Anchoring of protein kinase A by ERM (ezrin-radixin-moesin) proteins is required for proper netrin signaling through DCC (deleted in colorectal cancer).

Netrin-1, acting through its principal receptor DCC (deleted in colorectal cancer), serves as an axon guidance cue during neural development and also contributes to vascular morphogenesis, epithelial migration, and the pathogenesis of some tumors. Several lines of evidence suggest that netrin-DCC signaling can regulate and be regulated by the cAMP-dependent protein kinase, PKA, although the molecular details of this relationship are poorly understood. Specificity in PKA signaling is often achieved through differential subcellular localization of the enzyme by interaction with protein kinase A anchoring proteins (AKAPs). Here, we show that AKAP function is required for DCC-mediated activation of PKA and phosphorylation of cytoskeletal regulatory proteins of the Mena/VASP (vasodilator-stimulated phosphoprotein) family. Moreover, we show that DCC and PKA physically interact and that this association is mediated by the ezrin-radixin-moesin (ERM) family of plasma membrane-actin cytoskeleton cross-linking proteins. Silencing of ERM protein expression inhibits DCC-PKA interaction, DCC-mediated PKA activation, and phosphorylation of Mena/VASP proteins as well as growth cone morphology and neurite outgrowth. Finally, although expression of wild-type radixin partially rescued growth cone morphology and tropism toward netrin in ERM-knockdown cells, expression of an AKAP-deficient mutant of radixin did not fully rescue growth cone morphology and switched netrin tropism from attraction to repulsion. These data support a model in which ERM-mediated anchoring of PKA activity to DCC is required for proper netrin/DCC-mediated signaling.

AKAP-independent localization of type-II protein kinase A to dynamic actin microspikes.

Regulation of the cyclic AMP-dependent protein kinase (PKA) in subcellular space is required for cytoskeletal dynamics and chemotaxis. Currently, spatial regulation of PKA is thought to require the association of PKA regulatory (R) subunits with A-kinase anchoring proteins (AKAPs). Here, we show that the regulatory RIIalpha subunit of PKA associates with dynamic actin microspikes in an AKAP-independent manner. Both endogenous RIIalpha and a GFP-RIIalpha fusion protein co-localize with F-actin in microspikes within hippocampal neuron growth cones and the leading edge lamellae of NG108-15 cells. Live-cell imaging demonstrates that RIIalpha-associated microspikes are highly dynamic and that the coupling of RIIalpha to actin is tight, as the movement of both actin and RIIalpha are immediately and coincidently stopped by low-dose cytochalasin D. Importantly, co-localization of RIIalpha and actin in these structures is resistant to displacement by a cell-permeable disrupter of PKA-AKAP interactions. Biochemical fractionation confirms that a substantial pool of PKA RIIalpha is associated with the detergent-insoluble cytoskeleton and is resistant to extraction by a peptide inhibitor of AKAP interactions. Finally, mutation of the AKAP-binding domain of RIIalpha fails to disrupt its association with actin microspikes. These data provide the first demonstration of the physical association of a kinase with such dynamic actin structures, as well as the first demonstration of the ability of type-II PKA to localize to discrete subcellular structures independently of canonical AKAP function. This association is likely to be important for microfilament dynamics and cell migration and may prime the investigation of novel mechanisms for localizing PKA activity.

A Large Retrospective Cohort of Patients Receiving Intravenous Olanzapine in the Emergency Department.

BACKGROUND: Olanzapine is an atypical antipsychotic with similar pharmacologic properties to droperidol. Due to the current droperidol shortage, the authors' clinical practice has been to substitute olanzapine for droperidol in many situations. At this time, olanzapine is U.S. Food and Drug Administration approved for oral and intramuscular (IM) use only, but due to its increased utility, intravenous (IV) olanzapine was recently approved for use in the study emergency department (ED). OBJECTIVES: The authors sought to review the use and safety of IV olanzapine in the ED patient population. METHODS: A retrospective review of consecutive patients receiving IV olanzapine between January 1, 2014, and July 1, 2014, was conducted. Data were collected via an electronic medical record review. The study was deemed exempt from informed consent by our institutional review board. RESULTS: A total of 713 patients received IV olanzapine during the study period. The median age was 38 years (range = 18 to 85 years), and 313 patients were male (43.9%). Primary indications for IV olanzapine administration included acute agitation (n = 245, 34.4%), abdominal pain (n = 165, 23.1%), headache (n = 121, 17.0%), nausea and vomiting (n = 107, 15.0%), pain (other; n = 60, 8.4%), and unknown (n = 15, 2.1%). IV dosing varied: 1.25 mg (n = 20, 2.8%), 2.5 mg (n = 185, 25.9%), 5 mg (n = 507, 71.1%), and 10 mg (n = 1, 0.1%). Forty-nine patients required a second dose of olanzapine (22 IV, 26 IM, one oral). The maximum total dose of olanzapine was 20 mg. Ninety-eight patients required a total of 146 doses of additional sedatives during their ED course. Other sedative medications included ketamine (n = 17, 2.4%), haloperidol (n = 48, 6.7%), and benzodiazepines (n = 81, 11.4%). Hypoxia was noted in 74 patients (10.4%). Major respiratory complications, including airway stimulation or repositioning maneuvers and intubation, occurred in 15 patients (2.1%). After consensus review, one intubation was classified as "likely related" to olanzapine administration, and two were classified as "possibly related" to olanzapine. Akathisia likely occurred in four patients (0.6%), and no allergic reactions were identified. Electrocardiograms (ECGs) were performed in 322 patients. A total of 251 patients had an ECG performed before olanzapine administration (median QTc = 404 ms), and 88 patients had an ECG performed after olanzapine administration (median QTc = 415 ms). Acute alcohol and drug intoxication was common, 118 (16.5%) patients were positive for ethanol, and seven of 23 drug screens were positive for sympathomimetics. Thirty-four of 284 admissions (4.5%) were to intermediate or intensive care unit beds. No patients died while in the ED and no cases of sudden cardiac death were noted. CONCLUSIONS: In this large retrospective review, IV olanzapine appears to be a safe in the management of a variety of ED indications. Hypoxia was common, but serious airway compromise was rare.