by interleukin (IL)-17 and IL-22, pharmacologic inhibition of S1P lyase by SLI decreased proliferation and activated differentiation of HEKn cells simultaneously. In addition, SLI administration ameliorated imiquimod-induced psoriatic symptoms including erythema, scaling, and epidermal thickness in vivo. We thus demonstrated that S1P lyase inhibition reduces cell proliferation and induces keratinocyte differentiation, and that inhibition may attenuate psoriasiform changes. Collectively, these findings suggest that S1P lyase is a modulating factor for proliferation and differentiation, and support its potential as a therapeutic target for psoriasis in human keratinocytes.

Defective Replication Stress Response Is Inherently Linked to the Cancer Stem Cell Phenotype

Extensive spontaneous DNA damage from oncogene-induced replication stress is ubiquitous in precancerous lesions. While this damage induces differentiation, senescence, or apoptosis in normal cells, defects in DNA replication stress response (RSR) allow cells to continue proliferating, ultimately leading to early tumorigenesis. Using systems-level approaches, we developed a replication stress response defect gene signature that predicted risk of cancer development from hyperplastic lesions. Intriguingly, we found that replication stress response defects rewire non-malignant cells into a cancer stem cell (CSC)-like state, and analysis of CSCs indicated that they inherently harbor replication stress response defects. High-throughput drug screening to elucidate molecules required for survival of replication stress response defective cells identified a dependence on MEK/ERK signaling. Inhibition of this signaling cascade restored oncogene-induced senescence through a p53-independent MDM2/p21 axis. Moreover, MEK/ERK inhibition also depleted CSC populations. Together, these findings provide insights into the role of replication stress response defects in CSCs and an actionable pathway for therapeutic targeting.

Advances in heart regeneration based on cardiomyocyte proliferation and regenerative potential of binucleated cardiomyocytes and polyploidization

One great achievement in medical practice is the reduction in acute mortality of myocardial infarction due to identifying risk factors, antiplatelet therapy, optimized hospitalization and acute percutaneous coronary intervention. Yet, the prevalence of heart failure is increasing presenting a major socio-economic burden. Thus, there is a great need for novel therapies that can reverse damage inflicted to the heart. In recent years, data have accumulated suggesting that induction of cardiomyocyte proliferation might be a future option for cardiac regeneration. Here, we review the relevant literature since September 2015 concluding that it remains a challenge to verify that a therapy induces indeed cardiomyocyte proliferation. Most importantly, it is unclear that the detected increase in cardiomyocyte cell cycle activity is required for an associated improved function. In addition, we review the literature regarding the evidence that binucleated and polyploid mononucleated cardiomyocytes can divide, and put this in context to other cell types. Our analysis shows that there is significant evidence that binucleated cardiomyocytes can divide. Yet, it remains elusive whether also polyploid mononucleated cardiomyocytes can divide, how efficient proliferation of binucleated cardiomyocytes can be induced, what mechanism regulates cell cycle progression in these cells, and what fate and physiological properties the daughter cells have. In summary, we propose to standardize and independently validate cardiac regeneration studies, encourage the field to study the proliferative potential of binucleated and polyploid mononucleated cardiomyocytes, and to determine whether induction of polyploidization can enhance cardiac function post-injury.

Response of head and neck epithelial cells to a DNA damage-differentiation checkpoint involving polyploidization

BACKGROUND

Squamous epithelia of the head and neck undergo continuous cell renewal and are continuously exposed to mutagenic hazard, the main cause of cancer. How they maintain homeostasis upon cell cycle deregulation is unclear.

METHODS

To elucidate how head and neck epithelia respond to cell cycle stress, we studied human keratinocytes from various locations (oral mucosa, tonsil, pharynx, larynx, and trachea). We made use of genotoxic or mitotic drugs (doxorubicin [DOXO], paclitaxel, and nocodazole), or chemical inhibitors of the mitotic checkpoint kinases, Aurora B and polo-like-1. We further tested the response to inactivation of p53, ectopic cyclin E, or to the chemical carcinogen 7,12-dimethylbenz[a]anthracene (DMBA).

RESULTS

All treatments provoked DNA damage or mitosis impairment and strikingly triggered squamous differentiation and polyploidization, resulting in irreversible loss of clonogenic capacity.

CONCLUSION

Keratinocytes from head and neck epithelia share a cell-autonomous squamous DNA damage-differentiation response that is common to the epidermis and might continuously protect them from cancer.

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.

Polyploidy in tissue homeostasis and regeneration

Polyploid cells, which contain multiple copies of the typically diploid genome, are widespread in plants and animals. Polyploidization can be developmentally programmed or stress induced, and arises from either cell-cell fusion or a process known as endoreplication, in which cells replicate their DNA but either fail to complete cytokinesis or to progress through M phase entirely. Polyploidization offers cells several potential fitness benefits, including the ability to increase cell size and biomass production without disrupting cell and tissue structure, and allowing improved cell longevity through higher tolerance to genomic stress and apoptotic signals. Accordingly, recent studies have uncovered crucial roles for polyploidization in compensatory cell growth during tissue regeneration in the heart, liver, epidermis and intestine. Here, we review current knowledge of the molecular pathways that generate polyploidy and discuss how polyploidization is used in tissue repair and regeneration.

Long non-coding RNAs: crucial regulators of gastrointestinal cancer cell proliferation

Studies of long non-coding RNAs (lncRNAs) have been prevalent in the field of non-coding RNA regulation in recent years. LncRNAs exert crucial effects on malignant cell processes in the gastrointestinal system, including proliferation. Aberrant lncRNA expression, through both oncogenes and tumor suppressor genes, is instrumental to tumor cell proliferation. Here, we summarize the different molecular mechanisms and relevant signaling pathways through which multifarious lncRNAs regulate cell proliferation and we show that lncRNAs are potential biomarkers for gastrointestinal cancers.

Characterization of centriole duplication in human epidermis, Bowen's disease, and squamous cell carcinoma

BACKGROUND

Centrosomes contain two centrioles: a pre-existing mature centriole and a newly formed immature centriole. Each centriole is duplicated once within a cell cycle, which is crucial for proper centrosome duplication and cell division.

OBJECTIVE

To describe the centrosome duplication cycle in human epidermis, Bowen's disease (BD), and squamous cell carcinoma (SCC).

METHODS

Immunofluorescent staining of centriolar proteins and Ki-67 was used to evaluate cell cycles and the number of centrioles. Centrobin and Outer dense fiber of sperm tails 2 (ODF2) were used as markers for immature and mature centrioles, respectively.

RESULTS

Normal human primary epidermal keratinocytes in a monolayered culture have one centrobin⁺ centriole (CTRB¹⁺ cells) supposed in G0/G1 phases or have two centrobin⁺ centrioles (CTRB²⁺ cells) supposed in S-G2 phase. In a three-dimensional culture and in vivo human epidermis, the majority of suprabasal cells were CTRB²⁺ cells, in spite of their non-proliferative Ki-67^- nature. The tumor mass of BD and SCC contained CTRB¹⁺ cells and Ki-67⁺ proliferating and Ki-67^- non-proliferative CTRB²⁺ cells. Clumping cells in BD had increased numbers of centrioles, with an approximate 1:1 to 2:1 ratio of centrobin⁺ to ODF2⁺ centrioles.

CONCLUSIONS

The cell cycle arrest of suprabasal cells is distinct from the G0 arrest of monolayered epithelial cells. Tumor mass of BD and SCC contained non-proliferative cells with the characteristics of the suprabasal cells of normal epidermis. A constant ratio of the number of centrobin⁺ to ODF2⁺ centrioles indicates that multiple centrioles were induced by cell division failure rather than centriole overduplication in clumping cells.

Deregulation of the pRb-E2F4 axis alters epidermal homeostasis and favors tumor development

E2F/RB activity is altered in most human tumors. The retinoblastoma family of proteins plays a key role in regulating the progression of the cell cycle from the G1 to S phases. This is achieved through negative regulation of E2F transcription factors, important positive regulators of cell cycle entry. E2F family members are divided into two groups: activators (E2F1-E2F3a) and repressors (E2F3b-E2F8). E2F4 accounts for a large part of the E2F activity and is a main E2F repressor member in vivo. Perturbations in the balance from quiescence towards proliferation contribute to increased mitotic gene expression levels frequently observed in cancer. We have previously reported that combined Rb1-Rbl1 or Rb1-E2f1 ablation in epidermis produces important alterations in epidermal proliferation and differentiation, leading to tumor development. However, the possible roles of E2F4 in this context are still to be determined. Here, we show the absence of any discernible phenotype in the skin of mice lacking of E2f4. In contrast, the inducible loss of Rb1 in the epidermis of E2F4-null mice produced multiple skin abnormalities including altered differentiation and proliferation, spontaneous wounds, carcinoma in situ development and stem cell perturbations. All these phenotypic alterations are associated with extensive gene expression changes, the induction of c-myc and the Akt activation. Moreover the whole transcriptome analyses in comparison with previous models generated also revealed extensive changes in multiple repressive complexes and in transcription factor activity. These results point to E2F4 as a master regulator in multiple steps of epidermal homeostasis in Rb1 absence.

Mammalian endoreplication emerges to reveal a potential developmental timer

Among the most intriguing and relevant questions in physiology is how developing tissues correctly coordinate proliferation with differentiation. Endoreplication, in a broad sense, is a consequence of a cell division block in the presence of an active cell cycle, and it typically occurs as cells differentiate terminally to fulfill a specialised function. Until recently, endoreplication was thought to be a rare variation of the cell cycle in mammals, more common in invertebrates and plants. However, in the last years, endoreplication has been uncovered in various tissues in mammalian organisms, including human. A recent report showing that cells in the mammary gland become binucleate at lactation sheds new insight into the importance of mammalian polyploidisation. We here propose that endoreplication is a widespread phenomenon in mammalian developing tissues that results from an automatic, robust and simple self-limiting mechanism coordinating cell multiplication with differentiation. This mechanism might act as a developmental timer. The model has implications for homeostasis control and carcinogenesis.

Deciphering psoriasis. A bioinformatic approach

BACKGROUND

Psoriasis is an immune-mediated, inflammatory and hyperproliferative disease of the skin and joints. The cause of psoriasis is still unknown. The fundamental feature of the disease is the hyperproliferation of keratinocytes and the recruitment of cells from the immune system in the region of the affected skin, which leads to deregulation of many well-known gene expressions.

OBJECTIVE

Based on data mining and bioinformatic scripting, here we show a new dimension of the effect of psoriasis at the genomic level.

METHODS

Using our own pipeline of scripts in Perl and MySql and based on the freely available NCBI Gene Expression Omnibus (GEO) database: DataSet Record GDS4602 (Series GSE13355), we explore the extent of the effect of psoriasis on gene expression in the affected tissue.

RESULTS

We give greater insight into the effects of psoriasis on the up-regulation of some genes in the cell cycle (CCNB1, CCNA2, CCNE2, CDK1) or the dynamin system (GBPs, MXs, MFN1), as well as the down-regulation of typical antioxidant genes (catalase, CAT; superoxide dismutases, SOD1-3; and glutathione reductase, GSR). We also provide a complete list of the human genes and how they respond in a state of psoriasis.

CONCLUSION

Our results show that psoriasis affects all chromosomes and many biological functions. If we further consider the stable and mitotically inheritable character of the psoriasis phenotype, and the influence of environmental factors, then it seems that psoriasis has an epigenetic origin. This fit well with the strong hereditary character of the disease as well as its complex genetic background.

Inefficient differentiation response to cell cycle stress leads to genomic instability and malignant progression of squamous carcinoma cells

Squamous cell carcinoma (SCC) or epidermoid cancer is a frequent and aggressive malignancy. However in apparent paradox it retains the squamous differentiation phenotype except for very dysplastic lesions. We have shown that cell cycle stress in normal epidermal keratinocytes triggers a squamous differentiation response involving irreversible mitosis block and polyploidisation. Here we show that cutaneous SCC cells conserve a partial squamous DNA damage-induced differentiation response that allows them to overcome the cell division block. The capacity to divide in spite of drug-induced mitotic stress and DNA damage made well-differentiated SCC cells more genomically instable and more malignant in vivo. Consistently, in a series of human biopsies, non-metastatic SCCs displayed a higher degree of chromosomal alterations and higher expression of the S phase regulator Cyclin E and the DNA damage signal γH2AX than the less aggressive, non-squamous, basal cell carcinomas. However, metastatic SCCs lost the γH2AX signal and Cyclin E, or accumulated cytoplasmic Cyclin E. Conversely, inhibition of endogenous Cyclin E in well-differentiated SCC cells interfered with the squamous phenotype. The results suggest a dual role of cell cycle stress-induced differentiation in squamous cancer: the resulting mitotic blocks would impose, when irreversible, a proliferative barrier, when reversible, a source of genomic instability, thus contributing to malignancy.

Is Myc an Important Biomarker? Myc Expression in Immune Disorders and Cancer

The proto-oncogene Myc serves as a paradigm for understanding the dynamics of transcriptional regulation. Myc protein has been linked to immune dysfunction, cancer development and neoplastic transformation. We review recent research regarding functions of Myc as an important modulator in immune disorders, postallogeneic hematopoietic stem cell transplantation (HSCT) and several cancers. Myc overexpression has been repeatedly linked to immune disorders and specific cancers, such as myasthenia gravis, psoriasis, pemphigus vulgaris, atherosclerosis, long-term allogeneic survival among HSCT patients, (primary) inflammatory breast cancer, (primary) ovarian carcinoma and hematological malignancies: acute myeloid leukemia, chronic myelogenous leukemia, Hodgkin's lymphoma and diffuse large B-cell lymphoma. However, decreased expression of Myc has been observed in HSCT patients who did not survive. Understanding impaired or inappropriate expression of Myc may present a path for the discovery of new targets for therapeutic applications.

Characterisation of cell cycle arrest and terminal differentiation in a maximally proliferative human epithelial tissue: Lessons from the human hair follicle matrix

Human hair follicle (HF) growth and hair shaft formation require terminal differentiation-associated cell cycle arrest of highly proliferative matrix keratinocytes. However, the regulation of this complex event remains unknown. CIP/KIP family member proteins (p21^CIP1, p27^KIP1 and p57^KIP2) regulate cell cycle progression/arrest, endoreplication, differentiation and apoptosis. Since they have not yet been adequately characterized in the human HF, we asked whether and where CIP/KIP proteins localise in the human hair matrix and pre-cortex in relation to cell cycle activity and HF-specific epithelial cell differentiation that is marked by keratin 85 (K85) protein expression. K85 expression coincided with loss or reduction in cell cycle activity markers, including in situ DNA synthesis (EdU incorporation), Ki-67, phospho-histone H3 and cyclins A and B1, affirming a post-mitotic state of pre-cortical HF keratinocytes. Expression of CIP/KIP proteins was found abundantly within the proliferative hair matrix, concomitant with a role in cell cycle checkpoint control. p21^CIP1, p27^KIP1 and cyclin E persisted within post-mitotic keratinocytes of the pre-cortex, whereas p57^KIP2 protein decreased but became nuclear. These data imply a supportive role for CIP/KIP proteins in maintaining proliferative arrest, differentiation and anti-apoptotic pathways, promoting continuous hair bulb growth and hair shaft formation in anagen VI. Moreover, post-mitotic hair matrix regions contained cells with enlarged nuclei, and DNA in situ hybridisation showed cells that were >2N in the pre-cortex. This suggests that CIP/KIP proteins might counterbalance cyclin E to control further rounds of DNA replication in a cell population that has a propensity to become tetraploid. These data shed new light on the in situ-biography of human hair matrix keratinocytes on their path of active cell cycling, arrest and terminal differentiation, and showcase the human HF as an excellent, clinically relevant model system for cell cycle physiology research of human epithelial cells within their natural tissue habitat.

FOXM1 allows human keratinocytes to bypass the oncogene-induced differentiation checkpoint in response to gain of MYC or loss of p53

Tumour suppressor p53 or proto-oncogene MYC is frequently altered in squamous carcinomas, but this is insufficient to drive carcinogenesis. We have shown that overactivation of MYC or loss of p53 via DNA damage triggers an anti-oncogenic differentiation-mitosis checkpoint in human epidermal keratinocytes, resulting in impaired cell division and squamous differentiation. Forkhead box M1 (FOXM1) is a transcription factor recently proposed to govern the expression of a set of mitotic genes. Deregulation of FOXM1 occurs in a wide variety of epithelial malignancies. We have ectopically expressed FOXM1 in keratinocytes of the skin after overexpression of MYC or inactivation of endogenous p53. Ectopic FOXM1 rescues the proliferative capacity of MYC- or p53-mutant cells in spite of higher genetic damage and a larger cell size typical of differentiation. As a consequence, differentiation induced by loss of p53 or MYC is converted into increased proliferation and keratinocytes displaying genomic instability are maintained within the proliferative compartment. The results demonstrate that keratinocyte oncogene-induced differentiation is caused by mitosis control and provide new insight into the mechanisms driving malignant progression in squamous cancer.

Looking beyond the brain to improve the pathogenic understanding of Parkinson's disease: implications of whole transcriptome profiling of Patients' skin

BACKGROUND

Parkinson's Disease is a progressive neurodegenerative disease, characterized by symptoms of motor impairment, resulting from the loss of dopaminergic neurons in the midbrain, however non-neuronal symptoms are also common. Although great advances have been made in the pathogenic understanding of Parkinson's Disease in the nervous system, little is known about the molecular alterations occurring in other non-neuronal organ systems. In addition, a higher rate of melanoma and non-melanoma skin cancer has been observed in the Parkinson's Disease population, indicating crosstalk between these diseases.

METHODS

To understand the molecular pathogenesis and gene expression alterations of Parkinson's Disease in peripheral tissues, and in order to explore the possible link between skin cancer and neurodegeneration, whole transcriptomic profiling of patients' skin was performed. Skin biopsies from 12 patients and matched controls were collected, and processed with high-throughput RNA-sequencing analysis.

RESULTS

This analysis resulted in a large collection of over 1000 differentially expressed genes, among which clear biological and functional networks could be distinguished. The central functional processes altered in patients skin can be grouped into six broad categories: impaired cellular metabolism and mitochondrial dysfunction, defective protein metabolism, disturbed skin homeostasis, dysfunctional nuclear processes, altered signalling and tumour pathways, as well as disordered immune regulation.

CONCLUSIONS

These results demonstrate that the molecular alterations leading to neurodegeneration in the CNS are systemic and manifest also in peripheral tissues, thereby indicating the presence of "skin-brain" crosstalk in Parkinson's Disease. In addition, the extensive homeostatic imbalance and basal stress can lead to increased susceptibility to external and internal mutagenic hazards in these patients, and thus provide a possible molecular link for the crosstalk between skin cancer and Parkinson's Disease.

The human papillomavirus E7 oncoprotein as a regulator of transcription

High-risk human papillomaviruses (HPVs) encode oncoproteins which manipulate gene expression patterns in the host keratinocytes to facilitate viral replication, regulate viral transcription, and promote immune evasion and persistence. In some cases, oncoprotein-induced changes in host cell behavior can cause progression to cancer, but a complete picture of the functions of the viral oncoproteins in the productive HPV life cycle remains elusive. E7 is the HPV-encoded factor most responsible for maintaining cell cycle competence in differentiating keratinocytes. Through interactions with dozens of host factors, E7 has an enormous impact on host gene expression patterns. In this review, we will examine the role of E7 specifically as a regulator of transcription. We will discuss mechanisms of regulation of cell cycle-related genes by E7 as well as genes involved in immune regulation, growth factor signaling, DNA damage responses, microRNAs, and others pathways. We will also discuss some unanswered questions about how transcriptional regulation by E7 impacts the biology of HPV in both benign and malignant conditions.

The loss of ATP2C1 impairs the DNA damage response and induces altered skin homeostasis: Consequences for epidermal biology in Hailey-Hailey disease

Mutation of the Golgi Ca(2+)-ATPase ATP2C1 is associated with deregulated calcium homeostasis and altered skin function. ATP2C1 mutations have been identified as having a causative role in Hailey-Hailey disease, an autosomal-dominant skin disorder. Here, we identified ATP2C1 as a crucial regulator of epidermal homeostasis through the regulation of oxidative stress. Upon ATP2C1 inactivation, oxidative stress and Notch1 activation were increased in cultured human keratinocytes. Using RNA-seq experiments, we found that the DNA damage response (DDR) was consistently down-regulated in keratinocytes derived from the lesions of patients with Hailey-Hailey disease. Although oxidative stress activates the DDR, ATP2C1 inactivation down-regulates DDR gene expression. We showed that the DDR response was a major target of oxidative stress-induced Notch1 activation. Here, we show that this activation is functionally important because early Notch1 activation in keratinocytes induces keratinocyte differentiation and represses the DDR. These results indicate that an ATP2C1/NOTCH1 axis might be critical for keratinocyte function and cutaneous homeostasis, suggesting a plausible model for the pathological features of Hailey-Hailey disease.

The homeoprotein DLX3 and tumor suppressor p53 co-regulate cell cycle progression and squamous tumor growth

Epidermal homeostasis depends on the coordinated control of keratinocyte cell cycle. Differentiation and the alteration of this balance can result in neoplastic development. Here we report on a novel DLX3-dependent network that constrains epidermal hyperplasia and squamous tumorigenesis. By integrating genetic and transcriptomic approaches, we demonstrate that DLX3 operates through a p53-regulated network. DLX3 and p53 physically interact on the p21 promoter to enhance p21 expression. Elevating DLX3 in keratinocytes produces a G1-S blockade associated with p53 signature transcriptional profiles. In contrast, DLX3 loss promotes a mitogenic phenotype associated with constitutive activation of ERK. DLX3 expression is lost in human skin cancers and is extinguished during progression of experimentally induced mouse squamous cell carcinoma (SCC). Reinstatement of DLX3 function is sufficient to attenuate the migration of SCC cells, leading to decreased wound closure. Our data establish the DLX3-p53 interplay as a major regulatory axis in epidermal differentiation and suggest that DLX3 is a modulator of skin carcinogenesis.

When bigger is better: the role of polyploidy in organogenesis

Defining how organ size is regulated, a process controlled not only by the number of cells but also by the size of the cells, is a frontier in developmental biology. Large cells are produced by increasing DNA content or ploidy, a developmental strategy employed throughout the plant and animal kingdoms. The widespread use of polyploidy during cell differentiation makes it important to define how this hypertrophy contributes to organogenesis. I discuss here examples from a variety of animals and plants in which polyploidy controls organ size, the size and function of specific tissues within an organ, or the differentiated properties of cells. In addition, I highlight how polyploidy functions in wound healing and tissue regeneration.

Krüppel-like factors 4 and 5 expression and their involvement in differentiation of oral carcinomas

Proliferation-differentiation balance of epithelial cells is regulated by Krüppel-like factors (KLF) 4 and 5, and the unbalanced expression relates to carcinoma progression. However, little is known about the expression and role in oral carcinomas. This study examined expression of KLF4 and KLF 5 in the carcinomas by immunohistochemistry (n = 67) and the involvement in proliferation and differentiation of carcinoma cells. KLF4 was detected in keratinizing carcinoma cells and KLF5 in non-keratinizing cells. KLF4 staining declined in the patient with lymph node metastasis (P < 0.05) and in parallel with the histological dedifferentiation (P = 0.09). Exogenous overexpression of KLF4 arranged cells in a cobble-like structure with desmosomes and KLF5 elongated cells like fibroblasts without desmosomes. KLF4 suppressed fibronectin expression, and KLF5 down-regulated and degraded E-cadherin. The proliferation was not affected by KLFs. Thus, down-regulation of KLF4 and up-regulation of KLF5 may stimulate oral carcinoma progression through the dedifferentiation of carcinoma cells.

The functional sites of miRNAs and lncRNAs in gastric carcinogenesis

Gastric cancer is one of the most common malignant diseases and has one of the highest mortality rates worldwide. Its molecular mechanisms are poorly understood. Recently, the functions of non-coding RNAs (ncRNAs) in gastric cancer have attracted wide attention. Although the expression levels of various ncRNAs are different, they may work together in a network and contribute to gastric carcinogenesis by altering the expression of oncogenes or tumor suppressor genes. They affect the cell cycle, apoptosis, motility, invasion, and metastasis. Dysregulated microRNAs (miRNAs) and long non-coding RNAs (lncRNAs), including miR-21, miR-106, H19, and ANRIL, directly or indirectly regulate carcinogenic factors or signaling pathways such as PTEN, CDK, caspase, E-cadherin, Akt, and P53. Greater recognition of the roles of miRNAs and lncRNAs in gastric carcinogenesis can provide new insight into the mechanisms of tumor development and identify targets for anticancer drug development.

Knockdown of HMGB1 improves apoptosis and suppresses proliferation and invasion of glioma cells

BACKGROUND

The purposes of this study were to explore the effects of high mobility group protein box 1 (HMGB1) gene on the growth, proliferation, apoptosis, invasion, and metastasis of glioma cells, with an attempt to provide potential therapeutic targets for the treatment of glioma.

METHODS

The expressions of HMGB1 in glioma cells (U251, U-87MG and LN-18) and one control cell line (SVG p12) were detected by real time PCR and Western blotting, respectively. Then, the effects of HMGB1 on the biological behaviors of glioma cells were detected: the expression of HMGB1 in human glioma cell lines U251 and U-87MG were suppressed using RNAi technique, then the influences of HMGB1 on the viability, cycle, apoptosis, and invasion abilities of U251 and U-87MG cells were analyzed using in a Transwell invasion chamber. Also, the effects of HMGB1 on the expressions of cyclin D1, Bax, Bcl-2, and MMP 9 were detected.

RESULTS

As shown by real-time PCR and Western blotting, the expression of HMGB1 significantly increased in glioma cells (U251, U-87MG, and LN-18) in comparison with the control cell line (SVG p12); the vitality, proliferation and invasive capabilities of U251 and U-87MG cells in the HMGB1 siRNA-transfected group were significantly lower than those in the blank control group and negative control (NC) siRNA group (P<0.05) but showed no significant difference between the blank control group and NC siRNA group. The percentage of apoptotic U251 and U-87MG cells was significantly higher in the HMGB1 siRNA-transfected group than in the blank control group and NC siRNA group (P<0.05) but was similar between the latter two groups. The HMGB1 siRNA-transfected group had significantly lower expression levels of Cyclin D1, Bcl-2, and MMP-9 protein in U251 and U-87MG cells and significantly higher expression of Bax protein than in the blank control group and NC siRNA group (P<0.05); the expression profiles of cyclin D1, Bax, Bcl-2, and MMP 9 showed no significant change in both blank control group and NC siRNA group.

CONCLUSIONS

HMGB1 gene may promote the proliferation and migration of glioma cells and suppress its effects of apoptosis. Inhibition of the expression of HMGB1 gene can suppress the proliferation and migration of glioma cells and promote their apoptosis. Our observations provided a new target for intervention and treatment of glioma.

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.

Somatotropinomas, but not nonfunctioning pituitary adenomas, maintain a functional apoptotic RET/Pit1/ARF/p53 pathway that is blocked by excess GDNF

Acromegaly is caused by somatotroph cell adenomas (somatotropinomas [ACROs]), which secrete GH. Human and rodent somatotroph cells express the RET receptor. In rodents, when normal somatotrophs are deprived of the RET ligand, GDNF (Glial Cell Derived Neurotrophic Factor), RET is processed intracellularly to induce overexpression of Pit1 [Transcription factor (gene : POUF1) essential for transcription of Pituitary hormones GH, PRL and TSHb], which in turn leads to p19Arf/p53-dependent apoptosis. Our purpose was to ascertain whether human ACROs maintain the RET/Pit1/p14ARF/p53/apoptosis pathway, relative to nonfunctioning pituitary adenomas (NFPAs). Apoptosis in the absence and presence of GDNF was studied in primary cultures of 8 ACROs and 3 NFPAs. Parallel protein extracts were analyzed for expression of RET, Pit1, p19Arf, p53, and phospho-Akt. When GDNF deprived, ACRO cells, but not NFPAs, presented marked level of apoptosis that was prevented in the presence of GDNF. Apoptosis was accompanied by RET processing, Pit1 accumulation, and p14ARF and p53 induction. GDNF prevented all these effects via activation of phospho-AKT. Overexpression of human Pit1 (hPit1) directly induced p19Arf/p53 and apoptosis in a pituitary cell line. Using in silico studies, 2 CCAAT/enhancer binding protein alpha (cEBPα) consensus-binding sites were found to be 100% conserved in mouse, rat, and hPit1 promoters. Deletion of 1 cEBPα site prevented the RET-induced increase in hPit1 promoter expression. TaqMan qRT-PCR (real time RT-PCR) for RET, Pit1, Arf, TP53, GDNF, steroidogenic factor 1, and GH was performed in RNA from whole ACRO and NFPA tumors. ACRO but not NFPA adenomas express RET and Pit1. GDNF expression in the tumors was positively correlated with RET and negatively correlated with p53. In conclusion, ACROs maintain an active RET/Pit1/p14Arf/p53/apoptosis pathway that is inhibited by GDNF. Disruption of GDNF's survival function might constitute a new therapeutic route in acromegaly.

Endocycles: a recurrent evolutionary innovation for post-mitotic cell growth

In endoreplication cell cycles, known as endocycles, cells successively replicate their genomes without segregating chromosomes during mitosis and thereby become polyploid. Such cycles, for which there are many variants, are widespread in protozoa, plants and animals. Endocycling cells can achieve ploidies of >200,000 C (chromatin-value); this increase in genomic DNA content allows a higher genomic output, which can facilitate the construction of very large cells or enhance macromolecular secretion. These cells execute normal S phases, using a G1-S regulatory apparatus similar to the one used by mitotic cells, but their capability to segregate chromosomes has been suppressed, typically by downregulation of mitotic cyclin-dependent kinase activity. Endocycles probably evolved many times, and the various endocycle mechanisms found in nature highlight the versatility of the cell cycle control machinery.

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.

Disruption of prostate epithelial differentiation pathways and prostate cancer development

One of the foremost problems in the prostate cancer (PCa) field is the inability to distinguish aggressive from indolent disease, which leads to difficult prognoses and thousands of unnecessary surgeries. This limitation stems from the fact that the mechanisms of tumorigenesis in the prostate are poorly understood. Some genetic alterations are commonly reported in prostate tumors, including upregulation of Myc, fusion of Ets genes to androgen-regulated promoters, and loss of Pten. However, the specific roles of these aberrations in tumor initiation and progression are poorly understood. Likewise, the cell of origin for PCa remains controversial and may be linked to the aggressive potential of the tumor. One important clue is that prostate tumors co-express basal and luminal protein markers that are restricted to their distinct cell types in normal tissue. Prostate epithelium contains layer-specific stem cells as well as rare bipotent cells, which can differentiate into basal or luminal cells. We hypothesize that the primary oncogenic cell of origin is a transient-differentiating bipotent cell. Such a cell must maintain tight temporal and spatial control of differentiation pathways, thus increasing its susceptibility for oncogenic disruption. In support of this hypothesis, many of the pathways known to be involved in prostate differentiation can be linked to genes commonly altered in PCa. In this article, we review what is known about important differentiation pathways (Myc, p38MAPK, Notch, PI3K/Pten) in the prostate and how their misregulation could lead to oncogenesis. Better understanding of normal differentiation will offer new insights into tumor initiation and may help explain the functional significance of common genetic alterations seen in PCa. Additionally, this understanding could lead to new methods for classifying prostate tumors based on their differentiation status and may aid in identifying more aggressive tumors.

Differential expression of fatty acid-binding proteins and pathological implications in the progression of tongue carcinoma

Tongue carcinomas are common malignancies of the oral cavity. Understanding the molecular mechanisms behind the disease progression is a prerequisite for improving patient prognosis. Fatty acid-binding proteins (FABPs) are cytoplasmic lipid chaperones that affect cellular organization and energy production. Although their aberrant expression is involved in carcinoma progression, its role in the pathology of tongue carcinomas remains unclear. In the present study, the immunohistochemical expression of FABP4 and FABP5 in tongue carcinomas (n=58) and its involvement in the clinicopathological parameters were examined. Normal tongue epithelial cells expressed FABP5, an epidermal-type FABP, but not FABP4, an adipocyte-type FABP. The cytoplasmic staining of FABP5 was increased in carcinomas with advanced T-stage (P<0.05) and clinical stage (P<0.05). Ectopic expression of FABP4 was detected in almost all carcinomas, although its role in disease progression remains undetermined. Upregulation of FABP5 in the wounded skin of genetically normal mice indicated that microenvironmental tissue factors induce FABP5 expression. The results of the present study demonstrated the aberrant expression of FABP4 and FABP5 in tongue carcinomas and suggested the involvement of FABP5 in disease progression.

Progesterone signaling inhibits cervical carcinogenesis in mice

Human papillomavirus is the main cause of cervical cancer, yet other nonviral cofactors are also required for the disease. The uterine cervix is a hormone-responsive tissue, and female hormones have been implicated in cervical carcinogenesis. A transgenic mouse model expressing human papillomavirus oncogenes E6 and/or E7 has proven useful to study a mechanism of hormone actions in the context of this common malignancy. Estrogen and estrogen receptor α are required for the development of cervical cancer in this mouse model. Estrogen receptor α is known to up-regulate expression of the progesterone receptor, which, on activation by its ligands, either promotes or inhibits carcinogenesis, depending on the tissue context. Here, we report that progesterone receptor inhibits cervical and vaginal epithelial cell proliferation in a ligand-dependent manner. We also report that synthetic progestin medroxyprogesterone acetate promotes regression of cancers and precancerous lesions in the female lower reproductive tracts (ie, cervix and vagina) in the human papillomavirus transgenic mouse model. Our results provide the first experimental evidence that supports the hypothesis that progesterone signaling is inhibitory for cervical carcinogenesis in vivo.