IMMUNOCYTOCHEMICAL DISTRIBUTION OF THE CALCIUM-BINDING PROTEIN P9KA IN NORMAL RAT-TISSUES - VARIATION IN THE CELLULAR LOCATION IN DIFFERENTTISSUES

The family of S-100-related proteins consists of a number of small pot ential calcium-binding proteins of unknown function. Elevated expressi on of one of these proteins, p9Ka, or of its mRNA, correlates with the metastatic potential of cultured mammary epithelial cells from rat or mouse. Overexpression of p9Ka by transfection of benign rat mammary e pithelial tumor cells with the gene for p9Ka induces the metastatic ph enotype. At present there is little information on the occurrence of p 9Ka in normal rat tissues. A specific antiserum immunocytochemically d etects p9Ka intracellulary in most normal adult rat tissues studied, i ncluding smooth muscle, brown adipose tissue, and liver. In other tiss ues, p9Ka is localized specifically to some absorptive and keratinized epithelia, the acid-secreting parietal cells of the stomach, the neur onal cells within plexuses of the autonomic nervous system, and a prop ortion of cells of the immune system in spleen, lymph nodes, bone marr ow, and blood. p9Ka is found widely in both arteries and veins, partic ularly in the smooth muscle and in the endothelium of smaller veins. I n mammary gland, the pattern of staining suggests that p9Ka is extrace llularly located in a region surrounding the ducts.