Cell-derived stiffening and plasticizing factors in sea cucumber (Cucumaria frondosa) dermis

The stiffness of holothurian dermis can be altered experimentally in vitro by changing the concentration of extracellular Ca(2+). Previous experiments with Cucumaria frondosa have established that these Ca(2+) effects are due to Ca(2+)-dependent cellular processes rather than to direct effects of Ca(2+) on the extracellular matrix. The present report describes two protein factors that are released from cells of C. frondosa dermis by membrane lysis and that directly alter the stiffness of the extracellular matrix. One factor, isolated from the inner dermis, increased tissue stiffness in the absence of Ca(2+). The second factor, from the outer dermis, decreased tissue stiffness in the presence of normal Ca(2+) levels. The relative abundance of these two factors in the inner and outer dermis suggests the possibility that the cells that control tissue stiffness are spatially segregated. Both factors were partially purified under non-denaturing conditions by anion-exchange and gel-filtration chromatography. The partially purified protein preparations retained biological activity. These results suggest that the stiffness of sea cucumber dermis is regulated by cell-mediated secretion of either the stiffening or plasticizing protein and that alterations in dermis stiffness brought about by manipulation of Ca(2+) levels are mediated by effects on secretion of one or both of these proteins.