Human endogenous retrovirus onco-exaptation counters cancer cell senescence through calbindin

Increased levels and diversity of human endogenous retrovirus (HERV) transcription characterize most cancer types and are linked with disease outcomes. However, the underlying processes are incompletely understood. Here, we show that elevated transcription of HERVH proviruses predicted survival of lung squamous cell carcinoma (LUSC) and identified an isoform of CALB1, encoding calbindin, ectopically driven by an upstream HERVH provirus under the control of KLF5, as the mediator of this effect. HERVH-CALB1 expression was initiated in preinvasive lesions and associated with their progression. Calbindin loss in LUSC cell lines impaired in vitro and in vivo growth and triggered senescence, consistent with a protumor effect. However, calbindin also directly controlled the senescence-associated secretory phenotype (SASP), marked by secretion of CXCL8 and other neutrophil chemoattractants. In established carcinomas, CALB1-negative cancer cells became the dominant source of CXCL8, correlating with neutrophil infiltration and worse prognosis. Thus, HERVH-CALB1 expression in LUSC may display antagonistic pleiotropy, whereby the benefits of escaping senescence early during cancer initiation and clonal competition were offset by the prevention of SASP and protumor inflammation at later stages.

E3 ubiquitin ligase HECTD2 mediates melanoma progression and immune evasion

The ubiquitin-proteasome system maintains protein homoeostasis, underpins the cell cycle, and is dysregulated in cancer. However, the role of individual E3 ubiquitin ligases, which mediate the final step in ubiquitin-mediated proteolysis, remains incompletely understood. Identified through screening for cancer-specific endogenous retroviral transcripts, we show that the little-studied E3 ubiquitin ligase HECTD2 exerts dominant control of tumour progression in melanoma. HECTD2 cell autonomously drives the proliferation of human and murine melanoma cells by accelerating the cell cycle. HECTD2 additionally regulates cancer cell production of immune mediators, initiating multiple immune suppressive pathways, which include the cyclooxygenase 2 (COX2) pathway. Accordingly, higher HECTD2 expression is associated with weaker anti-tumour immunity and unfavourable outcome of PD-1 blockade in human melanoma and counteracts immunity against a model tumour antigen in murine melanoma. This central, multifaceted role of HECTD2 in cancer cell-autonomous proliferation and in immune evasion may provide a single target for a multipronged therapy of melanoma.

Abstract 2746: Stat3 labels a subpopulation of reactive astrocytes required for brain metastasis

The diagnosis of brain metastasis involves high morbidity and mortality and remains as an unmet clinical need in spite of being the most common tumor in the brain. Brain metastasis affects between 10-30% of cancer patients with 200.000 new cases yearly only in the US. Increasing evidences point out the relevance of the microenvironment to understand the biology of brain colonization by metastatic cells, however translation strategies targeting it are lacking. We have identified altered signaling pathways in pro-metastatic reactive astrocytes (RA), and translated that into a novel therapeutic application for brain metastasis. Specifically we have identified a subpopulation of RA characterized by activated STAT3 pathway (pSTAT3+). This subpopulation is located in the vicinity of metastatic lesions intermingled with pSTAT3- RA in several experimental models and in 89% of human brain metastases independently of the primary tumor source. The pro-metastatic behaviour of RA is regulated by the activation of the STAT3 pathway, which modulates the immune system locally promoting the survival of cancer cells. Specifically the secretome of pSTAT3+ RA decreases the anti-tumor activity of CD8+ T cells as well as promotes the expansion of the pro-tumor population of CD74+ microglia/macrophage, which infiltrates metastasis cores. Interestingly, the immunosuppressive nature of pSTAT3+ RA is linked to the acquisition of stem cell-like properties, which might reflect the misuse of brain responses to injury instigated by the presence of cancer cells. Genetic and pharmacologic approaches targeting STAT3 in RA impair the progression of brain metastasis, even at advanced stages of the disease. Moreover, a safe and orally bioavailable STAT3 inhibitor reduced brain metastasis in 75% of 18 stage IV lung adenocarcinoma patients with established brain metastases, improving the outcome of the disease by increasing patient survival from 4 to 15 months. Besides increasing therapeutic opportunities for patients with brain metastasis, we have described for the first time the role of reactive astrocytes as regulators of local immunosuppression in brain metastasis as well as the importance of uncovering the heterogeneity within the metastasis-associated microenvironment.

Citation Format: Neibla Priego, Lucía Zhu, Catia Monteiro, Manon Mulders, David Wasilewski, Wendy Bindeman, Laura Doglio, Elena Martínez-Saez, Santiago Ramón y Cajal, Coral Fustero-Torre, Elena Piñeiro-Yáñez, Aurelio Hernández-Laín, Valeria Poli, Javier A. Menéndez, Ricardo Soffietti, Joaquim Bosch-Barrera, Manuel Valiente. Stat3 labels a subpopulation of reactive astrocytes required for brain metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2746.

Author Correction: STAT3 labels a subpopulation of reactive astrocytes required for brain metastasis

In the version of this article originally published, the names of three authors were incorrect. The authors were listed as "Coral Fustero-Torres", "Elena Pineiro" and "Melchor Sánchez-Martínez". Their respective names are "Coral Fustero-Torre", "Elena Piñeiro-Yáñez" and "Melchor Sanchez-Martinez". The errors have been corrected in the print, HTML and PDF versions of this article.

STAT3 labels a subpopulation of reactive astrocytes required for brain metastasis

The brain microenvironment imposes a particularly intense selective pressure on metastasis-initiating cells, but successful metastases bypass this control through mechanisms that are poorly understood. Reactive astrocytes are key components of this microenvironment that confine brain metastasis without infiltrating the lesion. Here, we describe that brain metastatic cells induce and maintain the co-option of a pro-metastatic program driven by signal transducer and activator of transcription 3 (STAT3) in a subpopulation of reactive astrocytes surrounding metastatic lesions. These reactive astrocytes benefit metastatic cells by their modulatory effect on the innate and acquired immune system. In patients, active STAT3 in reactive astrocytes correlates with reduced survival from diagnosis of intracranial metastases. Blocking STAT3 signaling in reactive astrocytes reduces experimental brain metastasis from different primary tumor sources, even at advanced stages of colonization. We also show that a safe and orally bioavailable treatment that inhibits STAT3 exhibits significant antitumor effects in patients with advanced systemic disease that included brain metastasis. Responses to this therapy were notable in the central nervous system, where several complete responses were achieved. Given that brain metastasis causes substantial morbidity and mortality, our results identify a novel treatment for increasing survival in patients with secondary brain tumors.

A Simple Predictive Enhancer Syntax for Hindbrain Patterning Is Conserved in Vertebrate Genomes

Background

Determining the function of regulatory elements is fundamental for our understanding of development, disease and evolution. However, the sequence features that mediate these functions are often unclear and the prediction of tissue-specific expression patterns from sequence alone is non-trivial. Previous functional studies have demonstrated a link between PBX-HOX and MEIS/PREP binding interactions and hindbrain enhancer activity, but the defining grammar of these sites, if any exists, has remained elusive.

Results

Here, we identify a shared sequence signature (syntax) within a heterogeneous set of conserved vertebrate hindbrain enhancers composed of spatially co-occurring PBX-HOX and MEIS/PREP transcription factor binding motifs. We use this syntax to accurately predict hindbrain enhancers in 89% of cases (67/75 predicted elements) from a set of conserved non-coding elements (CNEs). Furthermore, mutagenesis of the sites abolishes activity or generates ectopic expression, demonstrating their requirement for segmentally restricted enhancer activity in the hindbrain. We refine and use our syntax to predict over 3,000 hindbrain enhancers across the human genome. These sequences tend to be located near developmental transcription factors and are enriched in known hindbrain activating elements, demonstrating the predictive power of this simple model.

Conclusion

Our findings support the theory that hundreds of CNEs, and perhaps thousands of regions across the human genome, function to coordinate gene expression in the developing hindbrain. We speculate that deeply conserved sequences of this kind contributed to the co-option of new genes into the hindbrain gene regulatory network during early vertebrate evolution by linking patterns of hox expression to downstream genes involved in segmentation and patterning, and evolutionarily newer instances may have continued to contribute to lineage-specific elaboration of the hindbrain.

Early signs of gait deviation in Duchenne muscular dystrophy

BACKGROUND

Most analytical studies found in literature only focus on specific aspects of Duchenne muscular dystrophy (DMD) gait and posture (joint range of motion, standing balance, variations of gait spatial-temporal parameters). Some of them analyze single cases and do not provide a comprehensive evaluation of locomotion. There are few studies about DMD gait patterns, most of them concerning small groups of patients, sometimes not homogeneous, in which the clinical manifestations of the next stages of DMD were present.

AIM

The goal of our study was to analyze the characteristics of gait patterns in early stage patients, when clinical and functional evaluation do not allow to quantify initial walking worsening or to identify the changes adopted to compensate for muscle weakness.

SETTING

Gait Analysis Laboratory by using a six-camera motion capture system (Vicon, Oxford Metrics, UK), set at a sampling rate of 60 Hz. Subjects were asked to walk barefoot at their usual cadence, along a 10-m walkway, where one force platform (Kistler, Switzerland), embedded in the middle portion of the pathway, measured the foot-ground reaction forces. Retroreflective markers were placed on the subjects according to the protocol described in Davis et al.

POPULATION

A group of 15 patients aging from 5 to 6.8 years was compared with a similar age control group composed of 9 healthy children.

RESULTS

Spatial and temporal parameters showed significant differences between the two groups: cadence was increased and step length was decreased significantly in the DMD group. We found a significant increase in the range of anterior-posterior pelvic tilt and in pelvic rotation. In the frontal plane there was a tendency for an increased pelvic obliquity. Dynamic range of motion in sagittal plane showed a significant difference at the ankle, with an increased plantarflexion in swing in the dystrophic patients. Maximum dorsiflexion was reduced in the DMD group. Kinetic analysis showed significant differences in power generation and absorption at the hip joint and at the ankle joint. At knee there was a reduced flexor moment in mid-stance. Ankle showed a reduced dorsiflexor moment in terminal stance and pre-swing with a consequent reduction in the peak-to-peak excursion.

CONCLUSION AND CLINICAL REHABILITATION IMPACT

It was shown that instrumented gait analysis, being more sensitive than other clinical and functional assessment methods, allowed to quantify the very early modifications characterizing locomotion worsening in the first stage of the DMD.

Reliability of the North Star Ambulatory Assessment in a multicentric setting

The aim of this study was to investigate the suitability of the North Star Ambulatory Assessment as a possible outcome measure in multicentric clinical trials. More specifically we wished to investigate the level of training needed for achieving a good interobserver reliability in a multicentric setting. The scale was specifically designed for ambulant children with Duchenne Muscular Dystrophy and includes 17 items that are relevant for this cohort. Thirteen Italian centers participated in the study. In the first phase of the study we provided two training videos and an example of the scale performed on a child. After the first session of training, all the 13 examiners were asked to send a video with an assessment performed in their centre and to score all the videos collected. There were no difficulties in performing the items and in obtaining adequate videos with a hand held camera but the results showed a poor interobserver reliability (<.5). After a second training session with review and discussion of the videos previously scored, the same examiners were asked to score three new videos. The results of this session had an excellent interobserver reliability (.995). The level of agreement was maintained even when the same videos were rescored after a month, showing a significant intra-observer reliability (.95). Our results suggest that the NSAA is a test that can be easily performed, completed in 10 min and can be used in a multicentric setting, providing that adequate training is administered.

U19/Eaf2 knockout causes lung adenocarcinoma, B-cell lymphoma, hepatocellular carcinoma and prostatic intraepithelial neoplasia

Upregulated gene 19 (U19)/ELL-associated factor 2 (Eaf2) is a potential human tumor suppressor that exhibits frequent allelic loss and downregulation in high-grade prostate cancer. U19/Eaf2, along with its homolog Eaf1, has been reported to regulate transcriptional elongation via interaction with the eleven-nineteen lysine-rich leukemia (ELL) family of proteins. To further explore the tumor-suppressive effects of U19/Eaf2, we constructed and characterized a murine U19/Eaf2-knockout model. Homozygous or heterozygous deletion of U19/Eaf2 resulted in high rates of lung adenocarcinoma, B-cell lymphoma, hepatocellular carcinoma and prostate intraepithelial neoplasia. Within the mouse prostate, U19/Eaf2 deficiency enhanced cell proliferation and increased epithelial cell size. The knockout mice also exhibited cardiac cell hypertrophy. These data indicate a role for U19/Eaf2 in growth suppression and cell size control as well as argue for U19/Eaf2 as a novel tumor suppressor in multiple mouse tissues. The U19/Eaf2 knockout mouse also provides a unique animal model for three important cancers: lung adenocarcinoma, B-cell lymphoma and hepatocellular carcinoma.

Noninvasive ventilation with positive airway pressure in paediatric intensive care

AIM

The aim of the present study is to retrospectively evaluate the effectiveness of noninvasive pressure ventilation in the 24-bed Pediatric Intensive Care Unit (PICU) of the G. Gaslini Institute during a 24-month period.

METHODS

A retrospective analysis of the characteristics (pH, CO2, SpO2, respiratory rate, oxygen requirement) of patients treated with noninvasive mechanical ventilation for different acute pathologies has been performed.

RESULTS

Twenty patients (mean age 7.4+/-0.28 years) with acute respiratory failure due to different pathologies were treated with noninvasive mechanical ventilation. They were divided into 2 groups: the hypoxic group, suffering from pulmonary diseases, and the hypercapnic group, presenting a failure of the mechanical strength or increased dead space. Modalities of ventilation were pressure assisted/controlled or pressure support, delivered through nasal or facial masks. Fifteen out of 20 patients presented a marked improvement of oxygenation and ventilation. Mean times of treatment were 69 and 200 h in the hypoxic and hypercapnic groups, respectively. Five patients required intubation. Two patients presented reversible skin lesions over the nasal bridge.

CONCLUSIONS

Noninvasive ventilation can be used in PICU. Major advantages regard immunocompromised children and patients with exacerbations from chronic respiratory diseases, whereas the exact role of noninvasive positive pressure ventilation in patients affected by acute respiratory distress syndrome is still controversial.

Vaccinia-virus-induced cellular contractility facilitates the subcellular localization of the viral replication sites

Poxviruses, such as vaccinia virus (VV), replicate their DNA in endoplasmic-reticulum-enclosed cytoplasmic sites. Here, we compare the dynamics of the VV replication sites with those of the attenuated strain, modified VV Ankara (MVA). By live-cell imaging, small, early replication sites of both viruses undergo motility typical of microtubule (MT)-motor-mediated movement. Over time, growing replication sites of VV collect around the nucleus in a MT-dependent fashion, whereas those of MVA remain mostly scattered in the cytoplasm. Surprisingly, blocking the dynein function does not impair the perinuclear accumulation of large VV replication sites. Live-cell imaging demonstrates that in contrast to small replication sites, large sites do not display MT-motor-mediated motility. Instead, VV infection induces cellular contractility that facilitates the collection of growing replication sites around the nucleus. In a subset of cells (30-40%), this VV-induced contractility is alternated by phases of directed cell migration, suggesting that the two processes may be linked. The MVA-infected cells do not display contractility or cell migration, supporting the idea that these cellular activities facilitate the efficient accumulation of the VV replication sites around the nucleus. We propose that the recently described cytoskeletal rearrangements induced by VV are a prerequisite for the observed cell contractility and migration activities that apparently contribute to the organization of the complex cytoplasmic life cycle of VV.

The vaccinia virus I3L gene product is localized to a complex endoplasmic reticulum-associated structure that contains the viral parental DNA

The vaccinia virus (VV) I3L gene product is a single-stranded DNA-binding protein made early in infection that localizes to the cytoplasmic sites of viral DNA replication (S. C. Rochester and P. Traktman, J. Virol. 72:2917-2926, 1998). Surprisingly, when replication was blocked, the protein localized to distinct cytoplasmic spots (A. Domi and G. Beaud, J. Gen. Virol. 81:1231-1235, 2000). Here these I3L-positive spots were characterized in more detail. By using an anti-I3L peptide antibody we confirmed that the protein localized to the cytoplasmic sites of viral DNA replication by both immunofluorescence and electron microscopy (EM). Before replication had started or when replication was inhibited with hydroxyurea or cytosine arabinoside, I3L localized to distinct cytoplasmic punctate structures of homogeneous size. We show that these structures are not incoming cores or cytoplasmic sites of VV early mRNA accumulation. Instead, morphological and quantitative data indicate that they are specialized sites where the parental DNA accumulates after its release from incoming viral cores. By EM, these sites appeared as complex, electron-dense structures that were intimately associated with the cellular endoplasmic reticulum (ER). By double labeling of cryosections we show that they contain DNA and a viral early protein, the gene product of E8R. Since E8R is a membrane protein that is able to bind to DNA, the localization of this protein to the I3L puncta suggests that they are composed of membranes. The results are discussed in relation to our previous data showing that the process of viral DNA replication also occurs in close association with the ER.

The Vaccinia virus E8R gene product: a viral membrane protein that is made early in infection and packaged into the virions' core

Vaccinia virus (VV), a member of the poxvirus family, is unique among most other DNA viruses in that both transcription and DNA replication occur in the cytoplasm of the host cell. It was recently shown by electron microscopy (EM) that soon after viral DNA synthesis is initiated in HeLa cells, the replication sites become enwrapped by the membrane of the endoplasmic reticulum (ER). In the same study, a novel VV membrane protein, the E8R gene product, that may play a role in the ER wrapping process was identified (N. Tolonen, L. Doglio, S. Schleich, and J. Krijnse Locker, Mol. Biol. Cell 12:2031-2046, 2001). In the present study, the gene product of E8R was characterized both biochemically and morphologically. We show that E8R is made predominantly early in infection but is packaged into the virion. On two-dimensional gel electrophoresis, the protein appeared as a single spot throughout the VV life cycle; however, in the assembled virion, the protein underwent several modifications which resulted in a change in its molecular weight and its isoelectric point. EM of labeled cryosections of infected HeLa cells showed that the protein localized to the ER and to membranes located on one side of the Golgi complex as early as 1 h postinfection. Late in infection, E8R was additionally associated with membranes of immature virions and with intracellular mature viruses. Although E8R is predominantly associated with membranes, we show that the protein is associated with viral cores; the protein is present in cores made with NP-40-dithiothreitol as well as in incoming cores, the result of the viral entry process, early in infection. Finally, we show that E8R can be phosphorylated in vitro by the viral kinase F10L. It is able to bind DNA in vitro, and this binding may be modulated by phosphorylation by F10L. A putative role of the E8R gene product throughout the VV life cycle is discussed.

Relationship between vaccinia virus intracellular cores, early mRNAs, and DNA replication sites

Virus assembly, a late event in the life cycle of vaccinia virus (VV), is preceded by a number of steps that all occur in the cytoplasm of the infected host cell: virion entry, delivery of the viral core into the cytoplasm, and transcription from these cores of early mRNAs, followed by the process of DNA replication. In the present study the quantitative and structural relationships between these distinct steps of VV morphogenesis were investigated. We show that viral RNA and DNA synthesis increases linearly with increasing amounts of incoming cores. Moreover, at multiplicities of infection that result in 10 to 40 cores per cell, an approximately 1:1 ratio between cores and sites of DNA replication exists, suggesting that each core is infectious. We have shown previously that VV early mRNAs collect in distinct granular structures that recruit components of the host cell translation machinery. Strikingly, these structures appeared to form some distance away from intracellular cores (M. Mallardo, S. Schleich, and J. Krijnse Locker, Mol. Biol. Cell 12:3875-3891, 2001). In the present study the intracellular locations of the sites of early mRNA accumulation and those of the subsequent process of DNA replication were compared. We show that these are distinct structures that have different intracellular locations. Finally, we study the fate of the parental DNA after core uncoating. By electron microscopy, cores were found close to membranes of the endoplasmic reticulum (ER) and the parental DNA, once it had left the core, appeared to associate preferentially with the cytosolic side of those membranes. Since we have previously shown that the process of DNA replication occurs in an ER-enclosed cytosolic "subcompartment" (N. Tolonen, L. Doglio, S. Schleich, and J. Krijnse Locker, Mol. Biol. Cell 12:2031-2046, 2001), the present data suggest that the parental DNA is released into the cytosol and associates with the same membranes where DNA replication is subsequently initiated. The combined data are discussed with respect to the cytosolic organization of VV morphogenesis.

GLI1 localization in the germinal epithelial cells alternates between cytoplasm and nucleus: upregulation in transgenic mice blocks spermatogenesis in pachytene

The zinc finger transcription factor GLI1 is the mediator of signaling by members of the Hedgehog (Hh) family. Male mice in which Desert hedgehog (Dhh), an Hh homologue expressed in Sertoli cells of the testis, was knocked out are sterile, suggesting that the Dhh/GLI1 pathway plays a role in spermatogenesis. Using an antiserum raised against human GLI1, we found that during the first round of spermatogenesis, GLI1 expression is initially cytoplasmic, then shifts to the nuclei of Sertoli and germ cells, and finally shifts back to the cytoplasm. In the adult mouse testis, GLI1 expression localized to the nuclei of germ cells, beginning with pachytene cells and persisting through round spermatids. Localization of GLI1 in elongating spermatids shifted from the nucleus to the cytoplasm and became associated with microtubules. We also examined a line of transgenic mice that overexpressed human GLI1. Male mice in this line were sterile. Spermatogenesis was blocked at the pachytene stage, and a subset of the morphologically indistinguishable pachytene cells underwent apoptosis. Patched-2, which is a Dhh receptor, and Fused, another component of the signal transduction pathway, are expressed in Leydig cells and in primary and secondary spermatocytes. Expression of GLI1 in the same cell types as Patched-2 and Fused and the disruption of spermatogenesis by GLI1 overexpression suggest that GLI1 is the mediator of the Dhh signal in the testis, and that it may be a regulator of spermatogenesis.

Vaccinia virus DNA replication occurs in endoplasmic reticulum-enclosed cytoplasmic mini-nuclei

Vaccinia virus (vv), a member of the poxvirus family, is unique among most DNA viruses in that its replication occurs in the cytoplasm of the infected host cell. Although this viral process is known to occur in distinct cytoplasmic sites, little is known about its organization and in particular its relation with cellular membranes. The present study shows by electron microscopy (EM) that soon after initial vv DNA synthesis at 2 h postinfection, the sites become entirely surrounded by membranes of the endoplasmic reticulum (ER). Complete wrapping requires ~45 min and persists until virion assembly is initiated at 6 h postinfection, and the ER dissociates from the replication sites. [(3)H]Thymidine incorporation at different infection times shows that efficient vv DNA synthesis coincides with complete ER wrapping, suggesting that the ER facilitates viral replication. Proteins known to be associated with the nuclear envelope in interphase cells are not targeted to these DNA-surrounding ER membranes, ruling out a role for these molecules in the wrapping process. By random green fluorescent protein-tagging of vv early genes of unknown function with a putative transmembrane domain, a novel vv protein, the gene product of E8R, was identified that is targeted to the ER around the DNA sites. Antibodies raised against this vv early membrane protein showed, by immunofluorescence microscopy, a characteristic ring-like pattern around the replication site. By electron microscopy quantitation the protein concentrated in the ER surrounding the DNA site and was preferentially targeted to membrane facing the inside of this site. These combined data are discussed in relation to nuclear envelope assembly/disassembly as it occurs during the cell cycle.

Absence of proximal duct apoptosis in the ventral prostate of transgenic mice carrying the C3(1)-TGF-beta type II dominant negative receptor

BACKGROUND

Prostatic epithelial cells are sensitive to the inhibitory effects of TGF-beta. However, TGF-beta signaling in the prostate is dependent on androgenic status. Under the in vivo conditions, it is difficult to dissociate the effect of TGF-beta from that of androgen on the prostate.

METHODS

The objective of the present study was to create and verify a transgenic mouse system in which epithelial cells of the ventral prostate are insensitive to the actions of TGF-beta. By using a modified prostate-specific promoter, C3(1), the TGF-beta dominant negative receptor is only expressed in the epithelial cells of the ventral prostate, and these cells are resistant to TGF-beta. Morphology of transgenic animal prostates was compared to wild-type animal prostates by immunohistochemistry and microscopy.

RESULTS

The prostate of transgenic mice exhibited an abnormal morphology with multiple layers of epithelial cells lining the proximal ducts, in contrast to the simple cuboidal monolayer of cells seen in the normal prostate. This observation was accompanied by a loss of apoptosis in this region, as seen by TUNEL assay. There was no significant difference in serum levels of testosterone between the wild-type and transgenic animals.

CONCLUSIONS

These results demonstrated that a loss of sensitivity to TGF-beta results in the accumulation of multiple layers of epithelial cells in the proximal region of the ventral prostate. This abnormal growth illustrates that TGF-beta plays an important role in regulating prostate growth. The current transgenic system can be used as an experimental model to study the functional role of TGF-beta in prostatic growth and function.

Transgenic mice demonstrate a testis-specific promoter for lactate dehydrogenase, LDHC

The mammalian genome encodes a family of lactate dehydrogenase (LDH) isozymes. Two of these, ldha and ldhb, are expressed ubiquitously. The ldhc gene is active only in the germinal epithelium during spermatogenesis. In our analysis of ldhc gene regulation, we found that a 60-base pair promoter sequence was sufficient for testis-specific expression in an in vitro transcription assay. To confirm these findings, a genomic fragment containing 100 base pairs overlapping the transcription start site was isolated and linked to the Escherichia coli lacZ gene. We report that this genomic fragment drives testis-specific expression in transgenic mice. We conclude that transcription of the transgene and possibly of the endogenous ldhc gene is restricted to leptotene/pachytene primary spermatocytes.

Expression of lambda and kappa genes can occur in all B cells and is initiated around the same pre-B-cell developmental stage

Transgenic mice that carry a lambda 2 transgene under the control of the V lambda 2 promoter and the E lambda 2-4 enhancer (lambda 2E lambda mice) are described. A high proportion of B cells in the spleen and the bone marrow express the lambda transgene on the cell membrane. lambda 2 protein is synthesized by all lambda 2E lambda-derived spleen B-cell hybridomas that have retained the transgene, suggesting that all B cells have the ability to express lambda genes. Feedback inhibition of endogenous kappa-gene rearrangement is significant, but not complete. The results are similar to those with transgenic mice expressing the same lambda 2 transgene under the control of the heavy-chain enhancer (lambda 2EH mice). Although the lambda 2EH transgene is expressed before the lambda 2E lambda transgene, feedback inhibition seems to occur at about the same stage of B-cell development, regardless of the timing of expression of the lambda transgenes. Apparently, feedback is not necessarily coincident with the assembly of a heavy-chain/light-chain complex in pre-B cells. Expression of lambda in the normal fetal liver coincides with the expression of kappa; thus, it appears that lambda-gene transcription is not delayed. The differential rearrangement of kappa and lambda genes is discussed in the light of these findings.

Immunoglobulin gamma 2b transgenes inhibit heavy chain gene rearrangement, but cannot promote B cell development

Transgenic mice with a gamma 2b transgene were produced to investigate whether gamma 2b can replace mu in the development of B lymphocytes. Transgenic gamma 2b is present on the surface of B cells. Young transgenic mice have a dramatic decrease in B cell numbers, however, older mice have almost normal B cell numbers. Strikingly, all gamma 2b-expressing B cells in the spleen also express mu. The same is true for mice with a hybrid transgene in which the mu transmembrane and intracytoplasmic sequences replace those of gamma 2b (gamma 2b-mumem). The B cell defect is not due to toxicity of gamma 2b since crosses between gamma 2b transgenic and mu transgenic mice have normal numbers of B cells. Presence of the gamma 2b transgene strongly enhances the feedback inhibition of endogenous heavy chain gene rearrangement. Light chain genes are expressed normally, and the early expression of transgenic light chains does not improve B cell maturation. When the endogenous mu locus is inactivated, B cells do not develop at all in gamma 2b transgenic mice. The data suggest that gamma 2b cannot replace mu in promoting the developmental maturation of B cells, but that it can cause feedback inhibition of heavy chain gene rearrangement. Thus, the signals for heavy chain feedback and B cell maturation appear to be different.

Rearrangement and expression of immunoglobulin genes in transgenic mice

Transgenic mice are discussed which carry a rearrangement test transgene. The methylation status of the transgene varies, depending on the background mouse strain. When the transgene is bred into the C57BL/6 strain, it is completely methylated and not rearranged in lymphoid organs. After several generations of crossing into DBA/2 or SJL the transgene becomes unmethylated and rearranges at high frequency. A strain specific modifier of DNA methylation (Ssm-1) was mapped close to the Friend virus susceptibility locus (Fv-1) on mouse chromosome 4. Rearranged transgenes from spleen, bone marrow and thymus of adult mice or fetal liver were cloned and sequenced. A great variety of joints was found, with about 1/3 being in the correct reading frame. Small deletions into the V- and J-coding ends as well as N region additions contributed to the variability. The fetal joints showed no N regions. Since no functional immunoglobulin (Ig) gene can be created from this artificial test gene, the data indicate that the rearrangement mechanism of the fetus differs from that of the adult.

A strain-specific modifier on mouse chromosome 4 controls the methylation of independent transgene loci

A transgene, pHRD, is highly methylated in 12 independent mouse lines when in a C57BL/6 strain background, but becomes progressively less methylated when bred into a DBA/2 background. Transgenes inherited from the mother are generally more methylated; however, this parental effect disappears following continued breeding into the nonmethylating strain. Mapping experiments using BXD recombinant inbred mice as well as other inbred strains indicate that a single strain-specific modifier (Ssm-1) linked to, but distinct from, Fv-1 is responsible for the strain effect. In addition to the methylated and unmethylated transgenic phenotypes, certain mice exhibit a partial methylation pattern that is a consequence of an unusual cellular mosaicism. The pHRD transgene, containing target sequences for the V(D)J recombinase, undergoes site-specific recombination only in lymphoid tissues. This V-J joining is restricted primarily to unmethylated transgene copies.