Repressed PKC delta activation in glycodelin-expressing cells mediates resistance to phorbol ester and TGF beta

Glycodelin is a glycoprotein mainly expressed in well-differentiated epithelial cells in reproductive tissues. In normal secretory endometrium, the expression of glycodelin is abundant and regulated by progesterone. In hormone-related cancers glycodelin expression is associated with well-differentiated tumors. We have previously found that glycodelin drives epithelial differentiation of HEC-1B endometrial adenocarcinoma cells, resulting in reduced tumor growth in a preclinical mouse model. Here we show that glycodelin-transfected HEC-1B cells have repressed protein kinase C delta (PKC delta) activation, likely due to downregulation of PDKI, and are resistant to phenotypic change and enhanced migration induced by phorbo112-myristate 13-acetate (PMA). In control cells, which do not express glycodelin, the effects of PMA were abolished by using PKC6 and PDKI inhibitors, and knockdown of PKC delta, MEK1 and 2, or ERK1 and 2 by siRNAs. Similarly, transforming growth factor beta (TGF beta)-induced phenotypic change was only seen in control cells, not in glycodelin-producing cells, and it was mediated by PKC delta. Taken together, these results strongly suggest that PKC delta, via MAPI( pathway, is involved in the glycodelin-driven cell differentiation rendering the cells resistant to stimulation by PMA and TGF beta. (C) 2016 Elsevier Inc. All rights reserved.