Cloning and sequence of cDNA for human placental cytokeratin 8. Regulation of the mRNA in trophoblastic cells by cAMP

Mutation analysis of human cytokeratin 8 gene in malignant rhabdoid tumor: a possible association with intracytoplasmic inclusion body formation

The rhabdoid cell, which is typically observed in malignant rhabdoid tumor (MRT) and other malignant neoplasms, has an eosinophilic cytoplasm containing a spheroid perinuclear inclusion body. This distinct cell is known to act as a highly aggressive indicator in many types of malignant tumors and is characterized by aggregates of intermediate filaments, comprising both vimentin and cytokeratin (CK) 8, which is mainly expressed in simple-type epithelium such as liver and intestine. To clarify the cause of the inclusion body formation, we analyzed the alteration of the complete human CK8 gene (KRT 8: 1724 base pairs) in seven samples of MRT (three from frozen materials and four from cultured cell lines) by reverse-transcriptase polymerase chain reaction, followed by direct sequencing. In addition, the two cell lines, Huh7 and HeLa, which lacked rhabdoid feature, six pediatric malignant tumors, including three cases of primitive neuroectodermal tumor (PNET) and three of Wilms' tumor; and 15 normal liver tissue (as a control) were also analyzed. All MRT samples had missense mutations in the human KRT 8 gene, i.e., Arg89 --> Cys (5/7); Arg --> Cys251 (3/7); Glu267 --> Lys (6/7); Ser290 --> Ile, Met; (7/7) and Arg301 --> His(4/7), none of which was detected in any control samples. Among these mutations, the most noteworthy findings were that Arg89 belongs to the H1 subdomain of the head domain and that Arg251 belongs to the short nonhelical linker segment, or L1-2. Both these mutations are noted for their relationships to lateral protofilament-protofilament interactions. In addition, Ser290 has been previously reported to be a phosphorylation site, which has been recognized to play an important role in filament organization, leading to conformational change of the CK8 filaments. In conclusion, mutated codons of CK8 gene in MRT were located in the important region involved in the conformational change of intermediate filament.

A role for the 1A and L1 rod domain segments in head domain organization and function of intermediate filaments: structural analysis of trichocyte keratin

A dynamic model is proposed to explain how the 1A and linker L1 segments of the rod domain in intermediate filament (IF) proteins affect the head domain organization and vice versa. We have shown in oxidized trichocyte IF that the head domain sequences fold back over and interact with the rod domain. This phenomenon may occur widely in reduced IF as well. Its function may be to stabilize the 1A segments into a parallel two-stranded coiled coil or something closely similar. Under differing reversible conditions, such as altered states of IF assembly, or posttranslational modifications, such as phosphorylation etc., the head domains may no longer associate with the 1A segment. This could destabilize segment 1A and cause the two alpha-helical strands to separate. Linker L1 would thus act as a hinge and allow the heads to function over a wide lateral range. This model has been explored using the amino acid sequences of the head (N-terminal) domains of Type I and Type II trichocyte keratin intermediate filament chains. This has allowed several quasi-repeats to be identified. The secondary structure corresponding to these repeats has been predicted and a model has been produced for key elements of the Type II head domain. Extant disulfide cross-link data have been used as structural constraints. A model for the head domain structure predicts that a twisted beta-sheet region may wrap around the 1A segment and this may reversibly stabilize a coiled-coil conformation for 1A. The evidence in favor of the swinging head model for IF is discussed.

Reduced placental 11beta-hydroxysteroid dehydrogenase type 2 mRNA levels in human pregnancies complicated by intrauterine growth restriction: an analysis of possible mechanisms

11beta-Hydroxysteroid dehydrogenase type 2 (11beta-HSD2) inactivates cortisol to cortisone. In the placenta 11beta-HSD2 activity is thought to protect the fetus from the deleterious effects of maternal glucocorticoids. Patients with apparent mineralocorticoid excess owing to mutations in the 11beta-HSD2 gene invariably have reduced birth weight, and we have recently shown reduced placental 11beta-HSD2 activity in pregnancies complicated by intrauterine growth restriction. This is reflected in the literature by evidence of hypercortisolemia in the fetal circulation of small babies. In this study we have determined the levels of placental 11beta-HSD2 mRNA expression across normal gestation (n = 86 placentae) and in pregnancies complicated by intrauterine growth restriction (n = 19) and evaluated the underlying mechanism for any aberrant 11beta-HSD2 mRNA expression in intrauterine growth restriction. 11beta-HSD2 mRNA expression increased more than 50-fold across gestation, peaking at term. Placental 11beta-HSD2 mRNA levels were significantly decreased in intrauterine growth restriction pregnancies when compared with gestationally matched, appropriately grown placentae [e.g. at term DeltaCt (11beta-hydroxysteroid dehydrogenase type 2/18S) 12.8 +/- 0.8 (mean +/- SE) vs. 10.2 +/- 0.2, respectively, P < 0.001]. These differences were not attributable to changes in trophoblast mass in intrauterine growth restriction placentae, as assessed by parallel analyses of cytokeratin-8 mRNA expression. No mutations were found in the 11beta-HSD2 gene in the intrauterine growth restriction cohort, and imprinting analysis revealed that the 11beta-HSD2 gene was not imprinted. Although the underlying cause is unknown, 11beta-HSD2 gene expression is reduced in intrauterine growth restriction pregnancies. These data highlight the important role of 11beta-HSD2 in regulating fetal growth, a known factor in determining fetal morbidity but also the subsequent development of cardiovascular disease in adulthood.

Cytokeratin 8 is a suitable epidermal marker during zebrafish development

We have cloned and characterized the zebrafish (Danio rerio) homologous cytokeratin 8 (zf-K8) cDNA. This cytokeratin belongs to the gene family of intermediate filaments and it is a component of the cytoskeleton of epithelial cells. Gene expression analysis during embryonic development and at adult stages presented here revealed that zf-K8 mRNA is inherited maternally and that it is present in the oocyte, the zygote and in the cleavage stage embryo. After mid blastula transition this gene is expressed in all surface cells, notably in those of the enveloping layer (EVL) and of the periderm, as well as in a subpopulation of the deep cells (DEL) presumed to be intestinal progenitors. During later embryonic stage zf-K8 mRNA is strongly expressed in the developing pectoral fin. In adult zebrafish, the zf-K8 gene is not only expressed in simple epithelia such as the colorectal intestine, but also, in contrast to other vertebrates, it is present in stratified skin and differentiated fins. These observations suggest that the zf-K8 gene is an appropriate epidermal marker during zebrafish ontogenesis.

Stress, apoptosis, and mitosis induce phosphorylation of human keratin 8 at Ser-73 in tissues and cultured cells

Simple epithelia express keratins 8 (K8) and 18 (K18) as their major intermediate filament proteins. We previously showed that several types of cell stress such as heat and virus infection result in a distinct hyperphosphorylated form of K8 (termed HK8). To better characterize K8/18 phosphorylation, we generated monoclonal antibodies by immunizing mice with hyperphosphorylated keratins that were purified from colonic cultured human HT29 cells pretreated with okadaic acid. One antibody specifically recognized HK8, and the epitope was identified as 71LLpSPL which corresponds to K8 phosphorylation at Ser-73. Generation of HK8 occurs in mitotic HT29 cells, basal crypt mitotic cells in normal mouse intestine, and in regenerating mouse hepatocytes after partial hepatectomy. Prominent levels of HK8 were also generated in HT29 cells that were induced to undergo apoptosis using anisomycin or etoposide. In addition, mouse hepatotoxicity that is induced by chronic feeding with griseofulvin resulted in HK8 formation in the liver. Our results demonstrate that a "reverse immunological" approach, coupled with enhancing in vivo phosphorylation using phosphatase inhibitors, can result in the identification of physiologic phosphorylation states. As such, K8 Ser-73 phosphorylation generates a distinct HK8 species under a variety of in vivo conditions including mitosis, apoptosis, and cell stress. The low steady state levels of HK8 during mitosis, in contrast to stress and apoptosis, suggest that accumulation of HK8 may represent a physiologic stress marker for simple epithelia.

Phosphorylation of human keratin 8 in vivo at conserved head domain serine 23 and at epidermal growth factor-stimulated tail domain serine 431

Dynamic phosphorylation is one mechanism that regulates the more than 20 keratin type I and II intermediate filament proteins in epithelial cells. The major type II keratin in "simple type" glandular epithelia is keratin 8 (K8). We used biochemical and mutational approaches to localize two major in vivo phosphorylation sites of human K8 to the head (Ser-23) and tail (Ser-431) domains. Since Ser-23 of K8 is highly conserved among all type II keratins, we also examined if the corresponding Ser-59 in stratified epithelial keratin 6e is phosphorylated. Mutation of K6e Ser-59 abolished its phosphorylation in 32PO4-labeled baby hamster kidney cell transfectants. With regard to K8 phosphorylation at Ser-431, it increases dramatically upon stimulation of cells with epidermal growth factor (EGF) or after mitotic arrest and is the major K8 phosphorylated residue after incubating K8 immunoprecipitates with mitogen-activated protein or cdc2 kinases. A monoclonal antibody that specifically recognizes phosphoserine 431-K8 manifests increased reactivity with K8 and recognizes reorganized K8/18 filaments after EGF stimulation. Our results suggest that in vivo serine phosphorylation of K8 and K6e within the conserved head domain motif is likely to reflect a conserved phosphorylation site of most if not all type II keratins. Furthermore, K8 Ser-431 phosphorylation occurs after EGF stimulation and during mitotic arrest and is likely to be mediated by mitogen-activated protein and cdc2 kinases, respectively.

Identification by subtractive hybridization of a spectrum of novel and unexpected genes associated with in vitro differentiation of human cytotrophoblast cells

We have previously demonstrated that epidermal growth factor (EGF), colony stimulating factor-1 (CSF-I), and granulocyte-monocyte colony stimulating factor (GMCSF) stimulate, while transforming growth factor beta 1 (TGF beta 1) inhibits, cytotrophoblast differentiation. To identify genes mediating EGF induced differentiation, we constructed a subtracted cDNA library between undifferentiated cytotrophoblast and differentiating cytotrophoblast. We identified six novel genes and four known syncytial products alpha-human chorionic gonadotrophin (alpha hCG) pregnancy-specific beta 1-glycoprotein, 3 beta-hydroxysteroid dehydrogenase, and plasminogen activator inhibitor type 1 whose mRNAs increased during differentiation. Ten other genes were identified whose mRNAs increased during differentiation. Five of these (keratin 19, calcreticulin, heat shock protein 27, serum and glucocorticoid-regulated kinase and adrenomedullin) were not previously reported to be expressed in placenta. Five other genes known to be expressed in placenta were identified. keratin 8, fibronectin, mitochondrial ATP synthase, 1119, and cytosolic copper-zinc superoxide dismutase (SOD-1). Several of these genes may have regulatory functions in trophoblast differentiation.

Upregulation of cytokeratins 8 and 18 in human breast cancer T47D cells is retinoid-specific and retinoic acid receptor-dependent

The mamary gland is chiefly composed of luminal epithelial cells expressing cytokeratins (K) 8, 18 and 19, and basal/myoepithelial cells expressing cytokeratins 5 and 14. Human breast cancer T47D cells have a luminal phenotype and are growth-inhibited by retinoids, a class of compounds known to regulate cytokeratin expression. To extend our knowledge of retinoid action in breast cancer, we have studied the retinoid regulation of cytokeratin expression in the T47D model. We found that retinoid inhibition of T47D cell growth was accompanied by increases in K8, K18 and K19 mRNA steady-state levels (Northern blot analysis). The effect on K8 was studied in greater detail. This effect was seen with as low as 1 nM all-trans retinoic acid (tRA) and was maximal (up to 7 fold over control) with 1 microM tRA (the highest dose tested). Time-course studies revealed a detectable effect at 1 h and a maximal effect at 8-24 h. Non-retinoidal growth inhibitors (tamoxifen, BrcAMP and genistein) did not modulate K8 expression, demonstrating that the effect of tRA was specific, K8 mRNA upregulation was blocked by actinomycin D and cycloheximide, suggesting, in accordance with other studies, that tRA exerted a transcriptional effect that was secondary to de novo protein synthesis. Five retinoids known to activate retinoic acid receptor (RAR) and/or retinoid X receptor (RXR) - tRA; 9-cis-retinoic acid, 9cRA; 13-cis RA, 13cRA; retinyl acetate; and N-(4-hydroxyphenyl) retinamide 4HPR - inhibited T47D cell growth and increased K8 expression, whereas an arotinoid (Ro-40-8757) that is not a RAR activator caused growth inhibition but did not upregulate K8. Activation of RAR alpha contributed to K8 upregulation, since this effect was partially blocked by the RAR alpha-selective antagonist Ro-41-5253. Analogous results were obtained throughout when blots were reprobed with K18 cDNA. Western blot and immunocytochemistry experiments demonstrated that protein levels of K8 and K18 increased by 2 days of treatment with 1 microM tRA. These results show that retinoids enhance the expression of cognate cytokeratin markers of luminal differentiation in T47D breast cancer cells.

Expression of cytokeratin-mRNAs in squamous-cell carcinoma and balloon-cell formation of human oesophageal epithelium

Using digoxigenin-labelled cRNA probes, relationships between morphological characteristics and in situ hybridization for cytokeratin (CK)-mRNAs were analysed in cases of squamous-cell carcinoma of variable differentiation and in balloon-cell formation within the oesophageal mucosa. The present results were correlated to our previous findings on normal oesophageal epithelium. Our results from in situ hybridization study on oesophageal squamous-cell carcinoma provide strong evidence that changes in CK expression occur with differences in malignant potential. Cells of poorly differentiated carcinoma lose an ability to produce CK-mRNAs characteristic of their normal progenitor cells. Moderately differentiated and, still more pronounced, well differentiated carcinoma cells retain an ability to produce CKs characteristic of their tissue of origin (CK 6, CK 14, CK 15 and CK 19). Furthermore, well differentiated carcinoma cells may also gain an ability to synthesize new types of CKs that are not characteristic of the normal oesophageal epithelium (CK 8 and CK 18 characteristic of most simple epithelia, and CK 10 characteristic of keratinizing epithelia). Moreover, some oesophageal CK-genes are expressed in an obviously higher amount (CK 6, CK 14, and CK 19), but the expression of genes coding for the oesophageal differentiation-related CKs (CK 4 and CK 13) is obviously decreased or apparently lost. At the interface zone, observed in sections of well differentiated carcinomas, CK 8 and CK 18 mRNA were expressed in intermediate cell layers, and the centrally located cell layers were found positive for CK 10 mRNA. These findings largely extend the existing results from immunoblotting and immunohistochemical studies. The reduced or non-detectable expression of oesophageal differentiation-related CK-mRNAs (CK 4 and CK 13) on the appearance of balloon cells, suggests molecular changes that may be a marker for pathological progression. In addition, the abundant expression of CK 6 and CK 14 mRNA within areas of balloon-cell formation showing basal hyperplasia, and the higher expression of CK 19 in comparison with normal epithelium, points rather to de-differentiation than to normal vertical differentiation of the oesophageal epithelium. Whether CK-mRNAs can be used as biomarkers for evaluation of oesophageal pathologies remains to be further elucidated.

Expression of cytokeratin mRNAs in normal human esophageal epithelium

BACKGROUND

The cytokeratin (CK) pattern is accepted to be characteristic of a given epithelial cell or tissue. Specific changes in the CK pattern or in the expression of individual CKs may be characteristic in the early development of particular epithelial pathologies. Up to now no systematic hybridohistochemical study on the expression of CKs in normal human esophageal epithelium has been performed. Nevertheless, this knowledge may be of great importance for further research concerning the understanding of the structure and differentiation of normal esophageal epithelium and of the development of non-neoplastic and neoplastic esophageal malignancies. Therefore, we investigated the expression and distribution of nine different CK mRNAs throughout the normal human esophageal mucosa.

METHODS

A non-radioactive in situ hydridization protocol was used to study the expression of CK mRNAs in fixed and paraffin-embedded human esophageal mucosa. Digoxigenin-labelled cRNA probes were produced by in vitro transcription of cDNA clones, coding for human CKs.

RESULTS

In situ hybridization and immunodetection of the hybrids revealed a distinct but different distribution pattern for each specific CK mRNA. The described signal pattern was consistently found at all levels of the esophagus. We observed differences in the expression of some CK mRNAs between the interpapillar and papillar compartment of the esophageal epithelium. Mainly in the papillar regions some mRNAs are already expressed in more basally located cells in comparison with the interpapillar regions. Our results substantiate the hypothesis concerning the formation of papillae in the esophageal mucosa. We have also described some observations on the expression of CK mRNAs in fortuitous sections through excretory ducts of esophageal submucosal glands.

CONCLUSIONS

The distinct, characteristic, and reproducible distribution pattern observed for each specific CK mRNA indicates that the expression of the genes encoding CKs in the esophageal epithelium as well depends on the cell proliferation, on vertical cell migration and differentiation, and on detachment from the basal lamina. The results presented should be considered as complementary to the already existing immunohistochemical results concerning the distribution of esophageal CK proteins.

Identification of the major physiologic phosphorylation site of human keratin 18: potential kinases and a role in filament reorganization

There is ample in vitro evidence that phosphorylation of intermediate filaments, including keratins, plays an important role in filament reorganization. In order to gain a better understanding of the function of intermediate filament phosphorylation, we sought to identify the major phosphorylation site of human keratin polypeptide 18 (K18) and study its role in filament assembly or reorganization. We generated a series of K18 ser-->ala mutations at potential phosphorylation sites, followed by expression in insect cells and comparison of the tryptic 32PO4-labeled patterns of the generated constructs. Using this approach, coupled with Edman degradation of the 32PO4-labeled tryptic peptides, and comparison with tryptic peptides analyzed after labeling normal human colonic tissues, we identified ser-52 as the major K18 physiologic phosphorylation site. Ser-52 in K18 is not glycosylated and matches consensus sequences for phosphorylation by CAM kinase, S6 kinase and protein kinase C, and all these kinases can phosphorylate K18 in vitro predominantly at that site. Expression of K18 ser-52-->ala mutant in mammalian cells showed minimal phosphorylation but no distinguishable difference in filament assembly when compared with wild-type K18. In contrast, the ser-52 mutation played a clear but nonexclusive role in filament reorganization, based on analysis of filament alterations in cells treated with okadaic acid or arrested at the G2/M stage of the cell cycle. Our results show that ser-52 is the major physiologic phosphorylation site of human K18 in interphase cells, and that its phosphorylation may play an in vivo role in filament reorganization.

Expression of the nonclassic histocompatibility antigen HLA-G by preeclamptic placenta

OBJECTIVE

Expression of the histocompatibility antigen HLA-G may be required for appropriate invasion and remodeling of uterine spiral arteries. Inappropriate expression of this antigen may result in failure of invasion, leading to partial placental ischemia and gestational disease.

STUDY DESIGN

To test the hypothesis that the level of expression of HLA-G is reduced in trophoblasts from patients with gestational complications (preeclampsia, intrauterine growth retardation, or gestational hypertension) compared with patients with normal pregnancy, total ribonucleic acid was isolated from the fetal membrane or decidual interface of term placenta from several patient groups. Ribonuclease protection assay was used to determine levels of HLA-G expression, which was normalized for total ribonucleic acid input with beta-actin and for trophoblast content in the tissue by cytokeratin 8.

RESULTS

When normalized for total ribonucleic acid input (beta-actin), term placental expression of HLA-G was reduced for all forms of preeclampsia but not for intrauterine growth retardation or gestational hypertension. When tissue expression of cytokeratin, an indicator of trophoblast input, was normalized for trophoblast input, was normalized for total ribonucleic acid input, primary preeclampsia and intrauterine growth retardation had reduced numbers of trophoblast per unit tissue. When controlled for trophoblast input HLA-G expression was similar to normal for all clinical groups, except for intrauterine growth retardation, which was slightly increased.

CONCLUSION

Level of expression of HLA-G in placental tissue was reduced in preeclampsia. This decrease in expression appears to be related to reduced numbers of trophoblasts in placental tissue examined at term from patients with primary preeclampsia.

cDNAs encoding members of a family of proteins related to human sterol carrier protein 2 and assignment of the gene to human chromosome 1 p21----pter

Sterol carrier protein 2 (SCP2) is believed to play a key role in intracellular lipid movement. Here we report the cloning and nucleotide sequences of cDNAs encoding SCP2-related proteins of 58.85 kD and 30.8 kD and the assignment of the SCP2 gene to human chromosome 1 p21-pter. The SCP2-related proteins share common deduced carboxyl amino acid sequences with SCP2 and the cDNAs have a common 3' untranslated nucleotide sequence. The mRNAs encoding these proteins increased in a coordinate fashion as human placental cytotrophoblasts differentiated into syncytiotrophoblasts in culture. Our observations document the existence of a family of related proteins encoded by the human SCP2 gene.

Cloning and expression of a cDNA encoding human sterol carrier protein 2

We report the cloning and expression of a cDNA encoding human sterol carrier protein 2 (SCP2). The 1.3-kilobase (kb) cDNA contains an open reading frame which encompasses a 143-amino acid sequence which is 89% identical to the rat SCP2 amino acid sequence. The deduced amino acid sequence of the polypeptide reveals a 20-residue amino-terminal leader sequence in front of the mature polypeptide, which contains a carboxyl-terminal tripeptide (Ala-Lys-Leu) related to the peroxisome targeting sequence. The expressed cDNA in COS-7 cells yields a 15.3-kDa polypeptide and increased amounts of a 13.2-kDa polypeptide, both reacting with a specific rabbit antiserum to rat liver SCP2. The cDNA insert hybridizes with 3.2- and 1.8-kb mRNA species in human liver poly(A)+ RNA. In human fibroblasts and placenta the 1.8-kb mRNA was most abundant. Southern blot analysis suggests either that there are multiple copies of the SCP2 gene in the human genome or that the SCP2 gene is very large. Coexpression of the SCP2 cDNA with expression vectors for cholesterol side-chain cleavage enzyme and adrenodoxin resulted in a 2.5-fold enhancement of progestin synthesis over that obtained with expression of the steroidogenic enzyme system alone. These findings are concordant with the notion that SCP2 plays a role in regulating steroidogenesis, among other possible functions.

A cDNA encoding a rat mitochondrial cytochrome P450 catalyzing both the 26-hydroxylation of cholesterol and 25-hydroxylation of vitamin D3: gonadotropic regulation of the cognate mRNA in ovaries

A cDNA expression library prepared from rat liver RNA was screened with a polyclonal antibody specific for mitochondrial vitamin D3 25-hydroxylase and a cDNA for rabbit liver mitochondrial cytochrome P450c26 (CYP 26), yielding cDNA clones with identical sequences. The deduced amino acid sequence derived from a 1.9-kb full-length cDNA was 73% identical to that of rabbit cytochrome P450c26. A monoclonal antibody was used to demonstrate that the product of the 1.9-kb cDNA clone was targeted to the mitochondrial compartment when expressed in COS cells. Mitochondrial membranes containing the expressed protein showed both vitamin D3 25-hydroxylase and cholesterol 26-hydroxylase activities when reconstituted with ferredoxin reductase and ferredoxin, demonstrating that the same P450, designated as P450c26/25, can catalyze both reactions. Northern blot analysis revealed that the P450c26/25 cDNA hybridizes with a 2.4-kb RNA from rat liver and unstimulated ovaries. Treatment of rats with pregnant mare's serum gonadotropin resulted in a fivefold increase in the 2.4-kb mRNA as well as the appearance of a 2.1-kb mRNA species in the ovaries. Our findings document the presence of a regulated bifunctional mitochondrial cytochrome P450 capable of catalyzing the 25-hydroxylation of vitamin D3 and the 26-hydroxylation of cholesterol.