Small GTPase Ras and Rho Expression in Rat Osteoblasts during Spaceflight

Abstract

Rat osteoblasts were cultured for 4 and 5 days aboard a space shuttle and solubilized after a 24-h treatment with 1alpha,25 dihydroxyvitamin D(3). The quantitative RT-PCR determined the mRNA levels of signaling molecules upstream and downstream Ras. The small GTPase is activated by guanine nucleotide exchange protein (GEF) and deactivated by GTPase-activating protein (GAP). When external stimuli are transduced into intracellular signals, various pathways are recruited: focal adhesion kinase (FAK) is associated with integrin-beta, and directs tyrosine phosphorylation of downstream substrates, including phospholipase C-gamma (PLC-gamma) and son of sevenless (SOS, a Ras GEF). The mRNA levels of FAK and PLC-gamma1 and -gamma2 in the flight cultures were increased 150% and 250% of the ground controls. The SOS mRNA levels in the flight cultures were increased 520% and 320% of the ground controls. Signals via G protein-coupled receptors are transmitted through PLC-beta and Ras GRF (another Ras GEF). Activated Ras then stimulates Raf, mitogen-activated protein kinase (MAPK) cascades. The mRNA levels of Raf, extracellular signal-regulated protein kinase of MAPK family (ERK-1 and -2), and PLC-beta were increased during spaceflight. Rho GAP expression in the flight cultures was increased twofold of the ground controls. Since Rho GAP deactivates Rho, microgravity may suppress Rho signals, regulating actin filament rearrangement. Microgravity signals may involve two pathways (G protein-coupled receptor-mediated pathway and tyrosine phosphorylation-mediated pathway) that activate Ras, Raf, and MAPK cascades in rat osteoblasts.

Effects of simulated weightlessness on cellular morphology and biological characteristics of cell lines SGC-7901 and HFE-145

“…**P < 0.05 and *P < 0.01 vs control. tion can affect cell junctions and the extracellular matrix, as well as cause a series of reactions in signal transduction, inducing changes in gene expression, which ultimately manifest as changes in biological characteristics (Ingber, 1999;Kumei et al, 2007). SGC-7901 cells are gastric carcinoma cells that grow malignantly and lose cell stability.…”

Mechanisms of Gravitational Sensitivity of Osteogenic Precursor Cells

“…Studies conducted in the last decade have conclusively demonstrated that cultured cells of osteoblast phenotype are sensitive to microgravity [3–8]. However, one question remains unanswered: How can microgravity affect the numerous functional aspects of less mature cell forms, namely the progenitor cells?…”

Altered Actin Dynamics and Functions of Osteoblast-Like Cells in Parabolic Flight may Involve ERK1/2

“…PD98059 and CB significantly decreased the activity of COL1A1 promoter using our effective EGFP-ROS cells. Taken together, the alternation of actin microfilament and MAPK signaling in parabolic flight participate the adaptation of cell activity (Reunanen et al 2000;Kumei et al 2007). …”