Flow cytometric analysis of the expression of 9A3 antigen, E-cadherin and EGF receptor in TMK-1 stomach cancer cells.

We have previously produced a monoclonal antibody (MAb) against TMK-1 cells, a poorly differentiated stomach-cancer cell line, and designated the antigen as 9A3. Immunohistochemical analysis of various tumor tissues revealed that the expression of 9A3 antigen is specific for human adenocarcinoma. In the present study, we analyzed the expression patterns of 9A3 antigen on TMK-1 cells and compared them with the expression patterns of E-cadherin and epidermal-growth-factor (EGF) receptors, using immunofluorescent microscopy and flow cytometry. The flow cytometric analysis revealed that the TMK-1 cell population consists of 9A3-positive cells and 9A3-negative cells. The isolated 9A3-negative cell population generates 9A3-positive cells as they divide, whereas the isolated 9A3-positive cell population does not generate 9A3-negative cells. The 9A3-positive cells grow as tight colonies, whereas the 9A3-negative cell form loose colonies in soft agar culture. E-cadherin was expressed only in the 9A3-positive TMK-1 cells and not in the 9A3-negative cells. In contrast, EGF receptor was expressed in both cell populations. The 9A3 antigen was localized mainly at the cell-cell adhesion sites where E-cadherin was apparently condensed.