N-cadherin is developmentally regulated and functionally involved in early hematopoietic cell differentiation

The cadherins, an important family of cell adhesion molecules, are known to play major roles during embryonic development and in the maintenance of solid tissue architecture. In the hematopoietic system, however, little is known of the role of this cell adhesion family. By RT-PCR, western blot analysis and immunofluorescence staining we show that N-cadherin, a classical type I cadherin mainly expressed on neuronal, endothelial and muscle cells, is expressed on the cell surface of resident bone marrow stromal cells. FACS analysis of bone marrow mononuclear cells revealed that N-cadherin is also expressed on a subpopulation of early hematopoietic progenitor cells. Triple-color FACS analysis defined a new CD34(+) CD19(+) N-cadherin(+) progenitor cell population. During further differentiation, however, N-cadherin expression is lost. Treatment of CD34(+) progenitor cells with function-perturbing N-cadherin antibodies drastically diminished colony formation, indicating a direct involvement of N-cadherin in the differentiation program of early hematopoietic progenitors. N-cadherin can also mediate adhesive interactions within the bone marrow as demonstrated by inhibition of homotypic interactions of bone-marrow-derived cells with N-cadherin antibodies. Together, these data strongly suggest that N-cadherin is involved in the development and retention of early hematopoietic progenitors within the bone marrow microenvironment.

Galectins and other endogenous carbohydrate-binding proteins of animal bladder

Defects in the glycocalyx of the bladder epithelium may be related to the development of bladder diseases including interstitial cystitis which is a chronic bladder disease of unknown etiology. Indirect evidence has implicated alterations in the bladder epithelial glycoconjugates in interstitial cystitis and vesicaler instillation of glycosaminoglycans is promoted as treatments. However, information on the nature of the glycoconjugates of the bladder epithelium and lectins that may interact with the exogenous instilled glycoconjugates is very limited. We have examined the endogenous lectin associated with bladder epithelium by immunohistochemistry using biotinylated neoglycoconjugates. The strong calcium-independent binding of beta-D-galactose probe suggested the presence of galectins in rabbit and human bladder. Extracts of rabbit bladder organ cultures metabolically labeled with [14C]-amino acids were subjected to affinity chromatography on immobilized lactose and the specifically bound material eluted with 0.2 M lactose. SDS-PAGE of the recovered proteins revealed a major band of approximately 30 kDa and a minor band of 21 kDa. Polymerase chain reaction and northern blot analysis showed that both galectin-3 and galectin-4 are expressed in rabbit bladder. Since galectin-3 from rabbit had been previously cloned, we cloned and sequenced galectin-4 from rabbit bladder. The deduced full length sequence of 328 amino acids revealed four distinct regions: a N-terminal peptide of 19 residues, two carbohydrate recognition domains of 130 residues each, and a linker region of 49 residues. Comparison of the rabbit galectin-4 sequence with those of human, pig, rat, and mouse revealed two invariant peptide motifs that are proposed as signature sequences for identifying related galectins.

Characterization and functional analysis of laminin isoforms in human bone marrow

Laminins are a family of disulfide-linked heterotrimeric proteins consisting of 3 different subunits termed alpha, beta, and gamma chains. Combinations of 11 characterized laminin subunits (alpha 1-alpha 5, beta 1-beta 3, and gamma 1-gamma 3) generate at least 12 laminin isoforms, which can serve different functions. Although expression of laminin in the hematopoietic microenvironment has been known for many years, the nature of the laminin isoforms present in the human bone marrow is poorly characterized. The present study attempts to clarify this issue. Reverse transcriptase-polymerase chain reaction analysis of human bone marrow stromal cells suggested the expression of many laminin isoforms in the marrow. Northern blot and immunoblot analysis, however, showed that laminin-8/9 and laminin-10/11 are the most abundant laminin isoforms synthesized by human bone marrow stromal cells. Other isoforms, if present, certainly play a minor role in the hematopoietic microenvironment. Functionally, laminin-10/11 preparations showed strong adhesive interactions with human CD34(+) cell lines. Antibodies against the beta 1 integrin subunit inhibited these interactions. Other laminin isoforms, especially laminin-1 and laminin-2/4, showed only weak or no adhesive interactions with the hematopoietic cell lines tested, explaining former negative results. In addition to its adhesion-mediating properties, laminin-10/11 preparations also showed a mitogenic activity for human hematopoietic progenitor cells. Taken together, these data suggest that laminin in the bone marrow plays a hitherto unexpected important function in the development of hematopoietic progenitor cells. (Blood. 2000;96:4194-4203)

Signature sequences for the galectin-4 subfamily

Galectins are a distinct family of animal lectins that have a cation-independent affinity for beta-galactoside sugars and share characteristic amino acid sequences. The cDNA encoding rabbit bladder galectin-4 has been cloned and sequenced (GenBank accession no. AF091738). The deduced 328 amino acid sequence predicts a multidomain structure consisting of an N-terminal peptide (19 residues) and two carbohydrate recognition domains (130 residues each) connected by a linker region (49 residues). Comparison of rabbit galectin-4 with related proteins reveals that two peptide motifs, M-A-F/Y-V-P-A-P-G-Y-Q-P-T-Y-N-P-T-L-P-Y in the N terminus and A-F-H-F-N-P-R-F-D-G-W-D-K-V-V-F in the first carbohydrate recognition domain are highly conserved in human, pig, rat, and mouse galectin-4 as well as in mouse galectin-6. The two peptide motifs are proposed here as the signature sequences to identify new members of the galectin-4 subfamily.

Endogenous carbohydrate-binding proteins of rabbit and human bladder

OBJECTIVES

To identify the endogenous lectins of the human bladder with the long-term goal of developing improved strategies for the treatment of interstitial cystitis and other bladder disorders.

METHODS

Rabbit and human bladder sections were examined histochemically using biotinylated neoglycoconjugates. Affinity chromatography of extracts of rabbit bladder was performed on immobilized lactose to purify the galactose-binding protein.

RESULTS

Biotinylated beta-D-galactose neoglycoconjugate showed the strongest specific staining of the rabbit and human bladder sections. The beta-D-N-acetylglucosamine neoglycoconjugate also showed significant staining; the alpha-L-fucose, alpha-D-mannose, alpha-D-N-acetylneuraminic acid, and alpha-D-N-acetylgalactosamine neoglycoconjugates showed either very weak or no reaction. The strong Ca2+ -independent binding of beta-D-galactose neoglycoconjugates suggested the presence of galectins in rabbit and human bladder. Affinity chromatography of rabbit bladder extract on lactose gel yielded a galectin of about 30 kDa, consistent with the molecular biological data confirming the expression of galectin-3 in bladder.

CONCLUSIONS

Beta-D-galactose binds strongly and specifically to rabbit and human bladder tissue sections. This information would be useful for the purpose of modifying drugs used for the treatment of bladder disorders with ligands of galactose-binding lectins to improve their retention in the bladder.