A secretory product of human mammary epithelial cells (MEC), termed tumor-associated antigen with an apparent molecular weight of 62 kilodaltons (TAA.62), was identified by a human monoclonal antibody. The study showed that TAA.62 was present at elevated levels in the cytoplasmic compartment of malignant as compared with normal or benign in tissue and non-tumorigenic immortalized MEC lines. A similar pattern of TAA.62 expression was also observed in cervix, colon, kidney, lung and stomach. The antigen was purified to homogeneity from the conditioned medium of malignant (tumorigenic) and immortalized (nontumorigenic) MEC lines and was termed TAA.62(T) and TAA.62(NT), respectively. Both TAA.62(T) and TAA.62(NT) were indistinguishable in terms of their sizes, sequence of their first twelve amino acid residues of the N-terminus and immunoreactivity with anti-TAA.62 antibody. However, purified TAA.62(T) interacted in vitro specifically with a 160 kd cell-surface component on the malignant and immortalized MEC lines, whereas TAA.62(NT) did not. Interestingly, addition of the purified TAA.62(T) to the culture medium resulted in an enhanced growth of both the malignant and immortalized MEC lines, whereas no such effect was observed when TAA.62(NT) was added. Finally, addition of anti-TAA.62 antibody to culture medium neutralized the growth-stimulatory effect of exogenously added TAA.62(T). The results suggest that TAA.62(T) may interact as a ligand with a 160 kd-receptor, having a possible growth function.

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