Calcium/Calmodulin-Dependent ProteinKinase Kinase 2: Roles in Signaling and Pathophysiology

minireview on functions of CaMKK2 and its potential as a target for therapeutic intervention

Central control of feeding

The rising rate of obesity in Western countries has led to intensified efforts to understand the molecular mechanisms underlying the central control of appetite and feeding behavior. This report highlights studies published from 2006 to 2008 revealing novel centrally acting anorexigenic hormones, the continued unraveling of complex hypothalamic intracellular signaling pathways that regulate feeding, and insights into leptin resistance

Domain II of calmodulin is involved in activation of calcineurin

AbstractA family of mutant proteins related to calmodulin (CaM) has been produced using cDNA constructs in bacterial expression vectors. The new proteins contain amino acid substitutions in Ca2+-binding domains I, II, both I and II, or both II and IV. The calmodulin-like proteins have been characterized with respect to mobility on SDS-polyacrylamide gels, Ca2+-dependent enhancement of tyrosine fluorescence, and abilities to activate the CaM-dependent phosphatase calcineurin. These studies suggest that an intact Ca2+-binding domain II is minimally required for full activation of calcineurin

Phase I dose-escalation trial of the oral AKT inhibitor uprosertib in combination with the oral MEK1/MEK2 inhibitor trametinib in patients with solid tumors.

PurposeThis study aimed to determine the safety, tolerability, and recommended phase II doses of trametinib plus uprosertib (GSK2141795) in patients with solid tumors likely to be sensitive to MEK and/or AKT inhibition.MethodsThis was a phase I, open-label, dose-escalation, and dose-expansion study in patients with triple-negative breast cancer or BRAF-wild type advanced melanoma. The primary outcome of the expansion study was investigator-assessed response. Among 126 enrolled patients, 63 received continuous oral daily dosing of trametinib and uprosertib, 29 received various alternative dosing schedules, and 34 were enrolled into expansion cohorts. Doses tested in the expansion cohort were trametinib 1.5 mg once daily (QD) + uprosertib 50 mg QD.ResultsAdverse events (AEs) were consistent with those reported in monotherapy studies but occurred at lower doses and with greater severity. Diarrhea was the most common dose-limiting toxicity; diarrhea and rash were particularly difficult to tolerate. Overall, 59% and 6% of patients reported AEs with a maximum severity of grade 3 and 4, respectively. Poor tolerability prevented adequate delivery of uprosertib with trametinib at a concentration predicted to have clinical activity. The study was terminated early based on futility in the continuous-dosing expansion cohorts and a lack of pharmacological or therapeutic advantage with intermittent dosing. The objective response rate was < 5% (1 complete response, 5 partial responses).ConclusionsContinuous and intermittent dosing of trametinib in combination with uprosertib was not tolerated, and minimal clinical activity was observed in all schedules tested

Modulation of Xenopus oocyte-expressed phospholemman-induced ion currents by co-expression of protein kinases

AbstractPhospholemman (PLM), the major sarcolemmal substrate for phosphorylation by cAMP-dependent kinase (PKA) protein kinase C (PKC) and NIMA kinase in muscle, induces hyperpolarization-activated anion currents in Xenopus oocytes, most probably by enhancing endogenous oocyte currents. PLM peptides from the cytoplasmic tail are phosphorylated by PKA at S68, by NIMA kinase at S63, and by PKC at both S63 and S68. We have confirmed the phosphorylation sites in the intact protein, and we have investigated the role of phosphorylation in the regulatory activity of PLM using oocyte expression experiments. We found: (1) the cytoplasmic domain is not essential for inducing currents in oocytes; (2) co-expression of PKA increased the amplitude of oocyte currents and the amount of PLM in the oocyte membrane largely, but not exclusively, through phosphorylation of S68; (3) co-expression of PKA had no effect on a PLM mutant in which all putative phosphorylation sites had been inactivated by serine to alanine mutation (SSST 62, 63, 68, 69 AAAA); (4) co-expression of PKC had no effect in this system; (5) co-expression of NIMA kinase increased current amplitude and membrane protein level, but did not require PLM phosphorylation. These findings point to a role for phosphorylation in the function of PLM

Calmodulin-dependent Protein Kinase IV Regulates Hematopoietic Stem Cell Maintenance

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Impact of genetic variation on human CaMKK2 regulation by Ca2+ -calmodulin and multisite phosphorylation

The Ca2+-calmodulin dependent protein kinase kinase-2 (CaMKK2) is a key regulator of neuronal function and whole-body energy metabolism. Elevated CaMKK2 activity is strongly associated with prostate and hepatic cancers, whereas reduced CaMKK2 activity has been linked to schizophrenia and bipolar disease in humans. Here we report the functional effects of nine rare-variant point mutations that were detected in large-scale human genetic studies and cancer tissues, all of which occur close to two regulatory phosphorylation sites and the catalytic site on human CaMKK2. Four mutations (G87R, R139W, R142W and E268K) cause a marked decrease in Ca2+-independent autonomous activity, however S137L and P138S mutants displayed increased autonomous and Ca2+-CaM stimulated activities. Furthermore, the G87R mutant is defective in Thr85-autophosphorylation dependent autonomous activity, whereas the A329T mutation rendered CaMKK2 virtually insensitive to Ca2+-CaM stimulation. The G87R and R139W mutants behave as dominant-negative inhibitors of CaMKK2 signaling in cells as they block phosphorylation of the downstream substrate AMP-activated protein kinase (AMPK) in response to ionomycin. Our study provides insight into functionally disruptive, rare-variant mutations in human CaMKK2, which have the potential to influence risk and burden of disease associated with aberrant CaMKK2 activity in human populations carrying these variants

Rho Kinase Differentially Regulates Phosphorylation of Nonmuscle Myosin II Isoforms A and B during Cell Rounding and Migration

The actin-myosin cytoskeleton is generally accepted to produce the contractile forces necessary for cellular processes such as cell rounding and migration. All vertebrates examined to date are known to express at least two isoforms of non-muscle myosin II, referred to as myosin IIA and myosin IIB. Studies of myosin IIA and IIB in cultured cells and null mice suggest that these isoforms perform distinct functions. However, how each myosin II isoform contributes individually to all the cellular functions attributed to "myosin II" has yet to be fully characterized. Using isoform-specific small-interfering RNAs, we found that depletion of either isoform resulted in opposing migration phenotypes, with myosin IIA- and IIB-depleted cells exhibiting higher and lower wound healing migration rates, respectively. In addition, myosin IIA-depleted cells demonstrated impaired thrombin-induced cell rounding and undertook a more motile morphology, exhibiting decreased amounts of stress fibers and focal adhesions, with concomitant increases in cellular protrusions. Cells depleted of myosin IIB, however, were efficient in thrombin-induced cell rounding, displayed a more retractile phenotype, and maintained focal adhesions but only in the periphery. Last, we present evidence that Rho kinase preferentially regulates phosphorylation of the regulatory light chain associated with myosin IIA. Our data suggest that the myosin IIA and IIB isoforms are regulated by different signaling pathways to perform distinct cellular activities and that myosin IIA is preferentially required for Rho-mediated contractile functions

Tumor suppressive activity of prolyl isomerase Pin1 in renal cell carcinoma

Pin1 specifically recognizes and catalyzes the cis-trans isomerization of phosphorylated-Ser/Thr-Pro bonds, which modulate the stability, localization, and function of numerous Pin1 targets involved in tumor progression. However, the role of Pin1 in cancer remains enigmatic as the gene is located on chromosome 19p13.2, which is a region subject to loss of heterozygosity in several tumors. Since Pin1 protein is frequently under-expressed in kidney cancer, we have explored its role in human clear cell renal cell carcinoma (ccRCC). Here we show evidence for PIN1 gene deletion and mRNA under-expression as a mechanism of Pin1 reduction in ccRCC tumors. We demonstrate that restoration of Pin1 in cell lines found to be deficient in Pin1 protein expression can attenuate the growth of ccRCC cells in soft agar and a xenograft tumor model. Moreover, this ability of Pin1 to negatively influence tumor growth in ccRCC cells may be dependent on the presence of functional p53, which is infrequently mutated in ccRCC. These observations suggest Pin1 may have a mild tumor suppressive role in ccRCC