The small tumor antigen of Merkel cell polyomavirus accomplishes cellular transformation by uniquely localizing to the nucleus despite the absence of a known nuclear localization signal.

BACKGROUND: Merkel Cell Carcinoma (MCC) is an aggressive skin cancer that is three times deadlier than melanoma. In 2008, it was found that 80% of MCC cases are caused by the genomic integration of a novel polyomavirus, Merkel Cell Polyomavirus (MCPyV), and the expression of its small and truncated large tumor antigens (ST and LT-t, respectively). MCPyV belongs to a family of human polyomaviruses; however, it is the only one with a clear association to cancer. METHODS: To investigate the role and mechanisms of various polyomavirus tumor antigens in cellular transformation, Rat-2 and 293A cells were transduced with pLENTI MCPyV LT-t, MCPyV ST, TSPyV ST, HPyV7 ST, or empty pLENTI and assessed through multiple transformation assays, and subcellular fractionations. One-way ANOVA tests were used to assess statistical significance. RESULTS: Soft agar, proliferation, doubling time, glucose uptake, and serum dependence assays confirmed ST to be the dominant transforming protein of MCPyV. Furthermore, it was found that MCPyV ST is uniquely transforming, as the ST antigens of other non-oncogenic human polyomaviruses such as Trichodysplasia Spinulosa-Associated Polyomavirus (TSPyV) and Human Polyomavirus 7 (HPyV7) were not transforming when similarly assessed. Identification of structural dissimilarities between transforming and non-transforming tumor antigens revealed that the uniquely transforming domain(s) of MCPyV ST are likely located within the structurally dissimilar loops of the MCPyV ST unique region. Of all known MCPyV ST cellular interactors, 62% are exclusively or transiently nuclear, suggesting that MCPyV ST localizes to the nucleus despite the absence of a canonical nuclear localization signal. Indeed, subcellular fractionations confirmed that MCPyV ST could achieve nuclear localization through a currently unknown, regulated mechanism independent of its small size, as HPyV7 and TSPyV ST proteins were incapable of nuclear translocation. Although nuclear localization was found to be important for several transforming properties of MCPyV ST, some properties were also performed by a cytoplasmic sequestered MCPyV ST, suggesting that MCPyV ST may perform different transforming functions in individual subcellular compartments. CONCLUSIONS: Together, these data further elucidate the unique differences between MCPyV ST and other polyomavirus ST proteins necessary to understand MCPyV as the only known human oncogenic polyomavirus.

Establishment and Characterization of SV40 T-Antigen Immortalized Porcine Muscle Satellite Cell.

Muscle satellite cells (MuSCs) are crucial for muscle development and regeneration. The primary pig MuSCs (pMuSCs) is an ideal in vitro cell model for studying the pig's muscle development and differentiation. However, the long-term in vitro culture of pMuSCs results in the gradual loss of their stemness, thereby limiting their application. To address this conundrum and maintain the normal function of pMuSCs during in vitro passaging, we generated an immortalized pMuSCs (SV40 T-pMuSCs) by stably expressing SV40 T-antigen (SV40 T) using a lentiviral-based vector system. The SV40 T-pMuSCs can be stably sub-cultured for over 40 generations in vitro. An evaluation of SV40 T-pMuSCs was conducted through immunofluorescence staining, quantitative real-time PCR, EdU assay, and SA-ß-gal activity. Their proliferation capacity was similar to that of primary pMuSCs at passage 1, and while their differentiation potential was slightly decreased. SiRNA-mediated interference of SV40 T-antigen expression restored the differentiation capability of SV40 T-pMuSCs. Taken together, our results provide a valuable tool for studying pig skeletal muscle development and differentiation.

Upregulated expression of lamin B receptor increases cell proliferation and suppresses genomic instability: implications for cellular immortalization.

Mammalian somatic cells undergo terminal proliferation arrest after a limited number of cell divisions, a phenomenon termed cellular senescence. However, cells acquire the ability to proliferate infinitely (cellular immortalization) through multiple genetic alterations. Inactivation of tumor suppressor genes such as p53, RB and p16 is important for cellular immortalization, although additional molecular alterations are required for cellular immortalization to occur. Here, we aimed to gain insights into these molecular alterations. Given that cellular immortalization is the escape of cells from cellular senescence, genes that regulate cellular senescence are likely to be involved in cellular immortalization. Because senescent cells show altered heterochromatin organization, we investigated the implications of lamin A/C, lamin B1 and lamin B receptor (LBR), which regulate heterochromatin organization, in cellular immortalization. We employed human immortalized cell lines, KMST-6 and SUSM-1, and found that expression of LBR was upregulated upon cellular immortalization and downregulated upon cellular senescence. In addition, knockdown of LBR induced cellular senescence with altered chromatin configuration. Additionally, enforced expression of LBR increased cell proliferation likely through suppression of genome instability in human primary fibroblasts that expressed the simian virus 40 large T antigen (TAg), which inactivates p53 and RB. Furthermore, expression of TAg or knockdown of p53 led to upregulated LBR expression. These observations suggested that expression of LBR might be upregulated to suppress genome instability in TAg-expressing cells, and, consequently, its upregulated expression assisted the proliferation of TAg-expressing cells (i.e. p53/RB-defective cells). Our findings suggest a crucial role for LBR in the process of cellular immortalization.

Unlicensed origin DNA melting by MCV and SV40 polyomavirus LT proteins is independent of ATP-dependent helicase activity.

Cellular eukaryotic replication initiation helicases are first loaded as head-to-head double hexamers on double-stranded (ds) DNA origins and then initiate S-phase DNA melting during licensed (once per cell cycle) replication. Merkel cell polyomavirus (MCV) large T (LT) helicase oncoprotein similarly binds and melts its own 98-bp origin but replicates multiple times in a single cell cycle. To examine the actions of this unlicensed viral helicase, we quantitated multimerization of MCV LT molecules as they assembled on MCV DNA origins using real-time single-molecule microscopy. MCV LT formed highly stable double hexamers having 17-fold longer mean lifetime (τ, >1,500 s) on DNA than single hexamers. Unexpectedly, partial MCV LT assembly without double-hexamer formation was sufficient to melt origin dsDNA as measured by RAD51, RPA70, or S1 nuclease cobinding. DNA melting also occurred with truncated MCV LT proteins lacking the helicase domain, but was lost from a protein without the multimerization domain that could bind only as a monomer to DNA. SV40 polyomavirus LT also multimerized to the MCV origin without forming a functional hexamer but still melted origin DNA. MCV origin melting did not require ATP hydrolysis and occurred for both MCV and SV40 LT proteins using the nonhydrolyzable ATP analog, adenylyl-imidodiphosphate (AMP-PNP). LT double hexamers formed in AMP-PNP, and melted DNA, consistent with direct LT hexamer assembly around single-stranded (ss) DNA without the energy-dependent dsDNA-to-ssDNA melting and remodeling steps used by cellular helicases. These results indicate that LT multimerization rather than helicase activity is required for origin DNA melting during unlicensed virus replication.

Mammary Tumor Growth and Proliferation Are Dependent on Growth Hormone in Female SV40 C3(1) T-Antigen Mice.

Female SV40 C3(1) T-antigen (C3(1)/TAg) transgenic mice develop mammary tumors that are molecularly similar to human basal-like breast cancers with 100% incidence at 16 weeks of age. To determine the requirement for growth hormone (GH) signaling in these tumors, genetic crosses were used to create cohorts of female mice that were homozygous for a floxed growth hormone receptor (Ghr) gene and carried one copy each of the Rosa-Cre-ERT2 transgene and the C3(1)/TAg transgene (Ghrflox/flox; Rosa-Cre-ERT2; C3(1)/TAg+/0 mice). When the largest mammary tumor reached 200 mm3, mice were treated with tamoxifen to delete Ghr or with vehicle as a control. An additional group of Ghrflox/flox; C3(1)/TAg+/0 mice were also treated with tamoxifen when the largest mammary tumor reached 200 mm3 as a control for the effects of tamoxifen. After 3 weeks, tumors in mice in which Ghr was deleted began to shrink while vehicle and tamoxifen treatment control mouse tumors continued to grow. Pathological analysis of tumors revealed similar growth patterns and varying levels of necrosis throughout all groups. A decrease in cancer cell proliferation in Ghr-/- tumors relative to controls was observed as measured by Ki67 immunohistochemistry labeling index. These data suggest that even established C3(1)/TAg mammary tumors are dependent on the GH/IGF-1 axis.

Merkel cell polyomavirus large T antigen binding to pRb promotes skin hyperplasia and tumor development.

Clear evidence supports a causal link between Merkel cell polyomavirus (MCPyV) and the highly aggressive human skin cancer called Merkel cell carcinoma (MCC). Integration of viral DNA into the human genome facilitates continued expression of the MCPyV small tumor (ST) and large tumor (LT) antigens in virus-positive MCCs. In MCC tumors, MCPyV LT is truncated in a manner that renders the virus unable to replicate yet preserves the LXCXE motif that facilitates its binding to and inactivation of the retinoblastoma tumor suppressor protein (pRb). We previously developed a MCPyV transgenic mouse model in which MCC tumor-derived ST and truncated LT expression were targeted to the stratified epithelium of the skin, causing epithelial hyperplasia, increased proliferation, and spontaneous tumorigenesis. We sought to determine if any of these phenotypes required the association between the truncated MCPyV LT and pRb. Mice were generated in which K14-driven MCPyV ST/LT were expressed in the context of a homozygous RbΔLXCXE knock-in allele that attenuates LT-pRb interactions through LT's LXCXE motif. We found that many of the phenotypes including tumorigenesis that develop in the K14-driven MCPyV transgenic mice were dependent upon LT's LXCXE-dependent interaction with pRb. These findings highlight the importance of the MCPyV LT-pRb interaction in an in vivo model for MCPyV-induced tumorigenesis.

Establishment of Down's syndrome periodontal ligament cells by transfection with SV40T-Ag and hTERT.

Down's syndrome is one of the most common human congenital genetic diseases and affected patients have increased risk of periodontal disease. To examine involvement of the disease with periodontal disease development, we established immortalized periodontal ligament cells obtained from a Down's syndrome patient by use of SV40T-Ag and hTERT gene transfection. Expressions of SV40T-Ag and hTERT were observed in periodontal ligament cell-derived immortalized cells established from healthy (STPDL) and Down's syndrome patient (STPDLDS) samples. Primary cultured periodontal ligament cells obtained from a healthy subject (pPDL) had a limited number of population doublings (< 40), while STPDL and STPDLDS cells continued to grow with more than 80 population doublings. Primary cultured periodontal ligament cells obtained from the patient showed a chromosome pattern characteristic of Down's syndrome with trisomy 21, whereas STPDLDS samples showed a large number of abnormal chromosomes in those results. Gene expression analysis revealed that expression of DSCR-1 in STPDLDS is greater than that in STPDL. These results suggest that the newly established STPDLDS cell line may be a useful tool for study of periodontal disease in Down's syndrome patients.

Detailed chromosome analysis of wild-type, immortalized fibroblasts with SV40T, E6E7, combinational introduction of cyclin dependent kinase 4, cyclin D1, telomerase reverse transcriptase.

Cell immortalization enables us to expand the cultured cell infinitely. However, the process of immortalization sometimes changes the nature of the original cell. In this study, we established immortalized embryonic fibroblasts with oncogenic SV40T and human papilla virus-derived E6E7, combinational expression of mutant cyclin-dependent kinase 4 (CDK4), cyclin D1, and telomerase reverse transcriptase (TERT) from identical primary wild-type human embryonic fibroblasts (HE16). After the establishment of immortalized cells, we compared the details of chromosome condition with the G-banding and Q-banding methods. There is no example of detailed analysis so far about chromosome abnormalities, such as trisomy, ring chromosome, reciprocal translocation, and dicentric chromosomes. The detailed chromosome analysis revealed that immortalized cells with SV40T and E6E7 showed intensive chromosome abnormalities, such as gain or loss of the chromosomes all through the genome. Furthermore, we detected that the incidence of chromosome abnormities in the immortalized cell with the combinational introduction of R24C mutant of CDK4, cyclin D1, and TERT is almost identical to that of wild-type cell. Furthermore, short tandem repeat analysis demonstrated that the origin of K4DT cell is primary HE16. These results showed that cellular immortalization with CDK4, cyclin D1, and TERT is more advantageous in keeping the chromosome's original condition than oncogenic immortalization methods.

Slit2-Mediated Metabolic Reprogramming in Bone Marrow-Derived Macrophages Enhances Antitumor Immunity.

Slit2 exerts antitumor effects in various cancers; however, the underlying mechanism, especially its role in regulating the immune, especially in the bone marrow niche, system is still unknown. Elucidating the behavior of macrophages in tumor progression can potentially improve immunotherapy. Using a spontaneous mammary tumor virus promoter-polyoma middle T antigen (PyMT) breast cancer mouse model, we observed that Slit2 increased the abundance of antitumor M1 macrophage in the bone marrow upon differentiation in vitro. Moreover, myeloablated PyMT mice injected with Slit2-treated bone marrow allografts showed a marked reduction in tumor growth, with enhanced recruitment of M1 macrophage in their tumor stroma. Mechanistic studies revealed that Slit2 significantly enhanced glycolysis and reduced fatty acid oxidation in bone marrow-derived macrophages (BMDMs). Slit2 treatment also altered mitochondrial respiration metabolites in macrophages isolated from healthy human blood that were treated with plasma from breast cancer patients. Overall, this study, for the first time, shows that Slit2 increases BMDM polarization toward antitumor phenotype by modulating immune-metabolism. Furthermore, this study provides evidence that soluble Slit2 could be developed as novel therapeutic strategy to enhance antitumor immune response.

Generation, Characterization, and Application of Inducible Proliferative Adult Human Epicardium-Derived Cells.

RATIONALE: In recent decades, the great potential of human epicardium-derived cells (EPDCs) as an endogenous cell source for cardiac regeneration has been recognized. The limited availability and low proliferation capacity of primary human EPDCs and phenotypic differences between EPDCs obtained from different individuals hampers their reproducible use for experimental studies. AIM: To generate and characterize inducible proliferative adult human EPDCs for use in fundamental and applied research. METHODS AND RESULTS: Inducible proliferation of human EPDCs was achieved by doxycycline-controlled expression of simian virus 40 large T antigen (LT) with a repressor-based lentiviral Tet-On system. In the presence of doxycycline, these inducible EPDCs (iEPDCs) displayed high and long-term proliferation capacity. After doxycycline removal, LT expression ceased and the iEPDCs regained their cuboidal epithelial morphology. Similar to primary EPDCs, iEPDCs underwent an epithelial-to-mesenchymal transition (EMT) after stimulation with transforming growth factor ß3. This was confirmed by reverse transcription-quantitative polymerase chain reaction analysis of epithelial and mesenchymal marker gene expression and (immuno) cytochemical staining. Collagen gel-based cell invasion assays demonstrated that mesenchymal iEPDCs, like primary EPDCs, possess increased invasion and migration capacities as compared to their epithelial counterparts. Mesenchymal iEPDCs co-cultured with sympathetic ganglia stimulated neurite outgrowth similarly to primary EPDCs. CONCLUSION: Using an inducible LT expression system, inducible proliferative adult human EPDCs were generated displaying high proliferative capacity in the presence of doxycycline. These iEPDCs maintain essential epicardial characteristics with respect to morphology, EMT ability, and paracrine signaling following doxycycline removal. This renders iEPDCs a highly useful new in vitro model for studying human epicardial properties.

Porcine pancreatic ductal epithelial cells transformed with KRASG12D and SV40T are tumorigenic.

We describe our initial studies in the development of an orthotopic, genetically defined, large animal model of pancreatic cancer. Primary pancreatic epithelial cells were isolated from pancreatic duct of domestic pigs. A transformed cell line was generated from these primary cells with oncogenic KRAS and SV40T. The transformed cell lines outperformed the primary and SV40T immortalized cells in terms of proliferation, population doubling time, soft agar growth, transwell migration and invasion. The transformed cell line grew tumors when injected subcutaneously in nude mice, forming glandular structures and staining for epithelial markers. Future work will include implantation studies of these tumorigenic porcine pancreatic cell lines into the pancreas of allogeneic and autologous pigs. The resultant large animal model of pancreatic cancer could be utilized for preclinical research on diagnostic, interventional, and therapeutic technologies.

The transcriptome of wild-type and immortalized corneal epithelial cells.

Cellular immortalization enables indefinite expansion of cultured cells. However, the process of cell immortalization sometimes changes the original nature of primary cells. In this study, we performed expression profiling of poly A-tailed RNA from primary and immortalized corneal epithelial cells expressing Simian virus 40 large T antigen (SV40) or the combination of mutant cyclin-dependent kinase 4 (CDK4), cyclin D1, and telomere reverse transcriptase (TERT). Furthermore, we studied the expression profile of SV40 cells cultured in medium with or without serum. The profiling of whole expression pattern revealed that immortalized corneal epithelial cells with SV40 showed a distinct expression pattern from wild-type cells regardless of the presence or absence of serum, while corneal epithelial cells with combinatorial expression showed an expression pattern relatively closer to that of wild-type cells.

Pituitary Tumors and Immortalized Cell Lines Generated by Cre-Inducible Expression of SV40 T Antigen.

Targeted oncogenesis is the process of driving tumor formation by engineering transgenic mice that express an oncogene under the control of a cell-type specific promoter. Such tumors can be adapted to cell culture, providing immortalized cell lines. To make it feasible to follow the process of tumorigenesis and increase the opportunity for generating cell lines, we developed a mouse strain that expresses SV40 T antigens in response to Cre-recombinase. Using CRISPR/Cas9 we inserted a cassette with coding sequences for SV40 T antigens and an internal ribosome entry site with green fluorescent protein cassette (IRES-GFP) into the Rosa26 locus, downstream from a stop sequence flanked by loxP sites: Rosa26LSL-SV40-GFP. These mice were mated with previously established Prop1-cre and Tshb-cre transgenic lines. Both the Rosa26LSL-SV40-GFP/+; Prop1-cre and Rosa26LSL-SV40-GFP/+; Tshb-cre mice developed fully penetrant dwarfism and large tumors by 4 weeks. Tumors from both of these mouse lines were adapted to growth in cell culture. We have established a progenitor-like cell line (PIT-P1) that expresses Sox2 and Pitx1, and a thyrotrope-like cell line (PIT-T1) that expresses Pou1f1 and Cga. These studies demonstrate the utility of the novel, Rosa26LSL-SV40-GFP mouse line for reliable targeted oncogenesis and development of unique cell lines.

Targeting the Aryl Hydrocarbon Receptor Signaling Pathway in Breast Cancer Development.

Activation of the aryl hydrocarbon receptor (AhR) through environmental exposure to known human carcinogens including dioxins can lead to the promotion of breast cancer. While the repressor protein of the AhR (AhRR) blocks the canonical AhR pathway, the function of AhRR in the development of breast cancer is not well-known. In the current study we examined the impact of suppressing AhR activity using its dedicated repressor protein AhRR. AhRR is a putative tumor suppressor and is silenced in several cancer types, including breast, where its loss correlates with shorter patient survival. Using the AhRR transgenic mouse, we demonstrate that AhRR overexpression opposes AhR-driven and inflammation-induced growth of mammary tumors in two different murine models of breast cancer. These include a syngeneic model using E0771 mammary tumor cells as well as the Polyoma Middle T antigen (PyMT) transgenic model. Further AhRR overexpression or knockout of AhR in human breast cancer cells enhanced apoptosis induced by chemotherapeutics and inhibited the growth of mouse mammary tumor cells. This study provides the first in vivo evidence that AhRR suppresses mammary tumor development and suggests that strategies which lead to its functional restoration and expression may have therapeutic benefit.

Insights from transgenic mouse models of PyMT-induced breast cancer: recapitulating human breast cancer progression in vivo.

Breast cancer is associated with the second highest cancer-associated deaths worldwide. Therefore, understanding the key events that determine breast cancer progression, modulation of the tumor-microenvironment and metastasis, which is the main cause of cancer-associated death, are of great importance. The mammary specific polyomavirus middle T antigen overexpression mouse model (MMTV-PyMT), first published in 1992, is the most commonly used genetically engineered mouse model (GEMM) for cancer research. Mammary lesions arising in MMTV-PyMT mice follow similar molecular and histological progression as human breast tumors, making it an invaluable tool for cancer researchers and instrumental in understanding tumor biology. In this review, we will highlight key studies that demonstrate the utility of PyMT derived GEMMs in understanding the molecular basis of breast cancer progression, metastasis and highlight its use as a pre-clinical tool for therapeutic discovery.

Resveratrol Rescues Human Corneal Epithelial Cells Cultured in Hyperosmolar Conditions: Potential for Dry Eye Disease Treatment.

PURPOSE: Dry eye disease (DED) is a common ocular surface condition across age groups. Recently, vitamin D deficiency has gained importance as a causative factor, and its supplementation alleviates symptoms of DED. Resveratrol (RES) regulates vitamin D receptors (VDRs) and Notch signaling. We investigated the role of RES on vitamin D levels and Notch signaling under hyperosmolar conditions. METHODS: Human corneal epithelial (HCE-T) cells were treated with RES in hyperosmolar and normal conditions. Quantitative real-time polymerase chain reaction (PCR), immunofluorescence, enzyme-linked immunosorbent assay, and western blot analysis were performed for estimating reactive oxygen species, VDR, secreted 25-hydroxyvitamin D3, and Notch signaling pathway molecules in treated and control cells. RESULTS: HCE-T cells in hyperosmolar conditions had increased reactive oxygen species levels and decreased vitamin D levels that got restored in the presence of RES. Hyperosmolarity also reduced VDR expression and Notch activity that normalized to original levels with RES. In the presence of Notch blocker LY-411575, RES could not restore VDR expression or secreted vitamin D levels in HCE-T cells exposed to hyperosmolar conditions, whereas recombinant Jagged1 restored vitamin D and VDR levels. CONCLUSIONS: RES restores vitamin D levels in hyperosmolar conditions most likely through activation of Notch signaling. Hence, RES can be a potential adjuvant in DED for patients considered for vitamin D treatment.

The RB gene family controls the maturation state of the EndoC-ßH2 human pancreatic ß-cells.

The functional maturation of human pancreatic ß-cells remains poorly understood. EndoC-ßH2 is a human ß-cell line with a reversible immortalized phenotype. Removal of the two oncogenes, SV40LT and hTERT introduced for its propagation, stops proliferation, triggers cell size increase and senescence, promotes mitochondrial activity and amplifies several ß-cell traits and functions. Overall, these events recapitulate several aspects of functional ß-cell maturation. We report here that selective depletion of SV40LT, but not of hTERT, is sufficient to revert EndoC-ßH2 immortalization. SV40LT inhibits the activity of the RB family members and of P53. In EndoC-ßH2 cells, the knock-down of RB itself, and, to a lesser extent, of its relative P130, precludes most events triggered by SV40LT depletion. In contrast, the knock-down of P53 does not prevent reversion of immortalization. Thus, an increase in RB and P130 activity, but not in P53 activity, is required for functional maturation of EndoC-ßH2 cells upon SV40LT-depletion. In addition, RB and/or P130 depletion in SV40LT-expressing EndoC-ßH2 cells decreases cell size, stimulates proliferation, and decreases the expression of key ß-cell genes. Thus, despite SV40LT expression, EndoC-ßH2 cells have a residual RB activity, which when suppressed reverts them to a more immature phenotype. These results show that the expression and activity levels of RB family members, especially RB itself, regulate the maturation state of EndoC-ßH2 cells.

Oncoprotein GT198 vaccination delays tumor growth in MMTV-PyMT mice.

Targeting early lesion in breast cancer is more therapeutically effective. We have previously identified an oncoprotein GT198 (PSMC3IP) in human breast cancer. Here we investigated GT198 in MMTV-PyMT mouse mammary gland tumors and found that GT198 is a shared early lesion in both species. Similar to human breast cancer even before a tumor appears, cytoplasmic GT198 is overexpressed in mouse tumor stroma including pericyte stem cells, descendent adipocytes, fibroblasts, and myoepithelial cells. Using recombinant GT198 protein as an antigen, we vaccinated MMTV-PyMT mice and found that the GT198 vaccine delayed mouse tumor growth and reduced lung metastasis. The antitumor effects were linearly correlated with vaccinated mouse serum titers of GT198 antibody, which recognized cell surface GT198 protein on viable tumor cells confirmed by FACS. Furthermore, GT198+ tumor cells isolated from MMTV-PyMT tumor induced faster tumor growths than GT198- cells when re-implanted into normal FVB/N mice. Together, this first study of GT198 vaccine in mouse showed its effectiveness in antitumor and anti-metastasis. The finding supports GT198 as a potential target in human immunotherapy since GT198 defect is shared in both human and mouse.

Human polyomavirus modulation of the host DNA damage response.

The human DNA damage response (DDR) is a complex signaling network constituting many factors responsible for the preservation of genomic integrity. Human polyomaviruses (HPyVs) are able to harness the DDR machinery during their infectious cycle by expressing an array of tumor (T) antigens. These molecular interactions between human polyomavirus T antigens and the DDR create conditions that promote viral replication at the expense of host genomic stability to cause disease as well as carcinogenesis in the cases of the Merkel cell polyomavirus and BK polyomavirus. This review focuses on the six HPyVs with disease association, emphasizing strain-dependent differences in their selective manipulation of the DDR. Appreciation of the HPyV-DDR interface at a molecular scale is conducive to the development of novel therapeutic approaches.

Knockout model reveals the role of Nischarin in mammary gland development, breast tumorigenesis and response to metformin treatment.

Previously, our lab discovered the protein Nischarin and uncovered its role in regulating cell migration and invasion via its interactions with several proteins. We subsequently described a role for Nischarin in breast cancer, in which it is frequently underexpressed. To characterize Nischarin's role in breast tumorigenesis and mammary gland development more completely, we deleted a critical region of the Nisch gene (exons 7-10) from the mouse genome and observed the effects. Mammary glands in mutant animals showed delayed terminal end bud formation but did not develop breast tumors spontaneously. Therefore, we interbred the animals with transgenic mice expressing the mouse mammary tumor virus-polyoma middle T-antigen (MMTV-PyMT) oncogene. The MMTV-PyMT mammary glands lacking Nischarin showed increased hyperplasia compared to wild-type animal tissues. Furthermore, we observed significantly increased tumor growth and metastasis in Nischarin mutant animals. Surprisingly, Nischarin deletion decreased activity of AMPK and subsequently its downstream effectors. Given this finding, we treated these animals with metformin, which enhances AMPK activity. Here, we show for the first time, metformin activates AMPK signaling and inhibits tumor growth of Nischarin lacking PyMT tumors suggesting a potential use for metformin as a cancer therapeutic, particularly in the case of Nischarin-deficient breast cancers.