DISTRIBUTION AND SUBCELLULAR-LOCALIZATION OF A LYSOSOME-ASSOCIATED PROTEIN IN HUMAN GENITAL ORGANS

The tissue distribution, preferentially in the human male genital syst em, and the subcellular localization of the lysosome-associated membra ne protein 2 (lamp 2) was studied immunohistochemically using a mouse monoclonal antibody, 2D5. Strong immunoreactivity was present in the t ubular system of the kidney, in acinar cells of salivary glands and pa ncreas, prostate, mammary glands, placenta and in cutaneous sweat glan ds. Moderate immunoreactivity was observed in cerebral neuronal cells, epidermal cells, testis, epididymis, seminal vesicle and endometrium. Very low immunoreactivity was found in liver. In some of the tissues mentioned, the distribution pattern of immunoreactivity is smooth and homogeneous, while in others it is granular and concentrated in the su pra- or perinuclear cytoplasm. The subcellular distribution was studie d on ultracryosections and on pre-embedding-processed chopper sections of human prostate. In the latter gland, the protein is not restricted to epithelium, but is also present in stromal cells. Ultrastructurall y, the immunoreactivity in secretory cells was localized in electron-t ranslucent vacuoles and granules, including the secretory granules. A close association with cell membranes was not generally the case. Only part of the immunoreactive material was linked to the apical plasma m embrane pointing to a biosynthesis independent from an association ste p with the apical plasma membrane. As shown by immunoelectron microsco py and Western blotting, a high amount of lamp 2 is secreted and is fo und in so-called prostasomes. The findings indicate that in the human prostate most of the membrane-bound lamp 2 is released from the secret ory cells, presumably in an apocrine fashion.