title: Platelet-activating factor receptor signals in rat osteoblasts during spaceflight.
abstract: The platelet-activating factor (PAF) is a lipid mediator. The G-protein-coupled receptor of PAF (PAF-R) is activated by inflammatory and stressful conditions in numerous cell types. PAF/PAF-R is involved in apoptotic and antiapoptotic processes. We examined microgravity effects on the expression of PAF-R and second messengers in rat osteoblasts. The PAF-R signals are transmitted via arachidonic acid, phospholipase C (PLC), protein kinase C (PKC), and mitogen-activated protein kinase. Rat osteoblasts were cultured for 4 and 5 days aboard a space shuttle and solubilized on board. PAF-R gene expression in flight cultures increased to 2-6-fold higher than in ground controls. Gene expression of the G-protein alpha subunit Galphaq in flight cultures increased to 3-fold and higher than in ground controls. It is known that Galphaq stimulates the effecter PLCbeta, activating PKC. The mRNA levels of PKCdelta and PKCtheta in flight cultures were increased to 2-5-fold higher than in ground controls. The PKCalpha mRNA level in flight cultures was increased to 3-fold higher than in ground controls on the 4th day. Gene expression of catalytic and regulatory subunits of protein kinase A was suppressed in flight cultures. PKCdelta and PKCtheta are novel PKCs that can be target substrates of caspases. The PAF-R gene may act as a mechano-sensitive gene that is involved in the apoptotic and antiapoptotic processes of osteoblasts under microgravity.
authors.affiliation: Department of Hard Tissue Engineering, Graduate School of Tokyo Medical and Dental University, Tokyo 113-8549, Japan. kumei.bch@tmd.ac.jp
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Kumei
authors.forename: Sadao
authors.initials: S
authors.lastname: Morita
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nakamura
authors.forename: Hideo
authors.initials: H
authors.lastname: Akiyama
authors.forename: Hisako
authors.initials: H
authors.lastname: Katano
authors.forename: Hitoyata
authors.initials: H
authors.lastname: Shimokawa
authors.forename: Kei'ichi
authors.initials: K
authors.lastname: Ohya
mesh_terms: D000818:Animals; D001483:Base Sequence; D017931:DNA Primers; D008297:Male; D010006:Osteoblasts / Q000201:enzymology / Q000378:metabolism*; D010980:Platelet Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D011493:Protein Kinase C / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D043562:Receptors, G-Protein-Coupled / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D013026:Space Flight
chemical_list: D017931:DNA Primers; D010980:Platelet Membrane Glycoproteins; D012333:RNA, Messenger; D043562:Receptors, G-Protein-Coupled; C039351:platelet activating factor receptor; D011493:Protein Kinase C