Sequence of a cDNA encoding human keratin No 10 selected according to structural homologies of keratins and their tissue-specific expression

The mRNA Export Factor Human Gle1 Interacts with the Nuclear Pore Complex Protein Nup155

The protein Gle1 is required for export of mRNAs from the nucleus to the cytoplasm in both lower and higher eukaryotic cells. In human (h) cells, shuttling of hGle1 between the nucleus and cytoplasm is essential for bulk mRNA export. To date, no hGle1-interacting proteins have been reported and the mechanism by which hGle1 interacts with the nuclear pore complex (NPC) and mediates export is unknown. To identify proteins that can interact with hGle1, a genome-wide yeast two-hybrid screen was performed. Three potential hGle1-interacting partners were isolated, including clones encoding the C-terminal region of the NPC protein hNup155. This interaction between hGle1 and full-length hNup155 was confirmed in vitro, and deletion analysis identified the N-terminal 29 residues of hGle1 as the hNup155-binding domain. Experiments in HeLa cells confirmed that the nuclear rim localization of the major hGle1 protein variant (hGle1B) was dependent on the presence of these 29 N-terminal residues. This suggests that this domain of hGle1 is necessary for targeting to the NPC. This work also characterizes the first domain in hNup155, a 177 C-terminal amino acid span that binds to hGle1. The mutual interaction between hGle1 and the symmetrically distributed nuclear pore protein Nup155 suggests a model in which hGle1's association with hNup155 may represent a step in the Gle1-mediated mRNA export pathway.

Mutation of human keratin 18 in association with cryptogenic cirrhosis

Mutations in 11 of the more than 20 keratin intermediate filaments cause several epidermal and oral associated diseases. No disease-associated mutations have been described in keratin 8 or 18 (K8/18) which are the major keratin pair in simple-type epithelia, as found in the liver, pancreas, and intestine. However, transgenic mice that express mutant keratin 18 develop chronic hepatitis, and have an increased susceptibility to drug-induced hepatotoxicity. Also, ectopic expression of epidermal K14 in mouse liver results in chronic hepatitis, and disruption of mouse K8 leads to embryo lethality with extensive liver hemorrhage. We tested if patients with liver disease of unknown cause may harbor mutations in K18. We describe a his127-->leu (H127L) K18 mutation in a patient with cryptogenic cirrhosis that is germline transmitted. The K18 H127L isolated from the liver explant, or after expression in bacteria, showed an altered migration on two-dimensional gel analysis as compared with normal human liver or bacterially expressed K18. Electron microscopy of in vitro assembled K18 H127L and wild type K8 showed an assembly defect as compared with normal K8/18 assembly. Our results suggest that mutations in K18 may be predispose to, or result in cryptogenic cirrhosis in humans.

Wavelength-specific upregulation of keratin mRNA expression in response to ultraviolet radiation

Keratin intermediate filaments are heteropolymers of coexpressed type I and type II protein chains, whose expression is tightly linked to the differentiation status of the keratinocyte. Epidermal basal keratinocytes coexpress keratins K5 and K14, whereas suprabasal keratinocytes downregulate K5 and K14 and begin to coexpress keratins K1 and K10. Using both isotopic and non-isotopic in situ hybridization, we have investigated the changes in expression of the messenger RNA species encoding the K5/K14 and K1/K10 keratin pairs in response to ultraviolet radiation. Here we report that following irradiation, the mRNA species encoding both keratin pairs is upregulated in a wavelength-specific manner, and that the link between the pattern of keratin mRNA expression and the differentiation status of the keratinocyte is disrupted. Forty-eight hours following ultraviolet B exposure, the amount of detectable mRNA encoding all four keratins studied had increased. Following UVA irradiation, the K1 and K10 signal increased to a much lesser extent than following ultraviolet B, whereas no change in the amount of mRNA encoding the K5/K14 pair was observed. Only two samples were examined following ultraviolet C exposure, but in both, increased K5/K14 signal, but not suprabasal K1/K10 signal, was observed. We suggest that the observations reported here may reflect important qualitative changes involved in photoadaptation of the epidermis, and provide further molecular markers of the different biological effects of ultraviolet radiation of different wavelengths.

Exons I and VII of the gene (Ker10) encoding human keratin 10 undergo structural rearrangements within repeats

A genomic fragment containing the K51 gene previously isolated from a rat genomic library by hybridization with the v-mos probe in nonstringent conditions [Chumakov et al., Dokl. Akad. Nauk SSSR 290 (1986) 1252-1254], resembles a human keratin type-I-encoding gene [Shvets et al., Mol. Biol. 24 (1990) 663-677]. This genomic clone, K51, has been used as a probe to search for related human genes. A recombinant clone, HK51, with a 1.5-kb insert, was isolated from a human embryonic skin cDNA library, and its nucleotide (nt) sequence was determined. Analysis has shown that the cloned cDNA encodes human keratin 10 (Ker10). All presently known nt sequences of the human Ker10-encoding gene (Ker10) are not identical. Differences are concentrated in the 5'-end of the first exon and in the middle of the seventh exon within repeats. In spite of structural rearrangements in two of eight exons, the reading frame and position of the stop codon are preserved. The genetic rearrangements cause changes in hydrophobicity profiles of the N and C termini of Ker10. It was also noticed that insertion of one nt leads to the formation of an unusual 3'-end of the transcript.

Delayed onset of epidermal differentiation in psoriasis

In normal epidermis, as previously reported, the first signs of differentiation occur within the basal layer in a subpopulation of keratinocytes that start to express K1 and K10 "supra-basal" keratin transcripts (20-30% of the basal cells) and proteins (5-10% of the basal cells). We found that in psoriatic lesions, the basal layer was devoid of cells expressing these early differentiation markers. This was already the case at the periphery of the lesions, where epidermis, although slightly acanthotic, still completes the keratinization process. In the center of the lesions, not only the basal layer, but also several rows of suprabasal cells, were negative for keratin K10 transcripts or protein. Moreover, the upper nucleated layers of involved epidermis were also devoid of K10 keratin transcripts or proteins. In normal epidermis, as previously reported, transcripts for the "basal" K5 keratin were mainly restricted to the basal layer, whereas the protein persisted in a few suprabasal layers. We found that in psoriatic epidermis, K5 keratin transcripts persisted in several suprabasal layers up to the level where K10 keratin transcripts appeared. These data, although not contradictory with previous reports showing a reduction of K1-K10 keratins and other differentiation markers in psoriasis, demonstrate that these quantitative changes are in fact the result of major qualitative differences in the distribution of these markers in psoriatic versus normal skin. Our results indicating that the onset of differentiation is delayed in psoriasis show that, contrary to conclusions accepted so far, not only the suprabasal compartment, but also the basal one, is abnormal in psoriatic epidermis.

Expression of loricrin is negatively controlled by retinoic acid in human epidermis reconstructed in vitro

In epidermis, the last steps of keratinocyte differentiation are characterized by the covalent cross-linking of cornified envelope precursors such as involucrin and loricrin, a hydrophobic protein recently described in mouse and human epidermis. In situ hybridization of normal human skin sections with a human loricrin cRNA probe and immunolabeling with an antiserum directed against a synthetic peptide corresponding to the carboxyterminus of human loricrin revealed the presence of loricrin transcripts and protein in the granular layers of epidermis. In human epidermis reconstructed in vitro by growing keratinocytes on dermal equivalents, loricrin and loricrin mRNAs were also restricted to granular cells, but their amounts seemed higher than in epidermis from skin biopsies. The reactivities for both loricrin and loricrin mRNAs were abolished by a treatment of the cultures with a retinoic acid concentration (10(-6) M) provoking a complete inhibition of terminal epidermal differentiation (parakeratosis). Thus, the regulation of loricrin synthesis is different from that of another envelope precursor, involucrin, which does not seem to be significantly modulated by retinoic acid. Together with the well-documented inhibition of epidermal transglutaminase by retinoic acid, our results provide a molecular basis for the inhibition of cornified envelope formation by retinoic acid.

Isolation of a GC-rich cDNA identifying mRNA present in human epidermis and modulated by calcium and retinoic acid in cultured keratinocytes. Homology with murine loricrin mRNA

Differential screening of a human epidermal cDNA library led to the isolation of cDNA clones homologous to mRNAs specifically expressed in epidermis but weakly or not expressed in the undifferentiated squamous carcinoma cell line TR146. One of these 'differentiation-specific' cDNA clones, A8, hybridized with a 1.7 kb transcript among RNAs isolated from normal human epidermis, but with several transcripts ranging from 1.4 to 2.1 kb when mRNAs were isolated from cultured keratinocytes. We examined the effects of modulators of epidermal differentiation such as calcium and retinoic acid on the production of these transcripts. Their amount was found to increase in the presence of high calcium concentration, but to decrease in the presence of retinoic acid. These results strongly suggest that A8 messages are up-regulated during epidermal differentiation. The sequence of the 1371 bp of A8 cDNA shows a very high GC content. Because of its homology with the murine loricrin mRNA, A8 is likely to correspond either to the human loricrin or to a related protein.

Keratin 19: predicted amino acid sequence and broad tissue distribution suggest it evolved from keratinocyte keratins

The type I keratin 19 is unusual in its tissue distribution in that under normal circumstances it does not seem to be restricted, as the other keratins are, to expression in either stratified or simple epithelia. In addition to the previously reported distribution of keratin 19 in human tissues, we have observed keratin 19 in epidermal basal cells, in a defined region of the hair follicle, and in nipple epidermis. We noticed that expression of keratin 19 appears to be especially characteristic of regions of labile or variable cellular differentiation as indicated by the presence of multiple keratin phenotypes in close proximity to each other. Using a monoclonal antibody recognizing keratin 19 (LP2K) to screen a human placenta cDNA expression library, we have isolated, cloned, and sequenced cDNA coding for full-length human keratin 19, as confirmed by its reactivity with several other known anti-keratin 19 monoclonal antibodies and by the near identity of its sequence with that of the bovine keratin 19 homologue. This similarity extends to both proteins being truncated at the C-terminal end to only 13 amino acids beyond the rod domain. Although the amino acid homology over the N-terminal and helical rod domains is particularly high, the human and bovine proteins diverge substantially over the short C-terminal domain, which suggests that this region has no conserved function. Comparison with other type I keratins indicates that the closest evolutionary neighbors of keratin 19 are keratinocyte keratins, probably 13 and 14, and not the simple epithelial keratin 18. Assessing the histochemistry and sequence data together, we propose that the cell may use this apparently deficient keratin as a "neutral" keratin. While unimpaired in its ability to polymerize (keeping the cell integrated into the epithelial sheet via filament-desmosome networks), keratin 19 expression does not irrevocably commit a cell to any one of the local differentiation options. Such predicted differentiational flexibility may also imply vulnerability to transformation.

Identification of an orthologous mammalian cytokeratin gene. High degree of intron sequence conservation during evolution of human cytokeratin 10

Among the human acidic (type I) cytokeratins, components 10 and 11 are especially interesting, as they are under various kinds of expression control. They are synthesized in the suprabasal cell layers of certain stratified epithelia, notably epidermis, in an endogenous differentiation program; they are expressed in certain epithelial tumours but not in others; they can appear de novo in certain pathological situations such as in squamous metaplasias; and their expression in vivo and in vitro is under positive influence of extracellular calcium concentrations and is reduced in the presence of vitamin A or other retinoids. To provide a basis for studies of the various regulatory elements, we have isolated the human gene encoding cytokeratin 10, using a cDNA probe derived from the corresponding bovine gene, and have sequenced the mRNA coding region as well as adjacent regions approximately 1500 bases 5' upstream and 1000 bases 3' downstream. The eight exons encode a polypeptide 59,535 Mr, i.e. somewhat larger than the corresponding bovine and murine proteins. The deduced amino acid sequences display a high degree of homology, which is not restricted to the exons and the 5' and 3' adjacent regions but, surprisingly, is also evident in the seven introns, some of which contain extended sequence elements with 70% identical nucleotides and more, i.e. similar to the homology in the adjacent exons. This exceptionally high level of conservation of intron sequences is discussed in relation to the recently accumulating evidence of the occurrence of intron sequences important in the regulation of the expression of members of other multigene families during development.

Isolation and characterization of a cDNA clone coding for human epidermal keratin K5. Sequence of the carboxyterminal half of this keratin

A cDNA clone encoding human epidermal keratin No. 5 (K5) has been isolated from a lambda gt10 cDNA library on the basis of crosshybridization with cDNAs coding for other basic keratins and differential hybridization with total cDNA probes. This clone contains a 1100-bp insert able to inhibit specifically translation of K5 in a hybrid-arrested translation test. Northern blots show that this insert hybridizes with a 2.4-kb message present in epidermal mRNAs. The 1100-bp sequence reported here corresponds to the 3' half of the K5 message. Comparison of the deduced aminoacid sequence shows that the protein exhibits characteristic features of a basic keratin. The 242 aminoacid sequence reported here extends from the carboxyterminal end up to the last helical portion of the central rod domain.