Purchase this article with an account.
Maria E. Arango, Peter Li, Masanobu Komatsu, Carlos Montes, Coralie A. Carothers Carraway, Kermit L. Carraway; Production and Localization of Muc4/Sialomucin Complex and Its Receptor Tyrosine Kinase ErbB2 in the Rat Lacrimal Gland. Invest. Ophthalmol. Vis. Sci. 2001;42(12):2749-2756.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
purpose. To show the presence and forms of sialomucin complex (rat Muc4) and
receptor tyrosine kinase ErbBs in the rat lacrimal gland and analyze
for complexes of ErbB2 and its ligand Muc4.
methods. Northern blot analyses were used to identify sialomucin complex/Muc4
(SMC/Muc4) mRNA in rat lacrimal gland. Immunoblot analyses were
performed to detect SMC/Muc4 and ErbBs. Sequential immunoprecipitation
and immunoblot analyses were used to differentiate membrane and soluble
forms of the SMC/Muc4 transmembrane subunit ASGP-2. Methacarn-fixed,
paraffin-embedded sections of lacrimal glands from female adult rats
were immunocytochemically stained using antisera to SMC/Muc4 and ErbBs
to determine their relative locations in the gland. Colocalization of
SMC/Muc4 and ErbB2 was confirmed by confocal immunofluorescence.
Sequential immunoprecipitation and immunoblot were performed to analyze
complexes of the SMC/Muc4 and ErbB2 in the lacrimal tissue.
results. Northern blot analyses of rat lacrimal glands, with a probe for
SMC/Muc4, demonstrated the presence of a ∼9-kb transcript, consistent
with observations in other tissues. Similarly, immunoblot analyses with
antibodies against both the transmembrane (ASGP-2) and mucin (ASGP-1)
subunits showed the presence of the two SMC/Muc4 subunits in lysates
from rat lacrimal gland. Significantly, two different forms of ASGP-2
were observed, a high-molecular-weight (∼200-kDa) form and the more
common 120- to 140-kDa form. Sequential immunoprecipitation and
immunoblot analyses to differentiate membrane and soluble forms of
SMC/Muc4 indicated that the high-molecular-weight form of ASGP-2 was
predominantly associated with membranes, whereas the 120- to 140-kDa
form was both membrane-associated and soluble. The lacrimal gland
consists of acini connected by intercalated and interlobular ducts.
Both acini and some intercalated ducts were stained by anti-ASGP-2
monoclonal antisera. Two patterns of acinar staining were observed:
membrane staining at the borders of the epithelial cells and a granular
staining within the cells. Staining of ductal surfaces with antibody to
the cytoplasmic domain of ASGP-2 suggests that membrane SMC/Muc4 is
being produced by the ductal cells and is not simply an adsorbed
soluble product from the acinar cells. Immunoblot and
immunocytochemical analyses demonstrated the presence of all four
ErbBs, with ErbB2 showing the most widespread distribution, similar to
that of SMC/Muc4. Immunofluorescence colocalization of membrane
SMC/Muc4 and ErbB2 and coimmunoprecipitation of a complex of the two
provided evidence of their association in membranes of lacrimal gland
conclusions. SMC/Muc4 is produced by the rat lacrimal gland as both membrane and
soluble forms, specifically associated with both acinar and ductal
cells. Because sialomucin complex is also present in the ocular tear
film, the rat lacrimal gland represents a second source of this mucin
for the tear film, in addition to the corneal and conjunctival
epithelia. Moreover, the presence of a complex of SMC/Muc4 and the
receptor tyrosine kinase ErbB2 in lacrimal tissue suggests that
SMC/Muc4 acts as a ligand for the receptor and has functions in the
lacrimal gland other than that of a mucin.
This PDF is available to Subscribers Only