CD44 expression in oro-pharyngeal carcinoma tissues and cell lines

Expression of CD44, a transmembrane hyaluronan-binding glycoprotein, is variably considered to have prognostic significance for different cancers, including oral squamous cell carcinoma. Although unclear at present, tissue-specific expression of particular isoforms of CD44 might underlie the different outcomes in currently available studies. We mined public transcriptomics databases for gene expression data on CD44, and analyzed normal, immortalized and tumour-derived human cell lines for splice variants of CD44 at both the transcript and protein levels. Bioinformatics readouts, from a total of more than 15,000 analyses, implied an increased CD44 expression in head and neck cancer, including increased expression levels relative to many normal and tumor tissue types. Also, meta-analysis of over 260 cell lines and over 4,000 tissue specimens of diverse origins indicated lower CD44 expression levels in cell lines compared to tissue. With minor exceptions, reverse transcribed polymerase chain reaction identified expression of the four main isoforms of CD44 in normal oral keratinocytes, transformed lines termed DT and HaCaT, and a series of paired primary and metastasis-derived cell lines from oral or pharyngeal carcinomas termed HN4/HN12, HN22/HN8 and HN30/HN31. Immunocytochemistry, Western blotting and flow cytometric assessments all confirmed the isoform expression pattern at the protein level. Overall, bioinformatic processing of large numbers of global gene expression analyses demonstrated elevated CD44 expression in head and neck cancer relative to other cancer types, and that the application of standard cell culture protocols might decrease CD44 expression. Additionally, the results show that the many variant CD44 exons are not fundamentally deregulated in a diverse range of cultured normal and transformed keratinocyte lines.

Differentiation-promoting culture of competent and noncompetent keratinocytes identifies biomarkers for head and neck cancer

Aberrant contact-inhibited proliferation and differentiation induction couple with tumor severity, albeit with an imprecise association with prognosis. Assessment of contact inhibition and differentiation-promoting culture in this study of normal and immortalized oral keratinocytes (NOK and SVpgC2a, respectively) demonstrated elevated cloning ability and saturation density in the immortalized versus normal state, including consistent absence of differentiated morphological features. Transcriptomic analysis implicated 48 gene ontology categories, 8 molecular networks, and 10 key regulator genes in confluency-induced differentiation of NOK, all of which remained nonregulated in SVpgC2a. The SVpgC2a versus NOK transcriptome enriched 52 gene ontology categories altogether, 18 molecular networks, and 39 key regulator genes, several of which were associated with epithelial-mesenchymal transition. Assessment of the previously described gene sets relative to training data sets of head and neck squamous cell carcinoma samples, one including data on tumor differentiation and patient outcome and one present in the Human Gene Expression Map, identified four genes with association to poor survival (COX7A1, MFAP5, MPDU1, and POLD1). This gene set predicted poor outcome in an independent data set of 71 head and neck squamous cell carcinomas. The present study defines, for the first time to our knowledge, the broad gene spectrum that couples to induction, and loss, of oral keratinocyte differentiation. Bioinformatics assessments of the results relative to clinical data generated novel differentiation-related tumor biomarkers relevant to patient outcome.

Variant CD44 expression by human fibroblasts

CD44 is a cell surface glycoprotein with roles in tumour invasion and metastasis. CD44 is variably spliced from ten variant exons and mis-splicing is a biomarker for detection of colon, urothelial and other carcinomas. Fibroblasts are normally considered to lack variant exons and thus should not generate false-positive signals. Transcription of variant exons by fibroblasts was investigated by exon-specific reverse transcription-polymerase chain reaction (RT-PCR) for variant exons v2-v10 using normal primary fibroblasts, immortalized and experimentally transformed fibroblasts. Flow cytometry, immunocytochemistry and Western blotting were used to determine expression. All types of fibroblasts, including normal primary culture fibroblasts, transcribed low levels of variant exon mRNA. Expression could not be detected by blotting or immunocytochemistry but flow cytometry revealed minor expression of some exons by all three types of cultured fibroblast. Fibroblasts do transcribe and express small amounts of variant exon CD44. This may need to be considered when using exon splicing as a biomarker for malignancy in clinical samples containing connective tissue.

Adducin expression in cutaneous and oral lesions: alpha- and beta-adducin transcripts down-regulate with keratinocyte differentiation in stratified epithelia

Adducin is a heterodimer of alpha- with beta- or gamma-subunits that regulates the assembly of the spectrin-based membrane skeleton in erythrocytes. Although adducin has been identified in various non-erythroid cells and tissues, it has been localized at intercellular junctions only in keratinocytes and epidermis. However, no data are available yet on the regulation of individual adducin genes in differentiating versus hyperproliferating keratinocytes. Due to the unavailability of mono-specific antibodies for individual adducins, this study has used RT-PCR and in situ hybridization to investigate the expression of alpha- and beta-adducins in cultured cells and in stratified epithelia including cutaneous and oral lesions. Using RT-PCR, the alpha-transcripts were consistently expressed in all cell lines tested, as well as in normal interfollicular epidermis, whereas the beta-transcripts were more variable and were strongly expressed in K562, A431, and primary keratinocytes. However, in normal skin, oral mucosa, and attached gingivae, the levels of alpha-transcripts closely paralleled those for the beta-subunit. In most normal tissues, adducin expression was observed primarily in the proliferating compartments including the basal layer and lower suprabasal layers. Expression of both genes was also up-regulated in skin diseases characterized by increased cell proliferation and keratinocyte activation, such as basal cell carcinoma (BCC), squamous cell carcinoma (SCC), and psoriasis. It was observed that, in most cases, the expression of both alpha- and beta-adducin was accompanied by increased expression of the proliferation marker Ki-67 and keratins K6 and K16. Differentiating keratinocytes in normal epithelia as well as in tumours appear to suppress the expression of adducin transcripts. The data suggest that the expression of adducin genes may be linked to cell proliferation and starts to down-regulate at the onset of differentiation.

Expression of keratin K2e in cutaneous and oral lesions: association with keratinocyte activation, proliferation, and keratinization

The cytoskeleton in keratinocytes is a complex of highly homologous structural proteins derived from two families of type I and type II polypeptides. Keratin K2e is a type II polypeptide that is expressed in epidermis late in differentiation. Here we report the influence of keratinocyte activation, proliferation, and keratinization on K2e expression in samples of cutaneous and oral lesions. The normal expression of K2e in the upper spinous and granular layers of interfollicular epidermis is increased in keloid scars but showed distinct down-regulation in psoriasis and hypertrophic scars where keratinocytes are known to undergo activation. Unlike normal and psoriatic skin, K2e expression in hypertrophic and keloid scars began in the deepest suprabasal layer. In cutaneous basal and squamous cell carcinomas, K2e was absent in most tumor islands but the overlying epidermis showed strong expression. No significant K2e expression in nonkeratinized or keratinized oral epithelia, including buccal mucosa, lateral border of tongue and gingiva was detected. In oral lichen planus K2e expression was undetectable, but in benign keratoses of lingual mucosa induction of K2e along with K1 and K10 was observed. In mild-to-moderate oral dysplasia with orthokeratinization, K2e was highly expressed compared with parakeratinized areas but in severe dysplasia as well as in oral squamous cell carcinoma, K2e expression was undetectable. Taken together, the data suggest that K2e expression in skin is sensitive to keratinocyte activation but its up-regulation in oral lesions is a reflection of the degree of orthokeratinization.

Analysis of proliferation, apoptosis and keratin expression in cultured normal and immortalized human buccal keratinocytes

The current study was undertaken to analyse growth and differentiation-related functions of normal keratinocytes (NOK) and an SV40T-immortalized keratinocyte line (SVpgC2a) from buccal mucosa, viewing the latter cell line as a model of a dysplastic epithelium. Morphological and immunohistochemical assessments of organotypic epithelia generated from 10 or 17 d of culture showed three- to five-fold higher apoptotic and proliferative activity in SVpgC2a relative to NOK. Conditions with or without serum (up to 10%) did not significantly influence these parameters in NOK whereas serum supported proliferation of SVpgC2a. Both cell types showed basal expression of collagen IV and laminin 1, indicating basal lamina, as well as vimentin, indicating an activated, proliferative state. Reduced expression of keratin, including the non-keratinizing marker K13, was seen in SVpgC2a. Assessment of proliferative monolayer cultures by microarray showed that NOK transcribed tissue-specific keratins, but also the epidermal keratin K2a, several simple epithelial keratins and low levels of hair keratins. SVpgC2a transcribed keratins seen in epithelial dysplasia, and K2a and hair keratins, albeit at low level. Overall, the results implied aberrant apoptosis, proliferation and keratin expression in the immortalized state of SVpgC2a. Comparison of NOK and SVpgC2a under identical culture conditions may serve to model the progression from a normal to a pre-neoplastic state of buccal epithelium.

Transcription and expression of CD44 variant exons by oro-pharyngeal squamous cell carcinomas

The CD44 cell surface hyaluronan binding protein has many isoforms formed by alternative splicing and glycosylation, and some variants have been associated with a malignant phenotype, invasion and metastasis. CD44 splicing patterns and intron 9 retention in 24 oro-pharyngeal squamous cell carcinomas (OSCC) were investigated by RT-PCR. Transcription efficiency and quantity were determined in 10 carcinomas and normal control mucosa by real-time PCR using dual-labeled fluorescent Taqman probes. Most of the carcinomas, regardless of grade, showed one major transcript including exons v2-v10, similar to that expressed by normal keratinocytes. In addition, most carcinomas expressed a variety of truncated transcripts of contiguous variant exons. Real-time PCR revealed that carcinomas showed both over-expression and down-regulation in transcription compared to normal keratinocytes, but this change was independent of the state of differentiation or the sub-site of biopsy. Intron 9 was not retained in normal keratinocytes or carcinomas. Overall, the results indicate that OSCC, like normal keratinocytes, constitutively express all variant exons and that the missplicing seen in other malignancies does not appear to occur. OSCC do not reproducibly over-express CD44 and show a wide range of transcription levels. CD44 expression does not appear to be fundamentally deranged in OSCC and is unlikely to be of value in early diagnosis, or as a prognostic marker.

Expression of keratins in normal, immortalized and malignant oral epithelia in organotypic culture

Keratins have been extensively studied in tissues and cultured keratinocytes but limited information is available on epithelia reconstructed in vitro. The aim of this study was to examine keratin expression in organotypic epithelia with normal (NOK), immortalized (SVpgC2a) and malignant (SqCC/Y1) human buccal cells. Organotypic epithelia were derived from 10 days of culture at the air-liquid interface of collagen gels containing human oral fibroblasts using a standardized serum-free medium. Sections were stained immunohistochemically with selected mono-specific antibodies to a range of keratins. Organotypic epithelia showed sharp differences in keratin expression and distribution. K4/K13, K1/K10, K6/K16 were variably expressed in NOK and SqCC/Y1 but were not detected in SVpgC2a. K5 was expressed in all organotypic epithelia but K14 was absent in SVpgC2a. K7 and K8 showed variable expression while K18 was expressed uniformly in all epithelia. K19 was expressed consistently in NOK and K20 was distributed heterogeneously in SVpgC2a. Overall, organotypic cultures of normal keratinocytes express many of the same keratins as buccal mucosa. Further, the loss of keratins in SVpgC2a and their retention in SqCC/Y1 have several features in common with the respective keratin profile of oral epithelial dysplasia and well-differentiated oral squamous cell carcinoma. Although qualitative and quantitative differences exist compared to keratin expression in vivo, these cell lines in organotypic culture may serve in studies of the multi-step progression of oral cancer.

Characterization of CD44 splicing patterns in normal keratinocytes, dysplastic and squamous carcinoma cell lines

The CD44 glycoprotein is spliced from a complex gene of 10 constitutive and 10 variant exons. In this study, CD44 splicing patterns and intron 9 retention were investigated by exon-specific RT-PCR for variant exons v1-v10 and intron 9 in normal, immortalized, dysplastic and malignant keratinocytes. Expression of product was determined immunohistochemically for some of the exons. Normal keratinocytes showed one major transcript including exons v2-v10 and 3 minor transcripts. No lines showed a normal CD44 splicing pattern but rather a variety of truncated transcripts of contiguous variant exons which overall correlated with expression. Squamous cell carcinoma (SCC)-4 and SCC-9 lines showed relatively normal transcripts although protein was expressed only by SCC-9. SCC-12B2, SCC-15, SCC-25 and SCC-27 showed a series of shorter overlapping transcripts, with loss of exons v8-v10 in the major transcripts. Intron 9 was not retained in normal keratinocytes or cell lines. Despite the fact that keratinocytes constitutively express all variant exons, splicing patterns are distinctly abnormal and merit investigation as potential markers for epidermal and oral squamous malignancy.

Gene expression of differentiation-specific keratins in oral epithelial dysplasia and squamous cell carcinoma

The aim of the study was to investigate the differentiation-specific keratins (K4, K13, K1 and K10) in oral epithelial dysplasia and squamous cell carcinoma (SCC). Alterations in keratin gene expression were determined by in situ hybridization using 35S-labeled riboprobes and immunohistochemistry with monoclonal antibodies. In mild dysplasia, both sets of differentiation keratins were expressed in the same group of cells but in moderate lesions, expression of K4 and K13 was reduced in the presence of enhanced K1 and K10 synthesis. In severe dysplasia, neither mRNAs nor proteins were detected. In tumor islands of well and moderately differentiated SCCs, the K4/K13 complex was co-expressed with K1/K10, but in poorly differentiated carcinomas, differentiation keratins were absent. Consequently, mild oral epithelial dysplasia and well differentiated SCC retain an essentially normal pattern of keratin gene expression and hence epithelial differentiation while in severe dysplasia and poorly differentiated SCC keratin gene expression reflects the gross changes in epithelial differentiation and maturation.

muc-1 gene expression in head and neck squamous cell carcinomas

Polymorphic epithelial mucin (PEM), the protein product of the gene muc-1, is a surface glycoprotein that is produced by a range of normal epithelial cells, but has been shown to be expressed at high levels in a range of adenocarcinomas. It has not been investigated extensively in head and neck related tissues, and not at all in head and neck squamous cell carcinomas (HNSCC). This immunohistochemical investigation using two monoclonal antibodies to muc-1 represents a baseline study of 18 HNSCC. In 13 cases, the glycoprotein was expressed at varying levels, usually in keratinizing foci. Although less prominent, expression was also present to some degree in nine of 23 control specimens of non-neoplastic mucosa, mostly at an epithelial level early in the parakeratinization process. Both antibodies showed a pattern of staining. The cellular basis for muc-1 expression is speculative at present and although it is at a lower level than in adenocarcinomas, it may help to provide further insight into epithelial cell differentiation in squamous cell carcinomas.

Gene expression of differentiation-specific keratins (K4, K13, K1 and K10) in oral non-dysplastic keratoses and lichen planus

Gene expression for the differentiation-specific keratins (K4, K13, K1 and K10) was analyzed in oral non-dysplastic keratoses, oral lichen planus (OLP) and lichenoid reactions (LR) by comparative in situ hybridization (ISH) and immunohistochemistry (IHC) to investigate molecular changes in the altered differentiation pattern from non- to para- or orthokeratinization. At the protein level, K4 and K13 were detected homogeneously in the suprabasal compartment of parakeratotic epithelium but showed reduced expression in orthokeratoses, particularly in the presence of lymphocytes. Corresponding transcripts were restricted to basal and lower prickle cells. Synthesis of K1 and K10 was upregulated and more pronounced in orthokeratotic epithelia. The study showed an alteration in the pattern of differentiation-specific keratins, although involvement of the lymphocytic infiltrate in OLP and LR resulted in further gene modulation. In both diseases, K1 and K10 showed transcriptional control, proteins having the same distribution as their transcripts. This represented a change from post-transcriptional regulation in normal buccal epithelium, in which mRNAs for K1 and K10 are more widely expressed than their proteins. Thus, the pattern of keratin gene expression may be altered in response to frictional/smoking stimuli or immune-mediated mechanisms.

Quantitative assessment of apoptosis in oral lichen planus

OBJECTIVE

The aims of this study were to examine the frequency of apoptoses in oral lichen planus by in situ end labeling, to ascertain whether this technique is as sensitive as conventional histologic analysis, and to examine the effect of lymphocytic infiltration.

STUDY DESIGN

Numbers of apoptoses in hematoxylin-eosin stained sections were compared with numbers of apoptotic nuclei identified by in situ end labeling in oral lichen planus (n = 26) and normal buccal epithelium (n = 8). Immunohistochemical staining with MIB-1 and for Bcl-2 and Bax enabled possible regulatory pathways to be investigated.

RESULTS

In oral lichen planus, approximately 1 apoptotic cell was detected per millimeter of basal layer, cell death increasing with lymphocytic infiltration. Epithelial cell proliferation did not correlate with apoptosis. Bcl-2 expression was weak or absent in basal cells, and Bax was localized to upper prickle cells.

CONCLUSIONS

Increased numbers of apoptoses were detected in oral lichen planus, especially in association with lymphocytic infiltration, higher numbers being seen with hematoxylin-eosin staining than with in situ end labeling.

Gene expression of differentiation-specific keratins (4/13 and 1/10) in normal human buccal mucosa

The aim of the present study was to compare gene expression of the major differentiation-specific keratins in oral epithelium: keratins 4, 13, 1, and 10. Previous studies have shown that the dominant keratins in normal buccal epithelium are K4 and K13, with minor populations of cells showing K1 and K10 expression; herein, we have further examined expression of these keratins at the mRNA level. Six biopsies from normal buccal mucosa were immunohistochemically stained for keratin proteins by means of monoclonal antibodies to K4, K13, K1, and K10. Adjacent sections were processed for mRNA by nonisotopic in situ hybridization, using specific riboprobes labeled with digoxigenin. Proteins for K4 and K13 were expressed suprabasally throughout buccal epithelium, with columns of cells staining additionally for K1 and K10. In situ hybridization revealed a comparable pattern of mRNA distribution for K4 and K13, with expression restricted to parabasal and lower prickle cells. Transcripts for K1 and K10 were present in basal, parabasal, and lower prickle layers, showing a much wider expression than that of their proteins. This study has shown that in buccal epithelium, there is extensive mRNA expression of the "inappropriate" differentiation-specific keratins, despite minimal protein expression. This suggests that K1 and K10 are regulated at the post-transcriptional level, so that they may be expressed adaptively as proteins. The findings will form a useful baseline for the study of these keratins in pathologically altered oral epithelia as well as in nonkeratinized epithelia from extra-oral sites.