Signal Transduction
Unequal twins: Unraveling the reaction mechanism of dimeric histidine kinases
Histidine kinases (HKs), together with their partner proteins, the response regulators (RRs), form the ubiquitous two-component systems that are global players in control and adjustment of microbial lifestyle. Although their basic function (i.e. the transfer of a phosphate group from the HK to its RR partner) is simple to articulate, deciphering the molecular details of this process has proven anything but simple, especially when quantitative aspects come into play. Bouillet et al. report a series of elegant and sophisticated experiments to quantitatively understand HK functions, clearing up several open questions and providing a new strategy for future work in the field.Learning the ABCs of ATP release
ATP plays important roles outside the cell, but the mechanism by which it is arrives in the extracellular environment is not clear. Dunn et al. now show that decreases in cellular cholesterol levels mediated by the ABCG1 transporter increase ATP release by volume-regulated anion channels under hypotonic conditions. Importantly, these results may imply that cells that handle cholesterol differently might experience differential extracellular ATP release during hypotonicity.Putting the brakes on a myosin motor
Insulin-stimulated trafficking of GLUT4 requires the myosin motor Myo1C and signaling adaptor 14-3-3β. Originally, it was thought that 14-3-3β promotes GLUT4 transport by binding the Myo1C lever arm and activating the Myo1C motor. New work by Ji and Ostap using in vitro assays reveals that 14-3-3β binding actually inhibits Myo1C motility, prompting reconsideration of the functional relationship between 14-3-3β and Myo1C and the regulatory potential of atypical light chains.The long-awaited structure of HIPK2
Homeodomain-interacting protein kinases (HIPKs) are kinases that phosphorylate transcription factors involved in cell proliferation, differentiation, and apoptosis. Their structures have been long sought because of their potential as drug targets in cancers and fibrosis. Agnew and colleagues present the first crystal structure of the HIPK2 kinase domain, complexed with the small-molecule inhibitor CX-4945, revealing important structural differences from related protein kinases of the DYRK family.A driving test for oncogenic mutations
Activating mutations in protein kinases are a frequent cause of cancer, and selecting drugs that act on these oncogenic kinases can lead to effective therapies. Targeted or whole-genome sequencing of tumor samples can readily reveal the presence of mutations, but discerning previously uncharacterized activating “driver” mutations that will respond to drug treatment from much more abundant but inconsequential “passenger” mutations is problematic. Chakroborty et al. apply a screening approach that leverages error-prone PCR and a proliferating cell model to identify such gain-of-function mutants in the epidermal growth factor receptor (EGFR) kinase.Keys to unlock androgen receptor translocation
The androgen receptor (AR) is tightly linked to prostate cancer, but the mechanisms by which AR transactivation is dysregulated during cancer progression are not fully explored. Dagar et al. examined AR translocation to the nucleus to identify a link between heat shock protein 90 (HSP90) and protein kinase A (PKA). Their findings provide a potential mechanism of the initiation of AR transactivation and potential targets for developing and refining treatments for prostate cancer.A promiscuous kinase inhibitor reveals secrets to cancer cell survival
Deregulated kinase signaling networks drive the growth and survival of many cancer cells. However, the genetic complexity and rapidly evolving nature of most cancer cells create challenges when identifying the most relevant kinases to inhibit to achieve optimal therapeutic benefits. A new strategy that takes advantage of a well-characterized multitargeted kinase inhibitor describes a nongenetic approach to tease out key kinases that promote proliferation of specific cancer cell types.Harnessing poxviral know-how for anti-cytokine therapies
Poxviruses have evolved efficient proteins that bind mammalian cytokines and chemokines to suppress host immunity. Here Pontejo et al. examine in detail how one such poxviral protein, CrmD, that has activity against both mammalian tumor necrosis factor and chemokines, interacts with its host targets. They apply their findings to refine a human anti-cytokine therapeutic and increase its specificity, providing an elegant example of the benefits of mining viral proteins for therapeutically useful information.“A-kinase” regulator runs amok to provide a paradigm shift in cAMP signaling
The activity of the archetypal protein kinase A (PKA) is typically thought of in regards to the catalytic subunit, which is inhibited by the regulatory subunits in the absence of cAMP. However, it is now reported that one of the regulatory subunit isoforms (PKA-RIα) takes on a function of its own upon binding to cAMP, acting independently of this canonical cAMP signaling mechanism. PKA-RIα instead binds to and stimulates the catalytic activity of a guanine nucleotide exchange factor (P-REX1) that itself promotes Rac1 GTPase activation.The discovery of GABA in the brain
Some scientific discoveries land with a boom only to fizzle out and become a small blip—but there are times when this order is reversed. Such was the case with the discovery of γ-aminobutyric acid (GABA) in the brain, reported in 1950. In a study published in the Journal of Biological Chemistry (1), preceded by a brief conference report shortly before that (2), Eugene Roberts (Fig. 1) and Sam Frankel not only identified GABA as a major amine in the brain, but also reported that it is produced and preferentially accumulates in this organ.
