High expression of the human hepatocarcinoma-intestine-pancreas/pancreatic-associated protein (HIP/PAP) gene in the mammary gland of lactating transgenic mice - Secretion into the milk and purification of the HIP/PAP lectin
L. Christa et al., High expression of the human hepatocarcinoma-intestine-pancreas/pancreatic-associated protein (HIP/PAP) gene in the mammary gland of lactating transgenic mice - Secretion into the milk and purification of the HIP/PAP lectin, EUR J BIOCH, 267(6), 2000, pp. 1665-1671
The human hepatocarcinoma-intestine-pancreas/pancreatic-associated protein
(HIPPAP) gene was previously identified because of its increased expression
in primary liver cancers and during the acute phase of pancreatitis. In no
rmal tissues, HIP/PAP is expressed both in endocrine and exocrine cells of
the intestine and pancreas. HIP/PAP is a lactose binding C-type lectin whic
h acts as an adhesion molecule for rat hepatocytes.
The aim of the work was to study the HIP/PAP secretory pathway and to produ
ce high levels of HIP/PAP in the milk of lactating transgenic mice. In view
of its lactose C-type lectin properties, we have studied the consequences
of the expression of HIP/PAP on mammary epithelial cells.
In homozygous mice, production reached 11.2 mg.mL(-1) of milk. High levels
of soluble and pure HIP/PAP (18.6 mg) were purified from 29 mL of milk. The
purified protein was sequenced and the N-terminal amino acid of the mature
HIP/PAP was identified as Glu27, thus localizing the site of cleavage of t
he signal peptide. The HIP/PAP transgene was only expressed in the mammary
gland of lactating transgenic mice. HIP/PAP was detected by immunofluoresce
nce in the whole gland, but labelling was heterogeneous between alveolar cl
usters, with strongly positive sparse cells. Using immuno electron microsco
py, HIP/PAP was observed in all the compartments of the secretory pathway w
ithin the mammary epithelial cells.
We provide evidence that HIP/PAP is secreted through the Golgi pathway. How
ever, the number of distended Golgi saccules was increased when compared to
that found in wild-type mouse mammary cells. These modifications could be
related to HIP/PAP C-type lectin specific properties.