؊ . This revealed the specific ability of bovine brain G␣ q/11 to bind to both GRK2 and GRK3 in an AlF 4 ؊ -dependent manner. In contrast, G␣ s , G␣ i , and G␣ 12/13 did not bind to GRK2 or GRK3 despite their presence in the extract. Additional studies revealed that bovine brain G␣ q/11 could also bind to an N-terminal construct of GRK2, while no binding of G␣ q/11 , G␣ s , G␣ i , or G␣ 12/13 to comparable constructs of GRK5 or GRK6 was observed. Experiments using purified G␣ q revealed significant binding of both G␣ q GDP/AlF 4 ؊ and G␣ q (GTP␥S), but not G␣ q (GDP), to GRK2. Activation-dependent binding was also observed in both COS-1 and HEK293 cells as GRK2 significantly co-immunoprecipitated constitutively active G␣ q (R183C) but not wild type G␣ q . In vitro analysis revealed that GRK2 possesses weak GAP activity toward G␣ q that is dependent on the presence of a G proteincoupled receptor. However, GRK2 effectively inhibited G␣ q -mediated activation of phospholipase C-␤ both in vitro and in cells, possibly through sequestration of activated G␣ q . These data suggest that a subfamily of the GRKs may be bifunctional regulators of G protein-coupled receptor signaling operating directly on both receptors and G proteins.

The pH-dependent partitioning of chemotherapeutic drugs is a fundamental yet understudied drug distribution mechanism that may underlie the low success rates of current approaches to counter multidrug resistance (MDR). This mechanism is influenced by the hypoxic tumour microenvironment and results in selective trapping of weakly basic drugs into acidified compartments such as the extracellular environment. Here we report that hypoxia not only leads to acidification of the tumour microenvironment but also induces endosome hyperacidification. The acidity of the vesicular lumen, together with the alkaline pH of the cytoplasm, gives rise to a strong intracellular pH gradient that drives intravesicular drug trapping and chemoresistance. Endosome hyperacidification is due to the relocalization of the Na+/H+ exchanger isoform 6 (NHE6) from endosomes to the plasma membrane, an event that involves binding of NHE6 to the activated protein kinase C–receptor for activated C kinase 1 complex. These findings reveal a novel mechanism of hypoxia-induced MDR that involves the aberrant intracellular distribution of NHE6.

No abstract

advice for both acute and chronic pain. 6 Both are referenced for providers to familiarize themselves and use accordingly. Although no perfect screening tools for aberrant behaviors exist, the Opioid Risk Tool may be used to identify patients who may be at high risk for aberrant behaviors, so appropriate referral and monitoring can occur. 7 We agree that further high-quality studies are needed to refine guidelines. In the interim, we advocate using best practices for pain control and integrating patient goals and preferences into patient care.