J. Tissari et al., NOVEL 13A ANTIGEN IS AN INTEGRAL PROTEIN OF THE BASOLATERAL MEMBRANE OF RAT GLOMERULAR PODOCYTES, Laboratory investigation, 71(4), 1994, pp. 519-527
BACKGROUND: We described recently the 13A monoclonal antibody recogniz
ing a 120 kilodalton protein located at the bases of podocyte foot pro
cesses in rat glomeruli. The antigen was extracellular, either a compo
nent of the glomerular basement membrane or an integral membrane prote
in. As only few markers exist for the basal domain of the podocyte mem
branes, we wanted to characterize the antigen further. EXPERIMENTAL DE
SIGN: The distribution of the 13A antigen in rat tissues and cultured
cells was studied by immunofluorescence and immunoelectron microscopy.
Cultured cells were also used for its biochemical and functional char
acterization. RESULTS: The antigen was detected in several rat epithel
ial and smooth muscle tissues. In polarized epithelia, it was restrict
ed to the basolateral membranes, and in stratified epithelia, to the b
asal cell layer. In contrast to its limited distribution in vivo, the
antigen was detected in vitro in several cultured fibroblastoid or epi
thelial rat cell lines, and in cultured mesangial cells. In nonpolariz
ed cells, it had a diffuse granular distribution at the cell surface,
and at the ventral surface, it colocalized with vinculin in areas rese
mbling focal adhesions, as shown by double immunofluorescence staining
. In polarized epithelial cells, the 13A antigen was concentrated at t
he basolateral membranes. By immunoelectron microscopy, it was often p
resent at the tips of cell extensions and at adhesion sites. Pretreatm
ent of cryostat sections or cultured cells with trypsin partially inhi
bited antibody binding, whereas detergents abolished it totally. The a
ntigen of cultured cells could not be identified by Western blotting o
r immunoprecipitation techniques. The antibodies did not seem to affec
t cell growth or adhesion. CONCLUSIONS: The 13A antigen is an integral
membrane protein of several rat epithelial tissues and cultured cells
, and is particularly abundant in the podocyte foot processes. Althoug
h its identity and function remain unknown, the 13A protein is a valua
ble marker for the basal membrane domain of the podocyte.