Altered cell cycle regulation in the lens of HPV-16 E6 or E7 transgenic mice: implications for tumor suppressor gene function in development

SUMO1-regulated DBC1 promotes p53-dependent stress-induced apoptosis of lens epithelial cells

Deleted in breast cancer 1 (DBC1) was initially identified from a homozygously deleted region in human chromosome 8p21. It has been well established that DBC1 plays a dual role during cancer development. Depending on the physiological context, it can promote or inhibit tumorigenesis. Whether it plays a role in lens pathogenesis remains elusive. In the present study, we demonstrated that DBC1 is highly expressed in lens epithelial cells from different vertebrates and in retina pigment epithelial cells as well. Moreover, DBC1 is SUMOylated through SUMO1 conjugation at K591 residue in human and mouse lens epithelial cells. The SUMOylated DBC1 is localized in the nucleus and plays an essential role in promoting stress-induced apoptosis. Silence of DBC1 attenuates oxidative stress-induced apoptosis. In contrast, overexpression of DBC1 enhances oxidative stress-induced apoptosis, and this process depends on p53. Mechanistically, DBC1 interacts with p53 to regulate its phosphorylation status at multiple sites and the SUMOylation of DBC1 enhances its interaction with p53. Together, our results identify that DBC1 is an important regulator mediating stress-induced apoptosis in lens, and thus participates in control of lens cataractogenesis.

Lens Epithelial Explants Treated with Vitreous Humor Undergo Alterations in Chromatin Landscape with Concurrent Activation of Genes Associated with Fiber Cell Differentiation and Innate Immune Response

Lens epithelial explants are comprised of lens epithelial cells cultured in vitro on their native basement membrane, the lens capsule. Biologists have used lens epithelial explants to study many different cellular processes including lens fiber cell differentiation. In these studies, fiber differentiation is typically measured by cellular elongation and the expression of a few proteins characteristically expressed by lens fiber cells in situ. Chromatin and RNA was collected from lens epithelial explants cultured in either un-supplemented media or media containing 50% bovine vitreous humor for one or five days. Chromatin for ATAC-sequencing and RNA for RNA-sequencing was prepared from explants to assess regions of accessible chromatin and to quantitatively measure gene expression, respectively. Vitreous humor increased chromatin accessibility in promoter regions of genes associated with fiber differentiation and, surprisingly, an immune response, and this was associated with increased transcript levels for these genes. In contrast, vitreous had little effect on the accessibility of the genes highly expressed in the lens epithelium despite dramatic reductions in their mRNA transcripts. An unbiased analysis of differentially accessible regions revealed an enrichment of cis-regulatory motifs for RUNX, SOX and TEAD transcription factors that may drive differential gene expression in response to vitreous.

The lens epithelium as a major determinant in the development, maintenance, and regeneration of the crystalline lens

The crystalline lens is a transparent and refractive biconvex structure formed by lens epithelial cells (LECs) and lens fibers. Lens opacity, also known as cataracts, is the leading cause of blindness in the world. LECs are the principal cells of lens throughout human life, exhibiting different physiological properties and functions. During the embryonic stage, LECs proliferate and differentiate into lens fibers, which form the crystalline lens. Genetics and environment are vital factors that influence normal lens development. During maturation, LECs help maintain lens homeostasis through material transport, synthesis and metabolism as well as mitosis and proliferation. If disturbed, this will result in loss of lens transparency. After cataract surgery, the repair potential of LECs is activated and the structure and transparency of the regenerative tissue depends on postoperative microenvironment. This review summarizes recent research advances on the role of LECs in lens development, homeostasis, and regeneration, with a particular focus on the role of cholesterol synthesis (eg., lanosterol synthase) in lens development and homeostasis maintenance, and how the regenerative potential of LECs can be harnessed to develop surgical strategies and improve the outcomes of cataract surgery (Fig. 1). These new insights suggest that LECs are a major determinant of the physiological and pathological state of the lens. Further studies on their molecular biology will offer possibility to explore new approaches for cataract prevention and treatment.

A comprehensive study of p53 protein

The protein p53 has been extensively investigated since it was found 43 years ago and has become a "guardian of the genome" that regulates the division of cells by preventing the growth of cells and dividing them, that is, inhibits the development of tumors. Initial proof of protein existence by researchers in the mid-1970s was found by altering and regulating the SV40 big T antigen termed the A protein. Researchers demonstrated how viruses play a role in cancer by employing viruses' ability to create T-antigens complex with viral tumors, which was discovered in 1979 following a viral analysis and cancer analog research. Researchers later in the year 1989 explained that in Murine Friend, a virus-caused erythroleukemia, commonly found that p53 was inactivated to suggest that p53 could be a "tumor suppressor gene." The TP53 gene, encoding p53, is one of human cancer's most frequently altered genes. The protein-regulated biological functions of all p53s include cell cycles, apoptosis, senescence, metabolism of the DNA, angiogenesis, cell differentiation, and immunological response. We tried to unfold the history of the p53 protein, which was discovered long back in 1979, that is, 43 years of research on p53, and how p53's function has been developed through time in this article.

Generation of Lens Progenitor Cells and Lentoid Bodies from Pluripotent Stem Cells: Novel Tools for Human Lens Development and Ocular Disease Etiology

In vitro differentiation of human pluripotent stem cells (hPSCs) into specialized tissues and organs represents a powerful approach to gain insight into those cellular and molecular mechanisms regulating human development. Although normal embryonic eye development is a complex process, generation of ocular organoids and specific ocular tissues from pluripotent stem cells has provided invaluable insights into the formation of lineage-committed progenitor cell populations, signal transduction pathways, and self-organization principles. This review provides a comprehensive summary of recent advances in generation of adenohypophyseal, olfactory, and lens placodes, lens progenitor cells and three-dimensional (3D) primitive lenses, "lentoid bodies", and "micro-lenses". These cells are produced alone or "community-grown" with other ocular tissues. Lentoid bodies/micro-lenses generated from human patients carrying mutations in crystallin genes demonstrate proof-of-principle that these cells are suitable for mechanistic studies of cataractogenesis. Taken together, current and emerging advanced in vitro differentiation methods pave the road to understand molecular mechanisms of cataract formation caused by the entire spectrum of mutations in DNA-binding regulatory genes, such as PAX6, SOX2, FOXE3, MAF, PITX3, and HSF4, individual crystallins, and other genes such as BFSP1, BFSP2, EPHA2, GJA3, GJA8, LIM2, MIP, and TDRD7 represented in human cataract patients.

Small DNA tumor viruses and human cancer: Preclinical models of virus infection and disease

Human tumor viruses cause various human cancers that account for at least 15% of the global cancer burden. Among the currently identified human tumor viruses, two are small DNA tumor viruses: human papillomaviruses (HPVs) and Merkel cell polyomavirus (MCPyV). The study of small DNA tumor viruses (adenoviruses, polyomaviruses, and papillomaviruses) has facilitated several significant biological discoveries and established some of the first animal models of virus-associated cancers. The development and use of preclinical in vivo models to study HPVs and MCPyV and their role in human cancer is the focus of this review. Important considerations in the design of animal models of small DNA tumor virus infection and disease, including host range, cell tropism, choice of virus isolates, and the ability to recapitulate human disease, are presented. The types of infection-based and transgenic model strategies that are used to study HPVs and MCPyV, including their strengths and limitations, are also discussed. An overview of the current models that exist to study HPV and MCPyV infection and neoplastic disease are highlighted. These comparative models provide valuable platforms to study various aspects of virus-associated human disease and will continue to expand knowledge of human tumor viruses and their relationship with their hosts.

Immune responses against autologous tumor and human papilloma virus in lymph nodes from patients with penile cancer

Purpose

Nearly half of penile cancers are related to human papillomavirus (HPV) infection. Investigations of tumor- and HPV-specific T cell reactivity in regional lymph nodes (LNs) from patients with penile cancer are warranted.

Materials and Methods

In this study, single-cell suspensions from LNs and peripheral blood from 11 patients with penile cancer were stained with antibodies for lymphocyte markers and analyzed by fluorescence-activated cell sorting (FACS). DNA was extracted from the tumor tissue and HPV status was investigated by PCR.

Results

T-cell reactivity against autologous tumor-extract and against the HPV-vaccine Gardasil® was tested by flow-cytometric assay of specific cell-mediated immune response in activated whole blood (FASCIA). CD4⁺/CD8⁺ ratios were significantly lower in HPV positive LNs (p<0.05). Immune responses to tumor extract assessed by blast transformation and expansion in vitro, of either CD4⁺ or CD8⁺ T-cells, were found in 9 of 13 LNs (69%). 5 of 6 tested patients demonstrated T cell recognition of tumor-associated antigen(s). In HPV-positive patients, dose-dependent T cell responses against L1 (late) HPV proteins (Gardasil vaccine) were demonstrated.

Conclusions

LN-derived T cells from patients with penile cancer recognize tumor antigen(s) and in HPV-positive cases, there is a response against L1 (late) HPV proteins, being constituents of the Gardasil vaccine.

Mus musculus Papillomavirus 1: a New Frontier in Animal Models of Papillomavirus Pathogenesis

Animal models of viral pathogenesis are essential tools in human disease research. Human papillomaviruses (HPVs) are a significant public health issue due to their widespread sexual transmission and oncogenic potential. Infection-based models of papillomavirus pathogenesis have been complicated by their strict species and tissue specificity. In this Gem, we discuss the discovery of a murine papillomavirus, Mus musculus papillomavirus 1 (MmuPV1), and how its experimental use represents a major advancement in models of papillomavirus-induced pathogenesis/carcinogenesis, and their transmission.

The Sumoylation Modulated Tumor Suppressor p53 Regulates Cell Cycle Checking Genes to Mediate Lens Differentiation

PURPOSE

The tumor suppressor p53 is a master regulator of apoptosis and also plays a key role in cell cycle checking. In our previous studies, we demonstrated that p53 directly regulates Bak in mouse JB6 cells and that p53-Bak signaling axis plays an important role in mediating EGCG-induced apoptosis. Furthermore, we have recently demonstrated that the same p53-Bak apoptotic signaling axis executes an essential role in regulating lens cell differentiation. In addition, we have also shown that p53 controls both transcription factors, C-Maf and Prox-1 as well as lens crystallin genes, αA, β- and γ-crystallins. Here, we have examined whether p53 also regulates other known target genes during its modulation of lens differentiation. The human and mouse lens epithelial cells, FHL124 and αTN4-1 were cultured in Dulbecco's modified Eagle's medium (DMEM) containing 10% fetal bovine serum (FBS) and 1% Penicillin-Streptomycin.

METHODS

Mice used in this study were handled in compliance with the "Protocol for the Care and Use of Laboratory Animals" (Sun Yat-sen University). Adult mice were used for the collection of lens cells. These samples were used for extraction of total proteins. A total of 32 embryonic mice {8 at 14.5 ED, 8 at 17.5 ED and 8 newborns for wild type} were used for immunohistochemistry, which were used for co-localization study. The mRNA levels were analysed with qRT-PCR. The protein levels were determined with western blot analysis and quantitated with Image J.

RESULTS

Immunohistochemistry revealed that both the cell cycle checking genes, p21 and Gadd45α and the apoptotic genes, Bcl-2 and PUMA, display developmental changes associated with p53 during mouse lens development. Knockdown of p53 in the mouse lens epithelial cells caused inhibition of lens differentiation. Associated with this inhibition, the cell cycle genes displayed significant downreglation, the apoptotic genes was also attenuated but to a much less degree. In addition, we found that bFGF can induce dose-dependent upregulation of the upstream kinases, CHK1/2 and ERK1/2, both known to phosphorylate p53 and activate the later. Furthermore, We showed that in both developing lens and human lens epithelial cells, p53 can be co-localized with the catalytic subunit of the protein phoshphatase-1 (PP-1), suggesting that PP-1 regulates p53 phosphorylation status both in vivo and in vitro.

CONCLUSION

Taken together, our results suggest that during mouse lens development, p53 activity is regulated by ERK and CHK kinases-mediated activation, and by PP-1-mediated inactivation. p53 can regulate multiple groups of genes to mediate lens differentiation.

Dotting the eyes: mouse strain dependency of the lens epithelium to low dose radiation-induced DNA damage

PURPOSE

Epidemiological evidence regarding the radiosensitivity of the lens of the eye and radiation cataract development has led to changes in the EU Basic Safety Standards for protection of the lens against ionizing radiation. However, mechanistic details of lens radiation response pathways and their significance for cataractogenesis remain unclear. Radiation-induced DNA damage and the potential impairment of repair pathways within the lens epithelium, a cell monolayer that covers the anterior hemisphere of the lens, are likely to be involved.

MATERIALS AND METHODS

In this work, the lens epithelium has been analyzed for its DNA double-strand break (DSB) repair response to ionizing radiation. The responses of epithelial cells located at the anterior pole (central region) have been compared to at the very periphery of the monolayer (germinative and transitional zones). Described here are the different responses in the two regions and across four strains (C57BL/6, 129S2, BALB/c and CBA/Ca) over a low dose (0-25 mGy) in-vivo whole body X-irradiation range up to 24 hours post exposure.

RESULTS

DNA damage and repair as visualized through 53BP1 staining was present across the lens epithelium, although repair kinetics appeared non-uniform. Epithelial cells in the central region have significantly more 53BP1 foci. The sensitivities of different mouse strains have also been compared.

CONCLUSIONS

129S2 and BALB/c showed higher levels of DNA damage, with BALB/c showing significantly less inter-individual variability and appearing to be a more robust model for future DNA damage and repair studies. As a result of this study, BALB/c was identified as a suitable radiosensitive lens strain to detect and quantify early low dose ionizing radiation DNA damage effects in the mouse eye lens specifically, as an indicator of cataract formation.

Transgenic Mouse Models of Tumor Virus Action

Genetically engineered mice (GEMs) have provided valuable insights into the carcinogenic properties of various human tumor viruses, which, in aggregate, are etiologically associated with over 15% of all human cancers. This review provides an overview of seminal discoveries made through the use of GEM models for human DNA tumor viruses. Emphasis is placed on the discoveries made in the study of human papillomaviruses, Merkel cell carcinoma-associated polyomavirus, Epstein-Barr virus, and Kaposi's sarcoma-associated herpesvirus, because GEMs have contributed extensively to our understanding of how these DNA tumor viruses directly contribute to human cancers.

HSF4 regulates lens fiber cell differentiation by activating p53 and its downstream regulators

Cataract refers to opacities of the lens that impede the passage of light. Mutations in heat shock transcription factor 4 (HSF4) have been associated with cataract; however, the mechanisms regarding how mutations in HSF4 cause cataract are still obscure. In this study, we generated an hsf4 knockout zebrafish model using TALEN technology. The mutant zebrafish developed an early-onset cataract with multiple developmental defects in lens. The epithelial cells of the lens were overproliferated, resulting in the overabundance of lens fiber cells in hsf4^null zebrafish lens. Consequently, the arrangement of the lens fiber cells became more disordered and irregular with age. More importantly, the terminal differentiation of the lens fiber cell was interrupted as the organelles cannot be cleaved in due time. In the cultured human lens epithelial cells, HSF4 could stabilize and retain p53 in the nucleus to activate its target genes such as fas cell surface death receptor (Fas) and Bcl-2-associated X apoptosis regulator (Bax). In the hsf4^null fish, both p53 and activated-caspase3 were significantly decreased. Combined with the finding that the denucleation defect could be partially rescued through microinjection of p53, fas and bax mRNA into the mutant embryos, we directly proved that HSF4 promotes lens fiber cell differentiation by activating p53 and its downstream regulators. The data we presented suggest that apoptosis-related genes are involved in the lens fiber cell differentiation. Our finding that HSF4 functions in the upstream to activate these genes highlighted the new regulatory modes of HSF4 in the terminal differentiation of lens fiber cell.

Codon optimization of Iranian human papillomavirus Type 16 E6 oncogene for Lactococcus lactis subsp. cremoris MG1363

Aim: The present study aimed to investigate the effect of codon optimization on E6 recombinant protein production in Lactococcus lactis. Method: Here we define the construction of shuttle vector harboring wild-type and codon-optimized HPV16 E6 oncogene, with maximum number of infrequent codons exchanged with codons that are frequently used in Lactococcus lactis subsp. cremoris MG1363. Results: Hence, the codons encoding 159 amino acids were modified, in which a total of 91 codons were changed, resulting in approximately threefold increase in protein expression of recombinant E6 (rE6). Conclusion: Our data revealed that codon usage optimization according to L. lactis desired codon usage can dramatically increase the expression of HPV16 E6, suggesting that this strategy is a valuable approach for immunization through DNA vaccine.

Long-distance interaction of the integrated HPV fragment with MYC gene and 8q24.22 region upregulating the allele-specific MYC expression in HeLa cells

Human papillomavirus (HPV) infection is the most important risk factor for cervical cancer development. In HeLa cell line, the HPV viral genome is integrated at 8q24 in one allele of chromosome 8. It has been reported that the HPV fragment integrated in HeLa genome can cis‐activate the expression of proto‐oncogene MYC, which is located at 500 kb downstream of the integrated site. However, the underlying molecular mechanism of this regulation is unknown. A recent study reported that MYC was highly expressed exclusively from the HPV‐integrated haplotype, and a long‐range chromatin interaction between the integrated HPV fragment and MYC gene has been hypothesized. In this study, we provided the experimental evidences supporting this long‐range chromatin interaction in HeLa cells by using Chromosome Conformation Capture (3C) method. We found that the integrated HPV fragment, MYC and 8q24.22 was close to each other and might form a trimer in spatial location. When knocking out the integrated HPV fragment or 8q24.22 region from chromosome 8 by CRISPR/Cas9 system, the expression of MYC reduced dramatically in HeLa cells. Interestingly, decreased expression was only observed in three from eight cell clones, when only one 8q24.22 allele was knocked out. Functionally, HPV knockout caused senescence‐associated acidic β‐gal activity in HeLa cells. These data indicate a long‐distance interaction of the integrated HPV fragment with MYC gene and 8q24.22 region, providing an alternative mechanism relevant to the carcinogenicity of HPV integration.

What's new?

Infection with human papillomavirus (HPV) is a well‐established risk factor for cervical cancer. The mechanism by which HPV integration into the host genome influences cervical oncogenesis, however, is not fully understood. Using chromosome conformation capture, the authors of this study provide evidence for carcinogenic involvement of a long‐range chromatin interaction between integrated HPV fragments, the proto‐oncogene MYC, and the 8q24.22 chromosomal region in HeLa cells. Knock‐out of either the integrated HPV fragment or the 8q24.22 region in HeLa cells significantly reduced MYC expression. The findings offer an alternative explanation for the carcinogenic mechanism of HPV viral genome integration.

In vitro and Animal Models for Antiviral Therapy in Papillomavirus Infections

The need for antiviral therapies for papillomavirus infections is well recognized but the difficulties of reproducing the infectious cycle of papillomaviruses in vitro has hindered our understanding of virus-cell interactions and the regulation of viral gene expression during permissive growth. Recent advances in understanding the temporal expression and function of papillomavirus proteins has enabled consideration of a targeted approach to papillomavirus chemotherapy and in particular the inhibition of viral replication by targeting the E1 and E2 proteins. There are in vitro culture systems available for the screening of new chemotherapeutic agents, since significant advances have been made with culture systems which promote epithelial differentiation in vitro. However, to date, there are no published data which show that virions generated in vitro can infect keratinocytes and initiate another round of replication in vitro. In vivo animal models are therefore necessary to assess the efficacy of antivirals in preventing and treating viral infection, particularly for the low-risk genital viruses which are on the whole refractory to culture in vitro. Although papillomaviruses affect a wide variety of hosts in a species-specific manner, the animals most useful for modelling papillomavirus infections include the rabbit, ox, mouse, dog, horse, primate and sheep. The ideal animal model should be widely available, easy to house and handle, be large enough to allow for adequate tissue sampling, develop lesions on anatomical sites comparable with those in human diseases and these lesions should be readily accessible for monitoring and ideally should yield large amounts of infectious virus particles for use in both in vivo and in vitro studies. The relative merits of the various papillomavirus animal models available in relation to these criteria are discussed.

Expressional Subpopulation of Cancers Determined by G64, a Co-regulated Module

Studies of cancer heterogeneity have received considerable attention recently, because the presence or absence of resistant sub-clones may determine whether or not certain therapeutic treatments are effective. Previously, we have reported G64, a co-regulated gene module composed of 64 different genes, can differentiate tumor intra- or inter-subpopulations in lung adenocarcinomas (LADCs). Here, we investigated whether the G64 module genes were also expressed distinctively in different subpopulations of other cancers. RNA sequencing-based transcriptome data derived from 22 cancers, except LADC, were downloaded from The Cancer Genome Atlas (TCGA). Interestingly, the 22 cancers also expressed the G64 genes in a correlated manner, as observed previously in an LADC study. Considering that gene expression levels were continuous among different tumor samples, tumor subpopulations were investigated using extreme expressional ranges of G64-i.e., tumor subpopulation with the lowest 15% of G64 expression, tumor subpopulation with the highest 15% of G64 expression, and tumor subpopulation with intermediate expression. In each of the 22 cancers, we examined whether patient survival was different among the three different subgroups and found that G64 could differentiate tumor subpopulations in six other cancers, including sarcoma, kidney, brain, liver, and esophageal cancers.

Prox1 and fibroblast growth factor receptors form a novel regulatory loop controlling lens fiber differentiation and gene expression

Lens epithelial cells differentiate into lens fibers (LFs) in response to a fibroblast growth factor (FGF) gradient. This cell fate decision requires the transcription factor Prox1, which has been hypothesized to promote cell cycle exit in differentiating LF cells. However, we find that conditional deletion of Prox1 from mouse lenses results in a failure in LF differentiation despite maintenance of normal cell cycle exit. Instead, RNA-seq demonstrated that Prox1 functions as a global regulator of LF cell gene expression. Intriguingly, Prox1 also controls the expression of fibroblast growth factor receptors (FGFRs) and can bind to their promoters, correlating with decreased downstream signaling through MAPK and AKT in Prox1 mutant lenses. Further, culturing rat lens explants in FGF increased their expression of Prox1, and this was attenuated by the addition of inhibitors of MAPK. Together, these results describe a novel feedback loop required for lens differentiation and morphogenesis, whereby Prox1 and FGFR signaling interact to mediate LF differentiation in response to FGF.

Identification of Distinct Tumor Subpopulations in Lung Adenocarcinoma via Single-Cell RNA-seq

Single-cell sequencing, which is used to detect clinically important tumor subpopulations, is necessary for understanding tumor heterogeneity. Here, we analyzed transcriptomic data obtained from 34 single cells from human lung adenocarcinoma (LADC) patient-derived xenografts (PDXs). To focus on the intrinsic transcriptomic signatures of these tumors, we filtered out genes that displayed extensive expression changes following xenografting and cell culture. Then, we performed clustering analysis using co-regulated gene modules rather than individual genes to minimize read drop-out errors associated with single-cell sequencing. This combined approach revealed two distinct intra-tumoral subgroups that were primarily distinguished by the gene module G64. The G64 module was predominantly composed of cell-cycle genes. E2F1 was found to be the transcription factor that most likely mediates the expression of the G64 module in single LADC cells. Interestingly, the G64 module also indicated inter-tumoral heterogeneity based on its association with patient survival and other clinical variables such as smoking status and tumor stage. Taken together, these results demonstrate the feasibility of single-cell RNA sequencing and the strength of our analytical pipeline for the identification of tumor subpopulations.

The cellular and molecular mechanisms of vertebrate lens development

The ocular lens is a model system for understanding important aspects of embryonic development, such as cell specification and the spatiotemporally controlled formation of a three-dimensional structure. The lens, which is characterized by transparency, refraction and elasticity, is composed of a bulk mass of fiber cells attached to a sheet of lens epithelium. Although lens induction has been studied for over 100 years, recent findings have revealed a myriad of extracellular signaling pathways and gene regulatory networks, integrated and executed by the transcription factor Pax6, that are required for lens formation in vertebrates. This Review summarizes recent progress in the field, emphasizing the interplay between the diverse regulatory mechanisms employed to form lens progenitor and precursor cells and highlighting novel opportunities to fill gaps in our understanding of lens tissue morphogenesis.

Aberrant activation of p53 due to loss of MDM2 or MDMX causes early lens dysmorphogenesis

Although forming a heterodimer or heterooligomer is essential for MDM2 and MDMX to fully control p53 during early embryogenesis, deletion of either MDM2 or MDMX in specific tissues using the loxp-Cre system reveals phenotypic diversity during organ morphogenesis, which can be completely rescued by loss of p53, suggesting the spatiotemporal independence and specificity of the regulation of p53 by MDM2 and MDMX. In this study, we investigated the role of the MDM2-MDMX-p53 pathway in the developing lens that is a relatively independent region integrating cell proliferation, differentiation and apoptosis. Using the mice expressing Cre recombinase specifically in the lens epithelial cells (LECs) beginning at E9.5, we demonstrated that deletion of either MDM2 or MDMX induces apoptosis of LEC and reduces cell proliferation, resulting in lens developmental defect that finally progresses into aphakia. Specifically, the lens defect caused by MDM2 deletion was evident at E10, occurring earlier than that caused by MDMX deletion. These lens defects were completely rescued by loss of two alleles of p53, but not one allele of p53. These results demonstrate that both MDM2 and MDMX are required for monitoring p53 activity during lens development, and they may function independently or synergistically to control p53 and maintain normal lens morphogenesis.

Manipulation of cellular DNA damage repair machinery facilitates propagation of human papillomaviruses

In general, the interplay among viruses and DNA damage repair (DDR) pathways can be divided based on whether the interaction promotes or inhibits the viral lifecycle. The propagation of human papillomaviruses is both promoted and inhibited by DDR proteins. As a result, HPV proteins both activate repair pathways, such as the ATM and ATR pathways, and inhibit other pathways, most notably the p53 signaling pathway. Indeed, the role of HPV proteins, with regard to the DDR pathways, can be divided into two broad categories. The first set of viral proteins, HPV E1 and E2 activate a DNA damage response and recruit repair proteins to viral replication centers, where these proteins are likely usurped to replicate the viral genome. Because the activation of the DDR response typically elicits a cell cycle arrest that would impeded the viral lifecycle, the second set of HPV proteins, HPV E6 and E7, prevents the DDR response from pausing cell cycle progression or inducing apoptosis. This review provides a detailed account of the interactions among HPV proteins and DDR proteins that facilitate HPV propagation.

The papillomavirus E7 proteins

E7 is an accessory protein that is not encoded by all papillomaviruses. The E7 amino terminus contains two regions of similarity to conserved regions 1 and 2 of the adenovirus E1A protein, which are also conserved in the simian vacuolating virus 40 large tumor antigen. The E7 carboxyl terminus consists of a zinc-binding motif, which is related to similar motifs in E6 proteins. E7 proteins play a central role in the human papillomavirus life cycle, reprogramming the cellular environment to be conducive to viral replication. E7 proteins encoded by the cancer-associated alpha human papillomaviruses have potent transforming activities, which together with E6, are necessary but not sufficient to render their host squamous epithelial cell tumorigenic. This article strives to provide a comprehensive summary of the published research studies on human papillomavirus E7 proteins.

Modulation of apoptotic pathways by human papillomaviruses (HPV): mechanisms and implications for therapy

The ability of the host to trigger apoptosis in infected cells is perhaps the most powerful tool by which viruses can be cleared from the host organism. To avoid elimination by this mechanism, human papillomaviruses (HPV) have developed several mechanisms that enable the cells they infect to elude both extrinsic and intrinsic apoptosis. In this manuscript, we review the current literature regarding how HPV-infected cells avoid apoptosis and the molecular mechanisms involved in these events. In particular, we will discuss the modifications in intrinsic and extrinsic apoptotic pathways caused by proteins encoded by HPV early genes. Many of the current efforts regarding anti-cancer drug development are focused on directing tumor cells to undergo apoptosis. However, the ability of HPV-infected cells to resist apoptotic signals renders such therapies ineffective. Possible mechanisms for overcoming the resistance of HPV-infected tumor cells to anticancer drugs will be discussed.

Protein damage, repair and proteolysis

Proteins are continuously affected by various intrinsic and extrinsic factors. Damaged proteins influence several intracellular pathways and result in different disorders and diseases. Aggregation of damaged proteins depends on the balance between their generation and their reversal or elimination by protein repair systems and degradation, respectively. With regard to protein repair, only few repair mechanisms have been evidenced including the reduction of methionine sulfoxide residues by the methionine sulfoxide reductases, the conversion of isoaspartyl residues to L-aspartate by L-isoaspartate methyl transferase and deglycation by phosphorylation of protein-bound fructosamine by fructosamine-3-kinase. Protein degradation is orchestrated by two major proteolytic systems, namely the lysosome and the proteasome. Alteration of the function for both systems has been involved in all aspects of cellular metabolic networks linked to either normal or pathological processes. Given the importance of protein repair and degradation, great effort has recently been made regarding the modulation of these systems in various physiological conditions such as aging, as well as in diseases. Genetic modulation has produced promising results in the area of protein repair enzymes but there are not yet any identified potent inhibitors, and, to our knowledge, only one activating compound has been reported so far. In contrast, different drugs as well as natural compounds that interfere with proteolysis have been identified and/or developed resulting in homeostatic maintenance and/or the delay of disease progression.

Physical labeling of papillomavirus-infected, immortal, and cancerous cervical epithelial cells reveal surface changes at immortal stage

A significant change of surface features of malignant cervical epithelial cells compared to normal cells has been previously reported. Here, we are studying the question at which progressive stage leading to cervical cancer the surface alteration happens. A non-traditional method to identify malignant cervical epithelial cells in vitro, which is based on physical (in contrast to specific biochemical) labelling of cells with fluorescent silica micron-size beads, is used here to examine cells at progressive stages leading to cervical cancer which include normal epithelial cells, cells infected with human papillomavirus type-16 (HPV-16), cells immortalized by HPV-16, and carcinoma cells. The study shows a statistically significant (at p < 0.01) difference between both immortal and cancer cells and a group consisting of normal and infected. There is no significant difference between normal and infected cells. Immortal cells demonstrate the signal which is closer to cancer cells than to either normal or infected cells. This implies that the cell surface, surface cellular brush changes substantially when cells become immortal. Physical labeling of the cell surface represents a substantial departure from the traditional biochemical labeling methods. The results presented show the potential significance of physical properties of the cell surface for development of clinical methods for early detection of cervical cancer, even at the stage of immortalized, premalignant cells.

Intact p53-dependent responses in miR-34-deficient mice

MicroRNAs belonging to the miR-34 family have been proposed as critical modulators of the p53 pathway and potential tumor suppressors in human cancers. To formally test these hypotheses, we have generated mice carrying targeted deletion of all three members of this microRNA family. We show that complete inactivation of miR-34 function is compatible with normal development in mice. Surprisingly, p53 function appears to be intact in miR-34–deficient cells and tissues. Although loss of miR-34 expression leads to a slight increase in cellular proliferation in vitro, it does not impair p53-induced cell cycle arrest or apoptosis. Furthermore, in contrast to p53-deficient mice, miR-34–deficient animals do not display increased susceptibility to spontaneous, irradiation-induced, or c-Myc–initiated tumorigenesis. We also show that expression of members of the miR-34 family is particularly high in the testes, lungs, and brains of mice and that it is largely p53-independent in these tissues. These findings indicate that miR-34 plays a redundant function in the p53 pathway and suggest additional p53-independent functions for this family of miRNAs.

MicroRNAs (miRNAs) are small, non-coding RNAs that broadly regulate gene expression. MicroRNA deregulation is a common feature of human cancers, and numerous miRNAs have oncogenic or tumor suppressive properties. Members of the miR-34 family (miR-34a, miR-34b, and miR-34c) have been widely speculated to be important tumor suppressors and mediators of p53 function. Despite the growing body of evidence supporting this hypothesis, previous studies on miR-34 have been done in vitro or using non-physiologic expression levels of miR-34. Here, we probe the tumor suppressive functions of the miR-34 family in vivo by generating mice carrying targeted deletion of the entire miR-34 family. Our results show that the miR-34 family is not required for tumor suppression in vivo, and they suggest p53-independent functions for this family of miRNAs. Importantly, the mice generated from this study provide a tool for the scientific community to further investigate the physiologic functions of the miR-34 family.

Small molecule inhibitors of human papillomavirus protein - protein interactions

Human papillomaviruses (HPV) have now been identified as a necessary cause of benign and malignant lesions of the differentiating epithelium, particularly cervical cancer, the second most prevalent cancer in women worldwide. While two prophylactic HPV vaccines and screening programs are available, there is currently no antiviral drug for the treatment of HPV infections and associated diseases. The recent progress toward the identification and characterization of specific molecular targets for small molecule-based approaches provides prospect for the development of effective HPV antiviral compounds. Traditionally, antiviral therapies target viral enzymes. HPV encode for few proteins, however, and rely extensively on the infected cell for completion of their life cycle. This article will review the functions of the viral E1 helicase, which encodes the only enzymatic function of the virus, of the E2 regulatory protein, and of the viral E6 and E7 oncogenes in viral replication and pathogenesis. Particular emphasis will be placed on the recent progress made towards the development of novel small molecule inhibitors that specifically target and inhibit the functions of these viral proteins, as well as their interactions with other viral and/or cellular proteins.

Lens fiber cell differentiation and denucleation are disrupted through expression of the N-terminal nuclear receptor box of NCOA6 and result in p53-dependent and p53-independent apoptosis

Nuclear receptor coactivator 6 (NCOA6) is a multifunctional protein implicated in embryonic development, cell survival, and homeostasis. An 81-amino acid fragment, dnNCOA6, containing the N-terminal nuclear receptor box (LXXLL motif) of NCOA6, acts as a dominant-negative (dn) inhibitor of NCOA6. Here, we expressed dnNCOA6 in postmitotic transgenic mouse lens fiber cells. The transgenic lenses showed reduced growth; a wide spectrum of lens fiber cell differentiation defects, including reduced expression of gamma-crystallins; and cataract formation. Those lens fiber cells entered an alternate proapoptotic pathway, and the denucleation (karyolysis) process was stalled. Activation of caspase-3 at embryonic day (E)13.5 was followed by double-strand breaks (DSBs) formation monitored via a biomarker, gamma-H2AX. Intense terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) signals were found at E16.5. Thus, a window of approximately 72 h between these events suggested prolonged though incomplete apoptosis in the lens fiber cell compartment that preserved nuclei in its cells. Genetic experiments showed that the apoptotic-like processes in the transgenic lens were both p53-dependent and p53-independent. Lens-specific deletion of Ncoa6 also resulted in disrupted lens fiber cell differentiation. Our data demonstrate a cell-autonomous role of Ncoa6 in lens fiber cell differentiation and suggest novel insights into the process of lens fiber cell denucleation and apoptosis.

Identification, characterization, and effects of Xenopus laevis PNAS-4 gene on embryonic development

Apoptosis plays an important role in embryonic development. PNAS-4 has been demonstrated to induce apoptosis in several cancer cells. In this study, we cloned Xenopus laevis PNAS-4 (xPNAS-4), which is homologous to the human PNAS-4 gene. Bioinformatics analysis for PNAS-4 indicated that xPNAS-4 shared 87.6% identity with human PNAS-4 and 85.5% with mouse PNAS-4. The phylogenetic tree of PNAS-4 protein was also summarized. An analysis of cellular localization using an EGFP-fused protein demonstrated that xPNAS-4 was localized in the perinuclear region of the cytoplasm. RT-PCR analysis revealed that xPNAS-4, as a maternally expressed gene, was present in all stages of early embryo development. Whole-mount in situ hybridization showed that xPNAS-4 was mainly expressed in ectoderm and mesoderm. Furthermore, microinjection of xPNAS-4 mRNA in vivo caused developmental defects manifesting as a small eye phenotype in the Xenopous embryos, and as a small eye or one-eye phenotype in developing zebrafish embryos. In addition, embryos microinjected with xPNAS-4 antisense morpholino oligonucleotides (MOs) exhibited a failure of head development and shortened axis.

Ubiquitin Family Members in the Regulation of the Tumor Suppressor p53

It is commonly assumed that the p53 tumor suppressor pathway is deregulated in most if not all human cancers. Thus, the past two decades have witnessed intense efforts to identify and characterize the growth-suppressive properties of p53 as well as the proteins and mechanisms involved in regulating p53 activity. In retrospect, it may therefore not be surprising that p53 was one of the very first mammalian proteins that were identified as physiologically relevant substrate proteins of the ubiquitin-proteasome system. Since then, plenty of evidence has been accumulated that p53 is in part controlled by canonical (i.e., resulting in proteasome-mediated degradation) and noncanonical (i.e., nonproteolytic) ubiquitination and by modification with the ubiquitin family members SUMO-1 and NED 8. In this chapter, we will largely neglect the plethora of mechanisms that have been reported to be involved in the regulation of p53 ubiquitination but will focus on the enzymes and components of the respective conjugation systems that have been implicated in p53 modification and how the respective modifications (ubiquitin, SUMO-1, NED 8) may impinge on p53 activity.

Cell-autonomous requirements for Dlg-1 for lens epithelial cell structure and fiber cell morphogenesis

Cell polarity and adhesion are thought to be key determinants in organismal development. In Drosophila, discs large (dlg) has emerged as an important regulator of epithelial cell proliferation, adhesion, and polarity. Herein, we investigated the role of the mouse homolog of dlg (Dlg-1) in the development of the mouse ocular lens. Tissue-specific ablation of Dlg-1 throughout the lens early in lens development led to an expansion and disorganization of the epithelium that correlated with changes in the distribution of adhesion and polarity factors. In the fiber cells, differentiation defects were observed. These included alterations in cell structure and the disposition of cell adhesion/cytoskeletal factors, delay in denucleation, and reduced levels of alpha-catenin, pERK1/2, and MIP26. These fiber cell defects were recapitulated when Dlg-1 was disrupted only in fiber cells. These results suggest that Dlg-1 acts in a cell autonomous manner to regulate epithelial cell structure and fiber cell differentiation.

Using mice to examine p53 functions in cancer, aging, and longevity

The p53 tumor suppressor is a multifaceted transcription factor that responds to a diverse array of stresses that include DNA damage and aberrant oncogene signaling. On activation, p53 prevents the emergence of cancer cells by initiating cell cycle arrest, senescence (terminal cell cycle arrest), or apoptosis. Although its role in assuring longevity by suppressing cancer is well established, recent studies obtained largely from genetically engineered mouse models suggest that p53 may regulate longevity and aging. In some contexts, it appears that altered p53 activity may enhance longevity, and in others, it appears to suppress longevity and accelerate aging phenotypes. Here, we discuss how genetically engineered mouse models have been used to explore antiproliferative functions of p53 in cancer suppression and how mouse models with altered aging phenotypes have shed light on how p53 might influence the aging process.

Cancer and viral infections in immunocompromised individuals

Over the last 30 years, the increasing use of organ and stem cell transplantation and the AIDS epidemic have led to the realization that some, but not all, human cancers occur more frequently in immunosuppressed individuals. With the notable exception of non-melanoma skin cancer (NMSC), most tumors that show strongly increased incidence rates in both transplant recipients and AIDS patients have been found to have a viral etiology. Among these are Kaposi sarcoma, diffuse large cell B-cell lymphoma, cervical cancer, liver cancer, Merkel cell carcinoma and a subset of Hodgkin's disease. A viral etiology for NMSC, i.e., beta- and gamma-subtypes of human papillomavirus, has been suggested and investigated for many years, but remains controversial. In addition, the moderately increased incidence rates of several other cancers in immunosuppressed individuals (e.g., Vajdic and van Leeuwen, Int J Cancer, in press) could indicate that additional infectious causes for at least some human cancers remain to be discovered. The controversy surrounding the role of cutaneous papillomavirus subtypes in the pathogenesis of NMSC illustrates the difficulties encountered when weighing the epidemiological and molecular biology evidence arguing for an involvement of highly prevalent viruses in certain types of cancer.

Pax6 is essential for lens fiber cell differentiation

The developing ocular lens provides an excellent model system with which to study the intrinsic and extrinsic cues governing cell differentiation. Although the transcription factors Pax6 and Sox2 have been shown to be essential for lens induction, their later roles during lens fiber differentiation remain largely unknown. Using Cre/loxP mutagenesis, we somatically inactivated Pax6 and Sox2 in the developing mouse lens during differentiation of the secondary lens fibers and explored the regulatory interactions of these two intrinsic factors with the canonical Wnt pathway. Analysis of the Pax6-deficient lenses revealed a requirement for Pax6 in cell cycle exit and differentiation into lens fiber cells. In addition, Pax6 disruption led to apoptosis of lens epithelial cells. We show that Pax6 regulates the Wnt antagonist Sfrp2 in the lens, and that Sox2 expression is upregulated in the Pax6-deficient lenses. However, our study demonstrates that the failure of differentiation following loss of Pax6 is independent of beta-catenin signaling or Sox2 activity. This study reveals that Pax6 is pivotal for initiation of the lens fiber differentiation program in the mammalian eye.

Induction of focal epithelial hyperplasia in tongue of young bk6-E6/E7 HPV16 transgenic mice

Squamous cell carcinoma (SCC) of the oral cavity is one of the most common neoplasms in the world. During the past 2 decades, the role of high-risk human papilloma virus (HR-HPV) has been studied and the data supporting HPV as a one of the causative agents in the development and progression of a sub-set of head and neck squamous cell carcinomas (HNSCC) has accumulated. In order to investigate the role of HR-HPV oncogene expression in early epithelial alterations in vivo, we produced transgenic mice expressing HPV16 early region genes from the promoter of the bovine keratin 6 gene (Tg[bK6-E6/E7]). In this article, we demonstrate that E6/E7 transgene was abundantly expressed and cellular proliferation was increased in the middle tongue epithelia of transgenic mice, and that in the same region young (27 weeks old) Tg[bK6-E6/E7] mice spontaneously developed histological alterations, mainly focal epithelial hyperplasia (FEH).

Gene expression profile of cervical and skin tissues from human papillomavirus type 16 E6 transgenic mice

Background

Although K14E6 transgenic mice develop spontaneous tumors of the skin epithelium, no spontaneous reproductive tract malignancies arise, unless the transgenic mice were treated chronically with 17β-estradiol. These findings suggest that E6 performs critical functions in normal adult cervix and skin, highlighting the need to define E6-controlled transcriptional programs in these tissues.

Methods

We evaluated the expression profile of 14,000 genes in skin or cervix from young K14E6 transgenic mice compared with nontransgenic. To identify differentially expressed genes a linear model was implemented using R and the LIMMA package. Two criteria were used to select the set of relevant genes. First a set of genes with a Log-odds ≥ 3 were selected. Then, a hierarchical search of genes was based on Log Fold Changes.

Results

Microarray analysis identified a total of 676 and 1154 genes that were significantly up and down-regulated, respectively, in skin from K14E6 transgenic mice. On the other hand, in the cervix from K14E6 transgenic mice we found that only 97 and 252 genes were significantly up and down-regulated, respectively. One of the most affected processes in the skin from K14E6 transgenic mice was the cell cycle. We also found that skin from transgenic mice showed down-regulation of pro-apoptotic genes and genes related to the immune response. In the cervix of K14E6 transgenic mice, we could not find affected any gene related to the cell cycle and apoptosis pathways but did observe alterations in the expression of immune response genes. Pathways such as angiogenesis, cell junction and epidermis development, also were altered in their gene expression profiles in both tissues.

Conclusion

Expression of the HPV16 E6 oncoprotein in our model alters expression of genes that fell into several functional groups providing insights into pathways by which E6 deregulate cell cycle progression, apoptosis, the host resistance to infection and immune function, providing new opportunities for early diagnostic markers and therapeutic drug targets.

E2f3a and E2f3b contribute to the control of cell proliferation and mouse development

The E2f3 locus encodes two Rb-binding gene products, E2F3a and E2F3b, which are differentially regulated during the cell cycle and are thought to be critical for cell cycle progression. We targeted the individual inactivation of E2f3a or E2f3b in mice and examined their contributions to cell proliferation and development. Chromatin immunoprecipitation and gene expression experiments using mouse embryo fibroblasts deficient in each isoform showed that E2F3a and E2F3b contribute to G(1)/S-specific gene expression and cell proliferation. Expression of E2f3a or E2f3b was sufficient to support E2F target gene expression and cell proliferation in the absence of other E2F activators, E2f1 and E2f2, suggesting that these isoforms have redundant functions. Consistent with this notion, E2f3a(-/-) and E2f3b(-/-) embryos developed normally, whereas embryos lacking both isoforms (E2f3(-/-)) died in utero. We also find that E2f3a and E2f3b have redundant and nonredundant roles in the context of Rb mutation. Analysis of double-knockout embryos suggests that the ectopic proliferation and apoptosis in Rb(-/-) embryos is mainly mediated by E2f3a in the placenta and nervous system and by both E2f3a and E2f3b in lens fiber cells. Together, we conclude that the contributions of E2F3a and E2F3b in cell proliferation and development are context dependent.

MAPK/ERK1/2 and PI3-kinase signalling pathways are required for vitreous-induced lens fibre cell differentiation

Lens epithelial cells withdraw from the cell cycle to differentiate into secondary fibre cells in response to vitreal factors. Fibroblast growth factor (FGF) in the vitreous has been shown to induce lens fibre differentiation in vivo and in vitro through the activation of defined intracellular signalling, namely via MAPK/ERK1/2 and PI3-K/Akt pathways. To better understand the role of these growth factor-activated signalling pathways in lens fibre differentiation, FGF- and vitreous-induced lens fibre differentiation was examined in primary rat lens epithelial cell explants. The induction of cell elongation and fibre specific beta- and gamma-crystallin expression in lens explants was accompanied by distinct phosphorylation profiles for ERK1/2 and Akt. Using selective inhibitors (U0126 and LY294002) in blocking studies, these pathways were shown to be required for different aspects of lens fibre differentiation. Furthermore, a short 'pulse' treatment of explants with FGF showed that the activation of ERK1/2 over 24 h was not sufficient for the progression of lens fibre differentiation and that cyclic ERK1/2 phosphorylation was required throughout the extended differentiation process. In conclusion, these results support a key role for both ERK1/2 and PI3-kinase/Akt signalling pathways in FGF- and vitreous-induced lens fibre differentiation.

Ubiquitin ligase E6-AP and its role in human disease

The ubiquitin ligase E6-AP (E6-associated protein) represents a prime example for the notion that deregulated modification of proteins with ubiquitin contributes to the development of human disease: loss of E6-AP function by mutation is responsible for the development of AS (Angelman syndrome), a neurological disorder, and unscheduled activation of E6-AP by complex formation with the E6 oncoprotein of HPVs (human papillomaviruses) contributes to cervical carcinogenesis. However, while there is a considerable amount of data concerning the oncogenic properties of the E6–E6-AP complex, only little is known about the function(s) of E6-AP in neurons. This is mainly due to the fact that although some E6-AP substrates have been identified, it is at present unclear whether deregulated modification/degradation of these proteins is involved in the pathogenesis of AS. Similarly, the cellular pathways involving E6-AP remain enigmatic. To obtain insights into the physiological functions of E6-AP, we are currently employing several strategies, including quantitative affinity proteomics and RNA interference approaches. The results obtained will eventually allow the introduction of E6-AP into functional protein networks and so reveal potential targets for molecular approaches in the treatment of E6-AP-associated diseases.

HPV E7 contributes to the telomerase activity of immortalized and tumorigenic cells and augments E6-induced hTERT promoter function

The E6 and E7 proteins of high-risk HPVs are both required for the immortalization of primary human keratinocytes and the maintenance of the malignant phenotype of HPV-positive cancer cell lines. Our previous studies have shown that E6 protein binds Myc protein and that both E6 and Myc associate with and cooperatively activate the hTERT promoter, thereby increasing cellular telomerase activity. In this study, we evaluated the role of E7 in the maintenance and activation of telomerase in immortalized and tumorigenic cells. siRNA knockdown of either E6 or E7 (or both) in HPV-immortalized cells or an HPV-positive cancer cell line reduced hTERT transcription and telomerase activity. Since telomerase was inhibited by E7 siRNA in cells that independently expressed the E6 and E7 genes, our results reveal an independent role for E7 in the maintenance of telomerase activity. However, E7 alone was insufficient to increase endogenous hTERT mRNA or telomerase activity, although it significantly augmented E6-induced hTERT transcription and telomerase activity. To further explore this apparent E7-induced promoter augmentation, we analyzed an exogenous hTERT core promoter in transduced keratinocytes. E7 alone induced the wt hTERT promoter and augmented E6-induced hTERT promoter activity. Mutation of the E2F site in the hTERT promoter abrogated the ability of E7 to induce the hTERT promoter or to enhance the ability of E6 to induce the promoter. Correspondingly, keratinocytes expressing E6 and a mutant E7 (defective for binding pRb pocket proteins) showed lower telomerase activity than cells expressing wt E6 and wt E7. Thus, HPV E7 plays a role in the maintenance of telomerase activity in stable cell lines and augments acute, E6-induced hTERT promoter activity.

Two cases of uveal amelanotic melanoma in transgenic Tyr-HRAS+ Ink4a/Arf heterozygous mice

Uveal melanoma (UM) is uncommon among wild type mice. Efforts to develop transgenic mice to study this disease have resulted in pigmented tumors derived from the retinal pigment epithelium (RPE) or mixed tumors of RPE and UM complicating the study of UM specifically. Reported here are two early stage intraocular amelanotic melanomas discovered in 2 Tyr-HRAS+ Ink4a/Arf heterozygous (1 normal CKDN2A allele) transgenic FVB/n mice. These tumors were morphologically and immunohistochemically similar to spontaneous UM recently reported in the Ink4a/Arf homozygous (CKDN2A knockout) parent strain. The tumors originated in the posterior uveal tract. The neoplasms were comprised of bundles of spindle-shaped melanocytes admixed with some epithelioid cells. Tumors were immunohistochemically positive for neuron-specific enolase, S-100, pan-ras, but negative for cytokeratin and Melan-A. The development of early lenticular opacity and bilateral cataracts is a consistent phenotype of transgenic mice in which the retinoblastoma signaling pathway has been disrupted. Lenticular opacity and cataracts are rarely observed clinically in Tyr-HRAS+ Ink4a/Arf heterozygotes, rendering this strain suitable for ophthalmoscopy. Consequently, Tyr-HRAS+ Ink4a/Arf heterozygotes provide practical advantages, compared to the cataract-prone CKDN2A knockout strains, for real-time ophthalomoscopic detection and monitoring of UM while developing chemotherapeutic regimens and other research to understand the biology of UM.

HECT E3s and human disease

In a simplified view, members of the HECT E3 family have a modular structure consisting of the C-terminal HECT domain, which is catalytically involved in the attachment of ubiquitin to substrate proteins, and N-terminal extensions of variable length and sequence that mediate the substrate specificity of the respective HECT E3. Although the physiologically relevant substrates of most HECT E3s have remained elusive, it is becoming increasingly clear that HECT E3s play an important role in sporadic and hereditary human diseases including cancer, cardiovascular (Liddle's syndrome) and neurological (Angelman syndrome) disorders, and/or in disease-relevant processes including bone homeostasis, immune response and retroviral budding. Thus, molecular approaches to target the activity of distinct HECT E3s, regulators thereof, and/or of HECT E3 substrates could prove valuable in the treatment of the respective diseases.

Publication history: Republished from Current BioData's Targeted Proteins database (TPdb; ).

The zebrafish udu gene encodes a novel nuclear factor and is essential for primitive erythroid cell development

Hematopoiesis is a complex process which gives rise to all blood lineages in the course of an organism's lifespan. However, the underlying molecular mechanism governing this process is not fully understood. Here we report the isolation and detailed study of a newly identified zebrafish ugly duckling (Udu) mutant allele, Udu(sq1). We show that loss-of-function mutation in the udu gene disrupts primitive erythroid cell proliferation and differentiation in a cell-autonomous manner, resulting in red blood cell (RBC) hypoplasia. Positional cloning reveals that the Udu gene encodes a novel factor that contains 2 paired amphipathic alpha-helix-like (PAH-L) repeats and a putative SANT-L (SW13, ADA2, N-Cor, and TFIIIB-like) domain. We further show that the Udu protein is predominantly localized in the nucleus and deletion of the putative SANT-L domain abolishes its function. Our study indicates that the Udu protein is very likely to function as a transcription modulator essential for the proliferation and differentiation of erythroid lineage.

HPV16 E6 confers p53-dependent and p53-independent phenotypes in the epidermis of mice deficient for E6AP

High-risk human papillomaviruses are the causative agents of cervical and other anogenital cancers. In these cancers, two viral oncogenes, E6 and E7, are expressed. E6 is best known for its ability to inactivate the tumor suppressor p53, which is thought to arise through ubiquitin-mediated degradation of p53 and involve a ternary complex between E6, p53 and the E3 ligase, E6AP. In mice transgenic for wild-type HPV16 E6, its expression leads to epithelial hyperplasia and an abrogation of normal cellular responses to DNA damage. Whereas only the latter phenotype is dependent upon E6's inactivation of p53, both are reduced in transgenic mice expressing an E6 mutant severely reduced in its binding to E6AP and other cellular proteins that bind E6 through a shared alpha-helix motif. Here, we investigated whether E6AP is required for the induction of the above phenotypes through the use of both E6AP-mutant and E6AP-null mice. E6, in the absence of E6AP retains an ability to induce epithelial hyperplasia, abrogate DNA damage responses and inhibit the induction of p53 protein following exposure to ionizing radiation. We conclude that E6 is able to induce both p53-dependent and p53-independent phenotypes through E6AP-independent pathways in the mouse.

Cell cycle regulation in the developing lens

Regulation of cell proliferation is a critical aspect of the development of multicellular organisms. The ocular lens is an excellent model system in which to unravel the mechanisms controlling cell proliferation during development. In recent years, several cell cycle regulators have been shown to be essential for maintaining normal patterns of lens cell proliferation. Additionally, many growth factor signaling pathways and cell adhesion factors have been shown to have the capacity to regulate lens cell proliferation. Given this complexity, understanding the cross talk between these many signaling pathways and how they are coordinated are important directions for the future.

Human papillomaviruses and cervical cancer

Carcinoma of the uterine cervix, a leading cause of cancer death in women worldwide, is initiated by infection with high-risk types of human papillomaviruses (HPVs). This review summarizes laboratory studies over the past 20 years that have elucidated the major features of the HPV life cycle, identified the functions of the viral proteins, and clarified the consequences of HPV infection for their host cells. This information has allowed the development of various strategies to prevent or treat infections, including prophylactic vaccination with virus-like particles, therapeutic vaccination against viral proteins expressed in cancer cells, and antiviral approaches to inhibit virus replication, spread, or pathogenesis. These strategies have the potential to cause a dramatic reduction in the incidence of cervical carcinoma and serve as the prototype for comprehensive efforts to combat virus-induced tumors.

Apoptosis in lens development and pathology

The ocular lens is a distinct system to study cell death for the following reasons. First, during animal development, the ocular lens is crafted into its unique shape. The crafting processes include cell proliferation, cell migration, and apoptosis. Moreover, the lens epithelial cells differentiate into lens fiber cells through a process, which utilizes the same regulators as those in apoptosis at multiple signaling steps. In addition, introduction of exogenous wild-type or mutant genes or knock-out of the endogenous genes leads to apoptosis of the lens epithelial cells followed by absence of the ocular lens or formation of abnormal lens. Finally, both in vitro and in vivo studies have shown that treatment of adult lens with stress factors induces apoptosis of lens epithelial cells, which is followed by cataractogenesis. The present review summarizes the current knowledge on apoptosis in the ocular lens with emphasis on its role in lens development and pathology.