Springer Science and Business Media LLCActa Medica Okayama1873-96011722023Do not overwork: cellular communication network factor 3 for life in cartilage353359ENSatoshiKubotaDepartment of Biochemistry and Molecular Dentistry, Okayama University Faculty of Medicine, Dentistry and Pharmaceutical SciencesHarumiKawakiDepartment of Oral Biochemistry, Asahi University School of DentistryBernardPerbalInternational CCN SocietyMasaharuTakigawaAdvanced Research Center for Oral and Craniofacial Sciences, Okayama University Faculty of Medicine, Dentistry and Pharmaceutical Sciences/Dental SchoolKazumiKawataDepartment of Biochemistry and Molecular Dentistry, Okayama University Faculty of Medicine, Dentistry and Pharmaceutical SciencesTakakoHattoriDepartment of Biochemistry and Molecular Dentistry, Okayama University Faculty of Medicine, Dentistry and Pharmaceutical SciencesTakashiNishidaDepartment of Biochemistry and Molecular Dentistry, Okayama University Faculty of Medicine, Dentistry and Pharmaceutical SciencesCellular communication network factor (CCN) 3, which is one of the founding members of the CCN family, displays diverse functions. However, this protein generally represses the proliferation of a variety of cells. Along with skeletal development, CCN3 is produced in cartilaginous anlagen, growth plate cartilage and epiphysial cartilage. Interestingly, CCN3 is drastically induced in the growth plates of mice lacking CCN2, which promotes endochondral ossification. Notably, chondrocytes in these mutant mice with elevated CCN3 production also suffer from impaired glycolysis and energy metabolism, suggesting a critical role of CCN3 in cartilage metabolism. Recently, CCN3 was found to be strongly induced by impaired glycolysis, and in our study, we located an enhancer that mediated CCN3 regulation via starvation. Subsequent investigations specified regulatory factor binding to the X-box 1 (RFX1) as a transcription factor mediating this CCN3 regulation. Impaired glycolysis is a serious problem, resulting in an energy shortage in cartilage without vasculature. CCN3 produced under such starved conditions restricts energy consumption by repressing cell proliferation, leading chondrocytes to quiescence and survival. This CCN3 regulatory system is indicated to play an important role in articular cartilage maintenance, as well as in skeletal development. Furthermore, CCN3 continues to regulate cartilage metabolism even during the aging process, probably utilizing this regulatory system. Altogether, CCN3 seems to prevent "overwork" by chondrocytes to ensure their sustainable life in cartilage by sensing energy metabolism. Similar roles are suspected to exist in relation to systemic metabolism, since CCN3 is found in the bloodstream.No potential conflict of interest relevant to this article was reported.WileyActa Medica Okayama0021-95412021RFX1]mediated CCN3 induction that may support chondrocyte survival under starved conditionsENTomomiMizukawaDepartment of Biochemistry and Molecular Dentistry, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical SciencesTakashiNishidaDepartment of Biochemistry and Molecular Dentistry, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical SciencesShoAkashiDepartment of Biochemistry and Molecular Dentistry, Okayama University Graduate School of Medicine Dentistry and Pharmaceutical Sciences Okayama JapanKazumiKawataDepartment of Biochemistry and Molecular Dentistry, Okayama University Graduate School of Medicine Dentistry and Pharmaceutical Sciences Okayama JapanSumireKikuchiDepartment of Biochemistry and Molecular Dentistry, Okayama University Graduate School of Medicine Dentistry and Pharmaceutical Sciences Okayama JapanHarumiKawakiDepartment of Biochemistry and Molecular Dentistry, Okayama University Graduate School of Medicine Dentistry and Pharmaceutical Sciences Okayama JapanMasaharuTakigawaAdvanced Research Center for Oral and Craniofacial Sciences, Okayama University Dental SchoolHiroshiKamiokaDepartment of Orthodontics, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical SciencesSatoshiKubotaDepartment of Biochemistry and Molecular Dentistry, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical SciencesCellular communication network factor (CCN) family members are multifunctional matricellular proteins that manipulate and integrate extracellular signals. In our previous studies investigating the role of CCN family members in cellular metabolism, we found three members that might be under the regulation of energy metabolism. In this study, we confirmed that CCN2 and CCN3 are the only members that are tightly regulated by glycolysis in human chondrocytic cells. Interestingly, CCN3 was induced under a variety of impaired glycolytic conditions. This CCN3 induction was also observed in two breast cancer cell lines with a distinct phenotype, suggesting a basic role of CCN3 in cellular metabolism. Reporter gene assays indicated a transcriptional regulation mediated by an enhancer in the proximal promoter region. As a result of analyses in silico, we specified regulatory factor binding to the X]box 1 (RFX1) as a candidate that mediated the transcriptional activation by impaired glycolysis. Indeed, the inhibition of glycolysis induced the expression of RFX1, and RFX1 silencing nullified the CCN3 induction by impaired glycolysis. Subsequent experiments with an anti]CCN3 antibody indicated that CCN3 supported the survival of chondrocytes under impaired glycolysis. Consistent with these findings in vitro, abundant CCN3 production by chondrocytes in the deep zones of developing epiphysial cartilage, which are located far away from the synovial fluid, was confirmed in vivo. Our present study uncovered that RFX1 is the mediator that enables CCN3 induction upon cellular starvation, which may eventually assist chondrocytes in retaining their viability, even when there is an energy supply shortage.No potential conflict of interest relevant to this article was reported.