Real-world tertiary referral centre experience stopping nucleos(t)ide analogue therapy in patients with chronic hepatitis B

BACKGROUND: Identifying strategies for stopping nucleos(t)ide analogues (NUC) in patients with chronic hepatitis B (CHB) is a major goal in CHB management. Our study describes our tertiary-centre experience stopping nucleos(t)ide analogues (NUC) in CHB. METHODS: We conducted a retrospective cohort study of all individuals with CHB seen at the Calgary Liver Unit between January 2009 and May 2020 who stopped NUC. We collected baseline demographics and HBV lab parameters before and after stopping NUC with results stratified by off-treatment durability. Clinical flare was defined as alanine aminotransferase (ALT) over twice the upper limit of normal and virological flare as HBV DNA >2000 IU/mL. RESULTS: Forty-seven (3.5%) of the 1337 individuals with CHB stopped NUC therapy. During follow-up, six patients (12.8%) restarted NUCs because of a flare. All flares occurred within six months of discontinuation. Median time to restart treatment was 90 days (Q1 65, Q3 133). Upon restarting, all showed suppression of HBV DNA and ALT normalization. Factors associated with restarting NUC therapy included hepatitis B e antigen (HBeAg) positive status at first appointment and longer NUC consolidation therapy. Age, sex, ethnicity, liver stiffness measurement, choice of NUC, and quantitative hepatitis B surface antigen (qHBsAg) level at stopping were not associated with sustained response off-treatment. Six patients had functional cure with HBsAg loss. CONCLUSIONS: Stopping long-term NUC is feasible in HBeAg negative CHB. Hepatic flares can occur despite low levels of qHBsAg. Finite NUC therapy can be considered in eligible patients who are adherent to close monitoring and follow-up, particularly in the first six months after stopping NUC therapy.

Real-world clinical and virological outcomes in a retrospective multiethnic cohort study of 341 untreated and tenofovir disoproxil fumarate-treated chronic hepatitis B pregnant patients in North America

BACKGROUND

There are limited long-term data on outcomes of chronic hepatitis B (CHB) in untreated and tenofovir disoproxil fumarate (TDF)-treated women during pregnancy.

AIMS

To assess clinical outcomes in a multiethnic cohort of patients during pregnancy and post-partum in a low HBV endemic region.

METHODS

Retrospective real-world study of women with CHB (treated or untreated with TDF) from 2011 to 2019; data including ALT, HBV DNA, HBeAg and liver stiffness measurement were collected during pregnancy and post-partum.

RESULTS

In 341 women (446 pregnancies) followed for a median of 33 months (IQR: 26.7-39.5) post-partum, 19% (65/341) received TDF (11 initiated pre-pregnancy, 53 for mother-to-child transmission (MTCT) prevention). During follow-up, 72/341 had subsequent pregnancy, including 18/53 on TDF for MTCT risk, of whom 7/18 were re-treated. In all TDF-treated women, HBV DNA declined but rebounded after TDF withdrawal (median baseline, near birth and early follow-up levels were 7.2, 3.0 and 5.5 log IU/mL respectively [P < 0.01]). In HBeAg+ patients (65/341) ALT flares were more common (P = 0.03), especially for those who stopped TDF post-partum, requiring re-treatment in 21% (11/53). In comparison, 54% (116/215) of untreated women had a post-partum ALT flare; one with fulminant hepatitis underwent transplant 13 months post-partum. HBsAg clearance occurred in 2.6% (9/341, 3/9 HBeAg+, 2/9 TDF treated) at median 30 months (IQR: 23-40) and 37% (24/65) of HBeAg+ patients had HBeAg loss at median 17 months (IQR: 12-26) post-partum.

CONCLUSIONS

Post-partum ALT flares were common, especially after TDF withdrawal. Overall, 37% achieved HBeAg clearance and 2.9% had HBsAg loss during long-term follow-up.

Assessment of Canadian policies regarding liver transplant candidacy of people who use alcohol, tobacco, cannabis, and opiates

BACKGROUND

When last assessed in 2013, all Canadian liver transplant programs required 6 months of abstinence from alcohol. New studies have questioned the validity of this policy. Moreover, with recreational cannabis now legal in Canada, more transplant candidates may use cannabis. Given these changes, our objective was to obtain an understanding of current Canadian practices regarding liver transplantation and candidates with addiction or alcohol, tobacco, cannabis, or opiate use.

METHODS

Electronic surveys were distributed to the medical directors of all seven adult liver transplant programs in Canada. Questions were based on either a Likert-scale ranking or free response. The complete data set was aggregated to provide a national perspective on this topic and ensure each individual program remained anonymous.

RESULTS

All seven programs responded to the survey. Of these programs, 43% always require 6-month abstinence from alcohol, 29% usually require it, and 14% sometimes require it. Formal alcohol rehabilitation is mandatory in two programs. The majority (57%) of programs never or rarely consider transplant for patients with acute alcoholic hepatitis; 29% require smoking cessation before consideration for transplant; and 71% felt that cannabis use is rarely or never a contraindication to liver transplantation.

CONCLUSIONS

Significantly more Canadian programs now perform liver transplant for patients who have less than 6 months abstinence from alcohol, and alcoholic hepatitis is no longer an absolute contraindication in Canada. Policies on smoking and opiates are quite variable. Further study and discussion are critical for development of national policies to obtain equitable access to liver transplant for all.

Long-Term Follow-up and Quantitative Hepatitis B Surface Antigen Monitoring in North American Chronic HBV Carriers

INTRODUCTION

Quantitative hepatitis B surface antigen (qHBsAg) combined with HBV DNA may be useful for predicting chronic hepatitis B (CHB) activity and nucleoside analogue (NA) response.

MATERIAL AND METHODS

In this retrospective cohort study we evaluated qHBsAg levels according to CHB disease phase and among patients on treatment. Random effect logistic regression analysis was used to analyze qHBsAg change with time in the NA-treated cohort.

RESULTS

545 CHB carriers [56% M, median age 48 y (IQR 38-59), 73% Asian] had qHBsAg testing. In the untreated group (44%), 8% were classified as immune tolerant, 10% immune clearance, 40% inactive, and 43% had HBeAg- CHB and the median HBsAg levels were 4.6 (IQR 3.4-4.9), 4.0 (IQR 3.4-4.5), 2.9 (IQR 1.4-3.8), and 3.2 log IU/mL (IQR 2.6-4.0), respectively; p < 0.001. In the NA-treated group (28% entecavir, 68% tenofovir, 4% lamivudine), no significant change in qHBsAg levels occured with time. However, 19% of patients on long-term NA had sustained qHBsAg < 2 log10 IU/mL.

CONCLUSION

qHBsAg titers were associated with CHB phase and remained stable in those on long-term NA. A significant number of treated patients had low-level qHBsAg, of which some may be eligible for treatment discontinuation without risk of flare.

Real-world treatment of hepatitis C with second-generation direct-acting antivirals: initial results from a multicentre Canadian retrospective cohort of diverse patients

BACKGROUND

High hepatitis C cure rates have been observed in registration trials with second-generation direct-acting antivirals. Real-world data also indicate high sustained viral response (SVR) rates. Our objective was to determine real-world SVR rates for patients infected with hepatitis C virus (HCV) who were treated with second-generation direct-acting antivirals in the first 18 months of their availability in Canada.

METHODS

Four centres in Calgary contributed their treatment data for a diverse patient population including those who had or had not undergone liver transplantation, those coinfected with HIV and vulnerable populations. We included all patients documented to have started hepatitis C treatment with direct-acting antivirals between October 2014 and April 2016, with follow-up through October 2016. We used multivariate analysis to determine independent predictors of treatment failure.

RESULTS

Outcome data were available for 351 patients, of whom 326 (92.9%) achieved an SVR (193/206 [93.7%], 57/59 [96.6%] and 44/51 [86.3%] for genotypes 1a, 1b and 3, respectively, p = 0.2). Independent predictors of not achieving SVR were older age (adjusted odds ratio [OR] 0.95 [95% confidence interval (CI) 0.90-1.00]), male sex (adjusted OR 0.30 [95% CI 0.10-0.89]) and, in patients with genotype 1a infection, history of hepatocellular carcinoma (adjusted OR 0.13 [95% CI 0.03-0.53]). In the entire cohort, the presence of cirrhosis, genotype and hepatocellular carcinoma were not associated with a lower SVR rate. There were no differences in SVR rate according to treatment centre, HIV coinfection or liver transplantation. Among patients with genotype 3 infection, a significantly lower SVR rate was observed for those treated outside of standard of care than for those treated within standard of care (33.3% v. 89.6%, p = 0.04). De novo hepatocellular carcinoma developed in 12 patients (3.4%) despite successful direct-acting antiviral therapy.

INTERPRETATION

We report high SVR rates in a real-world diverse cohort of HCV-infected patients treated with second-generation direct-acting antivirals. The results highlight the importance of conducting real-world analyses to elucidate clinical factors associated with poorer outcomes that may not be identified in registration trials.

Tenofovir disoproxil fumarate significantly decreases serum lipoprotein levels compared with entecavir nucleos(t)ide analogue therapy in chronic hepatitis B carriers

BACKGROUND

Tenofovir disoproxil fumarate (TDF) and entecavir (ETV) are first-line treatments for chronic hepatitis B (CHB). Studies suggest lipid lowering effect of TDF in human immunodeficiency virus positive (HIV+) individuals, but the effect on lipids and cardiovascular disease (CVD) risk in CHB is unknown.

AIM

To compare TDF vs ETV effects on lipid levels in CHB.

METHODS

In this retrospective cohort study, data on serum lipids and CVD risk factors at baseline and ~1 year on TDF or ETV were collected from CHB carriers. We used propensity score matched models to assess the effect on total cholesterol (TC), LDL-C, HDL and triglycerides (TGL).

RESULTS

In 348 patients, median age was 57 (IQR: 47-65 years), 63% were male, 77% were Asian, 19% were cirrhotic, 25% were HBeAg positive at baseline, and 72% received TDF vs 28% ETV. ETV-treated patients were older (median age: 60 vs 55, P<.01), had similar smoking and hypertension rates, but diabetes and dyslipidemia were more prevalent (19% vs 9%, P=.01; 14% vs 6%, P=.05, respectively). In propensity score matched models for age, gender, usage of lipid lowering agents, dyslipidemia and diabetes, TDF-treated patients were more likely to show a 20% decrease in TC (95% CI: 3%-25%), LDL-C (95% CI: 1%-25%) and HDL-C (CI: 10%-30%) levels compared with those on ETV. No change in TGL was observed in either group.

CONCLUSIONS

A greater decline in TC, LDL-C and HDL was observed in CHB carriers receiving TDF compared with ETV. These data may influence anti-viral choice in CHB carriers at risk for CVD.

Hepatitis B virus testing and linkage to care in a Canadian urban tertiary referral centre: a retrospective cohort study

BACKGROUND

Despite universal vaccination, chronic hepatitis B virus (HBV) infection remains a public health concern in North America owing to immigration. We aimed to characterize the number of people with a positive result of testing for HBV surface antigen (HBsAg) in Calgary, a large urban Canadian health care region, and to assess whether recommended laboratory tests and specialist consultation were done for those identified as HBsAg-positive.

METHODS

Based on laboratory and Alberta Health Services administrative data, we identified all adults (age > 18 yr) with a positive HBsAg test result from Jan. 1 to Dec. 31, 2014 within the Calgary Zone. Demographic and relevant laboratory data were extracted within 6 months of a positive HBsAg test result, and referral to hepatology (2011-2014) was identified from data on referral to a centralized clinic. Parametric and nonparametric statistical methods were used for analyses.

RESULTS

We identified 1214 HBsAg-positive people (584 women [48.1%]; median age 44 [interquartile range (IQR) 36-55] yr). A total of 1192 people (98.2%) had alanine aminotransferase testing (median level 23 [IQR 16-34] U/L; 117 [9.8%] with elevated levels), 682 (56.2%) had testing for HBV DNA (median level 2.8 [IQR 2.1-3.8] logIU/mL), 630 (51.9%) had HBV e antigen testing (negative result in 548 [87.0%]), and 145 (11.9%) had HBV e antibody testing (positive result in 111 [76.6%]). Overall, 144 people (11.9%) received anti-HBV treatment, and 390 (32.1%) were referred to a hepatologist.

INTERPRETATION

Many HBsAg-positive people in Calgary did not receive the recommended laboratory assessments. The results highlight the necessity of continual public health efforts to screen for chronic HBV infection in Canada and to ensure adequate follow-up in order to reach the World Health Organization's goal of viral hepatitis elimination by 2030.

Validation of coding algorithms for the identification of patients hospitalized for alcoholic hepatitis using administrative data

Background

Epidemiologic studies of alcoholic hepatitis (AH) have been hindered by the lack of a validated International Classification of Disease (ICD) coding algorithm for use with administrative data. Our objective was to validate coding algorithms for AH using a hospitalization database.

Methods

The Hospital Discharge Abstract Database (DAD) was used to identify consecutive adults (≥18 years) hospitalized in the Calgary region with a diagnosis code for AH (ICD-10, K70.1) between 01/2008 and 08/2012. Medical records were reviewed to confirm the diagnosis of AH, defined as a history of heavy alcohol consumption, elevated AST and/or ALT (<300 U/L), serum bilirubin >34 μmol/L, and elevated INR. Subgroup analyses were performed according to the diagnosis field in which the code was recorded (primary vs. secondary) and AH severity. Algorithms that incorporated ICD-10 codes for cirrhosis and its complications were also examined.

Results

Of 228 potential AH cases, 122 patients had confirmed AH, corresponding to a positive predictive value (PPV) of 54 % (95 % CI 47–60 %). PPV improved when AH was the primary versus a secondary diagnosis (67 % vs. 21 %; P < 0.001). Algorithms that included diagnosis codes for ascites (PPV 75 %; 95 % CI 63–86 %), cirrhosis (PPV 60 %; 47–73 %), and gastrointestinal hemorrhage (PPV 62 %; 51–73 %) had improved performance, however, the prevalence of these diagnoses in confirmed AH cases was low (29–39 %).

Conclusions

In conclusion the low PPV of the diagnosis code for AH suggests that caution is necessary if this hospitalization database is used in large-scale epidemiologic studies of this condition.

The Fatty Liver Index has limited utility for the detection and quantification of hepatic steatosis in obese patients

PURPOSE

Noninvasive tools for the detection of hepatic steatosis are needed. The Fatty Liver Index (FLI), which includes body mass index (BMI), waist circumference, triglycerides, and γ-glutamyl-transferase, has been proposed as a screening tool for fatty liver. Our objective was to validate the FLI for the detection and quantification of hepatic steatosis in an obese population.

METHODS

Patients with chronic liver disease and BMI ≥ 28 kg/m(2) underwent liver biopsy and FLI determination. FLI performance for diagnosing steatosis compared with biopsy was assessed using areas under receiver operating characteristic curves (AUROCs), and a novel model for the prediction of significant steatosis (≥5 %) was derived.

RESULTS

Among 250 included patients, 65 % were male, and the median BMI was 33 kg/m(2); 48 % had nonalcoholic fatty liver disease, and 77 % had significant (≥5 %) steatosis. The FLI was weakly correlated with the percentage (ρ = 0.25, p = 0.0001) and grade of steatosis (ρ = 0.28, p < 0.00005). The median FLI was higher among patients with significant steatosis (91 vs. 80 with <5 % steatosis; p = 0.0001) and the AUROC for this outcome was 0.67 (95 % CI 0.59-0.76). At an optimal FLI cut-off of 79, the FLI was 81 % sensitive and 49 % specific, and had positive and negative predictive values of 84 and 43 %, respectively. A novel index including triglycerides, glucose, alkaline phosphatase, and BMI outperformed the FLI for predicting significant steatosis [AUROCs 0.78 vs. 0.68; p = 0.009 (n = 247)].

CONCLUSIONS

In obese patients, the FLI is a poor predictor of significant steatosis and has limited utility for steatosis quantification compared with liver histology. A novel index including triglycerides, glucose, alkaline phosphatase, and BMI may be useful, but requires validation.

Mapping and functional characterization of the murine smoothelin-like 1 promoter

Background

Smoothelin-like 1 (SMTNL1, also known as CHASM) plays a role in promoting relaxation as well as adaptive responses to exercise, pregnancy and sexual development in smooth and skeletal muscle. Investigations of Smtnl1 transcriptional regulation are still lacking. Thus, in this study, we identify and characterize key regulatory elements of the mouse Smtnl1 gene.

Results

We mapped the key regulatory elements of the Smtnl1 promoter region: the transcriptional start site (TSS) lays -44 bp from the translational start codon and a TATA-box motif at -75 bp was conserved amongst all mammalian Smtnl1 promoters investigated. The Smtnl1 proximal promoter enhances expression up to 8-fold in smooth muscle cells and a second activating region lays 500 bp further upstream. Two repressing motifs were present (-118 to -218 bp and -1637 to -1869 bp). The proximal promoter is highly conserved in mammals and contains a mirror repeat sequence. In silico analysis suggests many transcription factors (notably MyoD) could potentially bind within the Smtnl1 proximal promoter sequence.

Conclusion

Smtnl1 transcript was identified in all smooth muscle tissues examined to date, albeit at much lower levels than found in skeletal muscle. It is unlikely that multiple SMTNL1 isoforms exist since a single Smtnl1 transcription start site was identified in both skeletal and intestinal smooth muscle. Promoter studies suggest restrictive control of Smtnl1 expression in non-muscle cells.

Tropomyosin-binding properties of the CHASM protein are dependent upon its calponin homology domain

The calponin homology-associated smooth muscle protein (CHASM) can modulate muscle contractility, and its biological action may involve an interaction with the contractile filament. In this study, we demonstrate an interaction between CHASM and tropomyosin. Deletion constructs of CHASM were generated, and pull-down assays revealed a minimal deletion construct that could bind tropomyosin. Removal of the calponin homology (CH) domain or expression of the CH domain alone did not enable binding. The interaction was characterized by microcalorimetry with a dissociation constant of 2.0x10(-6) M. Confocal fluorescence microscopy also showed green fluorescent protein (GFP)-CHASM localization to filamentous structures within smooth muscle cells, and this targeting was dependent upon the CH domain.

Ca2+-independent contraction of longitudinal ileal smooth muscle is potentiated by a zipper-interacting protein kinase pseudosubstrate peptide

As a regulator of smooth muscle contraction, zipper-interacting protein kinase (ZIPK) can directly phosphorylate the myosin regulatory light chains (LC20) and produce contractile force. Synthetic peptides (SM-1 and AV25) derived from the autoinhibitory region of smooth muscle myosin light chain kinase can inhibit ZIPK activity in vitro. Paradoxically, treatment of Triton-skinned ileal smooth muscle strips with AV25, but not SM-1, potentiated Ca2+-independent, microcystin- and ZIPK-induced contractions. The AV25-induced potentiation was limited to ileal and colonic smooth muscles and was not observed in rat caudal artery. Thus the potentiation of Ca2+-independent contractions by AV25 appeared to be mediated by a mechanism unique to intestinal smooth muscle. AV25 treatment elicited increased phosphorylation of LC20 (both Ser-19 and Thr-18) and myosin phosphatase-targeting subunit (MYPT1, inhibitory Thr-697 site), suggesting involvement of a Ca2+-independent LC20 kinase with coincident inhibition of myosin phosphatase. The phosphorylation of the inhibitor of myosin phosphatase, CPI-17, was not affected. The AV25-induced potentiation was abolished by pretreatment with staurosporine, a broad-specificity kinase inhibitor, but specific inhibitors of Rho-associated kinase, PKC, and MAPK pathways had no effect. When a dominant-negative ZIPK [kinase-dead ZIPK((1-320))-D161A] was added to skinned ileal smooth muscle, the potentiation of microcystin-induced contraction by AV25 was blocked. Furthermore, pretreatment of skinned ileal muscle with SM-1 abolished AV25-induced potentiation. We conclude, therefore, that, even though AV25 is an in vitro inhibitor of ZIPK, activation of the ZIPK pathway occurs following application of AV25 to permeabilized ileal smooth muscle. Finally, we propose a mechanism whereby conformational changes in the pseudosubstrate region of ZIPK permit augmentation of ZIPK activity toward LC(20) and MYPT1 in situ. AV25 or molecules based on its structure could be used in therapeutic situations to induce contractility in diseases of the gastrointestinal tract associated with hypomotility.

The role of the calponin homology domain of smoothelin-like 1 (SMTNL1) in myosin phosphatase inhibition and smooth muscle contraction

In this study, we provide further insight into the contribution of the smoothelin-like 1 (SMTNL1) calponin homology (CH)-domain on myosin light chain phosphatase (SMPP-1M) activity and smooth muscle contraction. SMTNL1 protein was shown to have inhibitory effects on SMPP-1M activity but not on myosin light chain kinase (MLCK) activity. Treatment of beta-escin permeabilized rabbit, ileal smooth muscle with SMTNL1 had no effect on the time required to reach half-maximal force (t(1/2)) during stimulation with pCa6.3 solution. The addition of recombinant SMTNL1 protein to permeabilized, smooth muscle strips caused a significant decrease in contractile force. While the calponin homology (CH)-domain was essential for maximal SMTNL1-associated relaxation, it alone did not cause significant changes in force. SMTNL1 was poorly dephosphorylated by PP-1C in the presence of the myosin targeting subunit (MYPT1), suggesting that phosphorylated SMTNL1 does not possess "substrate trapping" properties. Moreover, while full-length SMTNL1 could suppress SMPP-1M activity toward LC(20) in vitro, truncated SMTNL1 lacking the CH-domain was ineffective. In summary, our findings suggest an important role for the CH-domain in mediating the effects of SMTNL1 on smooth muscle contraction.

Solution structure of the calponin homology (CH) domain from the smoothelin-like 1 protein: a unique apocalmodulin-binding mode and the possible role of the C-terminal type-2 CH-domain in smooth muscle relaxation

The SMTNL1 protein contains a single type-2 calponin homology (CH) domain at its C terminus that shares sequence identity with the smoothelin family of smooth muscle-specific proteins. In contrast to the smoothelins, SMTNL1 does not associate with F-actin in vitro, and its specific role in smooth muscle remains unclear. In addition, the biological function of the C-terminal CH-domains found in the smoothelin proteins is also poorly understood. In this work, we have therefore determined the solution structure of the CH-domain of mouse SMTNL1 (SMTNL1-CH; residues 346-459). The secondary structure and the overall fold for the C-terminal type-2 CH-domain is very similar to that of other CH-domains. However, two clusters of basic residues form a unique surface structure that is characteristic of SMTNL1-CH. Moreover, the protein has an extended C-terminal alpha-helix, which contains a calmodulin (CaM)-binding IQ-motif, that is also a distinct feature of the smoothelins. We have characterized the binding of apo-CaM to SMTNL1-CH through its IQ-motif by isothermal titration calorimetry and NMR chemical shift perturbation studies. In addition, we have used the HADDOCK protein-protein docking approach to construct a model for the complex of apo-CaM and SMTNL1-CH. The model revealed a close interaction of SMTNL1-CH with the two Ca(2+) binding loop regions of the C-terminal domain of apo-CaM; this mode of apo-CaM binding is distinct from previously reported interactions of apo-CaM with IQ-motifs. Finally, we comment on the putative role of the CH-domain in the biological function of SMTNL1.

Inhibition of zipper-interacting protein kinase function in smooth muscle by a myosin light chain kinase pseudosubstrate peptide

As a regulator of smooth muscle contractility, zipper-interacting protein kinase (ZIPK) appears to phosphorylate the regulatory myosin light chain (RLC20), directly or indirectly, at Ser19 and Thr18 in a Ca2+-independent manner. The calmodulin-binding and autoinhibitory domain of myosin light chain kinase (MLCK) shares similarity to a sequence found in ZIPK. This similarity in sequence prompted an investigation of the SM1 peptide, which is derived from the autoinhibitory region of MLCK, as a potential inhibitor of ZIPK. In vitro studies showed that SM1 is a competitive inhibitor of a constitutively active 32-kDa form of ZIPK with an apparent Kivalue of 3.4 μM. Experiments confirmed that the SM1 peptide is also active against full-length ZIPK. In addition, ZIPK autophosphorylation was reduced by SM1. ZIPK activity is independent of calmodulin; however, calmodulin suppressed the in vitro inhibitory potential of SM1, likely as a result of nonspecific binding of the peptide to calmodulin. Treatment of ileal smooth muscle with exogenous ZIPK was accompanied by an increase in RLC20 diphosphorylation, distinguishing between ZIPK [and integrin-linked kinase (ILK)] and MLCK actions. Administration of SM1 suppressed steady-state muscle tension developed by the addition of exogenous ZIPK to Triton-skinned rat ileal muscle strips with or without calmodulin depletion by trifluoperazine. The decrease in contractile force was associated with decreases in both RLC20 mono- and diphosphorylation. In summary, we present the SM1 peptide as a novel inhibitor of ZIPK. We also conclude that the SM1 peptide, which has no effect on ILK, can be used to distinguish between ZIPK and ILK effects in smooth muscle tissues.

Staurosporine inhibition of zipper-interacting protein kinase contractile effects in gastrointestinal smooth muscle

Zipper-interacting protein kinase (ZIPK) is a serine–threonine kinase that has been implicated in Ca2+-independent myosin II phosphorylation and contractile force generation in vascular smooth muscle. However, relatively little is known about the contribution of this kinase to gastrointestinal smooth muscle contraction. The addition of a recombinant version of ZIPK that lacked the leucine zipper domain to permeabilized ileal strips evoked a Ca2+-independent contraction and resulted in myosin regulatory light chain diphosphorylation at Ser19and Thr18. Neither Ca2+-independent force development nor myosin regulatory light chain phosphorylation was elicited by the addition of kinase-dead ZIPK to the ileal strips. The sensitivity of ZIPK-induced contraction to various kinase inhibitors was similar to the in vitro sensitivity of purified ZIPK to these inhibitors. Staurosporine was the most effective ZIPK inhibitor, with a Kivalue calculated to be 2.6 ± 0.3 µmol/L. Through the use of specific kinase inhibitors, we determined that Rho-associated protein kinase and Ca2+/phospholipid-dependent protein kinase (protein kinase C) do not mitigate ZIPK-induced contraction in ileum. Our findings support a role for ZIPK in Ca2+-independent contractile force generation in gastrointestinal smooth muscle.

Modulation of smooth muscle contractility by CHASM, a novel member of the smoothelin family of proteins

Cyclic nucleotides acting through their associated protein kinases, the cGMP- and cAMP-dependent protein kinases, can relax smooth muscles without a change in free intracellular calcium concentration ([Ca2+]i), a phenomenon referred to as Ca2+ desensitization. The molecular mechanisms by which these kinases bring about Ca2+ desensitization are unknown and an understanding of this phenomenon may lead to better therapies for treating diseases involving defects in the contractile response of smooth muscles such as hypertension, bronchospasm, sexual dysfunction, gastrointestinal disorders and glaucoma. Utilizing a combination of real-time proteomics and smooth muscle physiology, we characterized a distinct subset of protein targets for cGMP-dependent protein kinase in smooth muscle. Among those phosphoproteins identified was calponin homology-associated smooth muscle (CHASM), a novel protein that contains a calponin homology domain and shares sequence similarity with the smoothelin family of smooth muscle specific proteins. Recombinant CHASM was found to evoke relaxation in a concentration dependent manner when added to permeabilized smooth muscle. A co-sedimentation assay with actin demonstrated that CHASM does not possess actin binding activity. Our findings indicate that CHASM is a novel member of the smoothelin protein family that elicits Ca2+ desensitization in smooth muscle.

Smooth Muscle Phosphatase Is Regulated in Vivo by Exclusion of Phosphorylation of Threonine 696 of MYPT1 by Phosphorylation of Serine 695 in Response to Cyclic Nucleotides

Regulation of smooth muscle myosin phosphatase (SMPP-1M) is thought to be a primary mechanism for explaining Ca(2+) sensitization/desensitization in smooth muscle. Ca(2+) sensitization induced by activation of G protein-coupled receptors acting through RhoA involves phosphorylation of Thr-696 (of the human isoform) of the myosin targeting subunit (MYPT1) of SMPP-1M inhibiting activity. In contrast, agonists that elevate intracellular cGMP and cAMP promote Ca(2+) desensitization in smooth muscle through apparent activation of SMPP-1M. We show that cGMP-dependent protein kinase (PKG)/cAMP-dependent protein kinase (PKA) efficiently phosphorylates MYPT1 in vitro at Ser-692, Ser-695, and Ser-852 (numbering for human isoform). Although phosphorylation of MYPT1 by PKA/PKG has no direct effect on SMPP-1M activity, a primary site of phosphorylation is Ser-695, which is immediately adjacent to the inactivating Thr-696. In vitro, phosphorylation of Ser-695 by PKA/PKG appeared to prevent phosphorylation of Thr-696 by MYPT1K. In ileum smooth muscle, Ser-695 showed a 3-fold increase in phosphorylation in response to 8-bromo-cGMP. Addition of constitutively active recombinant MYPT1K to permeabilized smooth muscles caused phosphorylation of Thr-696 and Ca(2+) sensitization; however, this phosphorylation was blocked by preincubation with 8-bromo-cGMP. These findings suggest a mechanism of Ca(2+) desensitization in smooth muscle that involves mutual exclusion of phosphorylation, whereby phosphorylation of Ser-695 prevents phosphorylation of Thr-696 and therefore inhibition of SMPP-1M.

Smooth muscle myosin phosphatase-associated kinase induces Ca2+ sensitization via myosin phosphatase inhibition

Smooth muscle calcium sensitization reflects an inhibition of myosin light chain phosphatase (SMPP-1m) activity; however, the underlying mechanisms are not well understood. SMPP-1m activity can be modulated through phosphorylation of the myosin targeting subunit (MYPT1) by the endogenous myosin phosphatase-associated kinase, MYPT1 kinase (MacDonald, J. A., Borman, M. A., Muranyi, A., Somlyo, A. V., Hartshorne, D. J., and Haystead, T. A. (2001) Proc. Natl. Acad. Sci. U. S. A. 98, 2419-2424). Recombinant chicken gizzard MYPT1 (M130) was phosphorylated in vitro by a recombinant MYPT1 kinase, and the sites of phosphorylation were identified as Thr(654), Ser(808), and Thr(675). Introduction of recombinant MYPT1 kinase elicited a calcium-independent contraction in beta-escin-permeabilized rabbit ileal smooth muscle. Using an antibody that specifically recognizes MYPT1 phosphorylated at Thr(654) (M130 numbering), we determined that this calcium-independent contraction was correlated with an increase in MYPT1 phosphorylation. These results indicate that SMPP-1m phosphorylation by MYPT1 kinase is a mechanism of smooth muscle calcium sensitization.

Dual Ser and Thr phosphorylation of CPI-17, an inhibitor of myosin phosphatase, by MYPT-associated kinase

Phosphorylation of CPI-17 and PHI-1 by the MYPT1-associated kinase (M110 kinase) was investigated. M110 kinase is a recently identified serine/threonine kinase with a catalytic domain that is homologous to that of ZIP kinase (ZIPK. GST-rN-ZIPK, a constitutively active GST fusion fragment, phosphorylates CPI-17 (but not PHI-1) to a stoichiometry of 1.7 mol/mol. Phosphoamino acid analysis revealed phosphorylation of both Ser and Thr residues. Phosphorylation sites in CPI-17 were identified as Thr 38 and Ser 12 using Edman sequencing with (32)P release and a point mutant of Thr 38.

Identification of the endogenous smooth muscle myosin phosphatase-associated kinase

Ca(2+) sensitization of smooth muscle contraction involves inhibition of myosin light chain phosphatase (SMPP-1M) and enhanced myosin light chain phosphorylation. Inhibition of SMPP-1M is modulated through phosphorylation of the myosin targeting subunit (MYPT1) by either Rho-associated kinase (ROK) or an unknown SMPP-1M-associated kinase. Activated ROK is predominantly membrane-associated and its putative substrate, SMPP-1M, is mainly myofibrillar-associated. This raises a conundrum about the mechanism of interaction between these enzymes. We present ZIP-like kinase, identified by "mixed-peptide" Edman sequencing after affinity purification, as the previously unidentified SMPP-1M-associated kinase. ZIP-like kinase was shown to associate with MYPT1 and phosphorylate the inhibitory site in intact smooth muscle. Phosphorylation of ZIP-like kinase was associated with an increase in kinase activity during carbachol stimulation, suggesting that the enzyme may be a terminal member of a Ca(2+) sensitizing kinase cascade.