S. Rubio et al., PULMONARY SURFACTANT PROTEIN-A (SP-A) IS EXPRESSED BY EPITHELIAL-CELLS OF SMALL AND LARGE-INTESTINE, The Journal of biological chemistry, 270(20), 1995, pp. 12162-12169
Surfactant protein A (SP-A) is the most abundant protein associated wi
th phospholipids in pulmonary surfactant, There are several lines of e
vidence that pulmonary and gastrointestinal epithelium produce closely
related surface-active materials, although the presence of SP-A in ga
strointestinal tract has so far not been reported, Indirect immunofluo
rescence experiments using different antibodies raised against rat pul
monary SP-A showed that some jejunal and colonic but not gastric epith
elial cells positively stained for SP-A. Analysis of the proteins in c
ell lysates from rat small intestine and colon studied by Western blot
revealed several immunoreactive bands, including the characteristic t
riplet of 26-, 32-, and 38-kDa monomeric proteins, less strongly label
ed than in lung cells, and higher molecular mass forms of 66 and 120 k
Da also present in lung cells, The 66- and 120-kDa bands displayed the
expected isoelectric pH of SP-A after two-dimensional electrophoresis
. Alkylation induced conversion of the 120-kDa form (almost completely
) and the 66-kDa form (partly) into the 26-38-kDa monomeric species, T
he presence of SP-A mRNA in rat stomach, small intestine, and colon wa
s then searched for by conventional cDNA/reverse transcriptase-polymer
ase chain reaction, Products of appropriate size (372 base pairs) iden
tical to that of pulmonary tissue were amplified in small intestine an
d colon but not in stomach or in other tissues used as controls. Cloni
ng and sequencing of rat colon SP-A cDNA revealed the same sequence as
the one reported for rat lung SP-A Furthermore, analysis of the trans
criptional initiation site of SP-A gene in colon by anchored-polymeras
e chain reaction showed that transcription was initiated at the same s
ite in both colon and lung. These data, which demonstrate that small i
ntestine and colon express SP-A constitutively and that this protein i
s present in some epithelial cells, extend the concept of intestinal s
urfactant and underline its close relationships to pulmonary surfactan
t.