Generation of monoclonal antibodies against tumor-associated antigen MX35/sodium-dependent phosphate transporter NaPi2b.

Tumor-associated antigen MX35, which is overexpressed in 70-90% of epithelial ovarian cancers, has been recently identified as phosphate transporter NaPi2b. This finding has raised significant interest in understanding NaPi2b function under physiological conditions and its deregulation in human pathologies, such as cancer. As a member of the sodium-dependent phosphate transporter family, NaPi2b is primarily involved in the maintenance of phosphate homeostasis in the human body. The role of NaPi2b in oncogenic transformation and malignant growth is not well understood. To date, several monoclonal antibodies specific to NaPi2b have been reported. However, available monoclonal antibodies are not very efficient in recognizing endogenous NaPi2b under reducing conditions. In addition, these antibodies could not recognize the mutant form of transporter (NaPi2b-T330V). In this study we describe the production of monoclonal antibodies raised against the N-terminal region of NaPi2b. One of them, designated N-NaPi2b(15/1), possesses very useful immunological characteristics. We found that N-NaPi2b(15/1) specifically recognizes NaPi2b protein in immunohistochemical analysis and immunoprecipitation assay. Importantly, N-NaPi2b(15/1) antibody detects very efficiently endogenous and expressed wild-type and mutant forms of NaPi2b under both reducing and non-reducing conditions in Western blot analysis. These features make N-NaPi2b(15/1) antibody a very useful tool for studying the pattern of NaPi2b expression in health and pathologies.