Kinome Profiling Reveals Abnormal Activity of Kinases in Skeletal Muscle From Adults With Obesity and Insulin Resistance

CONTEXT

Obesity-related insulin resistance (OIR) is one of the main contributors to type 2 diabetes and other metabolic diseases. Protein kinases are implicated in insulin signaling and glucose metabolism. Molecular mechanisms underlying OIR involving global kinase activities remain incompletely understood.

OBJECTIVE

To investigate abnormal kinase activity associated with OIR in human skeletal muscle.

DESIGN

Utilization of stable isotopic labeling-based quantitative proteomics combined with affinity-based active enzyme probes to profile in vivo kinase activity in skeletal muscle from lean control (Lean) and OIR participants.

PARTICIPANTS

A total of 16 nondiabetic adults, 8 Lean and 8 with OIR, underwent hyperinsulinemic-euglycemic clamp with muscle biopsy.

RESULTS

We identified the first active kinome, comprising 54 active protein kinases, in human skeletal muscle. The activities of 23 kinases were different in OIR muscle compared with Lean muscle (11 hyper- and 12 hypo-active), while their protein abundance was the same between the 2 groups. The activities of multiple kinases involved in adenosine monophosphate-activated protein kinase (AMPK) and p38 signaling were lower in OIR compared with Lean. On the contrary, multiple kinases in the c-Jun N-terminal kinase (JNK) signaling pathway exhibited higher activity in OIR vs Lean. The kinase-substrate-prediction based on experimental data further confirmed a potential downregulation of insulin signaling (eg, inhibited phosphorylation of insulin receptor substrate-1 and AKT1/2).

CONCLUSIONS

These findings provide a global view of the kinome activity in OIR and Lean muscle, pinpoint novel specific impairment in kinase activities in signaling pathways important for skeletal muscle insulin resistance, and may provide potential drug targets (ie, abnormal kinase activities) to prevent and/or reverse skeletal muscle insulin resistance in humans.

Beneficial Effects of Implementing Stroke Protocols Require Establishment of a Geographically Distinct Unit

BACKGROUND AND PURPOSE

Usefulness of multidisciplinary stroke units in acute stroke patients is well established. There is extensive western literature on usefulness of stroke units in outcome, but limited evidence from the rest of the world. We aim to evaluate the impact of establishing a stroke unit on outcome in patients presenting to a tertiary care facility.

METHODS

This is a retrospective study of 1003 patients with acute stroke admitted to Hamad General Hospital, Qatar, between January 2014 and February 2015. Patients directly admitted to intensive care unit (132) were excluded. We compared outcomes of pre- and poststroke ward (SW) establishment and in SW patients versus those of general medical wards.

RESULTS

Before the establishment of the SW, 175 patients were admitted to the hospital. From April 2014 to February 2015, 696 patients were admitted (SW, 545; medical ward, 151). There was a significant reduction in length of stay from 14.7±27.7 to 6.2±20.2 days (P=0.0001) and incidence of complications (23.6% versus 6.4%, P=0.0001) after implementation of stroke-specific protocols. Prognosis at discharge (modified Rankin Scale 0-2 in 56.0% versus 70.4%, P=0.001) and at 90 days (modified Rankin Scale 0-2 in 70.6% versus 95.0%, P=0.001) also significantly improved. Compared with medical ward patients, outcome was significantly better in SW patients with fewer complications (10.9% versus 5.0%, P=0.013) and shorter length of stay (8.9±30.7 versus 5.4±16.1 days, P=0.05).

CONCLUSIONS

Establishing a distinct SW is essential for achieving full benefits of stroke protocols implementation. SW patients have significantly fewer complications and better prognosis when compared with patients in medical wards.

Relationship of vitamin D and parathyroid hormone with obesity and body composition in African Americans

BACKGROUND

Obesity disproportionately affects African Americans (AA) (especially women), and is linked to depressed 25-hydroxyvitamin D (25-OH D) and elevated parathyroid hormone (PTH). The relationship of 25-OH D and PTH with body composition and size in AA is not well known.

OBJECTIVE

To determine the relationship of 25-OH D and PTH levels with body composition and anthropometric measures.

DESIGN

A cross-sectional study was conducted in 98 healthy, overweight, adult AA enrolled in an NIH/NIEHS-sponsored weight loss/salt-sensitivity trial.

MEASUREMENTS

Multivariable linear regression analyses were used to explore the relationship of 25-OH D and PTH with body composition, determined by dual-energy X-ray absorptiometry, and anthropometric measures. Body composition and size were contrasted across vitamin D/PTH groups using general linear models: (i) normal (25-OH D >50 nmol/l, PTH <or=65 pg/ml), (ii) low 25-OH D and normal PTH and (iii) low 25-OH D and high PTH.

RESULTS

Age, gender and season-adjusted regression analyses showed that PTH was directly correlated with total (P = 0.02), truncal (P = 0.03) and extremity (P = 0.03) fat mass, while 25-OH D was inversely related to truncal fat mass (P = 0.02). Total fat mass in groups 1-3, respectively, was 30.0, 34.0 and 37.4 kg (P = 0.008); truncal fat mass was 13.4, 15.9 and 17.6 kg (P = 0.006) and extremity fat mass was 15.8, 16.9 and 19.7 kg (P = 0.02). Lean mass did not differ across the three groups.

CONCLUSIONS

Our findings show that lower 25-OH D and raised PTH are both correlated, though in opposite directions, with fat mass, fat distribution and anthropometric measures in adult AA.

Protein kinase C regulates alpha(2A/D)-adrenoceptor constitutive activity

We investigated a possible role for protein kinases in the constitutive activity of alpha(2A/D) adrenoceptors in membranes from transfected PC12 cells, using a [35S]GTPgammaS binding assay. After treatment of intact cells with various protein kinase inhibitors, constitutive activity was assessed by the reduction in basal GTP binding caused by the inverse agonist rauwolscine (RAU). Inhibitors of protein kinase C (PKC) caused the loss of RAU-sensitive GTP binding, while inhibitors of other protein kinases were ineffective. Anti-G(alpha) antibody treatments showed that constitutive alpha(2A/D)-receptor activity is directed toward different G proteins than agonist-stimulated activity. T373A mutant receptors exhibited increased constitutive activity, including a component that was insensitive to PKC inhibition. Since T373 is located within a putative G(i/o) activator sequence, these results suggest that PKC-dependent phosphorylation of T373 increases alpha(2A/D)-adrenergic receptor constitutive activity and causes a switch in G protein preference.

Agonist-dependent phosphorylation of the parathyroid hormone/parathyroid hormone-related peptide receptor

Native PTH/PTHrP receptors in ROS 17/2.8 cells are downregulated after PTH treatment. Since downregulation may involve receptor phosphorylation, we examined PTH/PTHrP receptor phosphorylation in ROS 17/2.8 cells and we mapped the agonist-induced phosphorylation sites using recombinant PTH/PTHrP receptors expressed in LLCPK-1 and COS-7 cells. The data show that the PTH/PTHrP receptor is rapidly phosphorylated in ROS 17/2.8 cells with a maximum occurring at 20 min. The phosphorylation was dose-dependent; it occurred with PTH concentrations that are known to downregulate the PTH/PTHrP receptor in ROS 17/2.8 cells. The time course and the dose requirement for phosphorylation were similar in ROS 17/2.8 cells, which express native PTH/PTHrP receptors, and in LLCPK-1 cells stably transfected with the PTH/PTHrP receptor cDNA. PTH/PTHrP receptor phosphorylation in ROS 17/2.8, COS-7, and LLCPK-1 cells was also stimulated with forskolin and phorbol myristate acetate (PMA). Additionally, in LLCPK-1 cells, which express native clacitonin receptors, PTH/PTHrP receptor phosphorylation was stimulated by calcitonin. These data suggest involvement of second messenger-stimulated kinases in PTH/PTHrP receptor phosphorylation. However, staurosporine, which fully blocked the effects of PMA, forskolin, and clacitonin, partially decreased the effects of PTH on PTH/PTHrP receptor phosphorylation. These data indicate involvement of other kinase(s) in PTH-induced PTH/PTHrP receptor phosphorylation. CNBr cleavage of recombinant receptors expressed in COS-7 cells combined with site-directed mutagenesis revealed that the phosphorylated residues of the PTH/PTHrP receptor map to two regions of the carboxyl-terminal tail located between residues A480 and M499 and residues M499 and M553. These data indicate that the PTH/PTHrP receptor is phosphorylated after PTH stimulation on two regions of the carboxyl-terminal tail and that agonist-dependent phosphorylation involves both staurosporine-sensitive and -insensitive kinases.

Tissue-specific transcription start sites and alternative splicing of the parathyroid hormone (PTH)/PTH-related peptide (PTHrP) receptor gene: a new PTH/PTHrP receptor splice variant that lacks the signal peptide

The PTH/PTHrP receptor gene is expressed in bone and kidney as well as in many other tissues. Using primer extension followed by rapid cloning of amplified complementary DNA ends, we have isolated new PTH/PTHrP receptor complementary DNAs with different splicing patterns and have characterized a new upstream transcription start site. Three 5' nontranslated exons, U3, U2 and U1, located 4.8, 2.5, and 1.2 kb upstream of the exon that encodes the putative signal peptide of the classical receptor (exon S), have been characterized. Four types of splicing patterns were recognized. Type I splicing pattern is transcribed from exon U1 and is spliced to exons S and E1; this pattern was found in most tissues tested. Types II, III, and IV splicing patterns are transcribed from exon U3 and have a restricted tissue distribution. Type II splice pattern, containing exons U3, U2, and S and type III splicing pattern, containing exon U3, U2, and E1 (skipping exon S), was found only in kidney. Type IV splice pattern, containing exon U3 and S was found both in kidney and ovary. Because the type III splice variant skips exon S, translation of this splice variant initiates at a different AUG codon. The type III splice variant was weakly expressed on the cell surface of COS-7 cells, as assessed by double antibody binding assay, and no detectable ligand binding was observed on intact cells. The type III splice variant, however, increased cAMP accumulation in COS-7 cells when challenged with PTH(1-34), PTH(1-84) and hPTHrP(1-36) with EC50s that are similar to those observed in COS-7 cells expressing the type I variant but with a maximum stimulation that was lower than that observed in COS-7 cells expressing the type I variant. These data indicate low levels of cell surface expression of the type III splice variant. Treatment of COS-7 cells with tunicamycin decreased the size of the type I splice variant from a broad band of 85 kDa to a compact band of about 60 kDa. The type III splice variant did not change in size in COS-7 cells treated with tunicamycin, indicating that the type III splice variant did not undergo any glycosylation step. In conclusion, the PTH/PTHrP receptor gene uses alternate promoters in a tissue-specific manner that results in several tissue-specific alternatively spliced transcripts. One of these transcripts, the type III splice variant, is expressed in kidney and lacks the signal peptide.

Mutations in the second cytoplasmic loop of the rat parathyroid hormone (PTH)/PTH-related protein receptor result in selective loss of PTH-stimulated phospholipase C activity

To define the structural requirements of the parathyroid hormone (PTH)/PTH-related protein (PTHrP) receptor necessary for activation of phospholipase C (PLC), receptors with random mutations in their second cytoplasmic loop were synthesized, and their properties were assessed. A mutant in which the wild type (WT) rat PTH/PTHrP receptor sequence EKKY (amino acids 317-320) was replaced with DSEL had little or no PTH-stimulated PLC activity when expressed transiently in COS-7 cells, but it retained full capacity to bind ligand and to generate cAMP. This phenotype was confirmed in LLC-PK1 cells stably expressing the DSEL mutant receptor, where both PTH-stimulated PLC activity and sodium-dependent phosphate co-transport were essentially abolished. Individual mutations of these four residues point to a critical role for Lys-319 in receptor-G protein coupling. PTH-generated IPs were reduced to 27 +/- 13% when K319E, compared with the WT receptor, and PLC activation was fully recovered in a receptor revertant in which Glu-319 in the DSEL mutant cassette was restored to the WT residue, Lys. Moreover, the WT receptor and a mutant receptor in which K319R had indistinguishable properties, thus suggesting that a basic amino acid at this position may be important for PLC activation. All of these receptors had unimpaired capacity to bind ligand and to generate cAMP. To ensure adequacy of Galphaq-subunits for transducing the receptor signal, Galphaq was expressed in HEK293 and in LLC-PK1 cells together with either WT receptors or receptors with the DSEL mutant cassette. PTH generated no inositol phosphates (IPs) in either HEK293 or LLC-PK1 cells, when they expressed DSEL mutant receptors together with Galphaq. In contrast, PTH generated 2- and 2. 5-fold increases in IPs, respectively, when these cells co-expressed both the WT receptor and Galphaq. Thus, generation of IPs by the activated PTH/PTHrP receptor can be selectively abolished without affecting its capacity to generate cAMP, and Lys-319 in the second intracellular loop is critical for activating the PLC pathway. Moreover, alpha-subunits of the Gq family, rather than betagamma-subunits, transduce the signal from the activated receptor to PLC, and the PLC, rather than the adenylyl cyclase, pathway mediates sodium-dependent phosphate co-transport in LLC-PK1 cells.