Factors associated with clinical trial participation for patients with renal cell carcinoma

670

Background: Clinical trials are critical for the development of new treatment paradigms for renal cell carcinoma (RCC). The primary objective of this study was to characterize the factors associated with clinical trial participation for patients with RCC. The secondary objective was to examine survival outcomes in the clinical trial and control cohorts. Methods: The National Cancer Database (NCDB) was queried for patients with RCC who were coded as having enrolled in a clinical trial. Trial patients were matched in a 1:5 ratio to controls from the same institution based on clinical stage. Sociodemographic variables were compared between the two groups and univariate and multivariate logistic regression models evaluated factors associated with clinical trial participation. Kaplan-Meier product limit estimate was used to compare overall survival (OS) between the groups. Results: From 2004-2015, 681 patients enrolled in clinical trials were included for analysis. The mean age of trial patients was 56.4 compared to 62 in the matched cohort (p<0.0001). More patients in the trial group had a Charlson-Deyo comorbidity score of 0 (81.6% vs. 73.9%, p<0.0001). On multivariate analysis, male patients (OR 1.27; 95%CI 1.06-1.54, p=0.012) and white patients (OR 1.88, 95%CI 1.23-2.87; p=0.003) were more likely to participate in a trial. Having Medicaid (OR 0.42; 95%CI 0.27-0.64; p<0.0001) or Medicare (OR 0.6; 95%CI 0.46-0.77; p<0.0001) was negatively associated with clinical trial participation. Median OS was greater among clinical trial participants than that the control cohort (106.61 vs 87.62 months, p<0.0001). Conclusions: In this contemporary analysis of RCC patients from a national hospital registry database, we found that patient sociodemographic factors remain associated with clinical trial participation and that clinical trial participants experienced superior OS. Further work, both qualitative and quantitative, is necessary to identify clinical and non-clinical barriers to research participation in order to improve the validity of RCC trials.

Opportunities and Challenges in Activity-Based Protein Profiling of Mycobacteria

Mycobacteria, from saprophytic to pathogenic species, encounter diverse environments that demand metabolic versatility and rapid adaptation from these bacteria for their survival. The human pathogen Mycobacterium tuberculosis, for example, can enter a reversible state of dormancy in which it is metabolically active, but does not increase in number, and which is believed to enable its survival in the human host for years, with attendant risk for reactivation to active tuberculosis. Driven by the need to combat mycobacterial diseases like tuberculosis, efforts to understand such adaptations have benefitted in recent years from application of activity-based probes. These studies have been inspired by the potential of these chemical tools to uncover protein function for previously unannotated proteins, track shifts in protein activity as a function of environment, and provide a streamlined method for screening and developing inhibitors. Here we seek to contextualize progress thus far with achieving these goals and highlight the unique challenges and opportunities for activity-based probes to further our understanding of protein function and regulation, bacterial physiology, and antibiotic development.

Effect of alvimopan on gastrointestinal recovery and length of hospital stay after retroperitoneal lymph node dissection for testicular cancer

Objective

Alvimopan use has reduced the length of hospital stay in patients undergoing major abdominal surgeries and radical cystectomy. Retroperitoneal lymph node dissection for testicular cancer may be associated with delayed gastrointestinal recovery prolonging hospital length of stay. We evaluate whether alvimopan is associated with enhanced gastrointestinal recovery and shorter hospital length of stay in men undergoing retroperitoneal lymph node dissection for testicular cancer.

Materials and methods

From 2010 to 2016, 29 patients underwent open, transperitoneal bilateral template retroperitoneal lymph node dissection. Data for patients who received alvimopan were prospectively collected and compared to a historical cohort of patients who did not receive alvimopan. Primary outcome measures were length of stay and recovery of gastrointestinal function. Descriptive statistics were reported. Time-to-event outcomes were evaluated using cumulative incidence curves and log rank test. Factors associated with length of stay were analyzed for correlation using multiple linear regression.

Results

Of 29 men undergoing retroperitoneal lymph node dissection, eight received alvimopan and 21 did not. The two cohorts were well matched, with no significant differences. In the alvimopan cohort compared with those who did not receive alvimopan median time to return of flatus was 2 versus 4 days (p=0.0002), and median time to first bowel movement was 2.5 versus 5 days (p=0.046), respectively. Median length of stay in the alvimopan cohort was 4 days versus 6 days in those who did not receive alvimopan (p=0.074). In adjusted analyses, receipt of alvimopan did not influence length of stay.

Conclusion

Alvimopan may facilitate gastrointestinal recovery after retroperitoneal lymph node dissection for testicular cancer. Whether this translates into reduced length of stay needs to be determined by randomized controlled trials using larger cohorts.

Level of evidence

3b.

Collapsing Glomerulopathy- A Troublemaker for the Renal Allograft: Lessons Learnt

Collapsing glomerulopathy (CG) is a well-recognized distinct morphological pattern of proliferative parenchymal injury leading to rapid graft failure. We conducted a single-center retrospective study to evaluate the prevalence, clinicopathological features, and prognosis of CG in renal transplant recepient. We analyzed 2518 renal allograft biopsies performed from 2007 to 2015 and correlated their clinicopathological features. The prevalence of CG was 0.83% (21 out of 2518) of allograft biopsies with a higher prevalence of 1.4% during the period from 2012 to 2015. Out of 21 patients, 18 (85.71%) patients had undergone live donor and 3 (14.28%) patients had undergone deceased donor renal transplant. Hypertension was observed in 3 (14.28%) patients. The mean duration of diagnosis for CG was 1.85 ± 1.91 years. Urinalysis revealed microhematuria in 5 (23.8%) patients. The mean 24 h urinary protein excretion was 4.77 ± 5.3 g and serum creatinine was 2.12 ± 1.5 mg/dl. The predominant native kidney diseases in recipients were chronic glomerulonephritis of unknown etiology in 12 (57.14%) patients and hypertensive nephropathy in 3 (14.28%) patients. CG was associated with rejection in 9 (42.85%), calcineurin-inhibitor toxicity in 2 (9.5%), and BK virus nephropathy in 1 patient. All patients received standard triple immunosuppression. Eleven (52.38%) patients developed graft failure over a mean period of 2.2 ± 1.7 years and 6 (28.57%) patients recovered with stable graft function. CG can coexist with viral infection, drug toxicity, rejection, microvascular injury, etc. CG usually presents with moderate to severe proteinuria and may lead to rapid graft dysfunction and subsequent graft failure in most of the patients.

C1q nephropathy in India: a single-center study

C1q nephropathy (C1qN) is defined by conspicuous C1q deposits in the glomerular mesangial regions of patients who do not have any evidence of systemic lupus erythematosus (SLE). We present our experience with C1qN over the last three years. In total, 1775 native renal biopsies were reviewed and dominant/co-dominant C1q mesangial deposits in patients with absence of clinical and/or serological evidence of SLE were considered as C1qN. Their clinical profile and renal function status were studied and correlated. C1qN was observed in 11 patients (0.61%), and included eight males and three females; the mean age was 36.6 years. The most common presentation was nephrotic syndrome. Hematuria was noted in eight patients (72%). The mean serum creatinine was 2.78 mg/dL. Hypertension was seen in two patients (18%). Mesangial proliferative glomerulonephritis (MePGN) was the most common histological pattern, followed by focal and segmental glomerulosclerosis and other lesions. The common codeposits along with C1q were IgM, followed by C3 and others. MePGN had better prognosis than others. To conclude, C1qN was noted in 0.61% of all renal biopsies with bimodal age distribution and may present as podocytopathy or non-podocytopathy. The prognosis depends on the morphological pattern and C1q deposits per se are not prognostic indicators.

Mesangial proliferative glomerulonephritis with acute tubule interstitial nephritis leading to acute kidney injury in influenza A (H1N1) infection

Respiratory complications and renal failure are the leading causes for morbidity and mortality due to influenza (H1N1) virus infection. There has been limited information on histopathology of H1N1 influenza-related acute kidney injury (AKI). We describe AKI with H1N1 infection in a 52-year-old female. Renal biopsy showed mesangial proliferative glomerulonephritis with acute tubule interstitial nephritis. Her condition improved rapidly with oseltamivir, fluid replacement, steroid and dialysis. Our case suggests that H1N1 infection may have a causative link to the development of mesangial proliferative glomerulonephritis with acute tubulointerstitial nephritis.

Successful three-way kidney paired donation transplantation: The first Indian report

Providing transplantation opportunities for patients with incompatible live donors through kidney paired donation (KPD) is an important strategy for easing the crisis in organ availability. KPD is can overcome the barriers when the only living potential donors are deemed unsuitable owing to an incompatibility of blood type, of human leukocyte antigen cross-match, or both. In KPD, the incompatibility problems with two donor recipient pairs can be solved by exchanging donors. In the absence of well-organized deceased donor program, or transplantation with desensitization protocol and ABO incompatible transplantation, living donor KPD promises hope to the growing number of patients suffering from end-stage renal disease in India. We report our first successful three-way KPD transplantation from India. In an era of organ shortage, this approach is relevant to encourage wider participation from KPD donors and transplant centers to prevent commercial transplantation.

Outcome of live and deceased donor renal transplantation in patients aged ≥55 years: A single-center experience

Renal transplantation (RTx) has now become an accepted therapeutic modality of choice for elderly ESRD patients. This single-center study was undertaken to evaluate the outcome of RTx in ESRD patients ≥55 years. A total of 103 patients underwent RTx 79 living related living donors [LD], 24 deceased donors [DD]) at our center. Post-transplant immunosuppression consisted of calcineurin inhibitor-based regimen. The mean donor age was 58.3 years in the LD group and 59.5 years in the DD group. Male recipients constituted 92% in LD and 75% in DD group. In living donor renal transplantation, 1- and 5-year patient survival was 93% and 83.3% respectively and death-censored graft survival was 97.3% and 92.5% respectively. There were 12.6% biopsy proven acute rejection (BPAR) episodes and 12.6% patients were lost, mainly due to infections. In deceased donor renal transplantation, 1- and 5-year patient survival was 79.1% and 74.5% respectively and death-censored graft survival was 95.8% and 85.1% respectively. There were 12.5% BPAR episodes and 25% of patients were lost, mainly due to infections. RTx in ESRD (≥55 years) patients has acceptable patient and graft survival if found to have cardiac fitness and therefore should be encouraged.

Intercity deceased donor renal transplantation: a single-center experience from a developing country

In a developing country such as India, deceased donor renal transplantation (DDRTx) accounts for only about 1% of all renal transplants (RTx). Our institute initiated an intercity DDRTx in the year 2006, which significantly increased the number of RTx. We retrieved 74 kidneys from 37 deceased donors from various cities of Gujarat from January 2006 to December 2009. We transplanted the allografts in 66 recipients and a retrospective analysis of the donor profile and management and recipient outcome was performed. The mean age of the donors was 43.3 ± 18.8 years. The causes of death included road traffic accident in 51.35% of the donors and cerebrovascular stroke in 48.65% of the donors; 83.78% of the donors required ionotropes for hemodynamic stability in addition to vigorous intravenous fluid replacement. The average urine output of the donors was 350 ± 150 mL. The organs were perfused and stored in HTK solution. The mean cold ischemia time (CIT) was 9.12 ± 5.25 h. The mean anastomosis time in the recipient was 30.8 ± 8.7 min. 57.6% of the recipients established urine output on the operating table and 42.4% developed delayed graft function. At the end of 1 month after transplantation, the mean serum creatinine was comparable to the Ahmadabad city DDRTx, although the CIT was significantly longer in the intercity patients. Intercity organ harvesting is a viable option to increase the donor pool. Distance may not be an impediment, and good recipient outcome is possible in spite of prolonged CIT in case of proper harvesting and preservation.

Successful renal transplantation from a brain-dead deceased donor with head injury, disseminated intravascular coagulation and deranged renal functions

Deceased donors (DDs) with the brain death due to head injury are the major source of organs for transplantation. The incidence of post-head injury disseminated intravascular coagulation (DIC) ranges from 24% to 50%. Many centers do not accept organs from donors with DIC due to increased risk of primary graft non-function and/or high chances of morbidity/mortality. We performed two successful renal transplants from a DD with head injury with DIC and deranged renal function. One of the recipients developed transient thrombocytopenia, but there was no evidence of DIC or delayed graft functions in either of the recipients. Over a follow-up of 1 month, both are doing well with stable graft function and hematological profile. Thus, a carefully selected DD with severe DIC even with deranged renal function is not a contraindication for organ donation if other risk factors for primary non-function are excluded. This approach will also help in overcoming organ shortage.

Outcome and prognostic factors of malaria-associated acute kidney injury requiring hemodialysis: A single center experience

Acute kidney injury (AKI) is one of the most dreaded complications of severe malaria. We carried out prospective study in 2010, to describe clinical characteristics, laboratory parameters, prognostic factors, and outcome in 59 (44 males, 15 females) smear-positive malaria patients with AKI. The severity of illness was assessed using Acute Physiology and Chronic Health Evaluation (APACHE) II, Sequential Organ Failure Assessment (SOFA) score, Multiple Organ Dysfunction Score (MODS), and Glasgow Coma Scale (GCS) scores. All patients received artesunate and hemodialysis (HD). Mean age of patients was 33.63 ± 14 years. Plasmodium falciparum malaria was seen in 76.3% (n = 45), Plasmodium vivax in 16.9% (n = 10), and mixed infection in 6.8% (n = 4) patients. Presenting clinical features were fever (100%), nausea-vomiting (85%), oliguria (61%), abdominal pain/tenderness (50.8%), and jaundice (74.5%). Mean APACHE II, SOFA, MODS, and GCS scores were 18.1 ± 3, 10.16 ± 3.09, 9.71 ± 2.69, and 14.15 ± 1.67, respectively, all were higher among patients who died than among those who survived. APACHE II ≥20, SOFA and MODS scores ≥12 were associated with higher mortality (P < 0.05). 34% patients received blood component transfusion and exchange transfusion was done in 15%. Mean number of HD sessions required was 4.59 ± 3.03. Renal biopsies were performed in five patients (three with patchy cortical necrosis and two with acute tubular necrosis). 81.3% of patients had complete renal recovery and 11.8% succumbed to malaria. Prompt diagnosis, timely HD, and supportive therapy were associated with improved survival and recovery of kidney functions in malarial with AKI. Mortality was associated with higher APACHE II, SOFA, MODS, GCS scores, requirement of inotrope, and ventilator support.

Post-renal transplant cytomegalovirus infection: study of risk factors

OBJECTIVES

Cytomegalovirus (CMV) is a common opportunistic infection following renal transplantation (RTx). It responds promptly to antiviral treatment. The mortality rate reaches 90% if untreated. Identification of risk factors helps in the early diagnosis of CMV. We studied demographic features, risk factors, and outcomes associated with CMV infection in RTx recipients despite ganciclovir prophylaxis.

MATERIALS AND METHODS

We reviewed 720 RTx recipients between 2007 and 2009. We examined the serostatus of the donor and recipient before transplantation using an enzyme-linked immunosorbent assay, and diagnosed CMV infections in recipients by CMV DNA detection with a polymerase chain reaction.

RESULTS

A total of 42 of 750 (5.6%) patients were identified to display CMV infection (69.1%) or disease (30.9%). Their mean age was 34 ± 13.5 years, with 80.9% men. CMV serologic status was D+/R- in 21.4% and D+/R+ in 59.5% patients. Fever, malaise (76.2%), and leukopenia (52.3%) were the commonest presenting symptoms; diabetes (30.9%) and hepatitis C virus (28.6%) the commonest comorbid conditions. Risk factors were triple drug immunosuppression (47.6%), antithymocyte globulin ATG induction (54.8%), and a rejection episode (26.1%) and methylprednisolone (76.2%) which were more common in CMV disease than infection. Mean CMV DNA at diagnosis was 78,803; 71.2% patients developed CMV within 6 months posttransplantation, the majority occurring after 3 months. With a mean follow-up of 4 ± 1.9 years, patient and graft survival rates were 85.7% and 81% with a mean serum creatinine value of 1.83 ± 12 mg/dL.

CONCLUSIONS

Universal CMV prophylaxis was associated with a low incidence (5.6%) and mild form of CMV disease among our patients.

World kidney day 2010: medical aspects of 10 live-donor renal transplantations in a single center from a developing country

BACKGROUND

World Kidney Day (WKD) has become the most widely celebrated event associated with kidney disease in the world and the most successful effort to raise awareness among both the general public and government health officials about the dangers of kidney disease. We celebrated WKD 2010 in a unique way by performing 10 live-donor renal transplantations (RTx) on March 11, 2010.

PATIENTS AND METHODS

We report a single-center experience on RTx vis-à-vis patient/graft survival, graft function in terms of serum creatinine (SCr) level, and rejection episodes in 10 live-donor RTx performed on WKD. Recipient diseases leading to end-stage renal disease (ESRD) were chronic glomerulonephritis (60%), benign nephrosclerosis (20%), and chronic interstitial nephritis (20%). Mean recipient age was 35 ± 8.7 years. Nine recipients were males. Mean donor age was 37 ± 8.7 years, Nine donors were females. Donors were spouse (n = 6), mother (n = 2), sister (n = 1), and extended family member (n = 1), with mean HLA match 1.8 ± 1.48. All patients received steroids, calcinueurin inhibitors, and mycophenolate mofetil/azathioprime for maintenance immunosuppression.

RESULTS

During a mean follow-up time of 18 months, patient and graft survival rates were 90% and 90%, respectively, with a mean SCr level of 1.21 mg/dL; 20% had biopsy-proven acute rejection. One patient died due to infection after antirejection therapy.

CONCLUSION

RTx has acceptable graft and patient survival. RTx is the best cost-effective therapeutic modality for patients suffering from ESRD and should be encouraged in view of organ shortage on events such as WKD. To our knowledge, this is the first report from a developing country on 10 successful RTx on WKD.

Deceased donor organ transplantation: A single center experience

Renal transplantation (RTx) is the best therapeutic modality for patient suffering from end-stage renal disease (ESRD). Deceased donor organ transplantation (DDOT) accounts for <4% of RTx in India. We report 4 years single centre experience on DDOT vis-à-vis patient/graft survival, graft function in terms of serum creatinine (SCr), rejection episodes, and delayed graft function in 160 DDOT. Between January 2006 to December 2009, 160 RTx from 89 donors were performed, of which 25.2% were expanded criteria donors. Majority of the donors were brain dead due to road traffic/cerebrovascular accidents. The commonest recipient diseases leading to ESRD were chronic glomerulonephritis (49%), diabetes mellitus (10%), and benign nephrosclerosis (10%). Mean recipient/donor age was 35.6±14.68 and 44.03±18.19 years. Mean dialysis duration pretransplantation was 15.37±2.82 months. Mean cold ischemia time was 5.56±2.04 hours. All recipients received single dose rabbit-anti-thymocyte globulin induction and steroids, mycophenolate mofetil/calcinueurin inhibitor for maintenance of immunosuppression. Delayed graft function was observed in 30.6% patients and 14% had biopsy proven acute rejection. Over mean follow-up of 2.35±1.24 years, patient and graft survival rates were 77.5% and 89.3% with mean SCr of 1.40±0.36 mg/dl. DDOT has acceptable graft/patient survival over 4 years follow-up and should be encouraged in view of organ shortage.

Nocardia infection in a renal transplant recipient

Opportunistic infection occurs in up to 20% renal transplant patients and is associated with a high mortality. We report a 47-year-old diabetic female with 1-year-old deceased donor renal allograft on triple drug immunosuppression. She developed cytomegalovirus retinitis at ten months post-transplant followed by nocardiasis manifested by hemiparesis with comatose state due to lumbar epidural and multiple brain abscesses, in spite of immediately curtailing immunosuppression. She recovered with linezolid and cotrimoxazole and was discharged two weeks later. She is maintaining stable graft function with serum creatinine 1.4 mg/dL on cyclosporin 2.5 mg/kg/day and prednisone10 mg/day with maintenance therapy for nocardiasis.

Safety and efficacy of angiotensin converting enzyme inhibitors and angiotensin receptor blockers in chronic allograft injury

Angiotensin II plays a crucial role in the development of chronic allograft injury (CAI). Clinical experience with angiotensin converting enzyme inhibitor (ACEI) and angiotensin receptor blockade (ARBS) in CAI has unfortunately been limited. We carried out a prospective one year single center case controlled study to analyze the effect of ACEI /ARBS on the progression of CAI and in decreasing proteinuria. One hundred patients with CAI were evaluated. Of the 100 patients, 50 were selected to receive ACEI/ ARBS (group 1) and 50 managed without ACEI/ARBS (group 2). Their remaining management was similar in both the groups. Patients with hyperkalemia, history of allergic reactions, ACEI/ARBS intake and pregnancy were excluded. Average time for development of CAI was 19.6 ± 12.7 months in group 1 vs. 20.8 ± 12.8 in group 2. In group 1, mean systolic/diastolic BP was 136/82 mmHg at the time of establishment of CAI and 124/76 mmHg at the end of one year, and in group 2, it was 138/86 mmHg vs. 126/80 mmHg, respectively. Mean glomerular filtration rate (GFR) was 48.78 ± 13.4 in the former vs. 44.23 ± 8.14 in the latter. ACEI/ARBS administration was associated with stabilization of serum creatinine. GFR was maintained up to one year after CAI. Group 1 had a decrease in proteinuria by 1.41 g/day as compared with group 2 with proteinuria of 0.83 g/day. ACEI/ARBS administration is beneficial in CAI for BP control and significant decrease in proteinuria along with the stabilization of graft function.

Immunoglobulin M nephropathy nephropathy in adults and adolescents in India: a single-center study of natural history

BACKGROUND

Immunoglobulin M nephropathy (IgMN) is an idiopathic glomerulonephritis (GN) usually presenting clinically as steroid resistant/dependent nephrotic syndrome (NS) with pathology of mesangial proliferative GN or focal and segmental glomerulosclerosis with diffuse predominant mesangial IgM deposits. Not much information is available about its natural history. This is the first Indian study to our knowledge on IgMN in adults and adolescents.

MATERIALS AND METHODS

We evaluated renal biopsies performed at our center between January,'04 to September,'09. Biopsies of all adolescents and adults were evaluated for IgMN and we studied their age, gender distribution, blood pressure (BP), disease duration, steroid/immunosuppressive management and serial serum creatinine (SCr), urinary proteins, and BP values. Patients with other systemic diseases/infections and children were excluded.

RESULTS

IgMN constituted 4.3% of 2702 adult renal biopsies. No significant gender predilection was noted. Males presented at average age of 23.1 years, females at 30 years. Steroid-dependent NS was the commonest presentation noted in 75% followed by steroid-resistant NS. Hypertension was noted in 10% patients. Mesangial proliferative GN (MePGN) was commonest histopathological finding noted in 74.4%, followed by focal segmental glomerulosclerosis (FSGS) in 16.2%, and minimal change disease (MCD) in 9.4% biopsies. Sole IgM deposits were noted in 88.5%. All MCD, 35.6% MePGN reached remission, FSGS progressed to renal failure by 1 year. Hypertension, proteinuria, interstitial fibrosis, and FSGS were bad prognosticators.

CONCLUSIONS

This is the first Indian study of IgMN in adults and adolescents carried out over a period of 5.8 years, which has shown that hypertension, proteinuria, and interstitial fibrosis at presentation have bad prognosis.

Segregation of gangliosides GM1 and GD3 on cell membranes, isolated membrane rafts, and defined supported lipid monolayers

Lateral assemblies of sphingolipids, glycosphingolipids and cholesterol, termed rafts, are postulated to be present in biological membranes and to function in important cellular phenomena. We probed whether rafts are heterogeneous by determining the relative distribution of two gangliosides, GM1 and GD3, in artificial supported monolayers, in intact rat primary cerebellar granule neurones, and in membrane rafts isolated from rat cerebellum. Fluorescence resonance energy transfer (FRET) using fluorophore-labelled cholera toxin B subunit (which binds GM1) and mAb R24 (which binds GD3) revealed that GM1 spontaneously self-associates but does not co-cluster with GD3 in supported monolayers and on intact neurones. Cholera toxin and immunocytochemical labelling of isolated membrane rafts from rat cerebellum further demonstrated that GM1 does not co-localise with GD3. Furthermore, whereas the membrane raft resident proteins Lyn and caveolin both co-localise with GD3 in isolated membrane rafts, GM1 appears in separate and distinct aggregates. These data support prior reports that membrane rafts are heterogeneous, although the mechanisms for establishing and maintaining such heterogeneity remain to be determined.

A PPARgamma mutant serves as a dominant negative inhibitor of PPAR signaling and is localized in the nucleus

The peroxisomal proliferator-activated receptors (PPARs) are members of the nuclear receptor superfamily that act as ligand-activated transcription factors. PPARgamma plays a critical role in regulating adipocyte differentiation and lipid metabolism. Recently, thiazolidinedione (TZD) and select non-TZD antidiabetic agents have been identified as PPARgamma agonists. To further characterize this receptor subclass, a mutant hPPARgamma lacking five carboxyl-terminal amino acids was produced (hPPARgamma2Delta500). In COS-1 cells transfected with PPAR-responsive reporter constructs, the mutant receptor could not be activated by a potent PPARgamma agonist. When cotransfected with hPPARgamma2 or hPPARalpha, hPPARgamma2Delta500 abrogated wild-type receptor activity in a dose-responsive manner. hPPARgamma2Delta500 was also impaired with respect to binding of a high-affinity radioligand. In addition, its conformation was unaffected by normally saturating concentrations of PPARgamma agonist as determined by protease protection experiments. Electrophoretic mobility shift assays demonstrated that hPPARgamma2Delta500 and hPPARgamma2 both formed heterodimeric complexes with human retinoidxreceptor alpha (hRXRalpha) and could bind a peroxisome proliferator-responsive element (PPRE) with similar affinity. Therefore, hPPARgamma2Delta500 appears to repress PPAR activity by competing with wild type receptor to dimerize with RXR and bind the PPRE. In addition, the mutant receptor may titrate out factors required for PPAR-regulated transcriptional activation. Both hPPARgamma2 and hPPARgamma2Delta500 localized to the nucleus of transiently transfected COS-1 cells as determined by immunofluorescence using a PPARgamma-specific antibody. Thus, nuclear localization of PPARgamma occurs independently of its activation state. The dominant negative mutant, hPPARgamma2Delta500, may prove useful in further studies to characterize PPAR functions both in vitro and in vivo

Receptor-interacting protein 140 interacts with and inhibits transactivation by, peroxisome proliferator-activated receptor alpha and liver-X-receptor alpha

Receptor interacting protein 140 (RIP140), a previously identified putative ligand-dependent coactivator of nuclear hormone receptors, was isolated by yeast two-hybrid cloning as a factor that interacts with peroxisome proliferator-activated receptor alpha (PPARalpha). This interaction in yeast required the integrity of the carboxyl-terminal, ligand-dependent activation domain of PPARalpha. However, protein binding studies carried out in vitro showed that full-length RIP140 bound efficiently to PPARalpha in the absence of exogenously added ligand. RIP140 also bound strongly to the liver-X-receptor (LXRalpha) in the absence of an activator for this receptor. In contrast, a strong interaction of RIP140 with the PPARalpha and LXRalpha heterodimerization partner retinoid-X-receptor alpha (RXRalpha) required the presence of its cognate ligand, 9-cis retinoic acid. Transfection analysis in mammalian cells demonstrated that RIP140 antagonized PPARalpha/RXRalpha- and LXRalpha/RXRalpha-mediated signaling. Our findings identify RIP140 as a novel modulator of transcriptional activation mediated by PPARalpha and LXRalpha and indicate that RIP140 can also bind to nuclear hormone receptors in a ligand-independent manner and repress their activity.

Glycosaminoglycans bind to homologous cardiotoxins with different specificity

We have reported that some cardiotoxins (CTXs), homologous basic polypeptides of cobra venom, bind strongly to heparin. Herein we show that CTXs from spitting cobra venom bind avidly to chondroitin-6-sulfate (CS6) and dermatan sulfate (DS), the glycosaminoglycans (GAGs) abounding in the cornea and elsewhere. We compared the binding strength of Tgamma, a major component of spitting cobra, Naja nigricollis, venom with that of CTX A3, a major component of Naja atra venom to various GAGs including CS6, chondroitin-4-sulfate (CS4), DS, keratan sulfate (KS), hyaluronan (HYA), and heparin. The binding strength of Tgamma followed the order CS6 > KS > HYA > DS > CS4 > heparin, whereas that of CTX A3 was heparin > KS > CS4 > DS > CS6 > HYA. The binding specificity displayed by different CTXs toward GAGs is impressive, given the high homology among CTXs and among GAGs. Strong binding of Tgamma to CS6, rather than to the highly anionic and versatile cousin, heparin, implies specific interaction with CS6. Heparin, at high concentration, displaced CS6 from CS6-Tgamma and CS6-A3 complexes. We also show that corneal CS/DS likely allow Tgamma to bind to corneal epithelium. CTXs of spitting cobra venom are known to cause corneal opacity and/or blindness. Taken together with these observations, our results suggest that corneal CS/DS play a role in the action of CTX in the eye. Most importantly, the present results establish CTXs as cationic, readily available, avidly binding ligands of CS/DS.

SH3 domain of Bruton's tyrosine kinase can bind to proline-rich peptides of TH domain of the kinase and p120cbl

X-linked agammaglobulinemia (XLA), an inherited disease, is caused by mutations in the Bruton's tyrosine kinase (BTK). The absence of functional BTK leads to failure of B-cell differentiation; this incapacitates antibody production in XLA patients, who suffer from recurrent, sometimes lethal, bacterial infections. BTK plays an important role in B-cell development; it interacts with several proteins in the context of signal transduction. Point mutation in the BTK gene that leads to deletion of C-terminal 14 aa residues of BTK SH3 domain was found in a patient family. To understand the role of BTK, we studied binding of BTK SH3 domain (aa 216-273, 58 residues) and truncated SH3 domain (216-259, 44 residues) with proline-rich peptides; the first peptide constitutes the SH3 domain of BTK, while the latter peptide lacks 14 amino acid residues of the C terminal. Proline-rich peptides selected from TH domain of BTK and p120cbl were studied. It is known that BTK TH domain binds to SH3 domains of various proteins. We found that BTK SH3 domain binds to peptides of BTK TH domain. This suggests that BTK SH3 and TH domains may associate in inter- or intramolecular fashion, which raises the possibility that the kinase may be regulating its own activity by restricting the availability of both its ligand-binding modules. We also found that truncated SH3 domain binds to BTK TH domain peptide less avidly than does normal SH3 domain. Also, we show that the SH3 and truncated SH3 domains bind to peptide of p120cbl, but the latter domain binds weakly. It is likely that the truncated SH3 domain fails to present to the ligand the crucial residues in the correct context, hence the weaker binding. These results delineate the importance of C-terminal in binding of SH3 domains and indicate also that improper folding and the altered binding behavior of mutant BTK SH3 domain likely leads to XLA.

Identification by site-directed mutagenesis of three arginines in uncoupling protein that are essential for nucleotide binding and inhibition

Primary regulation of uncoupling protein is mediated by purine nucleotides, which bind to the protein and allosterically inhibit fatty acid-induced proton transport. To gain increased understanding of nucleotide regulation, we evaluated the role of basic amino acid residues using site-directed mutagenesis. Mutant and wild-type proteins were expressed in yeast, purified, and reconstituted into liposomes. We studied nucleotide binding as well as inhibition of fatty acid-induced proton transport in wild-type and six mutant uncoupling proteins. None of the mutations interfered with proton transport. Two lysine mutants and a histidine mutant had no effect on nucleotide binding or inhibition. Arg83 and Arg182 mutants completely lost both the ability to bind nucleotides and nucleotide inhibition. Surprisingly, the Arg276 mutant exhibited normal nucleotide binding, but completely lost nucleotide inhibition. To account for this dissociation between binding and inhibition, we propose a three-stage binding-conformational change model of nucleotide regulation of uncoupling protein. We have now identified three nucleotides by site-directed mutagenesis that are essential for nucleotide interaction with uncoupling protein.

Cloning and some novel characteristics of mitochondrial Hsp70 from Chinese hamster cells

The cDNA for Chinese hamster mitochondrial Hsp70 (mHsp70) was cloned and sequenced using a polymerase chain reaction probe based on conserved regions in the Hsp70 family of proteins. The encoded protein consists of 679 amino acids which includes a N-terminal mitochondrial targeting sequence of 46 amino acids. The mHsp70 protein contains several sequence signatures that are characteristics of prokaryotic and eukaryotic organellar Hsp70 homologs. In a phylogenetic tree based on Hsp70 sequences, it branches with the gram-negative proteobacteria, supporting the endosymbiotic origin of mitochondria from this group of prokaryotes. The mHsp70 cDNA was transcribed and translated in vitro and its import into isolated rat heart mitochondria was examined. The precursor mHsp70 was converted into a mature form of lower molecular mass (approximately 71 kDa) which became resistant to trypsin digestion. The import of mHsp70 into mitochondria was not observed in the presence of an uncoupler of energy metabolism or when the N-terminal presequence was lacking. The cDNA for mHsp70 was expressed in Escherichia coli and a polyclonal antibody to the purified recombinant protein was raised. The antibody shows no cross-reactivity to recombinant cytosolic Hsp70 protein and in 2-D gel blots it reacted specifically with the mHsp70 protein only. In immunofluorescence experiments, the antibody predominantly labeled mitochondria, and the observed labeling pattern was identical to that seen with a monoclonal antibody to the mitochondrial Hsp60 chaperonin. The affinity-purified antibody to mHsp70 was also employed to examine the subcellular distribution of the protein by cryoelectron microscopy and the immunogold-labeling technique. In these experiments, in addition to mitochondria, labeling with mitochondrial Hsp70 antibody was also observed on the plasma membrane and in unidentified cytoplasmic vesicles and granules. These studies raise the possibility that similar to the Hsp60 chaperonin and a number of other mitochondrial proteins, mHsp70 may have an extramitochondrial role.

Analysis of binding of cobra cardiotoxins to heparin reveals a new beta-sheet heparin-binding structural motif

Heparin and heparan sulfate have recently been shown to bind to snake cardiotoxin (CTX) and to potentiate its penetration into phospholipid monolayer under physiological ionic conditions. Herein we analyze the heparin-binding domain of CTX using 10 CTXs from Taiwan and African cobra venom. We also performed computer modeling to obtain more information of the binding at molecular level. The results provide a molecular model for interaction of CTX-heparin complex where the cationic belt of the conserved residues on the concave surface of three finger beta-sheet polypeptides initiates ionic interaction with heparin-like molecules followed by specific binding of Lys residues near the tip of loop 2 of CTX. The dissociation constants of CTXs differ by as much as 4 orders of magnitude, ranging from approximately 140 microM for toxin gamma to approximately 20 nM for CTX M3, depending on the presence of Lys residues near the tip of loop 2. High affinity heparin binding becomes possible due to the presence of Arg-28, Lys-33, or the so-called consensus heparin binding sequence of XKKXXXKRX near the tip of the loop. The well defined three-finger loop structure of CTX provides an interesting template for the design of high affinity heparin-binding polypeptides with beta-sheet structure. The finding that several cobra CTXs and phospholipase A2 bind to heparin with different affinity may provide information on the synergistic action of the two venom proteins.

Heparin and heparan sulfate bind to snake cardiotoxin. Sulfated oligosaccharides as a potential target for cardiotoxin action

Cardiotoxins (CTXs) from cobra venom show cytotoxicity toward several cell types. They cause systolic heart arrest and severe tissue necrosis. Their interaction with phospholipids is established but by itself fails to explain the specificity of these toxins; other component(s) of membrane must, therefore, intervene to direct them toward their target. We herein show, for the first time, that sulfated glycosaminoglycans, heparin, heparan sulfate (HS), chondroitin sulfate (CS), and dermatan sulfate (DS), interact with CTX A3, a major component of Taiwan cobra venom, by use of affinity chromatography, circular dichroism, absorbance, and fluorescence intensity and anisotropy measurements. The relative strength of binding, determined by the NaCl concentration required to dissociate the CTX-glycosaminoglycan complex, varied as follows: heparin > DS > CS > HS. In physiological buffer (8 mM Na2HPO4, 2.7 mM KCl, 1.8 mM KH2PO4, 138 mM NaCl, pH 7.4), however, only heparin and HS bound to CTX, with respective dissociation constants of 1.4 and 16 microM, while CS and DS failed to exhibit well defined binding behavior, as indicated by fluorescence measurements. We estimate that CTX makes 3-4 ionic contacts with heparin based on a salt-dependent binding study and that approximately 40% of binding free energy is derived from purely electrostatic interactions under physiological conditions. Sulfated pentasaccharide may be sufficient to bind to CTX. We also found that heparin accentuates the penetration of CTX into phospholipid membranes as analyzed by Langmuir monolayer measurement. In view of these results we propose that heparin-like moieties of the cell surface may modulate the action of CTX.

Stability and folding of the SH3 domain of Bruton's tyrosine kinase

Bruton's tyrosine kinase (BTK) plays an important role in B cell development. Deletion of C-terminal 14 amino acids of the SH3 domain of BTK results in X-linked agammaglobulinemia (XLA), an inherited disease. We report here on the stability and folding of SH3 domain of BTK. Peptides corresponding to residues 216-273 (58 residues) and 216-259 (44 residues) of BTK SH3 domain were synthesized by solid phase methods; the first peptide constitutes the entire SH3 domain of BTK while the latter peptide lacks 14 amino acid residues of the C-terminal. The 58 amino acid peptide forms mainly a beta-barrel type folding unit. Although small and lacking disulfide bonds, this peptide is extremely stable to thermal denaturation. Based on circular dichroism measurements, its melting temperature was found to be high, 82 degrees C at pH 6.0. However, the Gibbs free energy (delta GH2O) of the intrinsic stability and thermodynamic spontaneity of unfolding were found to be low, 2.6 kcal/mol by Gdn.HCl denaturation experiments, as compared to 12 kcal/mol obtained for larger single domain proteins, indicating poor stability of SH3 domain. Addition of 500 mM of Na2SO4 increased the free energy change delta GH2O to 4.0 kcal/mol, suggesting an ionic strength effect. The truncated peptide fails to fold correctly and adopts random coil conformation in contrast to 58 amino acid beta-barrel peptide, which exhibits high thermal stability but normal or low stability at ambient temperature. These results, to our knowledge the first to delineate the importance of C-terminal in structural integrity of SH3 domains, indicate also that improper folding and/or poor stability of mutant SH3 domain in BTK likely causes XLA.

The orphan nuclear hormone receptor LXR alpha interacts with the peroxisome proliferator-activated receptor and inhibits peroxisome proliferator signaling

The yeast two-hybrid system was used to isolate novel cellular factors that interact with the mouse peroxisome proliferator-activated receptor alpha (PPARalpha). One of the interacting clones isolated encoded LXRalpha, a recently described human orphan nuclear hormone receptor. LXRalpha bound directly to PPARalpha, as well as to the common heterodimerization partner 9-cis-retinoic acid receptor (RXRalpha). LXRalpha did not form a DNA binding complex with PPARalpha on synthetic hormone response elements composed of direct repeats of the TGACCT consensus half-site or on naturally occurring peroxisome proliferator response elements (PPREs) or LXRalpha response elements. However, LXRalpha inhibited binding of PPARalpha/RXRalpha heterodimers to PPREs, and coexpression of LXRalpha in mammalian cells antagonized peroxisome proliferator signaling mediated by PPARalpha/RXRalpha in vivo. These findings identify a novel partner for PPARalpha and suggest that LXRalpha plays a role in modulating PPAR-signaling pathways in the cell.

A single mutation in uncoupling protein of rat brown adipose tissue mitochondria abolishes GDP sensitivity of H+ transport

The uncoupling protein is one of a family of mitochondrial transport proteins involved in energy metabolism. It dissipates oxidative energy to generate heat, either by catalyzing proton transport directly or by catalyzing fatty acid anion transport, thus enabling fatty acids to act as cycling protonophores. This transport process is tightly regulated by purine nucleotides. We have expressed uncoupling protein in yeast and examined its proton transport activity after its reconstitution into proteoliposomes. A directed change of Arg276 to Leu or Gln completely abolished nucleotide inhibition of protonophoretic action of the reconstituted mutant uncoupling proteins without affecting the transport process. Arg276 is the first residue of functional importance to be identified in uncoupling protein. Mutation of the homologous residue in the yeast ADP/ATP translocator prevented the growth of yeast on a nonfermentable carbon source, presumably by interfering with nucleotide exchange (Nelson, D. R., Lawson, J. E., Klingenberg, M., and Douglas, M. G. (1993) J. Mol. Biol. 230, 1159-1170). Demonstration of the essential role of a single homologous residue in protein-nucleotide interaction within these two transporters is the first direct evidence that uncoupling protein and the ADP/ATP translocator belong to the same gene family.

Functional reconstitution of rat uncoupling protein following its high level expression in yeast

Small mammals, including human infants, rely on nonshivering thermogenesis for a substantial portion of their body heat during exposure to cold. This thermogenesis is mediated in large part by the uncoupling protein, which is found exclusively within the inner membrane of brown adipose tissue mitochondria. The sole function of uncoupling protein is to provide a regulated transport pathway for electrophoretic back-flux of H+ ions into the mitochondrial matrix, thereby dissipating the protonmotive force and producing heat. Thus, uncoupling protein is unique with respect to both its physiological role and its tissue expression. We have now achieved high level expression of rat uncoupling protein in yeast, with import into yeast mitochondria at levels, 70-100 micrograms/mg of mitochondrial protein, similar to those observed in brown adipose tissue mitochondria from cold-adapted rats. When the expressed protein was purified and reconstituted into liposomes, the proteoliposomes exhibited GDP-sensitive proton and chloride uniports that were inhibited by GDP with Ki values similar to those obtained with native protein. Moreover, the molecular activities of the expressed protein with respect to Cl- and H+ transport were indistinguishable from those of native protein. The availability of unlimited amounts of functional, expressed uncoupling protein will now permit application of site-directed mutagenesis to the many intriguing aspects of uncoupling protein structure and function.

Mitochondrial import of the human chaperonin (HSP60) protein

The mitochondrial import of a member of the "chaperonin" group of proteins which play an essential role in the import of protein into organelles and their subsequent proper folding has been examined. The cDNA for human hsp60 (synonyms: GroEL homolog, P1) was transcribed and translated in vitro and its import into isolated rat heart mitochondria examined. The protein was converted into a mature form of lower molecular mass (= 58 kDa) which was resistant to trypsin treatment. The import of human hsp60 into mitochondria was inhibited in the presence of an uncoupler and also no import occurred when the N-terminal presequence was lacking. These results indicate that the chaperonin protein(s) are transported into mitochondria by a process similar to other imported mitochondrial proteins. Our results also indicate that although the P1 protein precursor was efficiently imported into mitochondria, in comparison to precursors of other mitochondrial proteins (viz. ornithine carbamoyltransferase and uncoupling protein) much less binding of pre P1 to mitochondria was observed. The significance of this latter observation at present is unclear.

Rabbit brown adipose tissue uncoupling protein MRNA: use of only one of two polyadenylation signals in its processing

A cDNA containing the complete coding sequence of rabbit brown adipose tissue uncoupling protein was isolated and sequenced. The coding region is 80.6% identical to rat UCP cDNA and the protein is about 86% identical to the rat and hamster proteins. Despite the presence of 2 AATAAA polyadenylation consensus sequences in rabbit UCP cDNA, only one rabbit UCP mRNA was detected indicating that only the 3'-downstream signal is used in contrast to rat and mouse where both are used.