Lysosomal and cytosolic sialic acid 9-O-acetylesterase activities can be encoded by one gene via differential usage of a signal peptide-encoding exonat the N terminus
H. Takematsu et al., Lysosomal and cytosolic sialic acid 9-O-acetylesterase activities can be encoded by one gene via differential usage of a signal peptide-encoding exonat the N terminus, J BIOL CHEM, 274(36), 1999, pp. 25623-25631
9-O-Acetylation is one of the most common modifications of sialic acids, an
d it can affect several sialic acid-mediated recognition phenomena. We prev
iously reported a cDNA encoding a lysosomal sialic acid-specific 9-O-acetyl
esterase, which traverses the endoplasmic reticulum-Golgi pathway and local
izes primarily to lysosomes and endosomes, In this study, we report a varia
nt cDNA derived from the same gene that contains a different 5' region, Thi
s cDNA has a putative open reading frame lacking a signal peptide-encoding
sequence and is thus a candidate for the previously described cytosolic sia
lic acid 9-O-acetylesterase activity. Epitope-tagged constructs confirm tha
t the new sequence causes the protein product to be targeted to the cytosol
and has esterase activity. Using reverse transcription-polymerase chain re
action to distinguish the two forms of message, we show that although the l
ysosomal sialic acid-specific 9-O-acetylesterase message has a widespread p
attern of expression in adult mouse tissues, this cytosolic sialic acid 9-O
-acetylesterase form has a rather restricted distribution, with the stronge
st expression in the liver, ovary, and brain. Using a polyclonal antibody d
irected against the 69-amino acid region common to both proteins, we confir
med that the expression of glycosylated and nonglycosylated polypeptides oc
curred in appropriate subcellular fractions of normal mouse tissues. Rodent
liver polypeptides reacting to the antibody also co-purify with previously
described lysosomal sialic acid esterase activity and at least a portion o
f the cytosolic activity. Thus, two sialic acid 9-O-acetylesterases found i
n very different subcellular compartments can be encoded by a single gene b
y differential usage of a signal peptide-encoding exon at the N terminus. T
he 5'-rapid amplification of cDNA ends results and the differences in tissu
e-specific expression suggest that expression of these two products may be
differentially regulated by independent promoters.