Stimulation of protein (collagen) synthesis in sponge cells by a cardiac myotrophin-related molecule from Suberites domuncula

The body wall of sponges (Porifera), the lowest metazoan phylum, is formed by two epithelial cell layers of exopinacocytes and endopinacocytes, both o f which are associated with collagen fibrils. Here we show that a myotrophi n-like polypeptide from the sponge Suberites domuncula causes the expressio n of collagen in cells from the same sponge in vitro. The cDNA of the spong e myotrophin was isolated; the potential open reading frame of 360 nt encod es a 120 aa long protein (M-r of 12,837). The sequence SUBDOMYOL shares hig h similarity with the known metazoan myotrophin sequences. The expression o f SUBDOMYOL is lo tv in single cells but high after formation of primmorph aggregates as well as in intact animals. Recombinant myotrophin was found t o stimulate protein synthesis by fivefold, as analyzed by incorporation stu dies using [H-3] lysine. In addition, it is shown that after incubation of single cells with myotrophin, the primmorphs show an unusual elongated, ova l-shaped appearance. It is demonstrated that in the presence of recombinant myotrophin, the cells up-regulate the expression of the collagen gene. The cDNA for S. domuncula collagen was isolated; the deduced aa sequence shows that the collagenous internal domain is rather short, with only 24 G-x-y c ollagen triplets. We conclude that the sponge myotrophin causes in homologo us cells the same/similar effect as the cardiac myotrophin in mammalian cel ls, where it is involved in initiation of cardial ventricular hypertrophy. We assume that an understanding of sponge molecular cell biology will also contribute to a further elucidation of human diseases, here of the cardiova scular system.