Membrane Trafficking of Heterotrimeric G Proteins via the Endoplasmic Reticulum and Golgi

Membrane targeting of G-protein αβγ heterotrimers was investigated in live cells by use of Gα and Gγ subunits tagged with spectral mutants of green fluorescent protein. Unlike Ras proteins, Gβγ contains a single targeting signal, the CAAX motif, which directed the dimer to the endoplasmic reticulum. Endomembrane localization of farnesylated Gγ(1), but not geranylgeranylated Gγ(2), required carboxyl methylation. Targeting of the heterotrimer to the plasma membrane (PM) required coexpression of all three subunits, combining the CAAX motif of Gγ with the fatty acyl modifications of Gα. Gα associated with Gβγ on the Golgi and palmitoylation of Gα was required for translocation of the heterotrimer to the PM. Thus, two separate signals, analogous to the dual-signal targeting mechanism of Ras proteins, cooperate to target heterotrimeric G proteins to the PM via the endomembrane

Impaired phosphocreatine metabolism in white adipocytes promotes inflammation.

The mechanisms promoting disturbed white adipocyte function in obesity remain largely unclear. Herein, we integrate white adipose tissue (WAT) metabolomic and transcriptomic data from clinical cohorts and find that the WAT phosphocreatine/creatine ratio is increased and creatine kinase-B expression and activity is decreased in the obese state. In human in vitro and murine in vivo models, we demonstrate that decreased phosphocreatine metabolism in white adipocytes alters adenosine monophosphate-activated protein kinase activity via effects on adenosine triphosphate/adenosine diphosphate levels, independently of WAT beigeing. This disturbance promotes a pro-inflammatory profile characterized, in part, by increased chemokine (C-C motif) ligand 2 (CCL2) production. These data suggest that the phosphocreatine/creatine system links cellular energy shuttling with pro-inflammatory responses in human and murine white adipocytes. Our findings provide unexpected perspectives on the mechanisms driving WAT inflammation in obesity and may present avenues to target adipocyte dysfunction

Radiation-induced Activation of Nuclear Factor-κB Involves Selective Degradation of Plasma Membrane-associated IκBα

In contrast to nuclear factor-κB (NF-κB) activation by tumor necrosis factor-α (TNF-α), the specific processes involved in the activation of this transcription factor by ionizing radiation (IR) have not been completely defined. According to the classical paradigm, a critical event in NF-κB activation is the degradation of IκBα. Data presented herein show that, in contrast to treatment with TNF-α, IR-induced NF-κB activation was not accompanied by degradation of IκBα in the U251 glioblastoma cell line as determined in whole cell lysates. However, treatment with the proteosome inhibitor MG-132 inhibited NF-κB activation induced by IR, suggesting that IκBα degradation was a critical event in this process. To reconcile these results, U251 cell lysates were separated into soluble and insoluble fractions and IκBα levels evaluated. Although IκBα was found in both subcellular fractions, treatment with IR resulted in the degradation of IκBα only in the insoluble fraction. Further subcellular fractionation suggested that the IR-sensitive, insoluble pool of IκBα was associated with the plasma membrane. These data suggest that the subcellular location of IκBα is a critical determinant in IR-induced NF-κB activation