MATER protein as substrate of PKC in human cumulus cells

High activity of the phosphoinositide 3-kinase/Akt pathway in cumulus cells plays an important role in FSH regulation of cell function and Protein Kinase C epsilon (PKC1) collaborates with these signalling pathways to regulate cell proliferation. Relevant roles in fol- licular development are played by Maternal Antigen That Embryos Require (MATER) that is a cumulus cell- and oocyte-specific protein dependent on the maternal genome. We recently demonstrated that human MATER localizes at specific domains of oocytes and, for the first time, also in cumulus cells. MATER contains a carboxy-terminal leucine-rich repeat domain involved in protein -protein interactions regu- lating different cellular functions. Here we investigated the functional role of MATER. Thus, we performed coimmunoprecipitation exper- iments using HEK293T cells expressing human MATER; a similar approach was then followed in human cumulus/follicular cells. In MATER þ HEK293T cells, we observed that this protein acts as a phosphorylation substrate of PKC1. Western blot experiments indicate that, unlike oocytes, human cumulus cells express PKC1. Immunoprecipitation and confocal analysis suggest for the first time that MATER protein interacts with this protein kinase in cumulus cells under physiological conditions. Since PKC1 is known to collaborate with antiapoptotic signalling pathways, this suggests a novel mechanism for the function of MATER in follicular maturation.