Role of DDC-4/sFRP-4, a secreted frizzled-related protein, at the onset of apoptosis in mammary involution.

Using differential display, we isolated DDC-4, a secreted frizzled-related protein (sFRP), which is induced in the physiological apoptosis of hormonally regulated, reproductive tissues such as mammary gland, prostate, corpus luteum and uterus. The role of this gene in apoptosis was studied in animals overexpressing ectopic DDC-4/sFRP-4. Transgenic mice bearing the DDC-4/sFRP-4 cDNA under the control of the MMTV-LTR promoter showed lactational insufficiency and many apoptotic cells in the alveoli between day 19 of pregnancy and day 4 of lactation as demonstrated by TUNEL reaction and the presence of activated caspase-3. We performed a PKB/Akt kinase assay and studied several of its substrates using phosphorylation-specific antibodies to show reduced phosphorylation in PKB/Akt itself, as well as in glycogen synthetase kinase-3beta (GSK-3beta), BAD, and Forkhead. Taken together, our results show a role for DDC-4/sFRP-4 in abrogating an epithelial cell survival pathway at the onset of mammary gland involution.

Apoptosis-associated gene expression in the corpus luteum of the rat.

The involution of the corpus luteum (CL) at parturition is an example of physiological apoptosis, a complex process involving massive vascular regression while luteal cells undergo apoptosis. In the present study, changes in gene expression associated with physiological apoptosis were examined. Three genes isolated in our laboratory because of their association with apoptotic processes in the ovary, mammary gland, and prostate served as the focus of our investigation: Y81, Gas-1, and the gene IAP encoding integrin-associated protein. Y81 is a novel gene for which three transcripts are apparent. A Y81 cDNA clone representing the longest transcript has been isolated; it shows an open reading frame exhibiting a region of very high homology with members of the frizzled family, the prototypes of which are cell autonomous polarity genes encoding seven-pass transmembrane receptor proteins, for example the receptor for Wingless. Gas-1 is known as a growth-arrest gene that inhibits DNA synthesis when microinjected into cells. Integrin-associated protein is a beta 3-integrin-binding protein for which, recently, a thrombo-spondin-binding activity has been recognized. These three genes, all sharply up-regulated in the course of physiological involution processes in the ovarian CL, in mammary gland, and in prostate, seem promising candidates-by virtue of their specific expression in distinct tissues undergoing programmed cell death-as mediators of stimuli leading to apoptosis and subsequent phagocytosis. In this study, sulfated glycoprotein-2, previously observed in many instances of physiological apoptosis, was further employed as an indicator for incipient apoptosis, and stromelysin was followed as a marker for the tissue remodeling activity that is intimately associated with apoptosis during involution.

DDC-4, an apoptosis-associated gene, is a secreted frizzled relative.

The differential display method has been used in our laboratory as a coincidence analysis to isolate genes expressed in common in each of three different rat tissues undergoing physiological apoptosis: mammary gland, ovarian corpus luteum and ventral prostate. The most interesting of these isolates, DDC-4, shows a clear association with apoptosis, its expression being confined to these three organs, and only during their involution. Using DDC-4 as probe, we screened a rat ovarian cDNA library to obtain full-length isolates. One isolate, Y81 clone 40, gives rise to a protein of approximately 40 kDa with coupled in vitro transcription/translation. Sequencing of this clone indicates an open reading frame of 1044 nucleotides encoding a protein of 39.7 kDa with a putative signal sequence. This clone exhibits a high homology with the cysteine-rich domain, i.e. the ligand-binding domain, of the fizzled gene family originally defined as tissue polarity genes in Drosophila. The homology of Y81 clone 40 is most extensive with the newly described secreted frizzled relatives, the frzb subfamily.

Apoptosis in the rat mammary gland and ventral prostate: detection of cell death-associated genes using a coincident-expression cloning approach.

Apoptosis plays a striking role in the hormone-dependent involution of the mammary gland, but it has proved difficult to distinguish between the 'cell death' associated genes and the 'tissue remodelling' genes which are expressed concurrently. To identify cell death-associated genes, we have established a 'coincidence analysis' based on the previously described 'RNA differential display' method of Liang and Pardee (1992). Coincidence analysis allows the detection of genes expressed during related processes in different organs and was employed here to identify transcripts in which expression patterns are seen to be associated with apoptosis during involution of both rat mammary- and the ventral prostate glands. That the coincidence analysis is a promising approach can be seen from the fact that while widely accepted apoptosis markers such as transglutaminase (Fesus et al, 1987; Strange et al, 1992) and sulfated glycoprotein-2 (Buttyan et al, 1989; Strange et al, 1992; Guenette et al 1994) exhibited similar expression in both regressing tissues, transcription of tissue remodelling enzymes was minimal in the involuting prostate. We describe here the characteristics of five clones isolated which show coincident expression during programmed cell death in mammary and prostate tissues. Partial sequence analysis revealed for three clones high homologies with previously described genes; the putative rat homolog of the growth arrest gene gas-1 (Schneider et al, 1988; Del Sal et al, 1992), an homolog of the mouse 'Integrin Associated Protein' (IAP) (Brown et al, 1990; Lindberg et al, 1993) and the sequence encoding for the 'Allograft Inflammatory Factor' AIF-1 (Autieri et al, 1995; Utans et al, 1995). One clone displayed homology with an expressed human sequence tag and one clone unrelated to any known DNA sequence was isolated. The expression of these genes in involuting rat mammary and ventral prostate, was correlated with that in other organs and in situ hybridization was applied to establish that the secretory epithelial cells which undergo programmed cell death are the site of elevated expression during the course of involution. Furthermore, we conclude that the coincidence analysis approach described here could be easily applied to facilitate the characterization of gene expression i.e. for the detection and comparison of hormonally regulated genes in different organs.

Expression and activation of tissue transglutaminase in apoptotic cells of involuting rodent mammary tissue.

Apoptosis is a form of cell death in which cellular integrity is maintained and neither cytoplasmic nor nuclear content is released. The Ca(2+)-dependent tissue transglutaminase (tTG) is an enzyme that forms protein cross-links between specific glutamyl and lysyl side-chains of intra- and extracellular proteins, therefore it may be responsible for the structural stabilization observed during the death process. In this study, the expression of tTG was investigated following the physiological process of forced weaning which results in an almost complete elimination of secretory epithelium by apoptosis and remodelling of the tissue structure. A dramatic induction of tTG was detected by immunoblotting of total mammary gland homogenates prepared from the involuting glands. The concentration of epsilon(gamma-glutamyl)-lysine crosslinks was also elevated in these samples, showing that the enzyme is activated during apoptosis. To determine the distribution of tTG and its relationship to apoptotic cells, paraffin-embedded specimens were studied by RNA in situ hybridization and immunohistochemical methods as well as using in situ labeling for nuclear fragmentation. All of these approaches indicated that mammary secretory epithelium expressed tissue transglutaminase coincident with the onset of apoptosis. The apoptotic and tTG-expressing cells were found to be identical as demonstrated by a histological double-labeling technique.

Isolation of cell death-associated cDNAs from involuting mouse mammary epithelium.

Although apoptosis is important in determining cell fate and maintaining tissue homeostasis, the initiation and control of apoptotic cell death in epithelium is not well understood. Post-lactationai involution of the mammary gland provides both an important developmental process and a normal physiological setting for studying apoptosis of epithelium. We used a differential screening strategy, based on previous studies correlating morphology with gene expression and nucleic acid integrity during mammary gland involution, to isolate genes involved in the regulation and execution of apoptotic cell death in regressing mammary epithelium. This screening strategy yielded a large number of genes the expression of which is significantly altered during mammary gland involution. These include genes associated with cell death processes, tissue remodelling and mesenchymal differentiation. In addition, a number of novel genes have been isolated. We have used Northern analysis and in situ hybridisation to study the expression of a selection of these putative death-associated genes during post-lactational mouse mammary gland involution.

Expression of stromelysin-1 and TIMP-1 in the involuting mammary gland and in early invasive tumors of the mouse.

The mammary gland, during post-lactational involution, is subjected to extensive tissue reconstruction. This process is governed by the concerted expression of extracellular-matrix-degrading enzymes and their inhibitors. During carcinogenesis, the invasive growth of tumor cells is characterized by the penetration of the basement membrane and stromal invasion. We compared the expression of the tissue-remodeling enzymes stromelysin-1, a matrix metalloproteinase, and its inhibitor, tissue inhibitor of metalloproteinase-1 (TIMP-1), during mammary gland involution and carcinogenesis in mouse. In involuting mammary glands, stromelysin-1 was expressed in myoepithelial cells, whereas TIMP-1 was confined to the stromal tissue. To analyze the involvement of these tissue-remodeling genes in tumor development, we examined mammary tumors of transgenic mice expressing either the activated Ha-ras or c-myc oncogene under the control of a milk-protein gene promoter. In the undifferentiated and metastasizing Ha-ras-induced tumors, stromelysin-1 expression was comparable to that seen in involution, whereas TIMP-1 expression was greatly elevated. During Ha-ras-induced carcinogenesis, stromelysin-1 expression was first detected in the myo-epithelial cells surrounding preneoplastic lesions. In contrast, in the well-differentiated and non-metastatic mammary tumors induced by c-myc, no expression of either gene was observed. Thus, expression of stromelysin-1 and TIMP-1 is confined to the aggressively growing tumors and is induced in the earliest stages of carcinogenesis.

Apoptotic cell death and tissue remodelling during mouse mammary gland involution.

During post-lactational mammary gland involution, the bulk of mammary epithelium dies and is reabsorbed. This massive cell death and tissue restructuring was found to be accompanied by a specific pattern of gene expression. Northern blot analysis showed that weaning resulted in a dramatic drop in ODC, a gene involved in synthesis of a component of milk, and the nearly simultaneous induction of SGP-2, a gene associated with apoptotic cell death. These changes were followed by decreases in expression of milk protein genes to basal levels and expression of genes associated with regulation of cell proliferation and differentiation, p53, c-myc and TGF-beta 1. Subsequently, additional genes implicated in stress response, tissue remodelling, and apoptotic cell death were transiently expressed, expression peaking at about 6 days post-weaning. A non-random degradation of DNA yielding the oligonucleosomal length fragmentation pattern typical of apoptotic cell death (Wyllie, 1980; Wyllie et al., 1980) was detected in association with morphological changes and gene expression. The correlations between: (a) changes in morphology, (b) pattern of gene expression and (c) changes in DNA integrity suggest that complementary programs for cell death and tissue remodelling direct post-lactational mammary gland involution.

Dexamethasone and 1,25-dihydroxyvitamin D3, but not cyclosporine A, inhibit production of granulocyte-macrophage colony-stimulating factor in human fibroblasts.

Tumor necrosis factor alpha (TNF alpha) stimulates granulocyte-macrophage colony-stimulating factor (GM-CSF) production in human fibroblasts and other mesenchymal cells. However, relatively little is known about agents that downregulate cytokine production in these cells. In the present report we show that dexamethasone (Dexa), a synthetic glucocorticoid, markedly reduced GM-CSF production in TNF alpha-stimulated fibroblasts at both the protein and the RNA levels. CSF activity, GM-CSF protein, and RNA levels, determined by an in vitro colony-forming assay in normal human bone marrow cells, by an enzyme immunoassay, and by Northern blotting assay, were reduced to greater than 90% of control values by Dexa (1 mumol/L). Similarly, 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], a hormone with possible physiologic immunoregulatory significance, reduced GM-CSF expression in a concentration- and time-dependent manner. However, this repression was less pronounced than that of Dexa, and in part due to a decreased proliferative activity. In contrast, cyclosporine A (CsA), another immunosuppressive agent, did not alter GM-CSF expression in TNF alpha-stimulated fibroblasts. Our in vitro studies suggest that by inhibiting GM-CSF production in fibroblasts, glucocorticoids and possibly 1,25(OH)2D3, but not CsA, may attenuate TNF alpha-mediated inflammatory processes and influence the regulation of hematopoiesis.

mos-induced inhibition of glucocorticoid receptor function is mediated by Fos.

Activation of glucocorticoid hormone-dependent transcription involves the binding of the glucocorticoid hormone to its receptor followed by a specific interaction of the hormone/receptor complex with glucocorticoid responsive elements in the promoter region of hormone-inducible genes. In stably transfected NIH3T3 cells expressing the oncogene product of v-mos or fos, the expression from two glucocorticoid responsive promoters, MMTV LTR and metallothionein IIA (MtIIA), was shown to be impaired and was only transient. Cadmium-dependent MtIIA gene expression was not affected by the expression of v-mos in the cells. In transiently transfected NIH3T3 cells constitutive fos expression also inhibited glucocorticoid hormone-induced expression from the MMTV LTR. However, co-expression of antisense fos (here referred to as sof) inhibited the down-regulatory effect of Fos on glucocorticoid induced gene expression. v-mos expression in NIH3T3 cells induces fos mRNA and functional fos product (Fos) as reflected by its ability to induce expression of a transiently transfected AP-1 dependent reporter plasmid. We show that sof expression inhibits the down-regulatory effect of mos on expression of a transiently transfected pMMTV LTR-CAT. Our findings, thus, strongly suggest that the inhibition of glucocorticoid receptor function in cells expressing the v-mos oncogene is mediated by Fos.

Overexpression of the c-erbB-2 protein in human breast tumor cell lines.

The c-erbB-2 proto-oncogene is amplified in a high percentage of primary human breast tumors, suggesting that the overexpression of this gene may be involved in the development of human breast cancer. We have investigated five human breast tumor cell lines and have detected amplified c-erbB-2 gene copies in two of them. This amplification leads to overexpression of the c-erbB-2 protein. In addition, two other cell lines have elevated protein levels without gene amplification, suggesting that other mechanisms can lead to overexpression of the c-erbB-2 protein. These results are similar to those that we obtained during a study of primary breast tumors (Berger et al.: Cancer Res 48:1238-1243, 1988). These breast tumor cell lines should be useful for an analysis of c-erbB-2 expression and of the mechanisms that in some cases lead to overexpression.

Correlation of c-erbB-2 gene amplification and protein expression in human breast carcinoma with nodal status and nuclear grading.

Fifty-one primary human breast tumors were analyzed for amplification of the c-erbB-2 protooncogene. Thirteen (25%) of the DNA samples contained multiple gene copies. Paraffin-embedded tumor sections, available from 47 of the cases, were stained with a c-erbB-2 specific antiserum. Eighty-three % (10 of 12) of the tumors containing amplified c-erbB-2 gene copies stained positively with the c-erbB-2 specific antiserum (P = 0.03). Thirteen tumors containing single copy c-erbB-2 sequences also stained positively with the antiserum. This suggests that mechanisms other than gene amplification may lead to elevated levels of c-erbB-2 protein. Finally, there was a statistically significant correlation between c-erbB-2 protein expression and parameters used in breast cancer prognosis. Positive staining was associated with positive nodal status of the patient (P = 0.02) and with tumors showing a poor nuclear grade (P = 0.02). This is the first study showing that a determination of the level of c-erbB-2 protein in paraffin-embedded tumor sections may have prognostic value for the course of human breast cancer.

Activation of the receptor kinase domain of the trk oncogene by recombination with two different cellular sequences.

A new chimeric oncogene, trk-2h, has been generated by recombination of two segments of MDA-MB231 human breast carcinoma cell line DNA after transfection in NIH/3T3 cells. The rearranged DNA segments form a fused transcriptional unit. Sequences at the 3' end are homologous to the tyrosine kinase receptor moiety found in the trk oncogene which resembles a truncated growth factor receptor lacking part of its extracellular domain (Martin-Zanca et al., 1986). The 5' sequence of the trk-2h oncogene is contributed by a gene which is expressed in all human cells tested, and is not related to any known gene. Transfection of the receptor kinase domain DNA fragment into NIH/3T3 cells generated another oncogene, trk-3mh, which contains a mouse-specific sequence fused 5' to the receptor kinase. All three trk recombinants have the receptor kinase moiety fused to an activating amino terminus at the same nucleotide in their transcriptional product.

The human c-Kirsten ras gene is activated by a novel mutation in codon 13 in the breast carcinoma cell line MDA-MB231.

We have detected amplified human Ki-ras sequences in tumorigenic NIH 3T3 cells transfected with genomic DNA from the human breast carcinoma cell line MDA-MB231. Hybridization of synthetic oligonucleotides specific for human Ki-ras sequences showed a mutation at codon 13. The polymerase chain reaction with Ki-ras specific amplimers revealed a guanosine to adenosine transition at the second position of codon 13, resulting in a substitution of glycine by aspartic acid. The codon 13 mutation is also detected in one Ki-ras allele of the MDA-MB231 cell line.