W. Wimmer et al., Origin of the integrin-mediated signal transduction - Functional studies with cell cultures from the sponge Suberites domuncula, EUR J BIOCH, 260(1), 1999, pp. 156-165
Sponges (phylum Porifera) represent the phylogenetically oldest metazoan an
imals. Recently, from the marine sponge Geodia cydonium a first cDNA encodi
ng a putative integrin receptor molecule was isolated. In the present study
basic functional experiments have been conducted to test the hypothesis th
at in sponges integrin polypeptides also function as adhesion molecules and
as outside-in signaling molecules. The sponge Suberites domuncula has been
used for the experiments because from this sponge only has a cell culture
been established. Here we report that aggregation factor (AF)-mediated cell
-cell adhesion is blocked by the RGDS peptide which is known to interact wi
th beta integrin. Both RGDS and AF were found to stimulate DNA synthesis wi
thin 24 h. The beta subunit of the integrin receptor was cloned from S, dom
uncula: the estimated 91-kDa molecule comprises the characteristic signatur
es. Evolutionary conservation of the beta integrin was assessed by comparis
on with corresponding beta integrin subunits from evolutionary higher metaz
oan taxa. Addition of RGDS or of AF to isolated cells of S. domuncula cause
s a rapid (within 1-2 min) increase in the intracellular Ca2+ concentration
which is further augmented in the presence of Ca2+. Furthermore, incubatio
n of the cells with RGDS or AF causes an activation of the GTP-binding prot
ein Pas. In addition it is shown that after a prolonged incubation of the c
ells with RGDS and AF the expression of the genes coding for Pas and for ca
lmodulin is upregulated These results suggest that the integrin receptor fu
nctions in the sponge system not only as adhesion molecule but also as a mo
lecule involved in outside-in signaling.