The regulation by hormones of milk fat globule membrane antigens in human breast.

Light- and electron-microscopic immunohistochemistry and lectin histochemistry have been used to observe differences in glycoprotein expression, between benign breast epithelium and breast carcinomas, and for analysis of glycoprotein transport in carcinomas. The sites of intracellular localisation of these markers in tumours have been characterised as vesicular or as intracytoplasmic lumina at the ultrastructural level. The relationship between ultrastructural localisation in carcinomas and morphological/biochemical differentiation has been explored. Modulation of ultrastructural localisation after organ culture in the presence of insulin and/or hydrocortisone has been demonstrated. In a proportion of tumours, insulin causes increased peripheral expression of milk fat globule membrane markers. This redistribution has also been found to be epitope associated, which implies that glycosylation affects transport, or that peptides affected differentially with regard to failure of transport in the tumour cells are conscquently differentially glycosylated. Hydrocortisone stimulates milk fat globule, membrane synthesis, causing more intracellular vesicular accumulation in tumours and increased formation of small intracytoplasmic lumina. Hydrocortisone and insulin together cause a marked increase in the formation of large intracytoplasmic lumina in tumours. These changes imply that the cause of accumulation is a post-Golgi block to exocytotic transport. In vitro cell line models have been established, and used to demonstrate the effect of insulin on rates of post-Golgi transport. The role of the cytoskeleton has been demonstrated by pharmacological manipulations with cytoskeletal disrupting agents. Agents with activity against microtubules, but not those with activity against microfilamcuts, abrogate the effect of insulin in primary organ cultured tumours, suggesting that insulin may modify putatively "impaired" microtubule function, or that of related proteins such as MAP-2, in breast carcinomas. The role of the extracellular matrix and tissue architecture on expression and localisation has been explored by culturing established cell lines on extracellular matrix substrata.