Biomedical subjects

J Hilkens

Publications and source records attributed to J Hilkens.

At least 37 records · Page 2Linked to original sources

PubMed1992

Cell-associated episialin is a complex containing two proteins derived from a common precursor.

cDNA for the epithelial sialomucin episialin encodes a transmembrane molecule with a large extracellular domain, which mainly consists of repeats of 20 amino acids. Here we confirm the existence of a previously proposed proteolytic cleavage of episialin that occurs in the endoplasmic reticulum (Hilkens, J., and Buijs, F. (1988) J. Biol. Chem. 263, 4215-4222) and show that a similar cleavage takes place in in vitro translation systems. Using in vitro translation of truncated mRNAs, we map the cleavage site to a region located between 71 and 53 amino acids upstream of the transmembrane domain. Analysis of a mutant, in which this region has been deleted, indicates that the cleavage sites used in vitro and in vivo are identical or in close proximity. Both cleavage products remain associated although they are not linked through disulfide bonds. Therefore, the subunit derived from the N terminus, which represents the actual mucin-like domain, remains indirectly anchored to the cell membrane as a result of its interaction with the C-terminal subunit.

Amino Acid Sequence↗

PubMed1992

Carcinoma-associated monoclonal antibodies in head and neck carcinoma. Immunohistochemistry and biodistribution of monoclonal antibodies 175F4 and 175F11.

Monoclonal antibodies (mAbs) 175F4 (IgG1) and 175F11 (IgG2a), originally raised against the human mammary carcinoma cell line (ZR-75-1), react with a carcinoma-associated antigen in both adenocarcinomas and squamous cell carcinomas of different origins. Immunohistochemically, the mAbs exhibited reactivity with 42 out of 43 squamous cell carcinomas of the head and neck. Normal squamous epithelia were also reactive with the antibodies in the basal and suprabasal cell layer. 111In 175F4 F(ab')2 fragments localized a squamous cell carcinoma xenograft (HT-6) in nude mice with low blood pool activity, indicating a potential clinical usefulness for staging of squamous cell carcinomas in the head and neck.

Animals↗

PubMed1992

Cell membrane-associated mucins and their adhesion-modulating property.

A class of highly sialylated glycoproteins with very large mucin-like domains that protrude high above the plasma membrane have been shown to strongly reduce cellular adhesion. In normal epithelial cells, where the expression is restricted to the luminal side of the cell, these molecules may prevent inadvertent closing of the lumen as a result of weak, non-specific protein-protein interactions between opposite luminal membranes. In malignant tumors cellular polarization is often lost, which can lead to the entire cell surface being covered by these molecules. The resulting strongly reduced adhesion and immune recognition properties may play an important role during invasion and metastasis.

Animals↗

PubMed1991

The mouse episialin (Muc1) gene and its promoter: rapid evolution of the repetitive domain in the protein.

We have cloned the Muc1 gene of the mouse, encoding the murine equivalent of human episialin (also known as EMA or PEM), a mucin-like glycoprotein that is overexpressed in carcinoma cells. The extracellular domain of the mouse protein, that mainly consists of tandem repeats, contains 16 repeats of variable length and sequence, whereas the human protein usually contains between 30 and 90 nearly identical repeats. The murine repeats contain more potential O-glycan side chains and this may result in a more extended conformation of the murine protein. The transmembrane and cytoplasmic domains of the protein show about 90% conservation. The promoter region shows many conserved regions that could function as transcription factor binding sites.

Amino Acid Sequence↗

PubMed1991

Isolation of two distinct epithelial cell lines from a single feline mammary carcinoma with different tumorigenic potential in nude mice and expressing different levels of epidermal growth factor receptors.

From a single spontaneous feline mammary carcinoma, two subpopulations of epithelial tumor cells have been isolated. The variant cells were established as cell lines designated K248C and K248P. DNA ploidy analysis showed that the two cell lines represented cell populations already present in the original tumor. Chromosome analysis confirmed the feline origin of K248C and K248P and demonstrated that in addition to unique marker chromosomes characteristic for each cell line, both cell lines had several marker chromosomes in common. These data suggest that the two cell populations arose from a hypothetical single ancestor which diverged during tumor progression. The K248C and K248P cell lines differed from one another with respect to their tumorigenicity in athymic mice and epidermal growth factor (EGF) receptor content. The K248C cells were highly tumorigenic as indicated by a short latency period and high take rate. The K248P cells were poorly tumorigenic. Southern blot analysis revealed that the K248C cells contained an amplified EGF receptor gene that was accompanied by elevated levels of EGF receptor RNA and protein. The K248C cells were growth inhibited in vitro at EGF concentrations that stimulated growth of K248P cells. The amplification of the EGF receptor gene could be detected only in DNA derived from K248C cells at high passage numbers and not in DNA derived from the original tumor and K248C cells at low passage numbers. These data suggest that amplification of the EGF receptor gene occurred during establishment of the K248C cell line.

Animals↗

PubMed1991

A single nucleotide polymorphism in an exon dictates allele dependent differential splicing of episialin mRNA.

The episialin gene (MUC1) encodes an epithelial mucin containing a variable number of repeats with a length of twenty amino acids, resulting in many different alleles that can be subdivided into two size classes. The episialin pre-mRNA uses either one of two neighbouring splice acceptor sites for exon 2, which mainly encodes the repeats. Using the genetic polymorphism of the episialin gene to identify different alleles, we show here that the splice site recognition is allele dependent and is based on a single A/G nucleotide difference in exon 2 eight nucleotides downstream of the second splice acceptor site. Transfection experiments confirm that this polymorphic nucleotide regulates the splice site selection. The identity of this nucleotide is in most cases correlated with one of the size classes of the alleles, indicating that mutations altering the number of repeats seldom arise by unequal cross-over between the repeat regions.

Alleles↗

PubMed1990

Episialin, a carcinoma-associated mucin, is generated by a polymorphic gene encoding splice variants with alternative amino termini.

Episialin is a mucin-type glycoprotein present at the luminal side of most glandular epithelial cells. We have isolated cDNA clones encoding episialin and determined the structure of the gene. The gene encodes a transmembrane protein which consists of, for the greater part, tandem repeats of 20 amino acids. The number of these repeats varies between 40 and 90 among different alleles. The repeats and most of the remainder of the protein are very rich in potential O-linked glycosylation sites. Two different splice variants were found. Interestingly, the proteins encoded by these two variants differ in their signal sequences and in the extreme amino-terminal parts of the mature proteins, suggesting alternative processing of these two species.

Amino Acid Sequence↗

PubMed1989

Complexity of MAM-6, an epithelial sialomucin associated with carcinomas.

The complexity of epithelial sialomucins was investigated by immunoprecipitation and membrane immunofluorescence, using monoclonal antibodies (MAbs) against MAM-6 and other sialomucins. MAbs against MAM-6 immunoprecipitated from a variety of sources either one or two sialylated glycoproteins with apparent molecular weights of over 400,000 under reducing as well as nonreducing conditions. The electrophoretic mobility of each MAM-6 glycoprotein as isolated from serum, milk, and cell lines of different individuals showed considerable variation. The differences in molecular weight of the MAM-6 glycoproteins were also reflected at the level of MAM-6 precursors which are less heavily glycosylated. Therefore, large differences in apparent molecular weight (150,000 and over) are most likely due to a variable protein backbone. We used this molecular polymorphism to prove that 11 MAbs against different sialomucins, obtained from various investigators, precipitated sialomucins generated from common precursor molecules. The pattern of reactivity of the MAbs with carcinoma cell lines was complex. All but the two MAbs, directed against putative carbohydrate epitopes, immunoprecipitated the precursor molecule from each cell line. However, some of them were unable to immunoprecipitate the mature form of MAM-6 from these cell lines. These results indicate that those epitopes are masked, probably due to cell line- or possibly cell type-dependent variations in glycosylation of the epithelial sialomucin. Even within a single cell line mature molecules with different epitopes were observed. The differential reactivity of the MAbs was confirmed by membrane immunofluorescence. These results show that MAM-6 belongs to a family of epithelial sialomucins with a polymorphic protein backbone and extensive variation in glycosylation.

Antibodies, Monoclonal↗

PubMed1989

Molecular cloning and localization to chromosome 6 of mouse INT1L1 gene.

The human INT1L1 gene, which exhibits homology to the protooncogene INT1 is very closely linked to the MET gene and cystic fibrosis locus on human chromosome 7. In the present study we have isolated overlapping genomic clones that correspond to the mouse homolog of the INT1L1 gene and have used the cloned DNA as probes to examine the distribution of the mouse INT1L1 gene within a series of 35 mouse-hamster somatic cell hybrids. These analyses have localized the INT1L1 gene to mouse chromosome 6. In addition, we demonstrate that the mouse INT1L1 and MET genes are coamplified in lines of spontaneously transformed mouse NIH3T3 cells, indicating that these genes may remain closely linked within the mouse genome.

Amino Acid Sequence↗

PubMed1989

Preferential expression of cellular retinoic acid binding protein in a subpopulation of neural cells in the developing mouse embryo.

The cellular retinoic acid binding protein is thought to be involved in the retinoic-acid-mediated signal transduction pathway. We have isolated the mouse cellular retinoic acid binding protein cDNA from an embryonal-carcinoma-derived cell line by using differential cDNA cloning strategies. In situ hybridization on sections of mouse embryos of various developmental stages indicated that the cellular retinoic acid binding protein gene, which we localized on mouse chromosome 9, is preferentially expressed in a subpopulation of neurectodermal cells. This restricted expression pattern suggests an important role for cellular retinoic acid binding protein in murine neurogenesis.

Amino Acid Sequence↗

PubMed1988

Endocytosis and intracellular routing of an antibody-ricin A chain conjugate.

An immunotoxin (IT) was prepared from monoclonal antibody (MoAb) 115D8 and ricin A chain. MoAb 115D8 is directed against the carcinoma-associated sialomucin MAM-6. In a protein synthesis inhibition assay this IT was cytotoxic for the human breast cancer cell line T47D. Using postembedding immunoelectron microscopy the binding and intracellular routing of the IT in T47D cells were studied by simultaneous labeling of both IT moieties, MoAb and A chain, and compared with the fate of native ricin and MoAb 115D8. The IT was internalized into the cell by two different pathways: one via coated pits-coated vesicles followed by transport to the lysosomes and one via large enclosed invaginations of the plasma membrane which apparently fused with lysosomes. This internalization was similar to the endocytosis of MoAb 115D8. During transport via both pathways the IT remained intact until it reached the lysosomes as suggested by the observation that the labels for 115D8 and ricin A chain remained closely associated. Moreover, in areas with abundant endocytic vesicles the labels for both IT moieties were also found in the cytosol, suggesting that intact IT is translocated from the vesicles into the cytosol. In control experiments, native ricin, but not unconjugated MoAb 115D8, was found in the cytosol after internalization. Data presented here show for the first time the complete intracellular pathway of an antibody-ricin A chain conjugate, including the translocation of the A toxin subunit into the cytosol. This IT may be useful for therapy of those tumors which express a high level of MAM-6 on the cell surface.

Antibodies, Monoclonal↗

PubMed1988

Biosynthesis of MAM-6, an epithelial sialomucin. Evidence for involvement of a rare proteolytic cleavage step in the endoplasmic reticulum.

MAM-6 is a major epithelial sialomucin which is abundantly present at the apical surface of ductal and alveolar cells of normal tissues and on many different carcinoma cells. MAM-6, as defined by monoclonal antibodies, consists of one or two sialylated glycoproteins with apparent molecular masses of over 400 kDa under reducing as well as nonreducing conditions. The mobility and number of glycoproteins immunoprecipitated vary depending on the cell line of origin. We have employed immunoprecipitation techniques to study the biosynthesis and glycosylation of this mucin. The biosynthesis of MAM-6 was studied in the ZR-75-1 breast cancer cell line. Two glycoproteins with apparent molecular masses of approximately 450 and 650 kDa, representing the mature form, were immunoprecipitated. By pulse-chase analysis, we show that the biosynthesis of the 450-kDa glycoprotein proceeded through intermediates of 220, 200, and 500 kDa which became perceptible after 1, 4, and 30 min, respectively. The biosynthesis of the 650-kDa glycoprotein followed a similar course through 380, 350, and 700-kDa intermediates. The processing of the 220- and 350-kDa precursors involves a rare proteolytic cleavage step which occurs in the endoplasmic reticulum. The late precursors of 500/700 kDa, observed after 30 min chase, and the mature glycoproteins were generated by extensive O-linked glycosylation. The formation of the 500/700-kDa precursors was not affected by monensin. However, the final step of maturation, sialylation of the 500/700-kDa precursors, could be inhibited by monensin. The extensive O-linked glycosylation causes the apparent high molecular weight as observed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Our data on the biosynthesis show that the early MAM-6 precursors contain N-linked glycans, suggesting the presence of N-linked glycans on the mature MAM-6 molecule. Although the copresence of N- and O-linked glycans has been found on many molecules, no N-linked glycans have been reported on mucus glycoproteins previously.

Breast Neoplasms↗

PubMed1988

Monoclonal antibodies to epithelial sialomucins recognize epitopes at different cellular sites in adenolymphomas of the parotid gland.

Fourteen monoclonal antibodies (MAbs) to epithelial sialomucins were studied for their immunohistochemical reactivity on serial sections of 14 formalin-fixed and paraffin-embedded adenolymphomas of the parotid gland. Two types of reactivity were observed, suggesting different cellular distribution of the corresponding epitopes. Most antibodies reacted with the luminal membrane of the columnar tumor cells (type-A reaction). The other reaction (type B) was observed with the membrane of basal epithelial cells. The antibodies could be ranked according to their tendency to show type-A and/or type-B reactions. MAb Cal was the only one with a pure type-A reaction. A strong tendency to type-A reactivity (with traces of type-B reactions) was observed for the antibodies HMFG-2, M8, E29 and NCRC-II. Several antibodies gave good type-B reactions in addition to strong type-A reactivity (MAbs 126E7, 115G2, 115D8, 140C1, F36/22, 139H2). MAb DF3 showed equally strong reactions with both cell types. A clear-cut preference of the reactions with basal cells was seen with the antibodies HMFG-1 and 115F5. This subclassification of the antibodies is in accordance with epitope mapping data, obtained by conventional blocking studies reported in the literature.

Adenolymphoma↗

PubMed1988

Assignment of estradiol receptor gene to mouse chromosome 10.

Differences in restriction fragment lengths were detected with murine estrogen receptor cDNA (clone MOR-100) between Chinese hamster and mouse. These were used to determine the chromosomal location of the estrogen receptor in the mouse by Southern blot analysis of DNAs obtained from a panel of mouse-Chinese hamster somatic cell hybrids. The mouse estrogen receptor gene was localized on mouse chromosome 10.

Animals↗

PubMed1988

Chromosomal organization of the cytochrome P450-2C gene family in the mouse: a locus associated with constitutive aryl hydrocarbon hydroxylase.

Cytochromes P-450 represent a superfamily of enzymes with a central role in the metabolism of drugs, chemical toxins, and carcinogens. We have used genetic analysis to establish the complexity and catalytic function of a recently identified constitutively expressed murine hepatic cytochrome P-450 encoded by P450-2C. Southern blotting analysis shows that there are at least seven or eight genes within this family in the mouse and rat and that DNA restriction fragment length variants between different mouse inbred strains are observed. Analysis of recombinant inbred strains derived from these parent strains shows (i) these genes are clustered within 1 centimorgan, (ii) this gene family does not correspond to any of the known cytochrome P-450 loci or map near any well-characterized genomic markers, and (iii) this gene family segregates to within 1-2 centimorgans of a locus controlling constitutive aryl hydrocarbon hydroxylase activity in mice. With use of Chinese hamster/mouse somatic cell hybrids, the P450-2C locus was assigned to a region of mouse chromosome 19 that appears to be syntenic with the previously mapped human P450C2C locus on human chromosome 10. By in situ hybridization to mitotic mouse chromosomes, we have localized this region to the tip of chromosome 19. These results are discussed in relation to the physiological roles of this P-450 family in foreign compound metabolism and steroid oxidations.

Animals↗

PubMed1988

Characterization of the mouse met proto-oncogene.

The DNA sequence of cDNA clones prepared from transcripts of the mouse met proto-oncogene reveals that the mouse met gene encodes a 1380 amino acid protein with the characteristics of a growth factor receptor. This protein can be divided into several putative domains, including an intracellular protein tyrosine kinase domain, a transmembrane domain and a 929 amino acid extracellular domain, possessing a potential proteolytic cleavage site with the sequence Lys-Arg-Arg-Lys-Arg-Ser. To gain additional insights into the function of the met protein we have examined the level of met transcripts in tissues of the late-gestation mouse conceptus. Transcription of met was observed in most of the tissues analysed, but the highest levels of met mRNA were detected in the yolk sac, amnion and kidney; no transcripts were detectable in the calvaria. Chromosomal localization using a series of mouse-hamster hybrid cell lines has demonstrated that met is located on mouse chromosome 6.

Amino Acid Sequence↗

PubMed1987

A mouse homeobox containing gene on chromosome 11: sequence and tissue-specific expression.

We have molecularly cloned a mouse homeobox containing gene by isolating cDNA and genomic clones. The gene is located in a previously described cluster on chromosome 11 (Hart et al. (1985) Cell 43, 9-18) and was identified as the Hox2.3 gene. We present the complete mRNA sequence of this gene and describe similarities to other homeobox containing genes, among which its human homologue, the cl gene. High expression of the Hox2.3 gene was found in kidney, testis, and spinal cord of adult mice, in the spinal cord of 12.5-17.5 day embryos and in differentiating EC cells depending on their treatment. Three different treatments of the pluripotent EC cell line P19, each leading to the induction of a specific differentiation pathway, resulted in all cases in induction of Hox2.3; however, major quantitative differences in this response were observed.

Amino Acid Sequence↗

PubMed1987

Comparison of circulating MAM-6 and CEA levels and correlation with the estrogen receptor in patients with breast cancer.

MAM-6 and CEA serum levels of 136 staged breast cancer patients were determined concomitantly. The sensitivities of the MAM-6 assay using monoclonal antibody (MAb) 115D8 and a polyclonal CEA assay were equally low and only a limited number of patients with early stages of breast cancer showed elevated antigen levels. However, the sensitivity rose to 75% for MAM-6 and to 60% for CEA in stage-IV patients. The levels of both antigens correlated well in the sera of these patients, although MAM-6 serum levels were elevated more frequently, while only in a few cases were MAM-6-negative sera CEA-positive. A group of stage-II breast cancer patients who eventually developed distant metastases was followed in a longitudinal study. Tumor progression or regression was clinically determined and compared with the MAM-6 and CEA serum levels in order to establish the value of each assay for the monitoring of breast cancer. The course of the disease correlated significantly better with changes in MAM-6 antigen levels than with changes in CEA levels (p less than 0.05), being 79% and 42% respectively. The lower correlation of CEA levels with the course of the disease was mainly due to a lower sensitivity of the CEA assay for advanced breast cancer. The specificity of changing MAM-6 and CEA levels was not significantly different. The main advantage of the MAM-6 assay over the CEA assay is the higher sensitivity of the former. In a preliminary study among stage-IV patients a correlation was found between elevated MAM-6 levels and the presence of the estrogen receptor in the primary tumor.

Antigens↗