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

The stiffness of holothurian dermis can be altered experimentally in vitro by changing the concentration of extracellular Ca2+. Previous experiments w ith Cucumaria frondosa have established that these Ca2+ effects are due to Ca2+-dependent cellular processes rather than to direct effects of Ca2+ on the extracellular matrix. The present report describes two protein factors that are released from cells of C. frondosa dermis by membrane lysis and th at directly alter the stiffness of the extracellular matrix. One factor, is olated from the inner dermis, increased tissue stiffness in the absence of Ca2+. The second factor, from the outer dermis, decreased tissue stiffness in the presence of normal Ca2+ levels. The relative abundance of these two factors in the inner and outer dermis suggests the possibility that the cel ls that control tissue stiffness are spatially segregated, Both factors wer e 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 s ea cucumber dermis is regulated by cell-mediated secretion of either the st iffening or plasticizing protein and that alterations in dermis stiffness b rought about by manipulation of Ca2+ levels are mediated by effects on secr etion of one or both of these proteins.