Both acidic-type and neutral-type asparaginyl-oligosaccharides of host-cell glycoproteins are altered in Rous-sarcoma-virus-transformed chick-embryo fibroblasts

Neural cell adhesion molecule mediates contact-dependent inhibition of growth of near-diploid mouse fibroblast cell line m5S/1M

A near-diploid mouse fibroblast cell line m5S/1M used in this study shows a high sensitivity to contact-dependent inhibition of growth, and the addition of EGF causes both morphological change and loss of contact-dependent inhibition of growth. The m5S/1M cell and its transformants obtained by x-ray irradiation have been used to search for the cell surface glycoproteins that are responsible for the growth regulation via cell-cell interactions. Lectin blotting analyses showed that the expression of the cell surface glycoprotein of 140 kD (140KGP) is highly sensitive to the transformation induced either by x-ray irradiation or by the EGF stimulation. We purified the 140KGP and found that it was composed of two glycoproteins. The major component of 140KGP was identified as neural cell adhesion molecule (NCAM) by amino acid sequence analyses of the peptide fragments and by the cross-reactivity with anti-NCAM mAb, clone H28.1.2.3. Monoclonal antibody against 140KGP (clone LN-10) recognizes all three isoforms of NCAM expressed on m5S/1M cell and showed that the expression of NCAM was highly sensitive to the transformation. Furthermore, the immobilized LN-10 strongly inhibited the growth of actively proliferating m5S/1M cells and the LN-10 in a soluble form showed a significant growth-stimulating effect on the confluent quiescent cultures of m5S/1M cells. The results show that NCAM plays a major role in the contact-dependent inhibition of growth of m5S/1M, and that NCAM might be involved in the regulation of cell growth during embryogenesis and formation of nervous systems.

Cancer-associated carbohydrates identified by monoclonal antibodies

"New" carbohydrate structures on the surface of or secreted by cancer cells, identified as epitopes by monoclonal antibodies, are reviewed. These structures may represent the accumulation of precursor chains because of decreased activity of synthesizing enzymes, the production of new oligosaccharides due to increased or aberrant glycosylation of carbohydrate chains, a change in density of carbohydrates on the cell surface, or exposure of chains usually covered by other structures. Alterations in glycolipid synthesis include aberrant fucosylation and/or sialyation of the lacto series, sialylation or fucosylation of the globo series, and sialyation of the ganglio series. Many of these carbohydrate epitopes have become useful for the diagnosis, prognosis, and monitoring of patients with cancer. Some of the important markers include CA 15.3, CA 19.9, CA 50, CA 125, CA 242, MCA, SLEX, etc. Incomplete glycosylation of O-linked mucin oligosaccharide is recognized as the important "cancer antigen" B72.3, which is sialyated Tn. The oligosaccharide components of alpha-fetoprotein, carcinoembryonic antigen, and epidermal growth factor receptor are also reviewed. In many instances the glycosylation seen in cancer cells or their products reflects patterns seen during normal development. Thus, cancer-associated oligosaccharides are oncodevelopmental in nature. The biologic significance of carbohydrates on cell surfaces is not known, but several possibilities include a role in cell to cell recognition, intracellular processing of glycoproteins, cell activation, and ability of cancer cells to metastasize.

Purification of two glycoproteins expressing beta 1-6 branched Asn-linked oligosaccharides from metastatic tumour cells

Increased branching at the trimannosyl core of 'complex-type' Asn-linked oligosaccharides has been observed in both human and murine tumour cells, and appears to be associated with enhanced metastatic potential in several murine tumour models [Dennis, Laferte, Waghorne, Breitman & Kerbel (1987), Science 236, 582-585]. The lectin leucoagglutinin (L-PHA) requires the-GlcNAc beta 1-6Man alpha 1-6Man-linked lactosamine antenna in complex-type oligosaccharides for high-affinity binding and can be used to detect these structures in glycoproteins separated on SDS/polyacrylamide-gel electrophoresis. The major L-PHA-binding glycoproteins in the highly metastatic lymphoid tumour cell line called MDAY-D2 were purified and resolved into two major species, termed P2A (110 kDa) and P2B (130 kDa). P2A had L-PHA-reactive Asn-linked oligosaccharides with polylactosamine sequences as well as a large component of sialylated O-linked carbohydrates. The glycoprotein showed structural characteristics similar to those of leukosialin (i.e. CD43), a glycoprotein previously identified on the surface of leukocytes. Based on monosaccharide compositional analysis and glycosidase digestions, P2B was found to be 50-60% Asn-linked oligosaccharide containing polylactosamine sequences and sialic acid. The N-terminal peptide sequence of P2B was determined to be very similar to that of murine lysosomal membrane glycoprotein (LAMP-1), a ubiquitous glycoprotein found largely in the lysosomal membranes but also in the plasma membrane of several murine and human tumour cell lines.

Malignant cell glycoproteins and glycolipids

The cell surface is involved in cell growth and division, cell-cell interaction, communication, differentiation and migration, and other processes likely to be involved in malignant transformation and/or the metastatic spread of cancer. Although there are many alterations of glycoproteins and glycolipids on the malignant cell surface, it is unclear whether these alterations are epiphenomena or an integral part of the malignancy process. This article reviews the recent literature and some earlier studies relevant for understanding emerging concepts and trends with respect to malignant cell glycoconjugates. Emphasis is on structural alterations of the carbohydrate portions of malignant cell glycoproteins and glycolipids and on the enzymes (glycosyltransferases and glycosidases) involved in their metabolism. Practical applications derived from malignant cell glycoconjugate studies are discussed briefly with respect to the diagnosis, staging, monitoring, and treatment of malignant disease. The review concludes by indicating which research areas on malignant cell glycoconjugates are likely to be fruitful in increasing our basic understanding of, and ability to deal effectively with, malignant disease.

Purification and characterization of the glycoprotein hormone alpha-subunit-like material secreted by HeLa cells

The protein secreted by HeLa cells that cross-reacts with antiserum developed against the alpha-subunit of human chorionic gonadotropin (hCG) has been purified approximately 30,000-fold from concentrated culture medium by organic solvent fractionation followed by ion exchange, gel filtration, and lectin affinity chromatography. The final preparation had a specific activity (by RIA) of 6.8 x 10(5) ng of alpha/mg of protein and appeared homogeneous by electrophoresis on reducing/denaturing polyacrylamide gels (SDS-PAGE). Amino acid analysis indicated that HeLa-alpha had a composition very similar to that of the urinary hCG alpha-subunit. Peptide fingerprints of the HeLa protein and hCG-alpha revealed that several of the Tyr-, Met-, and Cys-containing tryptic peptides were held in common, thus identifying the tumor protein as a glycoprotein hormone alpha-subunit with a primary structure similar to that of hCG-alpha. However, comparison of hCG-alpha and HeLa-alpha demonstrated that the tumor-associated subunit was not identical with its normal counterpart. Only two of the three Tyr-containing tryptic peptides present in hCG-alpha could be detected in HeLa-alpha after iodination with 125I. HeLa-alpha eluted prior to hCG-alpha during Sephadex G-75 chromatography, but the subunits coeluted when the tumor protein was first subjected to mild acid hydrolysis. The purified tumor protein had an apparent molecular weight greater than that of the urinary alpha-subunit when analyzed by SDS-PAGE (Coomassie blue staining), and this difference was even greater when a partially purified preparation was examined by an immunoblot technique (Western). Isoelectric focusing of the HeLa and hCG subunits demonstrated that the tumor protein had a lower pI (4.7-5.5 compared to 6.5-7.8), and removal of sialic acid by mild acid hydrolysis did not entirely eliminate this difference. Immunoprecipitation and electrophoresis of alpha-subunit from HeLa cultures labeled with [3H]fucose indicated that the tumor subunit was fucosylated, whereas analysis of hCG-alpha hydrolysates by HPLC confirmed previous reports that the placental subunit does not contain fucose. HeLa alpha-subunit was unable to combine with hCG beta-subunit to form holo-hCG under conditions where the hCG alpha-subunit was able to do so. The results indicate that, regardless of whether or not a single alpha-subunit gene is being expressed in both normal and neoplastic tissues, posttranslational modifications lead to a highly altered subunit in the tumor. The differences observed may be useful in diagnosing neoplastic vs hyperplastic conditions and may lend insight into the mechanism of ectopic hormone production by tumors

The nature of lysosomal enzyme glycosylation in ALL: relevance to abnormal beta-hexosaminidase expression

The glycosylation of beta-hexosaminidase was investigated in the transformed cell-line, CCRF/CEM, derived from a human acute lymphoblastic leukaemia, and comparisons were made with enzyme from normal human skin fibroblasts. A series of studies including neuraminidase sensitivity, lectin chromatography, Biogel P4 chromatography of [3H]-mannose-labelled glycopeptides and endoglycosidase susceptibility, provided clear evidence that in CCRF/CEM cells, beta-hexosaminidase was abnormally glycosylated. The results indicate that leukemia-associated changes in beta-hexosaminidase expression are probably due to increased sialylation of highly-branched complex oligosaccharides.

Beta 1-6 branching of Asn-linked oligosaccharides is directly associated with metastasis

Neoplastic transformation has been associated with a variety of structural changes in cell surface carbohydrates, most notably increased sialylation and beta 1-6-linked branching of complex-type asparagine (Asn)-linked oligosaccharides (that is, -GlcNAc beta 1-6Man alpha 1-6Man beta 1-). However, little is known about the relevant glycoproteins or how these transformation-related changes in oligosaccharide biosynthesis may affect the malignant phenotype. Here it is reported that a cell surface glycoprotein, gp 130, is a major target of increased beta 1-6-linked branching and that the expression of these oligosaccharide structures is directly related to the metastatic potential of the cells. Glycosylation mutants of a metastatic tumor cell line were selected that are deficient in both beta 1-6 GlcNAc transferase V activity and metastatic potential in situ. Moreover, induction of increased beta 1-6 branching in clones of a nonmetastatic murine mammary carcinoma correlated strongly with acquisition of metastatic potential. The results indicate that increased beta 1-6-linked branching of complex-type oligosaccharides on gp 130 may be an important feature of tumor progression related to increased metastatic potential.

Oligosaccharides of the Hazelhurst vesicular stomatitis virus glycoprotein are more extensively processed in Rous sarcoma virus-transformed baby hamster kidney cells

Because of the extensive oligosaccharide heterogeneity of the membrane glycoprotein (G) from the Hazelhurst strain of vesicular stomatitis virus, this virus has been used as a specific intracellular probe of altered protein glycosylation in Rous sarcoma virus-transformed versus normal baby hamster kidney cells. Over 70% of G protein from virus released from the transformed cells had acidic-type oligosaccharides at both glycosylation sites, compared to less than 50% from the corresponding normal host cells. The remaining G protein contained an acidic-type oligosaccharide at one site and an endo-beta-N-acetylglucosaminidase H-sensitive oligosaccharide at the other. The major endoglycosidase-sensitive species were sialylated hybrid-type (NeuNAc-Gal-GlcNAc-Man5GlcNAc2-Asn) from the transformed and neutral-type (Man5-6GlcNAc2-Asn) from the normal host cells. The degree of branching of the acidic-type oligosaccharides was not increased in the transformed cells (approx. 80% biantennary for viral G protein from both cell types). At a reduced growth temperature (24 versus 37 degrees C), the G protein oligosaccharides were more extensively processed in both cell types (approximately 85-95% of G protein contained acidic-type structures at both sites), even though the level of viral protein synthesis and virus release was decreased. Essentially all of the minor, endoglycosidase-sensitive oligosaccharides on mature viral G protein were sialic acid-containing hybrid-type structures. At 24 degrees C the branching of the acidic-type oligosaccharides was increased in the virus released from the transformed cells versus normal cells.