title: Prosaposin regulates coenzyme Q10 levels in HepG2 cells, especially those in mitochondria.
abstract: Coenzyme Q10 (CoQ10) is a key component of the mitochondrial electron transfer chain and is one of the most important cellular antioxidants. We previously reported that glycoprotein saposin B (SapB) binds CoQ10 in human cells. To elucidate the physiological role of SapB and its precursor, prosaposin (Psap), we prepared stable transfectants of HepG2 that overexpress wild-type human Psap (Wt-Tf). We also established a SapB domain mutated Psap (Mt-Tf) in which cysteine(198) was replaced with serine to disrupt three dimensional protein structure by the loss of S-S bridging. Psap knockdown (KD) strains were also examined. Western blotting analysis confirmed overexpression or knockdown of Psap in these HepG2 cells. The cellular ratios of CoQ10 to free cholesterol (FC) significantly decreased in the order of Wt-Tf>parental>Mt-Tf>KD. Additionally, the ratios of CoQ10/FC in mitochondrial fractions decreased in the order of Wt-Tf>parental>KD. These data indicate that Psap and/or SapB regulate CoQ10 levels in HepG2 cells, especially in their mitochondria.
authors.affiliation: School of Health Sciences, Tokyo University of Technology, 1404-1 Katakura-cho, Hachioji, Tokyo 192-0982, Japan.
authors.forename: Misato
authors.initials: M
authors.lastname: Kashiba
authors.affiliation: School of Bioscience and Biotechnology, Tokyo University of Technology, 1404-1 Katakura-cho, Hachioji, Tokyo 192-0982, Japan.
authors.forename: Mikiko
authors.initials: M
authors.lastname: Oizumi
authors.affiliation: School of Bioscience and Biotechnology, Tokyo University of Technology, 1404-1 Katakura-cho, Hachioji, Tokyo 192-0982, Japan.
authors.forename: Masaru
authors.initials: M
authors.lastname: Suzuki
authors.affiliation: School of Bioscience and Biotechnology, Tokyo University of Technology, 1404-1 Katakura-cho, Hachioji, Tokyo 192-0982, Japan.
authors.forename: Yoshimi
authors.initials: Y
authors.lastname: Sawamura
authors.affiliation: School of Bioscience and Biotechnology, Tokyo University of Technology, 1404-1 Katakura-cho, Hachioji, Tokyo 192-0982, Japan.
authors.forename: Kohei
authors.initials: K
authors.lastname: Nagashima
authors.affiliation: School of Bioscience and Biotechnology, Tokyo University of Technology, 1404-1 Katakura-cho, Hachioji, Tokyo 192-0982, Japan.
authors.forename: Shinichi
authors.initials: S
authors.lastname: Yoshimura
authors.affiliation: School of Bioscience and Biotechnology, Tokyo University of Technology, 1404-1 Katakura-cho, Hachioji, Tokyo 192-0982, Japan.
authors.forename: Yorihiro
authors.initials: Y
authors.lastname: Yamamoto
keywords: HepG2; coenzyme Q10; mitochondria; prosaposin; saposin B