Expression of c-mos proto-oncogene in undifferentiated teratocarcinoma cells

Testicular Activity of Mos in the Frog, Rana esculenta: A New Role in Spermatogonial Proliferation1

Mos is a MAPK kinase kinase with an expression that is highly restricted to the gonads. Its function is mainly associated to the meiotic metaphase II arrest occurring during female gametogenesis, whereas to our knowledge, its role during spermatogenesis has not yet clarified. In the present paper, we report the isolation of c-mos cDNA and the identification of a 60-kDa Mos protein from the testis of the anuran amphibian, Rana esculenta. Both the transcript and the protein are always present at low levels in the testis during the frog annual sexual cycle, with single significant peaks of expression in March and May, respectively. Mos is mainly localized in the cytoplasm of primary and secondary spermatogonia (SPG). Therefore, we have used treatments with ethane-dimethane sulphonate (EDS), which blocks spermatogonial mitosis in frogs. Four days after a single EDS injection, Mos expression in SPG highly increases concomitantly with the temporary arrest of mitosis. From 8 to 28 days after the injection, the normal proliferative activity of SPG is restored, and Mos expression gradually decreases to control levels. These results strongly indicate that the c-mos proto-oncogene exerts a new role associated to the regulation of spermatogonial proliferation.

Identification of a cis acting element responsible for muscle specific expression of the c-mos protooncogene

A series of deletion constructs of the 5' flanking region of rat c-mos gene was positioned upstream to the CAT gene and transfected into muscle and non-muscle cells. CAT activities revealed that a region located downstream of a TATA box and containing the proximal transcription start site is the muscle c-mos promoter. This promoter is more efficient in L6 alpha 1 myoblasts than in L6 alpha 1 myotubes but not in C3H10T1/2 cells. Gel shift assays demonstrated that nuclear proteins from myoblasts and myotubes formed complexes migrating differently. Footprinting analyses showed that nuclear proteins from L6 alpha 1 myoblasts protected a DNA fragment located at position nt -979 to nt -938 relative to the first ATG of the rat c-mos ORF while nuclear proteins from myotubes protected the DNA between nt -998 to nt -928. Furthermore one of protein - DNA complexes containing the proximal transcription start site, included a consensus sequence TGTC(AGT/TCG)CC(A/T)G present in the initiator element (Inr) of several genes. Southwestern blot analysis pointed to a 82kDa polypeptide as a potential candidate for trans acting factor in myoblasts. In L6 alpha 1 myotubes this polypeptide is replaced by other proteins of 40-42kDa and 82kDa. An interplay between these two complexes may constitute a developmental as well as a physiologically regulated mechanism that modulates c-mos expression during the early stages of myogenesis.

Changes in c-onc expression during embryonal carcinoma cell differentiation

Protooncogenes expressed in murine embryonal carcinoma (EC) cells or their differentiated daughter cells include more or less ubiquitously expressed protooncogenes such as c-myc, c-K-ras, and c-abl, as well as c-onc genes with a very restricted expression pattern. Examples of the latter are N-myc, c-mos, and int-2. These c-onc genes are transcriptionally active in EC cells, as well as in germ cells and/or early embryonic cells. When EC cells are induced to differentiate some protooncogenes or oncogene-related products undergo changes in expression. Thus, EC cell differentiation has been associated with increased expression of c-src, c-fos, int-1, int-2, and the epidermal growth factor (EGF) receptor, whereas decreased expression has been observed for c-mos, c-K-ras, c-myc, N-myc, and platelet-derived growth factor. The relationships between these changes in expression and EC cell differentiation are not understood. They may be important for the differentiation process or for expression of a differentiated phenotype. They may, however, also be secondary events with no functional significance to EC cell differentiation.

Increased amount of a 25-kilodalton phosphoprotein after v-mos transfection of CHO cells

We transfected Chinese hamster ovary (CHO) cells with a cloned v-mos gene (pHT25). The mos family of oncogenes has previously been shown to have serine-threonine kinase activity. This kinase activity may be required for oncogenic transformation, although its exact biological role is unknown. We found that the transfected cells had an altered morphology, a slower doubling time, and an apparent increase in the amount of a 25-kilodalton (kDa) phosphoprotein that appeared to be of low abundance. Transfection of CHO cells with a cloned temperature-sensitive mos gene (ts159) led to isolation of a cell line that showed the presence of the 25-kDa phosphoprotein at the permissive but not at the nonpermissive temperature, suggesting a direct relationship between mos activity and the presence of this phosphoprotein. The characteristics of altered morphology and depressed growth rate were reminiscent of changes seen after the activation of the cyclic AMP-dependent protein kinase (PKA) in CHO cells. However, PKA activation did not stimulate phosphorylation of this 25-kDa protein, nor was there a change in total PKA activity in these cells. We suggest that the increased presence of the 25-kDa phosphoprotein is a consequence of the v-mos transfection and that it may be involved in the change of morphology and growth rate seen in the CHO cells. Phosphorylation of this protein may be a useful marker of mos and have some functional importance in the transformation of cells by the v-mos oncogene.

Changes of c-mos expression in response to 2-O-tetradecanoylphorbol-13-acetate in undifferentiated teratocarcinoma cells

Treatment of the cells of the 311 cell line, a pluripotent mouse teratocarcinoma cell line, with 12-O-tetradecanoylphorbol-13-acetate (TPA) modulates c-mos expression. Transient suppression of 6.1 and 4.6 kilobases (kb) transcripts and activation of 1.8 transcript indicate that TPA mediates concurrently positive and negative regulation of c-mos transcription. The results show that the c-mos gene is a TPA-modulated gene. In addition, a TPA-responsive element (GTGACTCA), which exists in the 5'-flanking region of c-mos gene of Balb/c mice [1,2], is suggested to be involved in this response. However, these changes were not accompanied by early marker changes associated with endodermal cell differentiation, i.e., morphological change, induction of plasminogen activator and suppression of glucose transport activity.

Regulation of human mesothelial cell differentiation: opposing roles of retinoids and epidermal growth factor in the expression of intermediate filament proteins

We report here the discovery that retinoids are potent regulators of epithelial morphology and keratin expression in cultured human mesothelial cells. When LP-9 cells are cultured in medium supplemented with vitamin A-depleted serum, they grow with an extreme spindle-shaped morphology and synthesize abundant levels of vimentin, but very little keratin. When retinoic acid is added to the medium at 1 X 10(-8) to 1 X 10(-6) M, keratin synthesis is increased, vimentin synthesis is decreased, and the cells assume an epithelioid morphology. Keratin synthesis, but not epithelioid morphology, seems to be dependent on cell density as well: even when vitamin A is present, sparse cultures cannot fully maintain keratin synthesis. In contrast, epidermal growth factor (EGF) acts in an antagonistic fashion to suppress both keratin synthesis and epithelial morphology. The effects of vitamin A, EGF, and cell shape on intermediate filament (IF) expression seem to occur in a growth-independent manner, and they appear to be at the level of transcription or mRNA stability. Even so, their effects on IF expression do not appear to be rapid ones, and hence it is unlikely that these agents interact directly at the gene level to cause changes in IF gene expression.

Suppression of c-mos expression in teratocarcinoma cells with a new type of inducer of differentiation, 3,5-di-tert-butylchalcone 4'-carboxylic acid

The treatment of 311 cells, a pluripotent mouse teratocarcinoma cell line, with a new type of inducer, 3,5-di-tert-butylchalcone 4'-carboxylic acid (Ch55), results in the suppression of the c-mos gene, accompanied by early marker changes associated with cell differentiation, i.e., the enhanced secretion of plasminogen activator and the decrease in peanut agglutinin receptors and glucose transport. This indicates that Ch55 is a potent inducer of teratocarcinoma cells and suppresses c-mos expression.

Distinct developmental patterns of c-mos protooncogene expression in female and male mouse germ cells

The protooncogene c-mos is expressed in murine reproductive tissues, producing transcripts of 1.7 and 1.4 kilobases in testis and ovary, respectively. In situ hybridization analysis of c-mos expression in histological sections of mouse ovaries revealed that oocytes are the predominant if not exclusive source of c-mos transcripts. c-mos transcripts accumulate in growing oocytes, increasing 40- to 90-fold during oocyte and follicular development. c-mos transcripts were also detected in male germ cells and are most abundant after the cells have entered the haploid stage of spermatogenesis. This developmentally regulated pattern of c-mos expression in oocytes and spermatogenic cells suggests that the c-mos gene product may have a function in normal germ-cell differentiation or early embryogenesis.