Human Secretoglobins in Normal and Neoplastic Cells and Tissues

Secretoglobins is a newly described polypeptide family that has gained a lot of interest in human cancer and inflammation research. Although the first secretoglobin polypeptide was discovered more than 30 years ago, their physiological function is still not known. The aim of this thesis was to study the expression of secretoglobins in normal and neoplastic human cells and tissues, and to clarify their possible involvement in human cancer. We established sensitive and specific quantitative real-time RT-PCR assays for uteroglobin, lipophilins A, B, C, mammaglobin, HIN-1, and UGRP1, and developed specific antibodies for lipophilin B and mammaglobin. By using quantitative real-time RT-PCR, immunohistochemistry, Western blotting, and in situ hybridization, we studied secretoglobin expression in normal and neoplastic cells and tissues. In normal tissues, real-time RT-PCR analysis showed high expression of mammaglobin in skin. The mammaglobin expression in skin tissue was further confirmed by in situ hybridization and immunohistochemistry, and the expression was shown to be localized to the coiled gland cells of the eccrine sweat glands and the apocrine sweat glands. In addition, we showed by using Western blotting, that mammaglobin was secreted into perspiration from the eccrine sweat glands. In pituitary gland, immunohistochemical analysis showed that lipophilin B was expressed by approximately half of the cells in the anterior pituitary. By using quantitative real-time RT-PCR it was shown that both lipophilins B and C mRNA were expressed in the pituitary gland, therefore we suggested that lipophilins B and C form heterodimers in human pituitary. In neoplastic tissues, real-time RT-PCR analysis showed dysregulated secretoglobin expression in lung tumors, with down-regulation of uteroglobin and frequent up-regulation of lipophilins A, B, C, and mammaglobin. Immunohistochemical analyses showed down-regulation of mammaglobin in cylindromas versus non-neoplastic eccrine sweat glands and of lipophilin B in pituitary adenomas versus non-neoplastic anterior pituitary. The majority of investigated cell lines showed low, or most often, lack of secretoglobin expression. Nevertheless, it has been shown that mammaglobin is over-expressed in human breast carcinomas. However, ectopic over-expression of mammaglobin and/or lipophilin B had no appreciable effect on cell proliferation rates of Hs578T breast carcinoma cells in vitro. This does not exclude the possibility that secretoglobins could confer some advantage to tumor cells in vivo, but, it indicates that the reported overexpression of mammaglobin is an epiphenomenon not causally involved in breast carcinogenesis. In summary, our major findings were that mammaglobin was expressed and secreted by the sweat glands of the skin and lipophilin B was expressed by the anterior pituitary gland; and, that expression of mammaglobin and lipophilin B were down-regulated in tumors derived from the same tissues, i.e, in cylindromas and pituitary adenomas, respectively. Furthermore, ectopic overexpression of mammaglobin and lipophilin B in breast carcinoma cells had no appreciable effect on cell proliferation rates in vitro.