Studies on the effect of lysosomotropic agents on the release of Gal <i>β</i> 1-4GlcNAc α-2,6-sialytransferase from rat liver slices during the acute-phase response

Yeh

et al. 1996

Treatment of mouse teratocarcinoma F9 cells with alltrans-retinoic acid (RA) causes a 9-fold increase in steady-state levels of mRNA for UDP-Gal:␤-D-Gal ␣1,3-galactosyltransferase (␣1,3GT) beginning at 36 h. Enzyme activity rises in a similar fashion, which also parallels the induction of laminin and type IV collagen. Nuclear run-on assays indicate that this increase in ␣1,3GT in RA-treated F9 cells, like that of type IV collagen, is transcriptionally regulated. Differentiation also results in increased secretion of soluble ␣1,3GT activity into the growth media. The major ␣-galactosylated glycoprotein present in the media of RA-treated F9 cells, but not of untreated cells, was identified as laminin. Differentiation of F9 cells is accompanied by an increase in ␣-galactosylation of membrane glycoproteins and a decrease in expression of the stage-specific embryonic antigen, SSEA-1 (also known as the Lewis X antigen or Le X ), which has the structure Gal␤1-4(Fuc␣1-3)GlcNAc␤1-R. However, flow cytometric analyses with specific antibodies and lectins, following treatment of cells with ␣-galactosidase, demonstrate that differentiated cells contain Le X antigens that are masked by ␣-galactosylation. Thus, RA induces ␣1,3GT at the transcriptional level, resulting in major alterations in the surface phenotype of the cells and masking of Le X antigens.

Section: Time Course Of Induction Of ␣13gt Enzyme Activity In F9 Celsupporting

confidence: 69%

Section: Discussionmentioning

confidence: 99%

Transcriptional Regulation of α1,3-Galactosyltransferase in Embryonal Carcinoma Cells by Retinoic Acid

Yeh

et al. 1996

“…In other words, it is most likely that the 34 amino acids between Arg 832 and Lys 866 (see sequence a in fig. 4A) are removed as small peptides and/or individually by enterocytic proteases, possibly including granzyme A (52), brush-border aminopeptidases, and perhaps lysosomal cathepsins (Golgi resident proteins have been shown to be exposed to cathepsins (49) and (pro)lactase itself is likely to be exposed to lysosomal proteolysis in COS-1 cells (40)). …”

Section: Furin Cleaves Human Prolactasementioning

confidence: 99%

Processing of Human Intestinal Prolactase to an Intermediate Form by Furin or by a Furin-like Proprotein Convertase

Mesonero

Gloor

Semenza³

1998

Human lactase-phlorizin hydrolase (human-LPH) is synthesized as a large precursor (prepro-LPH), then cleaved to a pro-LPH of 220 kDa which is further cut to a "mature-like LPH" of a size close to that of mature LPH, i.e. about 150 kDa (in the processing of rabbit pro-LPH the intermediate has a mass of approximately 180 kDa). By coexpression of human prepro-LPH with furin in COS-7 cells we show that furin generates a mature-like LPH. Radioactive amino acid sequence analysis reveals that furin recognizes the motif R-T-P-R 832 , a protein convertase consensus, to generate a NH 2 terminus located 36 amino acids upstream of the NH 2 terminal found in vivo at Ala 869 . This intermediate is ultimately cleaved to the mature LPH form by other proteases including the pancreatic ones. These data demonstrate that human pro-LPH, like the rabbit enzyme, is processed to the mature enzyme by furin or furin-like enzymes through at least an intermediate form that has, however, an apparent mass close to that of the mature enzyme.

“…It has been shown that soluble forms of the rat liver ␣2,6-sialyltransferase and the bovine ␤1,4-galactosyltransferase are derived by proteolysis within the stem domain (24,25). Cleavage of the membrane-associated ␣2,6-sialyltransferase may involve a cathepsin D-like protease (26) that recognizes peptides containing hydrophobic residues (54). Such an enzyme could participate in cleavage of the ␣1,3GT, since cleavages occur adjacent to aromatic residues.…”

Section: Discussionmentioning

confidence: 99%

“…N-terminal sequence analyses of soluble forms of the ␣2,6-sialyltransferase and ␤1,4-galactosyltransferase demonstrate that they arise through proteolysis within the stem region, thereby releasing the catalytic domain from the membrane (24,25). The proteases responsible for cleaving the enzymes are not defined, although evidence suggests that a cathepsin D-like protease may be responsible for the cleavage of ␣2,6-sialyltransferase (26). The functions of the soluble glycosyltransferases are not known.…”

mentioning

confidence: 99%

A Soluble Form of α1,3-Galactosyltransferase Functions within Cells to Galactosylate Glycoproteins

Cummings

1997

It has been assumed that membrane-bound glycosyltransferases function within the Golgi apparatus to glycosylate glycoproteins. We now report, however, that a truncated, soluble recombinant form of the murine ␣1,3-galactosyltransferase expressed in human 293 cells is highly efficient and comparable to the full-length enzyme in ␣-galactosylating both newly synthesized membrane-associated and secreted glycoproteins. Although the soluble enzyme was secreted by cells as expected, we also found that the full-length, membrane-associated form was secreted. Unexpectedly, both secreted forms are cleaved identically at two primary sites within the stem region by endogenous protease(s) at the indicated positions in the sequence 73 KDWW2FPS2WFKNG. These results demonstrate that the soluble ␣1,3-galactosyltransferase is functional within the cell and that specific proteolysis occurs in the stem region. The widespread occurrence of different soluble glycosyltransferases secreted by cells suggests that normal glycoconjugate biosynthesis may involve cooperation between membrane-bound and soluble enzymes.