Molecular aspects of adipoepithelial transdifferentiation in mouse mammary gland.

The circular, reversible conversion of the mammary gland during pregnancy and involution is a paradigm of physiological tissue plasticity. The two most prominent cell types in mammary gland, adipocytes and epithelial cells, interact in an orchestrated way to coordinate this process. Previously, we showed that this conversion is at least partly achieved by reciprocal transdifferentiation between mammary adipocytes and lobulo-alveolar epithelial cells. Here, we aim to shed more light on the regulators of mammary transdifferentiation. Using immunohistochemistry with cell type-specific lipid droplet-coating markers (Perilipin1 and 2), we show that cells with an intermediate adipoepithelial phenotype exist during and after pregnancy. Nuclei of cells with similar transitional structural characteristics are highly positive for Elf5, a master regulator of alveologenesis. In cultured adipocytes, we could show that transient and stable ectopic expression of Elf5 induces expression of the milk component whey acidic protein, although the general adipocyte phenotype is not affected suggesting that additional pioneering factors are necessary. Furthermore, the lack of transdifferentiation of adipocytes during pregnancy after clearing of the epithelial compartment indicates that transdifferentiation signals must emanate from the epithelial part. To explore candidate genes potentially involved in the transdifferentiation process, we devised a high-throughput gene expression study to compare cleared mammary fat pads with developing, contralateral controls at several time points during pregnancy. Incorporation of bioinformatic predictions of secretory proteins provides new insights into possible paracrine signaling pathways and downstream transdifferentiation factors. We discuss a potential role for osteopontin (secreted phosphoprotein 1 [Spp1]) signaling through integrins to induce adipoepithelial transdifferentiation.

The adipose organ: white-brown adipocyte plasticity and metabolic inflammation.

White adipocytes can store energy, whereas brown adipocytes dissipate energy for thermogenesis. These two cell types with opposing functions are contained in multiple fat depots forming the adipose organ. In this review, we outline the plasticity of this organ in physiological (cold exposure, physical exercise and lactation) and pathological conditions (obesity). We also highlight molecules and signalling pathways involved in the browning phenomena of white adipose tissue. This phenotypic change has proved to be effective in the protection against the metabolic disorders associated to obesity and diabetes, not only because brown adipocytes are more 'healthy' than white adipocytes, but also because the simple size reduction of white adipocytes that characterizes the first steps of transdifferentiation can be useful in determining how to avoid triggering death based on critical size and the consequent chronic low-grade inflammation due to macrophage infiltration. Thus, a better understanding of the molecular mechanisms at the basis of white-brown transdifferentiation can be extremely useful to exploit new therapeutic strategies to combat the increasing incidence of metabolic diseases.

Imiquimod and S-27609 as adjuvants of DNA vaccination in a transgenic murine model of HER2/neu-positive mammary carcinoma.

DNA vaccination against HER-2/neu is an effective way to induce an immune response able to oppose the spontaneous development of mammary tumours occurring in HER-2/neu transgenic mice. In this study, we have evaluated the potential of Imiquimod and the analogue S-27609 as adjuvants of DNA vaccination against HER-2/neu in transgenic mice. The association of a DNA vaccine encoding a portion of rat HER2/neu with either Imiquimod or S-27609 was found to delay the development of spontaneous mammary tumours and to reduce their incidence, in comparison with DNA vaccination alone. Almost 80 or 40% of tumour-free mice were found at the end of measurement time in mice vaccinated and supplemented with Imiquimod or S-27609, respectively. The antitumour preventive effect was associated with increased antibody and cell-mediated immune responsiveness against HER-2/neu. In mice vaccinated and supplemented with Imiquimod, a small but significant increase of rat p185neu-specific cytotoxicity and of IFN-gamma and IL-2-producing CD8T cells, together with a reduction of IL-4-producing CD4T cells, and a switch from an IgG1 towards a IgG2a phenotype of anti-p185neu antibodies, suggested a TH1 polarization of the immune response. The immunoregulatory efficacy of S-27609 was lower than that observed for Imiquimod. These data highlight the potential of Imiquimod, and, to a lower extent, of S-27609, as immunological adjuvants of therapeutic DNA vaccines.

Vaccination against the HER-2/neu oncogenic protein.

The HER-2/neu oncogenic protein is a well-defined tumor antigen. HER-2/neu is a shared antigen among multiple tumor types. Patients with HER-2/neu protein-overexpressing breast, ovarian, non-small cell lung, colon, and prostate cancers have been shown to have a pre-existent immune response to HER-2/neu. No matter what the tumor type, endogenous immunity to HER-2/neu detected in cancer patients demonstrates two predominant characteristics. First, HER-2/neu-specific immune responses are found in only a minority of patients whose tumors overexpress HER-2/neu. Secondly, immunity, if detectable, is of low magnitude. These observations have led to the development of vaccine strategies designed to boost HER-2/neu immunity in a majority of patients. HER-2/neu is a non-mutated self-protein, therefore vaccines must be developed based on immunologic principles focused on circumventing tolerance, a primary mechanism of tumor immune escape. HER-2/neu-specific vaccines have been tested in human clinical trials. Early results demonstrate that significant levels of HER-2/neu immunity can be generated with active immunization. The T-cell immunity elicited is durable after vaccinations have ended. Furthermore, despite the generation of CD8(+) and CD4(+) T-cells responsive to HER-2/neu in a majority of patients, there is no evidence of autoimmunity directed against tissues that express basal levels of the protein. Cancer vaccines targeting the HER-2/neu oncogenic protein may be useful adjuvants to standard therapy and aid in the prevention of relapse in patients whose tumors overexpress the protein. Furthermore, boosting HER-2/neu-specific T-cell frequencies via active immunization may allow the ex vivo expansion of HER-2/neu-specific T-cells for use in adoptive immunotherapy, a therapeutic strategy directed against the treatment of established disease.

Retrovirus-mediated gene transfer and galactocerebrosidase uptake into twitcher glial cells results in appropriate localization and phenotype correction.

Galactocerebrosidase (GALC) is deficient in all tissues from human patients and animal models with globoid cell leukodystrophy (GLD) or Krabbe disease. The deficiency results in decreased lysosomal catabolism of certain galactolipids including galactosylceramide and psychosine that are synthesized maximally during myelination. According to current theories, the accumulation of psychosine in humans and animals with GLD induces oligodendrocyte degeneration and myelination ceases. Transduction of oligodendrocytes from twitcher mice with a retroviral vector containing the GALC cDNA can correct the enzyme deficiency in these cells. Our data show that twitcher astrocytes and oligodendrocytes can internalize exogenous GALC, as well as donate the enzyme to the mutant glial cells. Antibodies against human GALC localized the GALC antigen in retrovirally transduced cells and cells receiving enzyme via cell to cell secretion and uptake to the lysosomal fraction. In fact immunocytochemical studies in transduced oligodendrocytes revealed that the GALC colocalizes in vesicles lysosomal-associated membrane protein-2 (LAMP2) (+). Moreover, labeling cells with anti-GALC and a marker for oligodendrocytes demonstrated that, upon differentiation, transduced, twitcher oligodendrocytes attained the normal branched process configuration, while untransduced cells show only abnormal morphology. Phenotype correction in mutant oligodendrocytes has also been observed after enzyme transfer. These studies indicate that GALC activity supplied to cultured oligodendrocytes from twitcher mice by different methods can correct the pathological phenotype of these cells.

Inhibition of mammary carcinogenesis by systemic interleukin 12 or p185neu DNA vaccination in Her-2/neu transgenic BALB/c mice.

Because BALB/c mice transgenic for the rat Her-2/neu oncogene develop multifocal carcinomas in all mammary glands by week 33, they constitute an aggressive model for investigation of treatments designed to oppose mammary carcinogenesis. Nonspecific immune reaction elicited by systemic interleukin (IL)-12 both delayed the appearance of the first tumor and reduced the number of glands affected. However, only 5% of mice were tumor free at week 33. On the other hand, specific vaccination with plasmids encoding for the rat p185neu resulted in a further delay, so much so that 58% of mice were tumor free at week 33. No CTL response was evoked in either IL-12-treated or DNA-vaccinated mice, whereas an anti-rat p185neu antibody response was evident in the latter. Pathological examinations showed that in both IL-12-treated and DNA-vaccinated mice, the tumor growth area was infiltrated by reactive cells associated with expression of endothelial adhesion molecules and antiangiogenic proinflammatory cytokines. In the vaccinated mice, reduction of the number of cells expressing rat p185neu was combined with down-regulation of its membrane expression and even a marked inhibition in development of the terminal ductal lobular units. The reactive infiltrate in vaccinated mice contained numerous granulocytes that likely played an antiangiogenic and angiodestructive role and also joined other cells in the antibody-mediated killing of the r-p185neu+ cells. These results suggest that the elicitation of nonspecific and specific immunity could be beneficially used in individuals with a high risk of developing tumors.

DNA vaccination against rat her-2/Neu p185 more effectively inhibits carcinogenesis than transplantable carcinomas in transgenic BALB/c mice.

The ability of vaccination with plasmids coding for the extracellular and the transmembrane domain of the product of transforming rat Her-2/neu oncogene (r-p185) to protect against r-p185(+) transplantable carcinoma (TUBO) cells and mammary carcinogenesis was evaluated. In normal BALB/c mice, DNA vaccination elicits anti-r-p185 Ab, but only a marginal CTL reactivity, and protects against a TUBO cell challenge. Massive reactive infiltration is associated with TUBO cell rejection. In BALB/c mice transgenic for the rat Her-2/neu gene (BALB-neuT), DNA vaccination elicits a lower anti-r-p185 Ab response, no CTL activity and only incompletely protects against TUBO cells, but markedly hampers the progression of carcinogenesis. At 33 wk of age, when control BALB-neuT mice display palpable tumors in all mammary glands, about 60% of immunized mice are tumor free, and tumor multiplicity is markedly reduced. Tumor-free mammary glands still display the atypical hyperplasia of the early stages of carcinogenesis, and a marked down-modulation of r-p185, along with a massive reactive infiltrate. However, BALB-neuT mice protected against mammary carcinogenesis fail to efficiently reject a TUBO cell challenge. This suggests that the mechanisms required for the rejection of transplantable tumors may not coincide with those that inhibit the slow progression of carcinogenesis.

DNA vaccination with full-length or truncated neu induces protective immunity against the development of spontaneous mammary tumors in HER-2/neu transgenic mice.

Genetic immunization against tumor antigens is an effective way to induce an immune response able to oppose cancer progression. Overexpression of HER-2/neu can lead to neoplastic transformation and has been found in many human primary breast cancers. We constructed DNA expression vectors encoding the full-length neu oncogene of rat cDNA (pCMV-NeuNT), the neu extracellular domain (pCMV-ECD), or the neu extracellular and transmembrane domains (pCMV-ECD-TM). We evaluated whether i.m. injection of these plasmids induces protection against the development of mammary tumors occurring spontaneously in FVB/N neu-transgenic mice. We found that pCMV-ECD-TM induced the best protection, whereas both pCMV-ECD and pCMV-NeuNT were less effective. The coinjection with a bicistronic vector for murine IL-12 increased the efficacy of pCMV-ECD and pCMV-NeuNT plasmids, and led to the same protection obtained with pCMV-ECD-TM alone. Anti-neuECD antibodies were detected in pCMV-ECD-TM vaccinated mice and, after coinjection with pCMV-IL12 plasmids, they appeared also in animals immunized with pCMV-ECD. Our data demonstrate the effectiveness of DNA vaccination using truncated Neu plasmids in inducing antitumor protection in a spontaneous mammary tumor model.

Binding of feline immunodeficiency viral gag-p24 polypeptide to nonimmune Igs.

Available data on the existence of lentivirus proteins with properties of unconventional Ag for B cells, have been so far restricted to human immunodeficiency virus (i.e. gp-120 of HIV-I). By using biotinylated-MAbs-anti-biotin IgG as readout system, we now report that gag-p24 antigen, either assembled in feline immunodeficiency virus (FIV) particles or expressed as recombinant polypeptide (rec.p24) may bind to nonimmune IgGs purified from mouse or cat sera. Moreover, FACS scanning experiments are consistent with the possibility that rec.p24 interacts with surface-Ig in a sub-population (5-6%) of rodent B cells. We hypothesize that gag-p24 peptide encoded regions may bind to unconventional Ig sites or, alternatively, that they may represent 'public' epitopes for natural polyreactive antibody.