Regulation of protein kinase C δ by estrogen in the MCF-7 human breast cancer cell line

We have previously shown that estrogen up-regulates expression of protein kinase C (PKC) delta in the rat and rabbit corpus luteum as well as in luteinized rat granulosa primary cell cultures. To determine whether a similar regulation of the PKC delta isoform by estrogen occurred in another estrogen responsive system, we investigated the estrogen receptor positive MCF-7 human breast cancer cells. In a characterization of PKC isoforms in MCF-7 cells we determined that PKC delta was the predominant PKC isoform. However in contrast to the effect of estrogen on PKC delta expression in ovarian cells, estrogen treatment of MCF-7 cells resulted in a significant decrease in PKC delta protein and mRNA expression in a time and dose dependent manner. Treatment of MCF-7 cells with 10(-10)-10(-8) M estrogen for 7 days down-regulated specifically PKC delta mRNA and protein while expression of other PKC isoforms was unchanged. The opposite regulation of PKC 6 expression in ovarian and breast cancer cells prompted us to evaluate the type of estrogen receptor present in both cell types. Results showed that luteinized I-at granulosa cells expressed predominantly estrogen receptor beta while the MCF-7 cells expressed predominantly estrogen receptor alpha and barely detectable levels be a result of differential signaling through the two estrogen receptor subtypes. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.