Normal keratinization in a spontaneously immortalized aneuploid human keratinocyte cell line

In contrast to mouse epidermal cells, human skin keratinocytes are rather resistant to transformation in vitro. Immortalization has been achieved by SV40 but has resulted in cell lines with altered differentiation. We have established a spontaneously transformed human epithelial cell line from adult skin, which maintains full epidermal differentiation capacity. This HaCaT cell line is obviously immortal (greater than 140 passages), has a transformed phenotype in vitro (clonogenic on plastic and in agar) but remains nontumorigenic. Despite the altered and unlimited growth potential, HaCaT cells, similar to normal keratinocytes, reform an orderly structured and differentiated epidermal tissue when transplanted onto nude mice. Differentiation-specific keratins (Nos. 1 and 10) and other markers (involucrin and filaggrin) are expressed and regularly located. Thus, HaCaT is the first permanent epithelial cell line from adult human skin that exhibits normal differentiation and provides a promising tool for studying regulation of keratinization in human cells. On karyotyping this line is aneuploid (initially hypodiploid) with unique stable marker chromosomes indicating monoclonal origin. The identity of the HaCaT line with the tissue of origin was proven by DNA fingerprinting using hypervariable minisatellite probes. This is the first demonstration that the DNA fingerprint pattern is unaffected by long-term cultivation, transformation, and multiple chromosomal alterations, thereby offering a unique possibility for unequivocal identification of human cell lines. The characteristics of the HaCaT cell line clearly document that spontaneous transformation of human adult keratinocytes can occur in vitro and is associated with sequential chromosomal alterations, though not obligatorily linked to major defects in differentiation.

Mesenchymal stem cells enhance wound healing through differentiation and angiogenesis

Although chronic wounds are common, treatment for these disabling conditions remains limited and largely ineffective. In this study, we examined the benefit of bone marrow-derived mesenchymal stem cells (BM-MSCs) in wound healing. Using an excisional wound splinting model, we showed that injection around the wound and application to the wound bed of green fluorescence protein (GFP)(+) allogeneic BM-MSCs significantly enhanced wound healing in normal and diabetic mice compared with that of allogeneic neonatal dermal fibroblasts or vehicle control medium. Fluorescence-activated cell sorting analysis of cells derived from the wound for GFP-expressing BM-MSCs indicated engraftments of 27% at 7 days, 7.6% at 14 days, and 2.5% at 28 days of total BM-MSCs administered. BM-MSC-treated wounds exhibited significantly accelerated wound closure, with increased re-epithelialization, cellularity, and angiogenesis. Notably, BM-MSCs, but not CD34(+) bone marrow cells in the wound, expressed the keratinocyte-specific protein keratin and formed glandular structures, suggesting a direct contribution of BM-MSCs to cutaneous regeneration. Moreover, BM-MSC-conditioned medium promoted endothelial cell tube formation. Real-time polymerase chain reaction and Western blot analysis revealed high levels of vascular endothelial growth factor and angiopoietin-1 in BM-MSCs and significantly greater amounts of the proteins in BM-MSC-treated wounds. Thus, our data suggest that BM-MSCs promote wound healing through differentiation and release of proangiogenic factors. Disclosure of potential conflicts of interest is found at the end of this article.

Cutting edge: 1,25-dihydroxyvitamin D3 is a direct inducer of antimicrobial peptide gene expression

The hormonal form of vitamin D(3), 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)), is an immune system modulator and induces expression of the TLR coreceptor CD14. 1,25(OH)(2)D(3) signals through the vitamin D receptor, a ligand-stimulated transcription factor that recognizes specific DNA sequences called vitamin D response elements. In this study, we show that 1,25(OH)(2)D(3) is a direct regulator of antimicrobial innate immune responses. The promoters of the human cathelicidin antimicrobial peptide (camp) and defensin beta2 (defB2) genes contain consensus vitamin D response elements that mediate 1,25(OH)(2)D(3)-dependent gene expression. 1,25(OH)(2)D(3) induces antimicrobial peptide gene expression in isolated human keratinocytes, monocytes and neutrophils, and human cell lines, and 1,25(OH)(2)D(3) along with LPS synergistically induce camp expression in neutrophils. Moreover, 1,25(OH)(2)D(3) induces corresponding increases in antimicrobial proteins and secretion of antimicrobial activity against pathogens including Pseudomonas aeruginosa. 1,25(OH)(2)D(3) thus directly regulates antimicrobial peptide gene expression, revealing the potential of its analogues in treatment of opportunistic infections.

beta-Catenin controls hair follicle morphogenesis and stem cell differentiation in the skin

beta-Catenin is an essential molecule in Wnt/wingless signaling, which controls decisive steps in embryogenesis. To study the role of beta-catenin in skin development, we introduced a conditional mutation of the gene in the epidermis and hair follicles using Cre/loxP technology. When beta-catenin is mutated during embryogenesis, formation of placodes that generate hair follicles is blocked. We show that beta-catenin is required genetically downstream of tabby/downless and upstream of bmp and shh in placode formation. If beta-catenin is deleted after hair follicles have formed, hair is completely lost after the first hair cycle. Further analysis demonstrates that beta-catenin is essential for fate decisions of skin stem cells: in the absence of beta-catenin, stem cells fail to differentiate into follicular keratinocytes, but instead adopt an epidermal fate.

Differentiation-related expression of a major 64K corneal keratin in vivo and in culture suggests limbal location of corneal epithelial stem cells

In this paper we present keratin expression data that lend strong support to a model of corneal epithelial maturation in which the stem cells are located in the limbus, the transitional zone between cornea and conjunctiva. Using a new monoclonal antibody, AE5, which is highly specific for a 64,000-mol-wt corneal keratin, designated RK3, we demonstrate that this keratin is localized in all cell layers of rabbit corneal epithelium, but only in the suprabasal layers of the limbal epithelium. Analysis of cultured corneal keratinocytes showed that they express sequentially three major keratin pairs. Early cultures consisting of a monolayer of "basal" cells express mainly the 50/58K keratins, exponentially growing cells synthesize additional 48/56K keratins, and postconfluent, heavily stratified cultures begin to express the 55/64K corneal keratins. Cell separation experiments showed that basal cells isolated from postconfluent cultures contain predominantly the 50/58K pair, whereas suprabasal cells contain additional 55/64K and 48/56K pairs. Basal cells of the older, postconfluent cultures, however, can become AE5 positive, indicating that suprabasal location is not a prerequisite for the expression of the 64K keratin. Taken together, these results suggest that the acidic 55K and basic 64K keratins represent markers for an advanced stage of corneal epithelial differentiation. The fact that epithelial basal cells of central cornea but not those of the limbus possess the 64K keratin therefore indicates that corneal basal cells are in a more differentiated state than limbal basal cells. These findings, coupled with the known centripetal migration of corneal epithelial cells, strongly suggest that corneal epithelial stem cells are located in the limbus, and that corneal basal cells correspond to "transient amplifying cells" in the scheme of "stem cells----transient amplifying cells----terminally differentiated cells."

Stem cells in the hair follicle bulge contribute to wound repair but not to homeostasis of the epidermis

The discovery of long-lived epithelial stem cells in the bulge region of the hair follicle led to the hypothesis that epidermal renewal and epidermal repair after wounding both depend on these cells. To determine whether bulge cells are necessary for epidermal renewal, here we have ablated these cells by targeting them with a suicide gene encoding herpes simplex virus thymidine kinase (HSV-TK) using a Keratin 1-15 (Krt1-15) promoter. We show that ablation leads to complete loss of hair follicles but survival of the epidermis. Through fate-mapping experiments, we find that stem cells in the hair follicle bulge do not normally contribute cells to the epidermis which is organized into epidermal proliferative units, as previously predicted. After epidermal injury, however, cells from the bulge are recruited into the epidermis and migrate in a linear manner toward the center of the wound, ultimately forming a marked radial pattern. Notably, although the bulge-derived cells acquire an epidermal phenotype, most are eliminated from the epidermis over several weeks, indicating that bulge stem cells respond rapidly to epidermal wounding by generating short-lived 'transient amplifying' cells responsible for acute wound repair. Our findings have implications for both gene therapy and developing treatments for wounds because it will be necessary to consider epidermal and hair follicle stem cells as distinct populations.

Changes in keratin gene expression during terminal differentiation of the keratinocyte

Cells of the inner layers of the epidermis contain small keratins (46-58K), whereas the cells of the outer layers contain large keratins (63-67K) in addition to small ones. The changes in keratin composition that take place within each cell during the course of its terminal differentiation result largely from changes in synthesis. Cultured epidermal cells resemble cells of the inner layers of the epidermis in synthesizing only small keratins. The cultured cells possess translatable mRNA only for small keratins, whereas mRNA extracted from whole epidermis can be translated into both large and small keratins. As no synthesis takes place in the outermost layer of the epidermis (stratum corneum), the keratins of this layer must be synthesized earlier, but in some cases they then become smaller: this presumably occurs by post-translational processing of the molecules during the final stages of differentiation. Stratified squamous epithelia of internal organs do not form a typical stratum corneum and do not make the large keratins characteristic of epidermis. Their keratins are also different from those of cultured keratinocytes, implying that they have embarked on an alternate route of terminal keratin synthesis.

Asymmetric cell divisions promote stratification and differentiation of mammalian skin

The epidermis is a stratified squamous epithelium forming the barrier that excludes harmful microbes and retains body fluids. To perform these functions, proliferative basal cells in the innermost layer periodically detach from an underlying basement membrane of extracellular matrix, move outward and eventually die. Once suprabasal, cells stop dividing and enter a differentiation programme to form the barrier. The mechanism of stratification is poorly understood. Although studies in vitro have led to the view that stratification occurs through the delamination and subsequent movement of epidermal cells, most culture conditions favour keratinocytes that lack the polarity and cuboidal morphology of basal keratinocytes in tissue. These features could be important in considering an alternative mechanism, that stratification occurs through asymmetric cell divisions in which the mitotic spindle orients perpendicularly to the basement membrane. Here we show that basal epidermal cells use their polarity to divide asymmetrically, generating a committed suprabasal cell and a proliferative basal cell. We further demonstrate that integrins and cadherins are essential for the apical localization of atypical protein kinase C, the Par3-LGN-Inscuteable complex and NuMA-dynactin to align the spindle.

A structural scaffolding of intermediate filaments in health and disease

The cytoplasm of animal cells is structured by a scaffolding composed of actin microfilaments, microtubules, and intermediate filaments. Intermediate filaments, so named because their 10-nanometer diameter is intermediate between that of microfilaments (6 nanometers) and microtubules (23 nanometers), assemble into an anastomosed network within the cytoplasm. In combination with a recently identified class of cross-linking proteins that mediate interactions between intermediate filaments and the other cytoskeletal networks, evidence is reviewed here that intermediate filaments provide a flexible intracellular scaffolding whose function is to structure cytoplasm and to resist stresses externally applied to the cell. Mutations that weaken this structural framework increase the risk of cell rupture and cause a variety of human disorders.

Preferential transformation of human neuronal cells by human adenoviruses and the origin of HEK 293 cells

The 293 cell line was derived by transformation of primary cultures of human embryonic kidney (HEK) cells with sheared adenovirus (Ad)5 DNA. A combination of immunostaining, immunoblot, and microarray analysis showed that 293 cells express the neurofilament (NF) subunits NF-L, NF-M, NF-H, and a-internexin as well as many other proteins typically found in neurons. Three other independently derived HEK lines, two transformed by Ad5 and one by Ad12, also expressed NFs, as did one human embryonic retinal cell line transformed with Ad5. Two rodent kidney lines transformed with Ad12 were also found to express NF proteins, although several rodent kidney cell lines transformed by Ad5 DNA and three HEK cell lines transformed by the SV40 early region did not express NFs. These results suggest that human Ads preferentially transform human neuronal lineage cells. We also demonstrate that the widely used HEK293 cells have an unexpected relationship to neurons, a finding that may require reinterpretation of many previous studies in which it was assumed that HEK293 cells resembled more typical kidney epithelial cells.

Keratin expression in human tissues and neoplasms

Keratin expression in human tissues and neoplasms Keratin filaments constitute type I and type II intermediate filaments (IFs), with at least 20 subtypes named keratin 1-20. Since certain keratin subtypes are only expressed in some normal human tissues but not others, and vice versa, various tissues have been subclassified according to the pattern of keratin staining. Simple epithelia generally express the simple epithelial keratins 7, 18, 19, and 20, while complex epithelia express complex epithelial keratins 5/6, 10, 14, and 15. When an epithelium undergoes malignant transformation, its keratin profile usually remains constant. The constitution and expression patterns of keratin filaments in human epithelial neoplasms are complex and often distinctive. In this article, we first briefly review the molecular and cell biology of keratin filaments. We then focus on the expression patterns of keratin filaments in various human neoplasms.

New consensus nomenclature for mammalian keratins

Keratins are intermediate filament–forming proteins that provide mechanical support and fulfill a variety of additional functions in epithelial cells. In 1982, a nomenclature was devised to name the keratin proteins that were known at that point. The systematic sequencing of the human genome in recent years uncovered the existence of several novel keratin genes and their encoded proteins. Their naming could not be adequately handled in the context of the original system. We propose a new consensus nomenclature for keratin genes and proteins that relies upon and extends the 1982 system and adheres to the guidelines issued by the Human and Mouse Genome Nomenclature Committees. This revised nomenclature accommodates functional genes and pseudogenes, and although designed specifically for the full complement of human keratins, it offers the flexibility needed to incorporate additional keratins from other mammalian species.

'Hard' and 'soft' principles defining the structure, function and regulation of keratin intermediate filaments

Keratins make up the largest subgroup of intermediate filament proteins and represent the most abundant proteins in epithelial cells. They exist as highly dynamic networks of cytoplasmic 10-12 nm filaments that are obligate heteropolymers involving type I and type II keratins. The primary function of keratins is to protect epithelial cells from mechanical and nonmechanical stresses that result in cell death. Other emerging functions include roles in cell signaling, the stress response and apoptosis, as well as unique roles that are keratin specific and tissue specific. The role of keratins in a number of human skin, hair, ocular, oral and liver diseases is now established and meshes well with the evidence gathered from transgenic mouse models. The phenotypes associated with defects in keratin proteins are subject to significant modulation by functional redundancy within the family and modifier genes as well. Keratin filaments undergo complex regulation involving post-translational modifications and interactions with self and with various classes of associated proteins.

The magical touch: genome targeting in epidermal stem cells induced by tamoxifen application to mouse skin

Gene knockout technology has provided a powerful tool for functional analyses of genes expressed preferentially in a particular tissue. Given marked similarities between human and mouse skin, such studies with epidermally expressed genes have often provided valuable insights into human genetic skin disorders. Efficient silencing of a specified gene in a temporally regulated and epidermal-specific fashion could extend functional analyses to broadly expressed genes and increase the categories of human skin disorders to which parallels could be drawn. We have generated transgenic mice expressing Cre and a fusion protein between Cre recombinase and the tamoxifen responsive hormone-binding domain of the estrogen receptor (CreER(tam)) under the control of the human keratin 14 (K14) promoter. This promoter is strongly active in dividing cells of epidermis and some other stratified squamous epithelia. With K14-Cre, transgenic embryos recombine genetically introduced loxP sequences efficiently and selectively in the genomes of keratinocytes that reside in embryonic day 14.5 skin, tongue, and esophagus. With K14-CreER(tam), postnatal transgenic mice show no Cre activity until tamoxifen is administered. If orally administered, tamoxifen activates keratinocyte-specific CreER(tam), allowing recombination of loxP sequences in epidermis, tongue, and esophagus. If topically administered, tamoxifen allows recombination in the area of skin where tamoxifen was applied. Finally, we show that epidermal cells harboring a Cre-dependent rearranged genome persist for many months after tamoxifen application, indicating that the epidermal stem cell population has been targeted efficiently. These tools now pave the way for testing the functional role of different somatic mutations that may exist in mosaic disorders of the skin, including squamous and basal cell carcinomas.

Point mutations in human keratin 14 genes of epidermolysis bullosa simplex patients: genetic and functional analyses

Previously we demonstrated that transgenic mice expressing mutant basal epidermal keratin genes exhibited a phenotype resembling a group of autosomal dominant human skin disorders known as epidermolysis bullosa simplex (EBS). EBS diseases affect approximately 1: 50,000 and are of unknown etiology, although all subtypes exhibit blistering arising from basal cell cytolysis. We now demonstrate that two patients with spontaneous cases of Dowling-Meara EBS have point mutations in a critical region in one (K14) of two basal keratin genes. To demonstrate function, we engineered one of these point mutations in a cloned human K14 cDNA, and showed that a K14 with an Arg-125----Cys mutation disrupted keratin network formation in transfected keratinocytes and perturbed filament assembly in vitro. Since we had previously shown that keratin network perturbation is an essential component of EBS diseases, these data suggest that the basis for the phenotype in this patient resides in this point mutation.

Side population purified from hepatocellular carcinoma cells harbors cancer stem cell-like properties

Recent advances in stem cell biology enable us to identify cancer stem cells in solid tumors as well as putative stem cells in normal solid organs. In this study, we applied side population (SP) cell analysis and sorting to established hepatocellular carcinoma (HCC) cell lines to detect subpopulations that function as cancer stem cells and to elucidate their roles in tumorigenesis. Among four cell lines analyzed, SP cells were detected in Huh7 (0.25%) and PLC/PRF/5 cells (0.80%), but not in HepG2 and Huh6 cells. SP cells demonstrated high proliferative potential and anti-apoptotic properties compared with those of non-SP cells. Immunocytochemistry examination showed that SP fractions contain a large number of cells presenting characteristics of both hepatocyte and cholangiocyte lineages. Non-obese diabetic/severe combined immunodeficiency (NOD/SCID) xenograft transplant experiments showed that only 1 x 10(3) SP cells were sufficient for tumor formation, whereas an injection of 1 x 10(6) non-SP cells did not initiate tumors. Re-analysis of SP cell-derived tumors showed that SP cells generated both SP and non-SP cells and tumor-initiating potential was maintained only in SP cells in serial transplantation. Microarray analysis discriminated a differential gene expression profile between SP and non-SP cells, and several so-called "stemness genes" were upregulated in SP cells in HCC cells. In conclusion, we propose that a minority population, detected as SP cells in HCC cells, possess extreme tumorigenic potential and provide heterogeneity to the cancer stem cell system characterized by distinct hierarchy.

Caspase cleavage of keratin 18 and reorganization of intermediate filaments during epithelial cell apoptosis

Keratins 8 (K8) and 18 (K18) are major components of intermediate filaments (IFs) of simple epithelial cells and tumors derived from such cells. Structural cell changes during apoptosis are mediated by proteases of the caspase family. During apoptosis, K18 IFs reorganize into granular structures enriched for K18 phosphorylated on serine 53. K18, but not K8, generates a proteolytic fragment during drug- and UV light-induced apoptosis; this fragment comigrates with K18 cleaved in vitro by caspase-6, -3, and -7. K18 is cleaved by caspase-6 into NH2-terminal, 26-kD and COOH-terminal, 22-kD fragments; caspase-3 and -7 additionally cleave the 22-kD fragment into a 19-kD fragment. The cleavage site common for the three caspases was the sequence VEVD/A, located in the conserved L1-2 linker region of K18. The additional site for caspases-3 and -7 that is not cleaved efficiently by caspase-6 is located in the COOH-terminal tail domain of K18. Expression of K18 with alanine instead of serine at position 53 demonstrated that cleavage during apoptosis does not require phosphorylation of serine 53. However, K18 with a glutamate instead of aspartate at position 238 was resistant to proteolysis during apoptosis. Furthermore, this cleavage site mutant appears to cause keratin filament reorganization in stably transfected clones. The identification of the L1-2 caspase cleavage site, and the conservation of the same or very similar sites in multiple other intermediate filament proteins, suggests that the processing of IFs during apoptosis may be initiated by a similar caspase cleavage.

Molecular characterization of human prostate carcinoma cell lines

BACKGROUND

This study presents a comprehensive survey and characterization of available prostate carcinoma cell lines, most of which have been widely used but are incompletely characterized.

METHODS

A total of 21 cell lines were investigated, including three "classical" (DU 145, LNCaP, and PC-3) and 18 "non-classical" lines (1013L, 22Rv1, ALVA-55, ALVA-101, ARCaP, CWR-R1, DuCaP, DuPro-1, LAPC-4, MDA PCa 1, MDA PCa 2a, MDA PCa 2b, NCI-H660, PC-346C, PC-93, PSK-1, UM-SCP-1, and VCaP). Cytogenetics, DNA profiling, expression of basal, luminal, and neuroendocrine differentiation markers, and mutation analyses of the TP53 and androgen receptor (AR) genes were performed.

RESULTS

Based on cytogenetics and DNA profiling analyses, out of the 18 "non-classical" lines, six were confirmed to be unique, eight (in four pairs) were confirmed to be related in origin, and four lines were identified as cross-contaminants. Of this latter group, PC-93 was found to be a derivative of HeLa, whereas DuPro-1, ALVA-55, and ALVA-101 were derivatives of PC-3. The 17 genuine prostate cell lines expressed keratin 8 (K8) and K18. Nine showed AR expression, of which five harbored mutations in the AR gene. Prostate-specific antigen and DD3 were exclusively detected in AR expressing cell lines. Seven lines expressed the basal cell marker K5, three of these lines showed co-expression of AR.

CONCLUSIONS

This study defines a collection of 17 genuine prostate carcinoma cell lines. This collection, although small, constitutes a variety of different types and stages of prostate cancer, while it also partly reflects the heterogeneous nature of this malignancy.

Expression of murine epidermal differentiation markers is tightly regulated by restricted extracellular calcium concentrations in vitro

Epidermal differentiation is characterized by a series of coordinated morphological and biochemical changes which result in a highly specialized, highly organized, stratified squamous epithelium. Among the specific markers expressed in differentiating epidermis are (a) two early spinous cell proteins, keratins 1 and 10 (K1 and K10); and (b) two later granular cell proteins, filaggrin and a cornified envelope precursor (CE). In vitro, epidermal basal cells are selectively cultured in 0.05 mM Ca2+ medium, and terminal differentiation is induced when the Ca2+ concentration is increased to 1 mM. However, only a small fraction of the cells express the markers K1, K10, CE, or filaggrin in the higher Ca2+ medium. To explore the factors required for marker expression, cultured epidermal cells were exposed to intermediate Ca2+ concentrations and extracts were analyzed using specific antibody and nucleic acid probes for the four markers of interest. These studies revealed that marker expression was enhanced at a restricted concentration of Ca2+ in the medium of 0.10-0.16 mM. At this Ca2+ concentration, both protein and mRNA levels for each marker were substantially increased, whereas at higher or lower Ca2+ concentrations they were diminished or undetected. The percentage of cells expressing each marker was increased two- to threefold in the permissive Ca2+ medium as determined by immunofluorescence analysis. This optimal level of Ca2+ was required both to initiate and sustain marker expression. At the permissive Ca2+ concentration, expression of the markers was sequential and similar to the order of appearance in vivo. K1 was expressed within 8-12 h and K10 was expressed in the ensuing 12-24-h period. CE and filaggrin were expressed in the subsequent 24 h. Inhibition of K1 expression by cycloheximide suggested that an inducible protein was involved. Other investigators have determined that a shallow Ca2+ gradient exists in epidermis, where the basal cells and spinous cells are in a Ca2+ environment substantially below serum Ca2+ levels. These in vitro results suggest that the Ca2+ environment is a fundamental regulator of expression of epidermal differentiation markers and provide an explanation for the existence of the Ca2+ gradient in vivo.

Interleukin 20: discovery, receptor identification, and role in epidermal function

A structural, profile-based algorithm was used to identify interleukin 20 (IL-20), a novel IL-10 homolog. Chromosomal localization of IL-20 led to the discovery of an IL-10 family cytokine cluster. Overexpression of IL-20 in transgenic (TG) mice causes neonatal lethality with skin abnormalities including aberrant epidermal differentiation. Recombinant IL-20 protein stimulates a signal transduction pathway through STAT3 in a keratinocyte cell line, demonstrating a direct action of this ligand. An IL-20 receptor was identified as a heterodimer of two orphan class II cytokine receptor subunits. Both receptor subunits are expressed in skin and are dramatically upregulated in psoriatic skin. Taken together, these results demonstrate a role in epidermal function and psoriasis for IL-20, a novel cytokine identified solely by bioinformatics analysis.

Expression of cytokeratins 17 and 5 identifies a group of breast carcinomas with poor clinical outcome

While several prognostic factors have been identified in breast carcinoma, the clinical outcome remains hard to predict for individual patients. Better predictive markers are needed to help guide difficult treatment decisions. In a previous study of 78 breast carcinoma specimens, we noted an association between poor clinical outcome and the expression of cytokeratin 17 and/or cytokeratin 5 mRNAs. Here we describe the results of immunohistochemistry studies using monoclonal antibodies against these markers to analyze more than 600 paraffin-embedded breast tumors in tissue microarrays. We found that expression of cytokeratin 17 and/or cytokeratin 5/6 in tumor cells was associated with a poor clinical outcome. Moreover, multivariate analysis showed that in node-negative breast carcinoma, expression of these cytokeratins was a prognostic factor independent of tumor size and tumor grade.

Brachyury, a crucial regulator of notochordal development, is a novel biomarker for chordomas

Chordomas are malignant tumours that occur along the spine and are thought to derive from notochordal remnants. There is significant morphological variability between and within chordomas, with some showing prominent areas of chondroid differentiation. Our microarray data from a broad range of connective tissue neoplasms indicate that, at the transcriptional level, chordomas resemble cartilaginous neoplasms. Here we show that chordomas express many genes known to be involved in cartilage development, but they also uniquely express genes distinguishing them from chondroid neoplasms. The brachyury transcription factor, known to be involved in notochordal development, is only expressed by chordomas. Using a polyclonal antibody, we show that brachyury is expressed in the embryonic notochord and in all 53 chordomas analysed, labelling both chondroid and chordoid areas of these tumours. In contrast, the protein was not detected in over 300 neoplasms, including 163 chondroid tumours. Brachyury was not detected in the nucleus pulposus, arguing against the hypothesis that this tissue derives directly from the notochord. These data provide compelling evidence that chordomas derive from notochord and demonstrate that brachyury is a specific marker for the notochord and notochord-derived tumours.

Keratins in health and cancer: more than mere epithelial cell markers

Keratins are the intermediate filament (IF)-forming proteins of epithelial cells. Since their initial characterization almost 30 years ago, the total number of mammalian keratins has increased to 54, including 28 type I and 26 type II keratins. Keratins are obligate heteropolymers and, similarly to other IFs, they contain a dimeric central α-helical rod domain that is flanked by non-helical head and tail domains. The 10-nm keratin filaments participate in the formation of a proteinaceous structural framework within the cellular cytoplasm and, as such, serve an important role in epithelial cell protection from mechanical and non-mechanical stressors, a property extensively substantiated by the discovery of human keratin mutations predisposing to tissue-specific injury and by studies in keratin knockout and transgenic mice. More recently, keratins have also been recognized as regulators of other cellular properties and functions, including apico-basal polarization, motility, cell size, protein synthesis and membrane traffic and signaling. In cancer, keratins are extensively used as diagnostic tumor markers, as epithelial malignancies largely maintain the specific keratin patterns associated with their respective cells of origin, and, in many occasions, full-length or cleaved keratin expression (or lack there of) in tumors and/or peripheral blood carries prognostic significance for cancer patients. Quite intriguingly, several studies have provided evidence for active keratin involvement in cancer cell invasion and metastasis, as well as in treatment responsiveness, and have set the foundation for further exploration of the role of keratins as multifunctional regulators of epithelial tumorigenesis.

Graded changes in dose of a Xenopus activin A homologue elicit stepwise transitions in embryonic cell fate

The protein XTC-MIF, a Xenopus homologue of activin A and a potent mesoderm-inducing factor, can induce responding animal pole explants to form several different cell types in a dose-dependent manner, higher doses eliciting more dorso-anterior tissues. This graded response, characteristic of classically postulated morphogens, may underlie pattern formation, but the response of intact animal caps to XTC-MIF provides only a crude indication of trends. Here we report the effects of XTC-MIF on dispersed blastomeres rather than intact animal caps. Under these conditions, responding cells distinguish sharply between doses of pure XTC-MIF differing by less than 1.5-fold. Two different response thresholds have been found, defining three cell states. This suggests that XTC-MIF has an instructive effect. Notochord and muscle are both induced in the same narrow dose-range. Mixing treated with untreated cells does not seem to shift the dose thresholds, showing that at least some cells can stably record the received dose of inducing factor.