Carcinoma-associated 38-kD membrane glycoprotein MH 99/KS 1/4 is related to proliferation and age of transformed epithelial cell lines

Expression and function of epithelial cell adhesion molecule EpCAM: where are we after 40 years?

EpCAM (epithelial cell adhesion molecule) was discovered four decades ago as a tumor antigen on colorectal carcinomas. Owing to its frequent and high expression on carcinomas and their metastases, EpCAM serves as a prognostic marker, a therapeutic target, and an anchor molecule on circulating and disseminated tumor cells (CTCs/DTCs), which are considered the major source for metastatic cancer cells. Today, EpCAM is reckoned as a multi-functional transmembrane protein involved in the regulation of cell adhesion, proliferation, migration, stemness, and epithelial-to-mesenchymal transition (EMT) of carcinoma cells. To fulfill these functions, EpCAM is instrumental in intra- and intercellular signaling as a full-length molecule and following regulated intramembrane proteolysis, generating functionally active extra- and intracellular fragments. Intact EpCAM and its proteolytic fragments interact with claudins, CD44, E-cadherin, epidermal growth factor receptor (EGFR), and intracellular signaling components of the WNT and Ras/Raf pathways, respectively. This plethora of functions contributes to shaping intratumor heterogeneity and partial EMT, which are major determinants of the clinical outcome of carcinoma patients. EpCAM represents a marker for the epithelial status of primary and systemic tumor cells and emerges as a measure for the metastatic capacity of CTCs. Consequentially, EpCAM has reclaimed potential as a prognostic marker and target on primary and systemic tumor cells.

Cleavage and cell adhesion properties of human epithelial cell adhesion molecule (HEPCAM)

Human epithelial cell adhesion molecule (HEPCAM) is a tumor-associated antigen frequently expressed in carcinomas, which promotes proliferation after regulated intramembrane proteolysis. Here, we describe extracellular shedding of HEPCAM at two α-sites through a disintegrin and metalloprotease (ADAM) and at one β-site through BACE1. Transmembrane cleavage by γ-secretase occurs at three γ-sites to generate extracellular Aβ-like fragments and at two ϵ-sites to release human EPCAM intracellular domain HEPICD, which is efficiently degraded by the proteasome. Mapping of cleavage sites onto three-dimensional structures of HEPEX cis-dimer predicted conditional availability of α- and β-sites. Endocytosis of HEPCAM warrants acidification in cytoplasmic vesicles to dissociate protein cis-dimers required for cleavage by BACE1 at low pH values. Intramembrane cleavage sites are accessible and not part of the structurally important transmembrane helix dimer crossing region. Surprisingly, neither chemical inhibition of cleavage nor cellular knock-out of HEPCAM using CRISPR-Cas9 technology impacted the adhesion of carcinoma cell lines. Hence, a direct function of HEPCAM as an adhesion molecule in carcinoma cells is not supported and appears to be questionable.

Regulated intramembrane proteolysis and degradation of murine epithelial cell adhesion molecule mEpCAM

Epithelial cell adhesion molecule EpCAM is a transmembrane glycoprotein, which is highly and frequently expressed in carcinomas and (cancer-)stem cells, and which plays an important role in the regulation of stem cell pluripotency. We show here that murine EpCAM (mEpCAM) is subject to regulated intramembrane proteolysis in various cells including embryonic stem cells and teratocarcinomas. As shown with ectopically expressed EpCAM variants, cleavages occur at α-, β-, γ-, and ε-sites to generate soluble ectodomains, soluble Aβ-like-, and intracellular fragments termed mEpEX, mEp-β, and mEpICD, respectively. Proteolytic sites in the extracellular part of mEpCAM were mapped using mass spectrometry and represent cleavages at the α- and β-sites by metalloproteases and the b-secretase BACE1, respectively. Resulting C-terminal fragments (CTF) are further processed to soluble Aβ-like fragments mEp-β and cytoplasmic mEpICD variants by the g-secretase complex. Noteworthy, cytoplasmic mEpICD fragments were subject to efficient degradation in a proteasome-dependent manner. In addition the γ-secretase complex dependent cleavage of EpCAM CTF liberates different EpICDs with different stabilities towards proteasomal degradation. Generation of CTF and EpICD fragments and the degradation of hEpICD via the proteasome were similarly demonstrated for the human EpCAM ortholog. Additional EpCAM orthologs have been unequivocally identified in silico in 52 species. Sequence comparisons across species disclosed highest homology of BACE1 cleavage sites and in presenilin-dependent γ-cleavage sites, whereas strongest heterogeneity was observed in metalloprotease cleavage sites. In summary, EpCAM is a highly conserved protein present in fishes, amphibians, reptiles, birds, marsupials, and placental mammals, and is subject to shedding, γ-secretase-dependent regulated intramembrane proteolysis, and proteasome-mediated degradation.

EpCAM regulates cell cycle progression via control of cyclin D1 expression

The epithelial cell adhesion molecule (EpCAM) is an integral transmembrane protein that is frequently overexpressed in embryonic stem cells, tissue progenitors, carcinomas and cancer-initiating cells. In cancer cells, expression of EpCAM is associated with enhanced proliferation and upregulation of target genes including c-myc. However, the exact molecular mechanisms underlying the observed EpCAM-dependent cell proliferation remained unexplored. Here, we show that EpCAM directly affects cell cycle progression via its capacity to regulate the expression of cyclin D1 at the transcriptional level and depending on the direct interaction partner FHL2 (four-and-a-half LIM domains protein 2). As a result, downstream events such as phosphorylation of the retinoblastoma protein (Rb) and expression of cyclins E and A are similarly affected. In vivo, EpCAM expression strength and pattern are both positively correlated with the proliferation marker Ki67, high expression and nuclear localisation of cyclin D1, and Rb phosphorylation. Thus, EpCAM enhances cell cycle progression via the classical cyclin-regulated pathway.

EpCAM is involved in maintenance of the murine embryonic stem cell phenotype

Epithelial cell adhesion molecule EpCAM is a transmembrane glycoprotein that is expressed on subsets of normal epithelia, numerous stem- and progenitor-type cells, and most carcinomas and highly overexpressed on cancer-initiating cells. The role of EpCAM in early development, particularly in stem-like cells, has remained unclear. Here, we show that the maintenance of self-renewal in murine embryonic stem (ES) cells depends on the high-level expression of EpCAM. Cultivation of ES cells under differentiation conditions in the absence of leukemia inhibitory factor (LIF) caused down-regulation of EpCAM along with decreased expression of cellular myelocytomatosis oncogene (c-Myc), Sex-determining region Y-Box 2, Octamer 3/4 (Oct3/4), and Stat3. As a consequence ES cells were morphologically differentiated and ceased to proliferate. RNA interference-mediated inhibition of EpCAM expression under self-renewal conditions resulted in quantitatively decreased proliferation, decreased Oct3/4, SSEA-1, and c-Myc expression, and diminished alkaline phosphatase activity. Conversely, exogenous expression of EpCAM partially compensated for the requirement of ES cells for LIF to retain a stem cell phenotype. Thus, murine EpCAM is a transmembrane protein, which is essential but by itself is not sufficient for maintenance of the ES cell phenotype.

Initial activation of EpCAM cleavage via cell-to-cell contact

BACKGROUND

Epithelial cell adhesion molecule EpCAM is a transmembrane glycoprotein, which is frequently over-expressed in simple epithelia, progenitors, embryonic and tissue stem cells, carcinoma and cancer-initiating cells. Besides functioning as a homophilic adhesion protein, EpCAM is an oncogenic receptor that requires regulated intramembrane proteolysis for activation of its signal transduction capacity. Upon cleavage, the extracellular domain EpEX is released as a soluble ligand while the intracellular domain EpICD translocates into the cytoplasm and eventually into the nucleus in combination with four-and-a-half LIM domains protein 2 (FHL2) and beta-catenin, and drives cell proliferation.

METHODS

EpCAM cleavage, induction of the target genes, and transmission of proliferation signals were investigated under varying density conditions using confocal laser scanning microscopy, immunoblotting, cell counting, and conditional cell systems.

RESULTS

EpCAM cleavage, induction of the target genes, and transmission of proliferation signals were dependent on adequate cell-to-cell contact. If cell-to-cell contact was prohibited EpCAM did not provide growth advantages. If cells were allowed to undergo contact to each other, EpCAM transmitted proliferation signals based on signal transduction-related cleavage processes. Accordingly, the pre-cleaved version EpICD was not dependent on cell-to-cell contact in order to induce c-myc and cell proliferation, but necessitated nuclear translocation. For the case of contact-inhibited cells, although cleavage of EpCAM occurred, nuclear translocation of EpICD was reduced, as were EpCAM effects.

CONCLUSION

Activation of EpCAM's cleavage and oncogenic capacity is dependent on cellular interaction (juxtacrine) to provide for initial signals of regulated intramembrane proteolysis, which then support signalling via soluble EpEX (paracrine).

Acitretin induces apoptosis through CD95 signalling pathway in human cutaneous squamous cell carcinoma cell line SCL-1

Skin cancers are by far the most common human malignancies. Retinoids have shown promising preventive and therapeutic effects against a variety of human malignancies. The aim of this study was to investigate the apoptosis-inducing effect of acitretin on human skin squamous cell carcinoma (SCC) SCL-1 cells. We found that acitretin preferentially inhibited the growth of SCL-1 cells in a dose- and time-dependent manner, but not of non-malignant keratinocyte HaCaT cells. This inhibition appeared to be due to induction of apoptosis as revealed by enzyme-linked immunosorbent assay. AnnexinV/propidium iodide assay and morphological observation confirmed the pro-apoptotic effect of acitretin on SCL-1 cells. We further demonstrated that apoptosis was induced within 1-2 days and involved activation of caspases-8, -9, -3 and poly (ADP-ribose) polymerase (PARP). Caspase-8 inhibitor effectively suppressed acitretin-induced apoptosis whereas caspase-9 inhibitor did not. Acitretin increased the levels of CD95 (Fas), CD95-ligand and Fas-associated death domain. Neutralizing ZB4 anti-Fas antibody significantly inhibited the apoptosis in SCL-1 cells induced by acitretin. These results suggest that acitretin is able to induce apoptosis in skin cancer cells possibly via death receptor CD95 apoptosis pathway without affecting the viability of normal keratinocyte.

A genome-wide expression analysis identifies a network of EpCAM-induced cell cycle regulators

Expression of the epithelial cell adhesion molecule EpCAM is upregulated in a variety of carcinomas. This antigen is therefore explored in tumour diagnosis, and clinical trials have been initiated to examine EpCAM-based therapies. Notably, the possible intracellular effects and signalling pathways triggered by EpCAM-specific antibodies are unknown. Here, we show treatment of the mouse lung carcinoma cell line A2C12, of the human lung carcinoma cell line A549 and the human colorectal cell line Caco-2 with the monoclonal EpCAM antibody G8.8 to cause dose dependently an increase in cell proliferation, as determined by the MTS and the 5′-bromo-2′-deoxyuridine (BrdU) labelling assay. Furthermore, a genome-wide approach identified networks of regulated genes, most notably cell cycle regulators, upon treatment with an EpCAM-specific antibody. Indeed, changes in the expression of cell cycle regulators agreed well with the BrdU labelling data, and an analysis of differentially expressed genes revealed the processes with the strongest over-representation of modulated genes, for example, cell cycle, cell death, cellular growth and proliferation, and cancer. These data suggest that EpCAM is involved in signal transduction triggering several intracellular signalling pathways. Knowing EpCAM signalling pathways might lead to a reassessment of EpCAM-based therapies.

Basal cell (trichoblastic) carcinoma common expression pattern for epithelial cell adhesion molecule links basal cell carcinoma to early follicular embryogenesis, secondary hair germ, and outer root sheath of the vellus hair follicle: A clue to the adnexal nature of basal cell carcinoma?

BACKGROUND

Basal cell carcinoma (BCC) is still viewed by many dermatologists as a tumor of the interfollicular epidermis, although references were made early in the dermatopathologic literature to the resemblance of BCC to the hair follicle.

OBJECTIVE

Our aim was to characterize the common expression pattern for the epithelial cell adhesion molecule (Ep-CAM) in BCCs, various stages of follicular embryogenesis, and adult hair follicles and, thereby, in analogy point to the similarity between BCC and the hair follicle.

METHODS

We studied immunohistochemically 16 superficial BCCs for Ep-CAM and compared the expression pattern with that during hair follicle, nail, and eccrine gland development in human embryos and fetuses. In addition, we examined terminal scalp and vellus hair follicles.

RESULTS

All BCCs expressed Ep-CAM similar to the early stages of the embryonic human hair follicle, the secondary hair germ, and the outer root sheath of the vellus hair follicle. The embryonic nail organ and the adult anagen hair follicles were completely negative.

LIMITATIONS

The conclusions are based on the similarity in the immunohistochemical expression profile for a single adhesion molecule.

CONCLUSION

BCC expresses the cell-cell adhesion molecule Ep-CAM similar to the embryonic hair germ, the secondary hair germ of the terminal hair follicle, and the outer root sheath of the vellus hair follicle. We suggest that this may be a clue to the adnexal nature of BCC and propose that BCC is the most primitive follicular tumor.

The tetraspanin D6.1A and its molecular partners on rat carcinoma cells

Tetraspanins function as molecular organizers of multi-protein complexes by assembling primary complexes of a relatively low mass into extensive networks involved in cellular signalling. In this paper, we summarize our studies performed on the tetraspanin D6.1A/CO-029/TM4SF3 expressed by rat carcinoma cells. Primary complexes of D6.1A are almost indistinguishable from complexes isolated with anti-CD9 antibody. Indeed, both tetraspanins directly associate with each other and with a third tetraspanin, CD81. Moreover, FPRP (prostaglandin F2alpha receptor-regulatory protein)/EWI-F/CD9P-1), an Ig superfamily member that has been described to interact with CD9 and CD81, is also a prominent element in D6.1A complexes. Primary complexes isolated with D6.1A-specific antibody are clearly different from complexes containing the tetraspanin CD151. CD151 is found to interact only with D6.1A if milder conditions, i.e. lysis with LubrolWX instead of Brij96, are applied to disrupt cellular membranes. CD151 probably mediates the interaction of D6.1A primary complexes with alpha3beta1 integrin. In addition, two other molecules were identified to be part of D6.1A complexes at this higher level of association: type II phosphatidylinositol 4-kinase and EpCAM, an epithelial marker protein overexpressed by many carcinomas. The characterization of the D6.1A core complex and additional more indirect interactions will help to elucidate the role in tumour progression and metastasis attributed to D6.1A.

ING-1, a Monoclonal Antibody Targeting Ep-CAM in Patients with Advanced Adenocarcinomas

PURPOSE

To determine the feasibility of administration, safety, toxicity, immunogenicity, pharmacokinetics, maximum tolerated dose, and biodistribution of ING-1, a high-affinity, Human-Engineered monoclonal antibody (heMAb) to the Mr 40,000 epithelial cell adhesion molecule Ep-CAM, in patients with advanced adenocarcinomas.

EXPERIMENTAL DESIGN

ING-1 was initially administered to patients as a 1-hour intravenous infusion every 3 weeks. Toxicity and pharmacokinetic data led to the evaluation of a weekly schedule. The distribution of iodine-131 (131I)-labeled ING-1 was studied.

RESULTS

Twenty-five patients received 82 courses of ING-1. Minimal toxicity was initially observed at the 0.03-, 0.10-, and 0.30-mg/kg dose levels. A patient dosed at 1.0 mg/kg developed acute pancreatitis with severe abdominal pain, nausea, and vomiting. A patient dosed at 0.3 mg/kg had an asymptomatic amylase and lipase elevation to 502 units/L and 1,627 units/L, respectively. Both patients made uncomplicated recoveries. No other dose-limiting toxicities were observed. Regardless of dose, the volume of distribution (mean +/- SEM) was 46.6 +/- 1.6 mL/kg. ING-1 clearance decreased with increasing dose. To minimize toxicity and increase dose intensity, we then administered ING-1 weekly. No significant toxicity was observed in 7 patients dosed at 0.1 mg/kg. Studies of 131I-labeled ING-1 biodistribution showed radiolocalization to colorectal and prostate cancers. A patient with colorectal cancer had an 80% decrement in the levels of carcinoembryonic antigen.

CONCLUSION

The recommended dose for ING-1 is 0.10 mg/kg by intravenous infusion weekly. The absence of severe toxicity at this dose, low immunogenicity, and preliminary evidence of ING-1 tumor localization and antitumor efficacy support the further clinical development of this antibody to treat Ep-CAM-positive malignant diseases.

Overexpression of epithelial cell adhesion molecule antigen in gallbladder carcinoma is an independent marker for poor survival

PURPOSE

Gallbladder carcinoma is an aggressive type of cancer that is difficult to cure by conventional procedures. There thus is a need to identify novel molecular markers for the assessment of prognosis and as potential therapeutic targets. This retrospective study was designed to investigate the prognostic significance of epithelial cell adhesion molecule (Ep-CAM) overexpression in human gallbladder carcinoma.

EXPERIMENTAL DESIGN

Ep-CAM expression was examined immunohistochemically on paraffin-embedded tissue specimens from 99 patients who underwent surgical treatment for gallbladder carcinoma in the period between August 1988 and May 1999.

RESULTS

Ep-CAM overexpression was found in 63 (63.6%) of the tumor samples. Kaplan-Meier curves showed that Ep-CAM overexpression was significantly related to decreased overall survival (P < 0.01). Overall survival gradually worsened with increasing Ep-CAM scores. Notably, in the subgroup of pT1 tumors (n = 17), patients without Ep-CAM overexpression had a 5-year overall survival rate of 100% compared with 38% (P = 0.01) for patients with Ep-CAM-overexpressing tumors. By univariate analysis, no correlation was found with conventional clinicopathological parameters. Multivariate analysis, including Ep-CAM expression, pT stage, tumor grade, and resection margin involvement, showed that Ep-CAM overexpression was an independent prognostic marker in gallbladder carcinoma (P = 0.03; relative risk, 1.8).

CONCLUSIONS

These results demonstrate for the first time that Ep-CAM overexpression is an independent prognostic marker in gallbladder carcinoma and that its prognostic impact should be validated prospectively. Furthermore, the Ep-CAM antigen represents an attractive target for specific therapies with monoclonal antibodies or specific vaccines in patients with Ep-CAM-overexpressing gallbladder carcinoma.

Preparation of recombinant MK-1/Ep-CAM and establishment of an ELISA system for determining soluble MK-1/Ep-CAM levels in sera of cancer patients

The MK-1 antigen, also termed as Ep-CAM, is a membrane glycoprotein that is overexpressed on the majority of tumor cells of epithelial origin and thereby can be used as a target of immunodetection and immunotherapy of cancer. It has previously been shown that several type-I transmembrane proteins, including E-cadherin, ErbB-2 and intercellular adhesion molecule-1 (ICAM-1), may be useful as tumor markers because they are released into the circulation of many cancer patients. To address the question of whether MK-1, the same type-I membrane protein, is also released into the sera, we developed a sandwich-type enzyme-linked immunosorbent assay (ELISA) system by preparing a recombinant MK-1 protein and two anti-MK-1 monoclonal antibodies with different epitope specificities. Using this ELISA, we found that the MK-1 levels in serum samples from healthy volunteers were all less than 2 ng/ml, whereas the Mk-1 levels in sera of about 10% of patients with malignant tumors of various tissue origins were increased to 2-78 ng/ml, indicating that MK-1 is released from tumor cells into the circulation under certain conditions. These findings should be borne in mind when trying to perform passive antibody therapy for cancer using anti-MK-1 antibody.

The structural analysis of adhesions mediated by Ep-CAM

The epithelial cell adhesion molecule Ep-CAM is capable of mediating Ca2+-independent homotypic cell-cell adhesion when introduced into cells lacking their own means of cell-cell interactions. We used (confocal) immunofluorescent and (immuno-) electron microscopy to investigate the structural organization of Ep-CAM-mediated adhesions and their relation to other types of intercellular adhesions. Ep-CAM-transfected cell lines, cells of epithelial origin, and epithelial tissues were analyzed. In transfected L cells Ep-CAM brings the opposing intercellular membranes into a close proximity (approximately 10-14 nm) at sporadic contacts; however, no structures resembling junctional complexes were observed. In L cells cotransfected with Ep-CAM and E-cadherin, both molecules localize at the sites of cell-cell contact, forming independent adhesion sites with no Ep-CAM detectable within the structurally distinguishable cadherin-mediated adherens junctions. In well-differentiated carcinoma cell lines Ep-CAM colocalized with E-cadherin practically along the whole lateral domain; however, no colocalization was observed between Ep-CAM and the components of the tight junction complex (occludin and ZO-1), desmosomes (desmoplakins I/II), or cell-substrate adhesions (beta1 integrins). This was confirmed by analysis of polarized epithelium of normal colon where Ep-CAM was present at the lateral membrane including the adherens junction areas, but was fully excluded from the apical cell membrane (microvilli), tight junctions, and desmosomes. We conclude that (1) Ep-CAM does not form junctional complexes in L cells, (2) in epithelial cells, cell surface Ep-CAM is present at the lateral cell membrane, but is excluded from tight junctions and desmosomes, and (3) in epithelial cells, Ep-CAM is present within adhesions mediated by the classic cadherins (especially E-cadherin) with both types of molecules remaining as independent clusters. The colocalization with cadherins might be important for the modulating effect of Ep-CAM on cadherin-mediated adhesions.

Increased expression of a 38kd cell-surface glycoprotein MH99 (KS 1/4) in oral mucosal dysplasias

A "window of expression" of a 38-kD cell-surface glycoprotein MH99 (KS 1/4 antigen) has been observed in dysplastic oral tissues using an MH99-specific monoclonal antibody. It appeared that expression of this epitope increases from baseline levels in normal oral epithelium to that of high levels in mild, moderate and severe dysplasia. In invasive squamous cell carcinoma, relatively low levels of expression were observed. In contrast, high levels of expression were demonstrated in basal cell carcinomas. Antibody reactivity could clearly distinguish between the margins of histologically normal and dysplastic tissues. It is envisaged that the expression of this cell-surface glycoprotein, which is possibly related to nidogen, a matrix-adhesion molecule with receptor-like function, could be used in monitoring progression or regression of these lesions and assessment of surgical excision margins. It could also be useful in in vivo and in vitro investigations into molecular changes underlying the formation of dysplastic lesions.

Characterization of an 80-kD membrane glycoprotein (gp80) of human keratinocytes: a marker for commitment to terminal differentiation in vivo and in vitro

We have characterized an 80-kD cell-surface glycoprotein (gp80) identified by monoclonal antibody BT 15, the expression of which is closely associated with a commitment to terminal squamous or follicular differentiation of keratinocytes in normal adult and fetal human epidermis. Maximum expression was found in the suprabasal layers, but basal cells located at the epidermal sulci were also clearly positive, in contrast to the virtually negative basal cells at the epidermal ridges. This protein was also present in benign hyperproliferative disorders of the epidermis (i.e., common warts, keratoacanthoma, psoriasis, and seborrhoic keratoses) with monoclonal antibody BT 15 preferentially staining suprabasal cells and some basal cells at the epidermal sulci. Gp80 was completely lacking in most basal cell carcinomas; the only exceptions were two cases of partially cornifying tumors that were strongly stained around keratotic pearls. In squamous cell carcinomas, gp80 was expressed in keratinized areas of the tumors. In organotypic keratinocyte cultures that resemble the in vivo situation, gp80 was strongly expressed in the suprabasal layers. However, unlike known markers for terminal differentiation, gp80 was weakly expressed by basal cells. Synthesis rates of gp80 were high in keratinocyte cell suspensions freshly prepared from skin, and decreased in primary cultures and first and second subcultures (ratio 10:4:2:1). Elevated concentrations of the Ca++ that increased stratification of cultured keratinocytes resulted in a two- to threefold increase of gp80 synthesis. GP80 was not synthesized at detectable levels by the immortal keratinocyte cell line HaCaT; however, it was expressed in HaCaT cultures treated with mitomycin C, indicating an association with cessation of growth. Pulse-chase experiments revealed that gp80 is synthesized from a 55-kD precursor molecule, the maturation of which was prevented by treating cells with tunicamycin. Glycosidase digestion of BT 15 immunoprecipitates from untreated cells indicated that the predominant post-translational modification of the protein is N-linked glycosylation. Our data indicate that gp80 is a glycoprotein that is expressed by growth-arrested human keratinocytes or as part of the terminal differentiation program.

The human hair follicle: glycoprotein-related antigenic profile of distinct keratinocyte populations in vivo and their alterations in vitro

The cell surface expression of three glycoprotein antigens, as defined by the monoclonal antibodies BT 15, T 43, and MH 99, was investigated in follicular keratinocyte populations in vivo. In addition, the regulation of glycoprotein synthesis was studied in follicular and interfollicular keratinocytes cultured in vitro. The BT 15 antigen was strongly expressed in the inner root sheath and the area above Auber's line of the hair bulb, whereas the T43 antigen was mainly seen in the outer root sheath. Selectively high expression of the MH 99 antigen was found only in outgrowing germ buds of early anagen follicles. Radioimmunoprecipitation revealed strong signals with BT 15 in freshly prepared follicular keratinocytes, two to three times stronger than those in interfollicular keratinocytes, but the signals clearly decreased by 80% under continuing culture conditions. The T 43 antigen was found by FACS analysis and radioimmunoprecipitation in initially low amounts in both populations, but the signals increased dramatically (up to 50 times) in long-term cultures and in subcultures. The MH 99 antigen was also initially present only in low amounts, in interfollicular rather than in follicular keratinocytes, but its expression increased up to 15-fold with continuing culture and any differences between the two populations disappeared. Our investigation revealed that at least three populations of hair follicle keratinocytes are characterized by different surface glycoprotein antigens, clearly related to their state of differentiation and proliferation.(ABSTRACT TRUNCATED AT 250 WORDS)

Properties of the carcinoma-associated antigen MH 99/KS 1/4 in normal and transformed human keratinocytes: regulation of synthesis, molecular cross-linking and ultrastructural localization

A 38-kDa cell-surface glycoprotein defined by monoclonal antibody MH 99 is markedly increased in many epithelial tumours. In normal human skin, it is a characteristic marker for germ-cell phenotypic tissues. Although the gene encoding the MH 99 antigen has recently been cloned, and several histological and biochemical studies have been performed, the biological function of this interesting antigen still remains unknown. In the present study, we examined the synthesis of MH 99 in keratinocyte populations showing different in vitro differentiation capacity. Normal keratinocytes, spontaneously immortalized keratinocytes (cell line HaCaT), three SV-40-transformed keratinocyte lines (130, 425, and HaSV), and two squamous cell carcinoma lines (SCL-1 and SCL-2), were compared. Radioimmunoprecipitation revealed the highest levels of synthesis in cell populations with the least differentiation. This was paralleled by an increase of MH 99 synthesis in normal keratinocytes cultured in low concentrations of Ca2+ and by an increase of MH 99 synthesis during subculture of normal keratinocytes. Both phenomena were paralleled by an opposite behaviour of a differentiation marker. Molecular cross-linking and subsequent immunoprecipitation led to a decrease of the MH 99 signal, but an increase of a high molecular weight protein signal was seen. After cleavage of the crosslinker, the MH 99 signal reappeared, whereas the signal of the large protein remained unchanged. Thus, the MH 99 antigen may be associated with a high molecular weight protein on the cell surface, supporting the suggestion of a receptor-like function. Phosphorylation of the molecule could not be detected. Immunoelectron microscopy revealed homogeneous distribution on the cell surface, but cells of the same culture exhibited clear differences in their MH 99 expression. A concept for MH 99 regulation in normal and transformed human keratinocyte populations in vitro is proposed, showing that the synthesis of MH 99 is inversely correlated with cell differentiation. The association with a high molecular weight protein supports the suggestion that the MH 99 antigen interacts with other molecules.

Transformation of human keratinocytes is characterized by quantitative and qualitative alterations of the T-16 antigen (Trop-2, MOv-16)

The regulation of synthesis and post-translational processing of the T-16 antigen, a human cell-surface glycoprotein of 50 to 60 kDa, was investigated in normal and transformed human keratinocytes in vitro. Normal keratinocytes of interfollicular and follicular origin were compared with squamous-cell-carcinoma lines, spontaneously immortalized keratinocytes, and SV-40 transformed keratinocytes. FACS analysis and radio-immunoprecipitation showed that the synthesis and expression of T-16 was 3- to 4-fold higher in transformed keratinocytes than in their normal counterparts. In normal keratinocytes, no quantitative differences were observed among freshly prepared cells, primary cultures and sub-cultures. In SDS-PAGE, a single broad band at 50 to 60 kDa was observed in normal keratinocytes, whereas 2 bands at 42 and 45 to 55 kDa were detected after transformation. Tunicamycin treatment of living cells and glycosidase digestion of immunopurified T-16 antigen revealed this molecular heterogeneity to be due to different N-glycosylation in normal and transformed keratinocytes. In pulse-chase experiments, 2 distinct precursor proteins at 38 and 42 kDa were detected in transformed keratinocytes, whereas in normal cells the 38-kDa signal was dramatically decreased. These findings indicate that quantitative and qualitative changes of T-16 mark the transformation process of human keratinocytes, showing similar post-translational alterations in all transformed populations investigated.