Epithelial cells perform their physiological functions by organizing into three-dimensional tissue structures. One of our laboratory focuses is on a protein called epimorphin (Hirai et al., Cell, 1992), that we have shown to stimulate epithelial cells to organize into three-dimensional structures and undergo functional differentiation in vitro. Although epimorphin lacks a signal peptide for secretion and has a transmembrane domain at the C-terminus, this protein is　released from the stromal fibroblast and acts as a morphoregulatory protein for epithelial cells. By understanding the molecular mechanisms underlying epimorphin's action this may　establish a novel concept regarding stromal influence on epithelial behaviors. This year, we addressed how epimorphin is presented at the outer cell surface without a signal peptide, secreted to pass through the basement membrane and captured by the target epithelia. We found that 1) cellular damage leads to extracellular projection of epimorphin, 2) extracellular epimorphin is cleaved near the C-terminal hydrophobic domain to be secreted, and 3) alphaV-　containing integrin on the target epithelia binds to this secreted epimorphin. Given that active tissue morphogenesis includes the process of apoptosis in certain cellular populations, cellular damage-dependent epimorphin release could be an important mechanism allowing epimorphin's extracellular action, albeit other mechanisms may also be exist. By combination of epimorphin with other molecules for morphogenesis we will try to establish technologies to control the morphological differentiation of various tissues. The target cells mainly used in the lab will include primate ES cells and its epithelial derivatives. (By Hirai, Y.)

Another project we are working on is the analysis of tight junction formation of keratinocyte. The wound healing is one of the regeneration systems that are intensively studied on. During this process, cells surrounding the wound move directionally toward this wound. For this directional moving, cell-cell and/or cell-ECM interaction are regulated cooperatively. Recent study demonstrated that cell-ECM interaction is regulated by the JNK, c-Jun N-term kinase. Meanwhile regulatory mechanism of cell-cell interaction during this process is still unclear. Recently, we found that the localization of ZO-1, one of the components of tight junction, change dramatically in HaCaT, human epidermal keratinocyte cell line, when this cell line is cultured with JNK inhibitor. This result suggests that the tight junction formation of HaCaT is repressed by JNK activity. Now we are analyzing the molecular mechanisms underlying this process for expecting that this study uncover the regulatory mechanism of cell-cell interaction during the wound healing.　　(By Aono, S.)