The ink4a/arf tumor suppressors cooperate with p21cip1/waf in the processes of mouse epidermal differentiation, senescence, and carcinogenesis

Irreversible cell cycle exit associated with senescence is mediated by constitutive MYC degradation

Cells can irreversibly exit the cell cycle and become senescent to safeguard against uncontrolled proliferation. While the p53-p21 and p16-Rb pathways are thought to mediate senescence, they also mediate reversible cell cycle arrest (quiescence), raising the question of whether senescence is actually reversible or whether alternative mechanisms underly the irreversibility associated with senescence. Here, we show that senescence is irreversible and that commitment to and maintenance of senescence are mediated by irreversible MYC degradation. Senescent cells start dividing when a non-degradable MYC mutant is expressed, and quiescent cells convert to senescence when MYC is knocked down. In early oral carcinogenesis, epithelial cells exhibit MYC loss and become senescent as a safeguard against malignant transformation. Later stages of oral premalignant lesions exhibit elevated MYC levels and cellular dysplasia. Thus, irreversible cell cycle exit associated with senescence is mediated by constitutive MYC degradation, but bypassing this degradation may allow tumor cells to escape during cancer initiation.

Transient Receptor Potential Melastatin 8, a sensor of cold temperatures mediates expression of cyclin-dependent kinase inhibitor, p21/Cip1, a regulator of epidermal cell proliferation

Transient Receptor Potential Melastatin 8 (TRPM8) is a calcium-permeable, non-selective cation channel of the transient receptor potential superfamily, required for the transduction of moderate cold temperatures. TRPM8 is also known to regulate proliferation of prostate, pancreatic, breast, and melanoma carcinoma cells. Here, we examined a key factor in the regulation of TRPM8-mediated proliferation of epidermal cells, which are directly affected by cold temperatures. Experiments involving knockdown and ectopic expression of TRPM8 in normal keratinocyte HaCaT and squamous carcinoma SAS cells suggest that TRPM8 inhibits cell proliferation by upregulating the expression of cyclin-dependent inhibitor p21/Cip1. Whereas these findings were observed in the absence of an endogenous agonists, additions of the synthetic TRPM8 agonist icilin reduced DNA synthesis in HaCaT cells but stimulated that in SAS cells by altering p21/Cip1 levels in a TRPM8-independent manner, indicating that icilin poses a risk of stimulating carcinoma cell proliferation. Unexpectedly, the TRPM8 blocker, used for the treatment of overactive bladder and bladder pain, N-(3-aminopropyl)-2-{[(3-methylphenyl) methyl] oxy}-N-(2-thienylmethyl) benzamide hydrochloride salt (AMTB) reduced DNA synthesis by upregulating p21/Cip1 expression. However, another TRPM8 blocker, N-(4-Tertiarybutylphenyl)-4-(3-chloropyridin- 2-yl) tetrahydropyrazine-1 (2H)-carbox-amide (BCTC), stimulated DNA synthesis by downregulating p21/Cip1 expression, indicating that it may pose a risk of carcinogenesis associated with dysregulated cell cycles when used to treat overactive bladder and bladder pain.

The Simplest Protocol for Rapid and Long-Term Culture of Primary Epidermal Keratinocytes from Human and Mouse

Although mouse models have been used as an essential tool for studying the physiology and diseases of the skin, propagation of mouse primary epidermal keratinocytes remains challenging. In this chapter, we introduce the simplest, at least to our knowledge, protocol that enables long-term expansion of p63⁺ mouse epidermal keratinocytes in low Ca²⁺ media without the need of progenitor cell-purification steps or support by a feeder cell layer. Pharmacological inhibition of TGF-β signaling in crude preparations of mouse epidermis robustly increases proliferative capacity of p63⁺ epidermal progenitor cells, while preserving their ability to differentiate. Suppression of TGF-β signaling also permits p63⁺ epidermal keratinocytes to form macroscopically large clones in 3T3-J2 feeder cell co-culture. Suppression of TGF-β signaling also enhances the clonal growth of human keratinocytes in co-culture with a variety of feeder cells. This simple and efficient approach will not only facilitate the use of mouse models by providing p63⁺ primary epidermal keratinocytes in quantity but also significantly reduce the time needed for preparing the customized skin grafts in Green method.

Defined factors to reactivate cell cycle activity in adult mouse cardiomyocytes

Adult mammalian cardiomyocytes exit the cell cycle during the neonatal period, commensurate with the loss of regenerative capacity in adult mammalian hearts. We established conditions for long-term culture of adult mouse cardiomyocytes that are genetically labeled with fluorescence. This technique permits reliable analyses of proliferation of pre-existing cardiomyocytes without complications from cardiomyocyte marker expression loss due to dedifferentiation or significant contribution from cardiac progenitor cell expansion and differentiation in culture. Using this system, we took a candidate gene approach to screen for fetal-specific proliferative gene programs that can induce proliferation of adult mouse cardiomyocytes. Using pooled gene delivery and subtractive gene elimination, we identified a novel functional interaction between E2f Transcription Factor 2 (E2f2) and Brain Expressed X-Linked (Bex)/Transcription elongation factor A-like (Tceal) superfamily members Bex1 and Tceal8. Specifically, Bex1 and Tceal8 both preserved cell viability during E2f2-induced cell cycle re-entry. Although Tceal8 inhibited E2f2-induced S-phase re-entry, Bex1 facilitated DNA synthesis while inhibiting cell death. In sum, our study provides a valuable method for adult cardiomyocyte proliferation research and suggests that Bex family proteins may function in modulating cell proliferation and death decisions during cardiomyocyte development and maturation.

Long-Term Expansion of Mouse Primary Epidermal Keratinocytes Using a TGF-β Signaling Inhibitor

Mouse models have been used to study the physiology and pathogenesis of the skin. However, propagation of mouse primary epidermal keratinocytes remains challenging. In this chapter, we introduce a newly developed protocol that enables long-term expansion of p63⁺ mouse epidermal keratinocytes in low-Ca²⁺ media without the need of progenitor cell purification steps or support by a feeder cell layer. Pharmacological inhibition of TGF-β signaling in crude preparations of mouse epidermis robustly increases proliferative capacity of p63⁺ epidermal progenitor cells while preserving their ability to differentiate. Suppression of TGF-β signaling also permits p63⁺ epidermal keratinocytes to form macroscopically large clones in 3T3-J2 feeder cell co-culture. This simple and efficient approach will facilitate the use of mouse models by providing p63⁺ primary epidermal keratinocytes in quantity.

Inhibition of TGF-β signaling supports high proliferative potential of diverse p63+ mouse epithelial progenitor cells in vitro

Mouse models have been used to provide primary cells to study physiology and pathogenesis of epithelia. However, highly efficient simple approaches to propagate mouse primary epithelial cells remain challenging. Here, we show that pharmacological inhibition of TGF-β signaling enables long-term expansion of p63⁺ epithelial progenitor cells in low Ca²⁺ media without the need of progenitor cell-purification steps or support by a feeder cell layer. We find that TGF-β signaling is operative in mouse primary keratinocytes in conventional cultures as determined by the nuclear Smad2/3 localization. Accordingly, TGF-β signaling inhibition in crude preparations of mouse epidermis robustly increases proliferative capacity of p63⁺ epidermal progenitor cells, while preserving their ability of differentiation in response to Ca²⁺ stimulation. Notably, inhibition of TGF-β signaling also enriches and expands other p63⁺ epithelial progenitor cells in primary crude cultures of multiple epithelia, including the cornea, oral and lingual epithelia, salivary gland, esophagus, thymus, and bladder. We anticipate that this simple and efficient approach will facilitate the use of mouse models for studying a wide range of epithelia by providing highly enriched populations of diverse p63⁺ epithelial progenitor cells in quantity.

Cellular senescence impact on immune cell fate and function

Cellular senescence occurs not only in cultured fibroblasts, but also in undifferentiated and specialized cells from various tissues of all ages, in vitro and in vivo. Here, we review recent findings on the role of cellular senescence in immune cell fate decisions in macrophage polarization, natural killer cell phenotype, and following T-lymphocyte activation. We also introduce the involvement of the onset of cellular senescence in some immune responses including T-helper lymphocyte-dependent tissue homeostatic functions and T-regulatory cell-dependent suppressive mechanisms. Altogether, these data propose that cellular senescence plays a wide-reaching role as a homeostatic orchestrator.

Development of oral epithelial cell line ROE2 with differentiation potential from transgenic rats harboring temperature-sensitive simian virus40 large T-antigen gene

We have developed an immortalized oral epithelial cell line, ROE2, from fetal transgenic rats harboring temperature-sensitive simian virus 40 large T-antigen gene. The cells grew continuously at either a permissive temperature of 33°C or an intermediate temperature of 37°C. At the nonpermissive temperature of 39°C, on the other hand, growth decreased significantly, and the Sub-G1 phase of the cell cycle increased, indicating that the cells undergo apoptosis at a nonpermissive temperature. Histological and immunocytochemical analyses revealed that ROE2 cells at 37°C had a stratified epithelial-like morphology and expressed cytokeratins Krt4 and Krt13, marker proteins for oral nonkeratinized epithelial cells. Global-scale comprehensive microarray analysis, coupled with bioinformatics tools, demonstrated a significant gene network that was obtained from the upregulated genes. The gene network contained 16 genes, including Cdkn1a, Fos, Krt13, and Prdm1, and was associated mainly with the biological process of skin development in the category of biological functions, organ development. These four genes were validated by quantitative real-time polymerase chain reaction, and the results were nearly consistent with the microarray data. It is therefore anticipated that this cell line will be useful as an in vitro model for studies such as physiological functions, as well as for gene expression in oral epithelial cells.

p16INK4a and its regulator miR-24 link senescence and chondrocyte terminal differentiation-associated matrix remodeling in osteoarthritis

INTRODUCTION

Recent evidence suggests that tissue accumulation of senescent p16INK4a-positive cells during the life span would be deleterious for tissue functions and could be the consequence of inherent age-associated disorders. Osteoarthritis (OA) is characterized by the accumulation of chondrocytes expressing p16INK4a and markers of the senescence-associated secretory phenotype (SASP), including the matrix remodeling metalloproteases MMP1/MMP13 and pro-inflammatory cytokines interleukin-8 (IL-8) and IL-6. Here, we evaluated the role of p16INK4a in the OA-induced SASP and its regulation by microRNAs (miRs).

METHODS

We used IL-1-beta-treated primary OA chondrocytes cultured in three-dimensional setting or mesenchymal stem cells differentiated into chondrocyte to follow p16INK4a expression. By transient transfection experiments and the use of knockout mice, we validate p16INK4a function in chondrocytes and its regulation by one miR identified by means of a genome-wide miR-array analysis.

RESULTS

p16INK4a is induced upon IL-1-beta treatment and also during in vitro chondrogenesis. In the mouse model, Ink4a locus favors in vivo the proportion of terminally differentiated chondrocytes. When overexpressed in chondrocytes, p16INK4a is sufficient to induce the production of the two matrix remodeling enzymes, MMP1 and MMP13, thus linking senescence with OA pathogenesis and bone development. We identified miR-24 as a negative regulator of p16INK4a. Accordingly, p16INK4a expression increased while miR-24 level was repressed upon IL-1-beta addition, in OA cartilage and during in vitro terminal chondrogenesis.

CONCLUSIONS

We disclosed herein a new role of the senescence marker p16INK4a and its regulation by miR-24 during OA and terminal chondrogenesis.

Skin Tumors Rb(eing) Uncovered

The Rb1 gene was the first bona fide tumor suppressor identified and cloned more than 25 years ago. Since then, a plethora of studies have revealed the functions of pRb and the existence of a sophisticated and strictly regulated pathway that modulates such functional roles. An emerging paradox affecting Rb1 in cancer connects the relatively low number of mutations affecting Rb1 gene in specific human tumors, compared with the widely functional inactivation of pRb in most, if not in all, human cancers. The existence of a retinoblastoma family of proteins pRb, p107, and p130 and their potential unique and overlapping functions as master regulators of cell cycle progression and transcriptional modulation by similar processes, may provide potential clues to explain such conundrum. Here, we will review the development of different genetically engineered mouse models, in particular those affecting stratified epithelia, and how they have offered new avenues to understand the roles of the Rb family members and their targets in the context of tumor development and progression.

p21 suppresses inflammation and tumorigenesis on pRB-deficient stratified epithelia

The retinoblastoma gene product (pRb) controls proliferation and differentiation processes in stratified epithelia. Importantly, and in contrast to other tissues, Rb deficiency does not lead to spontaneous skin tumor formation. As the cyclin-dependent kinase inhibitor p21 regulates proliferation and differentiation in the absence of pRb, we analyzed the consequences of deleting p21 in pRb-ablated stratified epithelia (hereafter pRb(ΔEpi);p21-/-). These mice display an enhancement of the phenotypic abnormalities observed in pRb(ΔEpi) animals, indicating that p21 partially compensates pRb absence. Remarkably, pRb(ΔEpi);p21-/- mice show an acute skin inflammatory phenotype and develop spontaneous epithelial tumors, particularly affecting tongue and oral tissues. Biochemical analyses and transcriptome studies reveal changes affecting multiple pathways, including DNA damage and p53-dependent signaling responses. Comparative metagenomic analyses, together with the histopathological profiles, indicate that these mice constitute a faithful model for human head and neck squamous cell carcinomas. Collectively, our findings demonstrate that p21, in conjunction with pRb, has a central role in regulating multiple epithelial processes and orchestrating specific tumor suppressor functions.

p21WAF1 and tumourigenesis: 20 years after

PURPOSE OF REVIEW

This review provides an overview of the structure, regulation and physiological functions of p21, the product of the cyclin-dependent kinase inhibitor 1A (CDKN1A) gene, with a focus on its dual role in promoting and repressing biological processes that are hallmarks of tumourigenesis.

RECENT FINDINGS

Recent work has provided a better understanding of the molecular mechanisms of how oncogenic signalling pathways influence p21 expression. In response to cellular stimuli, p21 expression is tightly regulated at transcriptional and post-translational levels through mechanisms involving RNA stabilization, phosphorylation and ubiquitination. As a result, growing evidence reveals that several important tumour suppressor and oncogenic signalling pathways alter p21 expression to elicit their effects on cell cycle progression and survival. Thus, p21 expression can both promote and inhibit tumourigenic processes, depending on the cellular context.

SUMMARY

Since its discovery, it has become increasingly clear that p21 can function as both a classical tumour suppressor and an oncogene. In order to effectively utilize p21 as a therapeutic target, it will be necessary to design therapeutic strategies that preferentially block the ability of p21 to promote senescence, stem cell renewal and cyclin/CDK activation, while leaving its tumour suppressive functions intact.

p21, an important mediator of quiescence during pituitary tumor formation, is dispensable for normal pituitary development during embryogenesis

A delicate balance between proliferation and differentiation must be maintained in the developing pituitary to ensure the formation of the appropriate number of hormone producing cells. In the adult, proliferation is actively restrained to prevent tumor formation. The cyclin dependent kinase inhibitors (CDKIs) of the CIP/KIP family, p21, p27 and p57, mediate cell cycle inhibition. Although p21 is induced in the pituitary upon loss of Notch signaling or initiation of tumor formation to halt cell cycle progression, its role in normal pituitary organogenesis has not been explored. In wildtype pituitaries, expression of p21 is limited to a subset of cells embryonically as well as during the postnatal proliferative phase. Mice lacking p21 do not have altered cell proliferation during early embryogenesis, but do show a slight delay in separation of proliferating progenitors from the oral ectoderm. By embryonic day 16.5, p21 mutants have an alteration in the spatial distribution of proliferating pituitary progenitors, however there is no overall change in proliferation. At postnatal day 21, there appears to be no change in proliferation, as assessed by cells expressing Ki67 protein. However, p21 mutant pituitaries have significantly less mRNA of Myc and the cyclins Ccnb1, Ccnd1, Ccnd2 and Ccne1 than wildtype pituitaries. Interestingly, unlike the redundant role in cell cycle inhibition uncovered in p27/p57 double mutants, the pituitary of p21/p27 double mutants has a similar proliferation profile to p27 single mutants at the time points examined. Taken together, these studies demonstrate that unlike p27 or p57, p21 does not play a major role in control of progenitor proliferation in the developing pituitary. However, p21 may be required to maintain normal levels of cell cycle components.

A functional role of RB-dependent pathway in the control of quiescence in adult epidermal stem cells revealed by genomic profiling

Continuous cell renewal in mouse epidermis is at the expense of a pool of pluripotent cells that lie in a well defined niche in the hair follicle known as the bulge. To identify mechanisms controlling hair follicle stem cell homeostasis, we developed a strategy to isolate adult bulge stem cells in mice and to define their transcriptional profile. We observed that a large number of transcripts are underexpressed in hair follicle stem cells when compared to non-stem cells. Importantly, the majority of these downregulated genes are involved in cell cycle. Using bioinformatics tools, we identified the E2F transcription factor family as a potential element involved in the regulation of these transcripts. To determine their functional role, we used engineered mice lacking Rb gene in epidermis, which showed increased expression of most E2F family members and increased E2F transcriptional activity. Experiments designed to analyze epidermal stem cell functionality (i.e.: hair regrowth and wound healing) imply a role of the Rb-E2F axis in the control of stem cell quiescence in epidermis.

Transcriptome profiles of carcinoma-in-situ and invasive non-small cell lung cancer as revealed by SAGE

Background

Non-small cell lung cancer (NSCLC) presents as a progressive disease spanning precancerous, preinvasive, locally invasive, and metastatic lesions. Identification of biological pathways reflective of these progressive stages, and aberrantly expressed genes associated with these pathways, would conceivably enhance therapeutic approaches to this devastating disease.

Methodology/Principal Findings

Through the construction and analysis of SAGE libraries, we have determined transcriptome profiles for preinvasive carcinoma-in-situ (CIS) and invasive squamous cell carcinoma (SCC) of the lung, and compared these with expression profiles generated from both bronchial epithelium, and precancerous metaplastic and dysplastic lesions using Ingenuity Pathway Analysis. Expression of genes associated with epidermal development, and loss of expression of genes associated with mucociliary biology, are predominant features of CIS, largely shared with precancerous lesions. Additionally, expression of genes associated with xenobiotic metabolism/detoxification is a notable feature of CIS, and is largely maintained in invasive cancer. Genes related to tissue fibrosis and acute phase immune response are characteristic of the invasive SCC phenotype. Moreover, the data presented here suggests that tissue remodeling/fibrosis is initiated at the early stages of CIS. Additionally, this study indicates that alteration in copy-number status represents a plausible mechanism for differential gene expression in CIS and invasive SCC.

Conclusions/Significance

This study is the first report of large-scale expression profiling of CIS of the lung. Unbiased expression profiling of these preinvasive and invasive lesions provides a platform for further investigations into the molecular genetic events relevant to early stages of squamous NSCLC development. Additionally, up-regulated genes detected at extreme differences between CIS and invasive cancer may have potential to serve as biomarkers for early detection.

Susceptibility of pRb-deficient epidermis to chemical skin carcinogenesis is dependent on the p107 allele dosage

Functional inactivation of the pRb-dependent pathway is a general feature of human cancer. However, only a reduced spectrum of tumors displays inactivation of the Rb gene. This can be attributed, at least partially, to the possible overlapping functions carried out by the related retinoblastoma family members p107 and p130. We observed that loss of pRb in epidermis, using the Cre/LoxP technology, results in proliferation and differentiation defects. These alterations are partially compensated by the elevation in the levels of p107. Moreover, epidermis lacking pRb and p107, but not pRb alone, develops spontaneous tumors, and double deficient primary keratinocytes are highly susceptible to Ha-ras-induced transformation. Two-stage chemical carcinogenesis experiments in mice lacking pRb in epidermis revealed a reduced susceptibility in papilloma formation and an increase in the malignant conversion. We have now explored whether the loss of one p107 allele, inducing a decrease in the levels of p107 up to normal levels could restore the susceptibility of pRb-deficient skin to two-stage protocol. We observed partial restoration in the incidence, number, and size of tumors. However, there is no increased malignancy despite sustained p53 activation. We also observed a partial reduction in the levels of proapoptotic proteins in benign papillomas. These data confirm our previous suggestions on the role of p107 as a tumor suppressor in epidermis in the absence of pRb.

p107 acts as a tumor suppressor in pRb-deficient epidermis

The specific deletion of Rb gene in epidermis leads to altered proliferation and differentiation, but not to the development of spontaneous tumors. Our previous data have demonstrated the existence of a functional compensation of Rb loss by Rbl1 (p107) in as the phenotypic differences with respect to controls are intensified. However, the possible evolution of this aggravated phenotype, in particular in relationship with tumorigenesis, has not been evaluated due to the premature death of the double deficient mice. We have now investigated whether p107 can also act as a tumor suppressor in pRb-deficient epidermis using different experimental approaches. We found spontaneous tumor development in doubly-deficient skin grafts. Moreover, Rb-deficient keratinocytes are susceptible to Ha-ras-induced transformation, and this susceptibility is enhanced by p107 loss. Further functional analyses, including microarray gene expression profiling, indicated that the loss of p107, in the absence of pRb, produces the reduction of p53-dependent pro-apoptotic signals. Overall, our data demonstrate that p107 behaves as a tumor suppressor in epidermis in the absence of pRb and suggest novel tumor-suppressive roles for p107 in the context of functional p53 and activated Ras.

HIF-1alpha controls keratinocyte proliferation by up-regulating p21(WAF1/Cip1)

The cyclin-dependent kinase inhibitor p21(WAF1/Cip1) plays a central role in a spatial and temporal balance of epidermal keratinocyte proliferation and growth arrest. However, what controls p21 expression in keratinocytes remains uncertain. Hypoxia-inducible factor 1alpha (HIF-1alpha) does not only express a variety of genes essential for hypoxic adaptation, but also up-regulates p21 so as to slow down cell cycle under hypoxic conditions. In the present study, we examined the role of HIF-1alpha in p21-mediated growth arrest of keratinocyte. Keratinocyte proliferation was arrested in the G1 phase at a high cell density. p21 was also up-regulated in a cell density-dependent manner and was found to be highly expressed in epidermal keratinocytes of normal human skins. In addition, in the same specimens and cells, we noted robust HIF-1alpha expression. HIF-1alpha siRNAs inhibited p21 expression and released the G1 arrest. In vivo, moreover, the intradermal injection of HIF-1alpha siRNA attenuated p21 expression in rat epidermis and induced skin hyperplasia. Mechanistically, we propose that the production of mitochondrial reactive oxygen species and the activation of the MEK/ERK pathway are involved in the HIF-1alpha stabilization in keratinocytes. These results imply that HIF-1alpha functions as an up-stream player in the p21-mediated growth arrest of keratinocytes.

E2F1 suppresses skin carcinogenesis via the ARF-p53 pathway

The E2F1 transcription factor, which is deregulated in most human cancers by mutations in the p16-cyclin D-Rb pathway, has both oncogenic and tumor-suppressive properties. This is dramatically illustrated by the phenotype of an E2F1 transgenic mouse model that spontaneously develops tumors in the skin and other epithelial tissues but is resistant to papilloma formation when subjected to a two-stage carcinogenesis protocol. Here, this E2F1 transgenic model was used to further explore the tumor-suppressive property of E2F1. Transgenic expression of E2F1 was found to inhibit ras-driven skin carcinogenesis at the promotion stage independent of the type of promoting agent used. E2F1 transgenic epidermis displayed increased expression of p19(ARF), p53, and p21(Cip1). Inactivation of either p53 or Arf in E2F1 transgenic mice restored sensitivity to two-stage skin carcinogenesis. While Arf inactivation impaired tumor suppression and p21 induction by E2F1, it did not reduce the level of apoptosis observed in E2F1 transgenic mice. Based on these findings, we propose that E2F1 suppresses ras-driven skin carcinogenesis through a nonapoptotic mechanism involving ARF and p53.

Unexpected roles for pRb in mouse skin carcinogenesis

The mouse skin carcinogenesis represents one of the best models for the understanding of malignant transformation, including the multistage nature of tumor development. The retinoblastoma gene product (pRb) plays a critical role in cell cycle regulation, differentiation, and inhibition of oncogenic transformation. In epidermis, Rb-/- deletion leads to proliferation and differentiation defects. Numerous evidences showed the involvement of the retinoblastoma pathway in this model. However, the actual role of pRb is still unknown. To study the possible involvement of pRb in keratinocyte malignant transformation, we have carried out two-stage chemical skin carcinogenesis on Rb(F19/F19) (thereafter Rb+/+) and Rb(F19/F19);K14Cre (thereafter Rb-/-) animals. Unexpectedly, we found that Rb-/- mice developed fewer and smaller papillomas than the Rb+/+ counterparts. Moreover, the small size of the pRb-deficient tumors is associated with an increase in the apoptotic index. Despite this, pRb-deficient tumors display an increased conversion rate to squamous cell carcinomas. Biochemical analyses revealed that these characteristics correlate with the differential expression and activity of different pathways, including E2F/p19arf/p53, PTEN/Akt, c-jun NH2-terminal kinase/p38, and nuclear factor-kappaB. Collectively, our findings show unexpected and hitherto nondescribed roles of pRb during the process of epidermal carcinogenesis.

Altered T cell differentiation and Notch signaling induced by the ectopic expression of keratin K10 in the epithelial cells of the thymus

Transgenic mice expressing hK10 under the keratin K5 promoter display several alterations in the epidermis including decreased cell proliferation, and reduced susceptibility to tumor development. Given that K5 promoter is also active in the epithelial cells of the thymus, we explored the possible alterations of the thymus because of K10 transgene expression. We found severe thymic alterations, which affect not only the thymic epithelial cells (TEC), but also thymocytes. We observed altered architecture and premature thymus involution in the transgenic mice associated with increased apoptosis and reduced proliferation of the thymocytes. Interestingly, prior to the development of this detrimental phenotype, thymocytes of the transgenic mice also displayed altered differentiation, which is aggravated later on. Molecular characterization of this phenotype indicated that Akt activity is reduced in TEC, but not in thymocytes. In addition, we also observed altered expression of Notch family members and some of their ligands both in TEC and T cells. This produces reduced Notch activity in TEC but increased Notch activity in thymocytes, which is detectable prior to the disruption of the thymic architecture. In addition, we also detect altered Notch expression in the epidermis of bK5hK10 transgenic mice. Collectively the present data indicate that keratin K10 may induce severe alterations not only in a cell autonomous manner, but also in neighboring cells by the modulation of signals involved in cell-cell interactions.

p21WAF1/Cip1 is a negative transcriptional regulator of Wnt4 expression downstream of Notch1 activation

In keratinocytes, the cyclin/CDK inhibitor p21(WAF1/Cip1) is a direct transcriptional target of Notch1 activation; loss of either the p21 or Notch1 genes expands stem cell populations and facilitates tumor development. The Notch1 tumor-suppressor function was associated with down-regulation of Wnt signaling. Here, we show that suppression of Wnt signaling by Notch1 activation is mediated, at least in part, by down-modulation of Wnts gene expression. p21 is a negative regulator of Wnts transcription downstream of Notch1 activation, independently of effects on the cell cycle. More specifically, expression of the Wnt4 gene is under negative control of endogenous p21 both in vitro and in vivo. p21 associates with the E2F-1 transcription factor at the Wnt4 promoter and causes curtailed recruitment of c-Myc and p300, and histone hypoacetylation at this promoter. Thus, p21 acts as a selective negative regulator of transcription and links the Notch and Wnt signaling pathways in keratinocyte growth control.

Genetic pathways required for epidermal morphogenesis

The epidermis is composed of keratinocytes which undergo a highly reproducible terminal differentiation program resulting in the formation of a protective barrier, which is established during embryogenesis. Significant progress has recently been made in understanding the genetic pathways associated with the earliest event characteristic of epidermal morphogenesis, commitment to stratification. This process depends on the expression of p63, a transcription factor which is transcribed into isoforms that contain (TA) or lack (AN) a transactivation domain. In the absence of p63 expression, epithelia remain single-layered, while ectopic TAp63alpha expression in single-layered epithelia initiates stratification. Later events during epidermal morphogenesis require withdrawal from the cell cycle and commitment to terminal differentiation. Some of the genetic pathways underlying these events are beginning to be elucidated, however, the exact molecular events remain to be determined. In this review, we summarize the involvement of several signaling pathways in different stages of epidermal morphogenesis.

Signalling in the epidermis: the E2F cell cycle regulatory pathway in epidermal morphogenesis, regeneration and transformation

The epidermis is the outermost layer in the skin, and it is the first line of defence against the environment. The epidermis also provides a barrier against loss of fluids and electrolytes, which is crucial for life. Essential in the maintenance of this tissue is its ability to continually self-renew and regenerate after injury. These two characteristics are critically dependent on the ability of the principal epidermal cell type, the keratinocyte, to proliferate and to respond to differentiation cues. Indeed, the epidermis is a multilayered tissue composed of keratinocyte stem cells and their differentiated progeny. Central for the control of cell proliferation is the E2F transcription factor regulatory network. This signaling network also includes cyclins, cdk, cdk inhibitors and the retinoblastoma (pRb) family of proteins. The biological importance of the E2F/pRb pathway is emphasized by the fact that a majority of human tumours exhibit alterations that disrupt the ability of pRb proteins to inhibit E2F, leading to permanent activation of the latter. Further, E2F is essential for normal epidermal regeneration after injury. Other member of the E2F signaling pathway are also involved in epidermal development and pathophysiology. Thus, whereas the pRb family of proteins is essential for epidermal morphogenesis, abnormal regulation of cyclins and E2F proteins results in tumorgenesis in this tissue. In this review, we discuss the role of each member of this important growth regulatory network in epidermal formation, homeostasis and carcinogenesis.

Growth inhibition by the tumor suppressor p33ING1 in immortalized and primary cells: involvement of two silencing domains and effect of Ras

ING1 was identified as an inhibitor of growth and has been described as a tumor suppressor. Furthermore, the expression of ING1 is induced in senescent cells and antisense ING1 extends the proliferative life span of primary human fibroblasts. Cooperation of p33ING1 with p53 has been suggested to be an important function of ING1 in cell cycle control. Intriguingly, it has been shown that p33ING1 is associated with histone acetylation as well as with histone deacetylation function. Here we show that p33ING1 is a potent transcriptional silencer in various cell types. However, the silencing function is independent of the presence of p53. By use of deletion mutants two potent autonomous and transferable silencing domains were identified, but no evidence of an activation domain was found. The amino (N)-terminal silencing domain is sensitive to the histone deacetylase inhibitor trichostatin A (TSA) whereas the carboxy-terminal silencing function is resistant to TSA, suggesting that p33ING1 confers gene silencing through both HDAC-dependent and -independent mechanisms. Interestingly, the presence of oncogenic Ras, which is able to induce premature senescence, increases the p33ING1-mediated silencing function. Moreover, ING1-mediated silencing was reduced by coexpressing dominant-negative Ras or by treatment with the mitogen-activated protein kinase inhibitor PD98059 but not by treatment with SB203580, an inhibitor of the p38 pathway. In addition, we show that both silencing domains of ING1 are involved in cell cycle control, as measured by inhibition of colony formation of immortalized cells and by thymidine incorporation of primary human diploid fibroblasts (HDF). Interestingly, p33ING1 expression induces features of cellular senescence in HDFs.

Intrinsic tumour suppression

Mutations that drive uncontrolled cell-cycle progression are requisite events in tumorigenesis. But evolution has installed in the proliferative programmes of mammalian cells a variety of innate tumour-suppressive mechanisms that trigger apoptosis or senescence, should proliferation become aberrant. These contingent processes rely on a series of sensors and transducers that act in a coordinated network to target the machinery responsible for apoptosis and cell-cycle arrest at different points. Although oncogenic mutations that disable such networks can have profound and varied effects on tumour evolution, they may leave intact latent tumour-suppressive potential that can be harnessed therapeutically.

The role of p63 in development and differentiation of the epidermis

Expression of p63, a transcription factor that is transcribed into six isoforms, is required for proper development of stratified epithelia, such as the epidermis. In the absence of p63, epithelia remain single-layered. The molecular role of p63 in development and differentiation of stratified epithelia, however, remains controversial. Based on recent studies, we now believe that p63 has a dual role and is essential for development as well as maintenance of the epidermis. During embryogenesis, p63 may be the molecular switch required for initiation of epithelial stratification. This is based on our recent data demonstrating that ectopic expression of a p63 isoform in single-layered epithelia results in the induction of a stratification program. Furthermore, in the mature epidermis, p63 may maintain the proliferative potential of basal keratinocytes. This is suggested by the observation that p63 is primarily expressed in the basal compartment of the epidermis, that p63 expression induces hyperproliferation, and that its expression needs to be downregulated for terminal differentiation to take place. In this review, we discuss recent evidence supporting this dual role for p63 and place it in the context of our increasing knowledge of epidermal development and differentiation.

The role of replicative senescence in cancer and human ageing: utility (or otherwise) of murine models

Replicative senescence has the potential both to act as an anti-tumour mechanism, and to contribute to age-related changes in tissue function. Studies on human cells have revealed much, both about the nature of cell division counters, some of which utilize the gradual erosion of chromosomal telomeres, and the downstream signalling pathways that initiate and maintain growth arrest in senescence. A powerful test of the hypothesis that senescence is linked to either ageing or tumour prevention now requires a suitable animal model system. Here we overview the current understanding of replicative senescence in human cells, and address to what extent the senescence of murine cells in culture mirrors this phenomenon. We also discuss whether examples of telomere-independent senescence, such as those seen in mouse embryonic fibroblasts (MEFs) and several human cells types, should be viewed not as a consequence of "inadequate growth conditions", but rather as a powerful potential model system to dissect the selective pressures that occur in the early stages of tumour development, ones that we speculate lead to the observed high frequency of abrogation of p16INK4a function in human cancer.

Effect of HIV-1 Vpr on cell cycle regulators

Cell cycle is one of the most complex processes in the life of a dividing cell. It involves numerous regulatory proteins, which direct the cell through a specific sequence of events for the production of two daughter cells. Cyclin-dependent kinases (cdks), which complex with the cyclin proteins, are the main players in the cell cycle. They can regulate the progression of the cells through different stages regulated by several proteins including p53, p21(WAF1), p19, p16, and cdc25. Downstream targets of cyclin-cdk complexes include pRB and E2F. A cell cycle can be altered to the advantage of many viral agents, most notably polyomaviruses, papillomaviruses, adenoviruses, and retroviruses. In addition, viral protein R (Vpr) is a protein encoded by the human immunodeficiency virus type 1 (HIV-1). HIV-1, the causative agent of acquired immunodeficiency syndrome (AIDS), is a member of the lentivirus class of retroviruses. This accessory protein plays an important role in the regulation of the cell cycle by causing G(2) arrest and affecting cell cycle regulators. Vpr prevents infected cells from proliferating, and collaborates with the matrix protein (MA) to enable HIV-1 to enter the nucleus of nondividing cells. Studies from different labs including ours showed that Vpr affects the functions of cell cycle proteins, including p53 and p21(WAF1). Thus, the replication of HIV-1, and ultimately its pathogenesis, are intrinsically tied to cell-cycle control.

Unique and overlapping functions of pRb and p107 in the control of proliferation and differentiation in epidermis

The retinoblastoma gene product, pRb, plays a crucial role in cell cycle regulation, differentiation and inhibition of oncogenic transformation. pRb and its closely related family members p107 and p130 perform exclusive and overlapping functions during mouse development. The embryonic lethality of Rb-null animals restricts the phenotypic analysis of these mice to mid-gestation embryogenesis. We employed the Cre/loxP system to study the function of Rb in adult mouse stratified epithelium. RbF19/F19;K14cre mice displayed hyperplasia and hyperkeratosis in the epidermis with increased proliferation and aberrant expression of differentiation markers. In vitro, pRb is essential for the maintainance of the postmitotic state of terminally differentiated keratinocytes, preventing cell cycle re-entry. However, p107 compensates for the effects of Rb loss as the phenotypic abnormalities of RbF19/F19;K14cre keratinocytes in vivo and in vitro become more severe with the concurrent loss of p107 alleles. p107 alone appears to be dispensable for all these phenotypic changes, as the presence of a single Rb allele in a p107-null background rescues all these alterations. Luciferase reporter experiments indicate that these phenotypic alterations might be mediated by increased E2F activity. Our findings support a model in which pRb in conjunction with p107 plays a central role in regulating epidermal homeostasis.

UCN-01-Induced Cell Cycle Arrest Requires the Transcriptional Induction of p21waf1/cip1 by Activation of Mitogen-Activated Protein/Extracellular Signal-Regulated Kinase Kinase/Extracellular Signal-Regulated Kinase Pathway

The small molecule UCN-01 is a cyclin-dependent kinase (CDK) modulator shown to have antiproliferative effects against several in vitro and in vivo cancer models currently being tested in human clinical trials. Although UCN-01 may inhibit several serine-threonine kinases, the exact mechanism by which it promotes cell cycle arrest is still unclear. We have reported previously that UCN-01 promotes G(1)-S cell cycle arrest in a battery of head and neck squamous cancer cell lines. The arrest is accompanied by an increase in both p21(waf1/cip1) and p27(kip1) CDK inhibitors leading to loss in G(1) CDK activity. In this report, we explore the role and the mechanism for the induction of these endogenous CDK inhibitors. We observed that p21 was required for the cell cycle effects of UCN-01, as HCT116 lacking p21 (HCT116 p21(-/-)) was refractory to the cell cycle effects of UCN-01. Moreover, UCN-01 promoted the accumulation of p21 at the mRNA level in the p53-deficient HaCaT cells without increase in the p21 mRNA half-life, suggesting that UCN-01 induced p21 at the transcriptional level. To study UCN-01 transcriptional activation of p21, we used several p21(waf1/cip1) promoter-driven luciferase reporter plasmids and observed that UCN-01 activated the full-length p21(waf1/cip1) promoter and a construct lacking p53 binding sites. The minimal promoter region required for UCN-01 (from -110 bp to the transcription start site) was the same minimal p21(waf1/cip1) promoter region required for Ras enhancement of p21(waf1/cip1) transcription. Neither protein kinase C nor PDK1/AKT pathways were relevant for the induction of p21 by UCN-01. In contrast, the activation of mitogen-activated protein/extracellular signal-regulated kinase kinase (MEK)/extracellular signal-regulated kinase mitogen-activated protein kinase pathways was required for p21 induction as UCN-01 activated this pathway, and genetic or chemical MEK inhibitors blunted p21 accumulation. These results demonstrated for the first time that p21 is required for UCN-01 cell cycle arrest. Moreover, we showed that the accumulation of p21 is transcriptional via activation of the MEK pathway. This novel mechanism, by which UCN-01 exerts its antiproliferative effect, represents a promising strategy to be exploited in future clinical trials.

Transcriptional Activation of p21waf1/cip1 by Alkylphospholipids

Alkylphospholipids (ALKs) are a novel class of antitumor agents with an unknown mechanism of action. The first ALK tested in the clinic, miltefosine, has been approved recently in Europe for the local treatment of patients with cutaneous metastasis. Perifosine, the only available oral ALK, is being studied currently in human cancer clinical trials. We have shown previously that perifosine induces p21(waf1/cip1) in a p53-independent fashion and that induction of p21(waf1/cip1) is required for the perifosine-induced cell cycle arrest because cell lines lacking p21(waf1/cip1) are refractory to perifosine. In this report, we investigated the mechanism by which perifosine induces p21(waf1/cip1) protein expression. We observed that perifosine induces the accumulation of p21(waf1/cip1) mRNA without affecting p21(waf1/cip1) mRNA stability. Using several p21(waf1/cip1) promoter-driven luciferase reporter plasmids, we observed that perifosine activates the 2.4-kb full-length p21(waf1/cip1) promoter as well as a p21 promoter construct lacking p53-binding sites, suggesting that perifosine activates the p21(waf1/cip1) promoter independent of p53. The minimal p21 promoter region required for perifosine-induced p21 promoter activation contains four consensus Sp1-binding sites. Mutations in each particular Sp1 site block perifosine-induced p21(waf1/cip1) expression. Moreover, we showed that perifosine activates the mitogen-activated protein/extracellular signal-regulated kinase pathway, and this activation promotes the phosphorylation of Sp1 in known mitogen-activated protein kinase residues (threonine 453 and 739), thereby leading to increased Sp1 binding and enhanced p21(waf1/cip1) transcription. These results represent a novel mechanism by which alkylphospholipids modulate transcription, and may contribute to the discovery of new signal transduction pathways crucial for normal and neoplastic cell cycle control.

Control of apoptosis by p53

The p53 tumor suppressor acts to integrate multiple stress signals into a series of diverse antiproliferative responses. One of the most important p53 functions is its ability to activate apoptosis, and disruption of this process can promote tumor progression and chemoresistance. p53 apparently promotes apoptosis through transcription-dependent and -independent mechanisms that act in concert to ensure that the cell death program proceeds efficiently. Moreover, the apoptotic activity of p53 is tightly controlled, and is influenced by a series of quantitative and qualitative events that influence the outcome of p53 activation. Interestingly, other p53 family members can also promote apoptosis, either in parallel or in concert with p53. Although incomplete, our current understanding of p53 illustrates how apoptosis can be integrated into a larger tumor suppressor network controlled by different signals, environmental factors, and cell type. Understanding this network in more detail will provide insights into cancer and other diseases, and will identify strategies to improve their therapeutic treatment.

Intracellular calcium pool emptying induces DNA synthesis in HaCaT keratinocytes

Calcium signaling provides a central control mechanism for growth, differentiation and apoptosis of epidermal keratinocytes. Moreover, calcium signaling is important for carcinogenesis in view of the observations suggesting that emptying of intracellular stores in keratinocytes [e.g. by a selective blocker of calcium pump in the endoplasmic reticulum (ER), thapsigargin] facilitates skin cancer development. In this work, we analyzed whether calcium content in the intracellular stores is linked to HaCaT keratinocyte growth and apoptosis control. Treatment with thapsigargin caused calcium release from the intracellular pool and permanent pool depletion (up to 24 h) could be achieved using a high dose (1 micro M) of this inhibitor. HaCaT cells cultured in these conditions exhibited an increased rate of DNA synthesis, assessed by the BrdU incorporation assay. Moreover, a weak stimulation of involucrin (terminal differentiation marker) was observed. Studies where intracellular free calcium (Cai2+) was chelated with BAPTA [1,2-bis(o-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid] revealed that abrogation of thapsigargin-induced Cai2+elevation did not counteract its effects on DNA synthesis, but blocked thapsigargin-induced involucrin expression. Apoptosis was readily achieved by extracellular calcium chelation using EGTA [ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid], but was not observed after thapsigargin or BAPTA alone or in combination. In conclusion, depletion of intracellular calcium stores causes stimulation of keratinocyte proliferation independently of the elevation of Cai2+.

Abnormal epidermal differentiation and impaired epithelial-mesenchymal tissue interactions in mice lacking the retinoblastoma relatives p107 and p130

The functions of p107 and p130, members of the retinoblastoma family, include the control of cell cycle progression and differentiation in several tissues. Our previous studies suggested a role for p107 and p130 in keratinocyte differentiation in vitro. We now extend these data using knockout animal models. We found impaired terminal differentiation in the interfollicular keratinocytes of p107/p130-double-null mice epidermis. In addition, we observed a decreased number of hair follicles and a clear developmental delay in hair, whiskers and tooth germs. Skin grafts of p107/p130-deficient epidermis onto NOD/scid mice showed altered differentiation and hyperproliferation of the interfollicular keratinocytes, thus demonstrating that the absence of p107 and p130 results in the deficient control of differentiation in keratinocytes in a cell-autonomous manner. Besides normal hair formation, follicular cysts, misoriented and dysplastic follicles, together with aberrant hair cycling, were also observed in the p107/p130 skin transplants. Finally, the hair abnormalities in p107/p130-null skin were associated with altered Bmp4-dependent signaling including decreased DeltaNp63 expression. These results indicate an essential role for p107 and p130 in the epithelial-mesenchimal interactions.

P21Waf1 control of epithelial cell cycle and cell fate

As a broad-acting cyclin-dependent kinase inhibitor, p21(WAF1) occupies a central position in the cell cycle regulation of self-renewing tissues such as oral mucosa and skin. In addition to regulating normal cell cycle progression decisions, p21(WAF1) integrates genotoxic insults into growth arrest and apoptotic signaling pathways that ultimately determine cell fate. As a result of its complex interactions with cell cycle machinery and response to mutagenic agents, p21(WAF1) also has stage-specific roles in epithelial carcinogenesis. Finally, a view is emerging of p21(WAF1) as not merely a cyclin-dependent kinase inhibitor, but also as a direct participant in regulating genes involved in growth arrest, senescence, and aging, thus providing an additional layer of control over matters of the cell cycle. This review discusses these various roles played by p21(WAF1) in cell cycle control, and attempts to relate these to epithelial cell biology, with special emphasis on keratinocytes.

Loss of the cell cycle inhibitors p21(Cip1) and p27(Kip1) enhances tumorigenesis in knockout mouse models

Events that contribute to tumor formation include mutations in the ras gene and loss or inactivation of cell cycle inhibitors such as p21(Cip1) and p27(Kip1). In our previous publication, we showed that mice expressing the MMTV/v-Ha-ras transgene developed tumors earlier and at higher multiplicities in the absence than in the presence of p21(Cip1). To further evaluate the combinatorial role of genetic alterations and loss of cell cycle inhibitors in tumorigenesis, we performed two companion studies. In the first study, wild type and p21(Cip1)-null mice were exposed to the chemical carcinogen, urethane. Similar to its effects in v-Ha-ras mice, loss of p21(Cip1) accelerated tumor onset and increased tumor multiplicity in urethane-treated mice. Lung tumors were the predominant tumor type in urethane-treated mice regardless of p21(Cip1) status. In the second study, tumor formation was monitored in v-Ha-ras mice expressing or lacking p27(Kip1). Unlike p21(Cip1), the absence of p27(Kip1) had no effect on the timing or multiplicity of tumor formation, which was largely restricted to mammary and salivary glands. However, once tumors appeared, they grew faster in p27(Kip1)-null mice than in p27(Kip1)-wild type mice. Increases in growth rate were particularly striking for salivary tumors in ras/p27(-/-) mice. Loss of p21(Cip1), on the other hand, had no effect on tumor growth rate in v-Ha-ras mice. Collectively, our data suggest that p21(Cip1) suppresses tumor formation elicited by multiple agents and that p21(Cip1) and p27(Kip1) suppress tumor formation in different ways.

Hyperproliferation, induction of c-Myc and 14-3-3σ, but no cell fragility in keratin-10-null mice

In the past, keratins have been established as structural proteins. Indeed,mutations in keratin 10 (K10) and other epidermal keratins lead to severe skin fragility syndromes. Here, we present adult K10-/- mice, which reveal a novel connection between the regulation of cell proliferation and K10. Unlike most keratin mutant mice, the epidermis of adult K10-/-mice showed no cytolysis but displayed hyperproliferation of basal keratinocytes and an increased cell size. BrdU labelling revealed a shortened transition time for keratinocytes migrating outwards and DAPI staining of epidermal sheets uncovered an impaired organization of epidermal proliferation units. These remarkable changes were accompanied by the induction of c-Myc,cyclin D1, 14-3-3σ and of wound healing keratins K6 and K16. The phosphorylation of Rb remained unaltered. In line with the downregulation of K10 in squamous cell carcinomas and its absence in proliferating cells in vivo, our data suggest that the tissue-restricted expression of some members of the keratin gene family not only serves structural functions. Our results imply that the altered composition of the suprabasal cytoskeleton is able to alter the proliferation state of basal cells through the induction of c-Myc. A previous model based on transfection of K10 in immortalized human keratinocytes suggested a direct involvement of K10 in cell cycle control. While those experiments were performed in human cultured keratinocytes, our data establish, that in vivo, K10 acts by an indirect control mechanism in trans.

The expression of keratin k10 in the basal layer of the epidermis inhibits cell proliferation and prevents skin tumorigenesis

Forced expression of K10, a keratin normally expressed in postmitotic, terminally differentiating epidermal keratinocytes, inhibits the progression of the cell cycle in cultured cells (Paramio, J. M., Casanova, M. Ll., Segrelles, C., Mittnacht, S., Lane, E. B., and Jorcano, J. L. (1999) Mol. Cell. Biol. 19, 3086-3094). This process requires a functional retinoblastoma (pRb) gene product and is mediated by K10-induced inhibition of Akt and PKCzeta, two signaling intermediates belonging to the phosphoinositide (PI) 3-kinase signal transduction pathway (Paramio, J. M., Segrelles, C., Ruiz, S., and Jorcano, J. L. (2001) Mol. Cell. Biol. 21, 7449-7459). Extending earlier in vitro studies to the in vivo situation, this work analyzes the alterations found in transgenic mice that ectopically express K10 in the proliferative basal cells of the epidermis. Increased expression of K10 led to a hypoplastic and hyperkeratotic epidermis due to a dramatic decrease in skin keratinocyte proliferation in association with the inhibition of Akt and PKCzeta activities. The inhibition of cell proliferation and Akt and PKCzeta activities was also observed although to a minor extent in low hK10-expressing mice. These animals displayed no overt epidermal phenotype nor overexpression of K10. In these non-phenotypic mice, ectopic K10 expression also resulted in decreased skin tumorigenesis. Collectively, these data demonstrate that keratin K10 in vivo functions include the control of epithelial proliferation in skin epidermis.