The hyaluronate (HA) receptor is a glycoprotein of approximately Mr 85,000 which mediates the adhesion of cells to HA in the extracellular matrix. It is present on a wide variety of cells including proliferating epithelia, macrophages, lymphocytes and variety of tumor cells. Recently this receptor has been shown to be closely related or identical to a protein termed CD44 which mediates the homing of lymphocytes to mucosal lymphoid tissue. Thus, the HA receptor/CD44 molecule is able to carry out several distinct functions. The central hypothesis of this application is that invasive tumor cells express a form of CD44 which is capable of binding HA, and this in turn allows these cells to invade through and degrade matrix containing HA. Aspects of this hypothesis will be evaluated in the following specific aims. The first specific aim is to examine the structural requirements of CD44 binding to HA. Preliminary studies have shown that CD44 from the invasive MDA-231 cell line binds HA, whereas that from the non-invasive MCF-7 cell line does not. To determine the structural nature of this difference, the CD44 from the two cell lines will be purified and directly tested for their ability to bind HA. Also, the cell lines will be compared by Northern Blotting and by the polymerase chain reaction to determine if there are differences at the level of mRNA. And finally, the CD44 will be tested for possible post-translational modifications such as glycosylation and the presence of disulfide bonded material, which might interfere with its ability to bind HA. The second specific aim is to investigate the role of the HA receptor/CD44 in the migration of tumor cells through a matrix rich in HA. For this, an assay will be developed to measure the migration of cells through cryostat sections of umbilical cord, a natural matrix containing large amounts of HA. A panel of tumor cell lines will be examined in this assay to determine if there is a correlation between their invasive properties and their ability to bind [3H] HA. In addition, the role of the receptor/CD44 in the invasive process will be examined using specific antibodies and other blocking agents. The final specific aim is to examine the role of the HA receptor/CD44 in the degradation of HA by tumor cells. Preliminary studies demonstrated that macrophages can degrade HA and this process is blocked by monoclonal antibodies to the HA receptor. To determine if a similar phenomenon occurs wit invasive tumor cells, a panel of tumor cells will be examined for their ability to degrade [3H] HA, and correlated with their invasive behavior. The relationship between invasion and degradation of HA will be further tested using antibodies to the HA receptor/CD44.
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