Retinoic acid and IFN inhibition of cell proliferation is associated with apoptosis in squamous carcinoma cell lines: role of IRF-1 and TGase II-dependent pathways

Both retinoids and IFNs are known to inhibit proliferation of many normal and transformed cells and to have an in vivo antitumor effect against a variety of cancers, including squamous cell carcinoma. Because the combination of IFNs and all-trans retinoic acid (RA) could improve their antitumor effectiveness (depending on the histological origin and state of differentiation of the cells), we compared the activity of RA and/or IFN-alpha 2b with regard to the mechanism of growth inhibition of ME180 and SiHa cell lines, derived from squamous cervix carcinoma at different stages of differentiation. We reported previously that, in the ME180 cell line, the combined treatment significantly increased the growth inhibitory effect of the single agents. Here, we show that the SiHa cell line appears more sensitive to IFN-alpha 2b than the ME180 cell line, and resistant to RA, which does not significantly inhibit SiHa cell growth. Induction of apoptotic cell death clearly occurs and correlates with the inhibition of cell proliferation in both cell lines. It is interesting that the induction of the transcription factor IFN regulatory factor 1 correlates with the subsequent induction of apoptosis, whereas TGase I and II expression does not. In particular, TGase I and II appear differentially expressed in the ME180 and SiHa cell lines; i.e., TGase I is expressed in ME180 and specifically inhibited by RA, whereas TGase II is expressed in SiHa. It is interesting that both IFN-alpha and RA are able to increase TGase II expression and activity in this cell line.

Interferon alpha-2b and retinoic acid combined treatment affects proliferation and gene expression of human cervical carcinoma cells

The in vivo and in vitro antitumor effectiveness of IFNs is well documented. Their combination with differentiating agents, such as retinoic acid, has been demonstrated to be a promising therapy for patients with advanced squamous cell cancer of the skin and the cervix. However, the mechanisms that mediate these antitumor responses are not yet known. We studied the epidermoid cell line ME 180 derived from human cervical carcinoma to test its responsiveness to IFN-alpha-2b (INTRON A) and all-trans-retinoic acid (RA). Both agents have demonstrated ability to inhibit the growth of ME 180 cells in a dose- and time-dependent manner. The antiproliferative effect was further increased by the treatment with IFN-alpha-2b and RA combined. In accordance with this result, we found that the combination of the two agents has the effect of increasing the expression of the 2-5A synthetase gene, which is thought to play a key role in antigrowth responses to IFNs. At increased levels of 2-5A synthetase mRNA corresponds a significant increase in 2-5A synthetase activity. Although RA per se has no effect on the 2-5A synthetase expression, when it is combined with IFN-alpha-2b it appears to be able to potentiate the IFN-induced 2-5A synthetase expression. Moreover, the combination of IFN-alpha-2b and RA produces a similar effect also on the expression of the HLA-A2 gene, which has been shown to be induced in ME 180 cells both by IFN-alpha-2b and RA alone. In view of the possible mechanisms of action of the two agents, it is interesting to note that their combination increases, although transiently, the expression of IRF1, which codes for a transcription factor that regulates IFN gene expression and is thought to be involved in the regulation of IFN-induced effects and in mediating cell death or apoptosis.

Retinoid status controls the appearance of reserve cells and keratin expression in mouse cervical epithelium

We describe an animal model to induce the histogenesis of squamous metaplasia of the cervical columnar epithelium, a condition usually preceding cervical neoplasia. This model is based on dietary retinoid depletion in female mice. Control sibling mice fed the same diet but with all-trans-retinoic acid (at 3 micrograms/g diet) showed the normal endocervical epithelial and glandular columnar morphology, typical of a simple epithelium without subcolumnar reserve cells. The stratified squamous ectocervical epithelium of these mice fed all-trans retinoic acid showed intense immunohistochemical staining in basal and suprabasal cells with mono-specific antibodies against keratins K5, K14, K6, K13, and, suprabasally, with antibodies specific for K1 and K10. At the squamocolumnar junction, the adjacent columnar epithelium (termed "suprajunctional") did not show staining for K5, K14, K6, K13, K1, and K10 but specifically stained for keratin K8, typical of simple epithelia and absent from the adjacent ectocervical squamous stratified lining (termed "subjunctional"), in striking contrast. Sections of the squamocolumnar junction from mice kept on the vitamin A-deficient diet for 10 weeks showed suprajunctional isolated patches of reserve cells, proximal and distal to the junction. These cells were detected prior to any symptoms of vitamin A deficiency, such as loss of body weight or respiratory discomfort. The subcolumnar reserve cells induced by vitamin A deficiency displayed positive staining for K5 and K14. As deficiency became severe, the reserve cells occupied the entirety of the suprajunctional basement membrane. This epithelium eventually became stratified and squamous metaplastic, the squamocolumnar junction was no longer discernible, and the entire endocervical epithelium and the endometrial glands lost K8 positivity, while acquiring K5, K14, K6, K13, K1, and K10 keratins typical of the ectocervix under normal conditions of vitamin A nutriture. Vitamin A deficiency also altered keratin expression and localization in squamous subjunctional epithelium. In situ hybridization studies for K1 and K5 mRNA showed their major site of expression at the basal (K5) and immediately suprabasal (K1) cell layers. The localization of both K5 and K1 proteins in these same cell layers, and above, is consistent with transcriptional regulation of these keratins. Early vitamin A deficiency caused the appearance of single subcolumnar reserve cells expressing K5 mRNA. After these cells grew into a squamous focus, K1 mRNA became expressed suprabasally. We conclude that retinoid status plays a key role in maintaining differentiative characteristics of the cervical and glandular epithelia and, as such, may be a modulating factor in the development of cervical cancer.

Retinoid status and the control of keratin expression and adhesion during the histogenesis of squamous metaplasia of tracheal epithelium

We induced vitamin A depletion to define early and late changes during the histogenesis of squamous metaplasia of hamster tracheal epithelium. An early change is the "minimal morphological change" (MMC), in which the mucociliary epithelium is separated from the basement membrane by a continuous layer of basal cells. Immunohistochemistry showed an exclusive localization of the keratins K5 and K14 in basal cells of normal and MMC epithelia. At the MMC stage no staining was observed above the basal layer with antibodies to K5, but upon progression of the lesion to a squamous focus all cells from basal to terminally differentiated were positive for K5 and K14. In contrast, when we used antibodies to the keratins K6 or K13 all cells were negative in the normal epithelium and in the MMC epithelium. Successive layers of suprabasal squamous cells found in squamous metaplasia failed to express normal epidermal differentiation marker keratins K1 and K10 but expressed the proliferation marker keratin K6 and the internal stratified epithelium keratin K13, not normally found in the epidermis or in the trachea. Hamster tracheal epithelial cells could be maintained in culture in serum-free medium for at least 4 weeks in the presence of retinoic acid (RA). In non-RA-containing medium, cells from vitamin A-deficient hamsters showed markedly reduced growth and an increase in the expression of keratins K5, K6, K13, and K14. Since our previous work had implicated retinoids in the control of cell adhesiveness, we were interested to find out whether changes in cell adhesion occur in vitamin A-deficient hamster tracheal epithelial cells, compared to normal cells. Functional assays demonstrated that hamster tracheal epithelial cells, obtained from non-RA-treated tracheas or maintained in culture, displayed reduced attachment to laminin, compared to RA-treated cells. Immunofluorescence studies did not show a decrease either in the alpha 6 integrin subunit, which was localized in the basal aspect of basal cells, or in basement membrane laminin. However, the expression of laminin-binding protein 37 decreased as the epithelium changed from pseudostratified to stratified. Therefore, a coordinated pattern of changes in keratin gene expression, as well as in the expression of laminin-binding protein 37, the precursor to the cell surface laminin receptor 67LR, and in adhesive properties takes place in tracheal epithelium when its phenotype changes from mucociliary to the preneoplastic stage of squamous metaplasia.

Molecular cloning of a Drosophila potential Z-DNA forming sequence hybridizing in situ to a developmentally regulated subdivision of the polytene chromosomes

We describe the selection of a group of plasmids with potential to form Z-DNA, from libraries of Drosophila hydei nuclear DNA using anti Z-DNA monoclonal (22) or polyclonal (10c) antibodies. The supercoiled closed circular forms of most of the selected recombinant plasmids from the 10c Z-DNA library show affinity to the polyclonal 10c antibody as indicated by DNA binding assays. One of these plasmids, pF17, was selected for further study. The insert in this plasmid adopts the Z conformation at bacterial supercoiled density. Analysis of deletion plasmids indicates that a Z-epitope is located within a short fragment of the insert in which 3 GC repetitions are found. The Drosophila DNA insert in pF17 hybridizes in situ with locus 4-75C1-2 of the polytene chromosomes, a locus whose transcriptional activity is developmentally regulated during the third instar.

Z-DNA in transcriptionally active chromosomes

Due to the striking correlation between the distribution of transcriptionally active subdivisions of the polytene chromosomes and Z-DNA, we have addressed the question of whether the Z-DNA configuration exists in native, transcriptionally active chromosomes of Drosophila hydei prepared without interference by procedures known to induce the B to Z conformation. Our experiments indicate that Z-DNA forms are present in a specific set of sites on the native chromosomes. They occur on interbands and other subdivisions of dispersed DNA, but there is no correlation between the amount of Z-DNA detected and DNA compaction. The results suggest, moreover, that Z-DNA forms are restricted to specific genes, because various subdivisions induced to transcription in puffs show different patterns of Z-DNA. We show, in addition, that removal of chromosomal proteins by proteinase K has a strong influence on the level of anti-Z-DNA reactivity.

Locations of Z-DNA in polytene chromosomes

In polytene chromosomes of Drosophila hydei and D. melanogaster, Z-DNA was identified in varying distribution after different conditions for fixation were used. When salivary glands were fixed and squashed in 50% acetic acid alone, Z-DNA was found in the less dense DNA regions, such as interbands, some puffs, and a few of the less dense bands. Prefixation that combined ethanol and acetic acid exposure led to prominent immunofluorescent staining of the bands, generally but not strictly correlating with the total DNA content. Separate exposure to ethanol and acetic acid did not cause this band to stain, but if residual ethanol was present after ethanol fixation, subsequent exposure to acid did cause it. Under the more selective acid fixation conditions, Z-DNA reactivity was seen in portions of certain ecdysone-inducible puffs in the induced but not in the resting state; in other inducible regions, the Z-DNA immunoreactivity was not changed on induction. Z-DNA was also identified in polytene chromosomes within isolated nuclei that had been frozen and fixed in ethanol without exposure to acid; this Z-DNA was present in regions of low DNA density.