Identification of mitogenic factor in rice bran for better mammalian cell culture

Introduction In cell culture for biopharmaceutical production, serumfree culture is required in order to avoid the risks associated with components of mammal origin such as BSE. Although many serum-free medium have been developed, there is yet room for improvement and protein hydrolysates from crops are widely used as additives to improve the culture. We found that rice bran extract (RBE), not hydrolysate, successfully improved the proliferation of various cells as well as recombinant protein production of CHO cells when RBE was added into serum-free culture. Several studies have been done and reported that rice bran has antioxidant potential [1,2] and a rice bran 57-kDa protein showed cell adhesion activity for murine Lewis lung carcinoma cells [3]. RBE contains various components such as proteins and the factors activating mammalian cells are not identified yet. In this study, we aim to identify the effective factor in RBE. Our colleague reports that heavier molecular weight fraction of RBE improves the proliferation of various cells. Additionally, protein is the most abundant component in RBE. Together with them, some of the proteins in RBE would be the effective factor or the mitogen. We first determined whether some of the proteins in RBE are the bio-active factor or not, and then tried to identify which protein in RBE is the bio-active factor.