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PubMed1991

The Yersinia pseudotuberculosis invasin protein and human fibronectin bind to mutually exclusive sites on the alpha 5 beta 1 integrin receptor.

The Yersinia pseudotuberculosis invasin protein promotes bacterial penetration into mammalian cells by binding to several beta 1 chain integrins. We show here that proteins containing the cell-binding domain of invasin bind to the fibronectin receptor alpha 5 beta 1 isolated from human placenta and immobilized on a filter membrane. Two forms of the receptor, each having a molecular weight of about 290,000, were immunodepleted by monoclonal antibodies specific for the beta 1 subunit or the alpha 5 beta 1 heterodimer. The binding of invasin to the receptor immobolized on the filter, or to whole JAR cells, reaches saturation after 90 min and has an apparent dissociation constant (Kd) of 5.0 x 10(-9) M. Invasin binding to alpha 5 beta 1 is inhibited by the 120-kDa chymotryptic fragment of fibronectin in a competitive manner with an inhibition constant (Ki) of 7.5 x 10(-7) M. Furthermore, invasin-receptor binding is also inhibited by the hexapeptide GRGDSP, and monoclonal antibodies that block cell attachment to invasin-coated surfaces also block cell attachment to fibronectin-coated surfaces. These results indicate that invasin and fibronectin bind to the same, or closely located sites on alpha 5 beta 1, although invasin binds with a much higher affinity than does fibronectin.

Adhesins, Bacterial↗
PubMed1991

The dyad symmetry element is the molecular target for c-fos induction and inhibition during K 562 differentiation along mutually exclusive lineages.

The c-fos proto-oncogene seems to play an important role during differentiation and activation of cells from the hematopoietic lineage. Therefore, it is of interest to investigate the mechanism underlying its transcriptional activation in these cells. To delineate the sequences and factors involved in c-fos transcriptional activation during the course of myeloid cell differentiation, we have used the K 562 chronic leukemic cell line as a model. K 562 cells were transfected with chloramphenicol transacetylase (CAT) reporter constructs, including various regions of the human c-fos promoter, and induced to differentiate by two distinct agents: 12-O-tetradecanoyl phorbol-13-acetate (TPA), which activates a differentiation program along the megakaryoblastic pathway; and hemin, which induces erythroid differentiation. We show here that TPA treatment of K 562 cells induces fos CAT reporter constructs activation, whereas treatment with hemin does not. Furthermore, predifferentiation of the cells with hemin blocks a subsequent induction by TPA, in correlation with the inhibition by hemin of megakaryoblastic differentiation markers appearance. Both the induction by TPA and the inhibition by hemin are mediated by a dyad symmetry element (DSE) located in the upstream regulatory region, between -318 and -296. These results suggest that the protein complex binding to the DSE regulatory element is the target for c-fos activation by TPA and inhibition by hemin in K 562 cells. However, no modulation of protein affinity for the DSE sequence was detected by gel shift assay during the course of induction or inhibition, suggesting that the structural change responsible for the transcriptional modulation is too unstable or too subtle to be detected by this method.

Base Sequence↗
PubMed1990

The processing of N-linked glycans in yeast. Mutually exclusive steps in the processing of a Man6 derivative by yeast membrane preparations.

When a derivatized oligosaccharide isolated from ovalbumin and containing 6 mannose residues was incubated with yeast membranes and GDP-mannose, two sets of products were obtained, a high molecular weight one containing about 25 mannose residues and a low molecular weight one consisting of compounds with 7, 8, and 9 mannose residues, respectively. When the low molecular weight products were reincubated with the yeast membranes and GDP-mannose, no further mannose incorporation was observed, showing that these compounds must be of the wrong structure as substrates for yeast glycan processing enzymes. The structures were investigated by 1H NMR spectroscopy. The high molecular weight products contained an outer chain of an average length of 18 1----6-linked mannose residues attached to a core structure made up of the original 6 mannose residues with one additional 1----2-linked mannose added. The low molecular weight product with 8 mannose residues was deduced to contain a terminal 1----6-linked mannose (on the 1----6 arm) substituted by mannose at the 2-position, and the ones with 7 and 9 mannose residues were identified as having an additional 1----3-linked mannose on the starting Man6 substrate and on the Man8 product, respectively. The results lend further support to the picture that the processing steps must occur in proper sequence for specific products to form.

Carbohydrate Conformation↗
PubMed1985

Induction-dependent and lineage-dependent models for cell diversification are mutually exclusive.

The purpose of this brief review is to put into perspective just how little is known about the mechanisms that control the assembly of the differentiation program of any cell type. Any number of "trivial" changes in the microenvironment of a Friend erythroleukemic or of a neuroblastoma cell induces both covertly differentiated cells to reveal their lineage affiliations. Demethylating molecules, BudR, retinoic acid, cAMP, butyrate or other "inducing molecules" do not, however, transform the descendents of the neuroblastoma cell into a Hb- synthesizing cell or vice versa. For thousands of generations both of these immortialized lines transmit to their daughters their unique, lineage-dependent differentiation programs with great fidelity. The stability of the inherited transcription complex that is ultimately responsible for this covert differentiation program of these cell lines--or of normal precursor cells--is awesome. Clearly, with these immortalized cells as with normal chick blastodisc cells, the cell's microenvironment plays a major role in permitting or blocking the expression of the cell's inherited differentiation program. But the program itself must be generated by intracellular mechanisms and must be inherited; its assembly is not dependent upon inductive events initiated by exogenous molecules.

Animals↗
PubMed1979

Mutually exclusive genetic signatures of human breast tumor cell lines with a common chromosomal marker.

Seventeen recently established human breast carcinoma cell lines of metastatic origin (MDA series), HeLa cells, and MCF-7 (a well-established breast carcinoma cell line) were studied by starch gel electrophoresis for allozymic differences at 17 enzyme loci. Ten loci proved to be informative in establishing unique genetic signatures for all of the lines with the exception of MDA-134 and -309, which had the same genetic signatures. The probability of these latter two lines being of independent origin and finding their similar genetic signatures by chance is 0.07. These studies enable us to conclude that the chromosomal marker shown to be common to these breast carcinoma cell lines of metastatic origin is not present because of cross-contamination of the lines with other long-term lines or each other.

Breast Neoplasms↗
PubMed1994

Mutually exclusive binding of peptide and invariant chain to major histocompatibility complex class II antigens.

The invariant chain is a membrane protein associated with the major histocompatibility complex class II antigens both intra- and extracellularly. The extracellular portion of the human invariant chain (Ii) was expressed in Escherichia coli as a fusion protein with a polyhistidine tail and purified by metal affinity chromatography. The recombinant Ii was used as a ligand to probe binding to the cell surface of Chinese hamster ovary cells stably transfected with human class II alpha and beta genes of the DR4 isotype. We show that recombinant Ii inhibits peptide loading on class II polypeptides and also the converse; the presence of peptide in the antigen groove prevents binding of fluorescein-conjugated Ii. Moreover, blocking of Ii binding by peptide did not require a transition of the class II dimers to an SDS-stable state. A monoclonal antibody, L243, known to bind to (or close to) the peptide pocket of the class II molecule likewise blocked Ii-fluorescein binding. Further, we investigated whether or not the Ii, a variety of bacterial superantigens or the CD4 molecule, have overlapping binding sites on the class II heterodimer. Of the class II ligands tested, reduced binding was detected for the Staphylococcus superantigen type SEB on cells precincubated with soluble Ii while the binding of the other ligands was either unchanged or marginally changed. These data clarify by a direct biochemical approach the binding characteristics of Ii in comparison with other class II ligands.

Amino Acid Sequence↗
PubMed1994

Mutually exclusive exon use and reactive center diversity in insect serpins.

We have isolated 38 cDNA clones for serpins from a lepidopteran insect, Manduca sexta, and have found that they are identical in sequence, except for a region encoding the carboxyl-terminal 40-45 residues, which includes the reactive center. Among these clones, there are 11 variants of the reactive center region, each encoded by a different version of the ninth exon in the serpin gene. Thus, evolution of this insect serpin gene has resulted from duplication and sequence divergence of only the exon encoding the reactive site. Alternative pre-mRNA splicing then generates inhibitor diversity and the potential to regulate a variety of proteinases, using the same protein framework joined to different reactive site region cassettes.

Alternative Splicing↗