Mechanisms of nucleophosmin (NPM)-mediated regulated cell death elucidated by Hsp70 during renal ischemia.

Nucleophosmin (NPM), a nucleolar-based protein chaperone, promotes Bax-mediated mitochondrial injury and regulates cell death during acute kidney injury. However, the steps that transform NPM from an essential to a toxic protein during stress are unknown. To localize NPM-mediated events causing regulated cell death during ischemia, wild type (WT) and Hsp70 mutant proteins with characterized intracellular trafficking defects that restrict movement to either the nucleolar region (M45) or cytosol (985A) were expressed in primary murine proximal tubule epithelial cells (PTEC) harvested from Hsp70 null mice. After ischemia in vitro, PTEC survival was significantly improved and apoptosis reduced in rank order by selectively overexpressing WT > M45 > 985A Hsp70 proteins. Only Hsp70 with nuclear access (WT and M45) inhibited T95 NPM phosphorylation responsible for NPM translocation and also reduced cytosolic NPM accumulation. In contrast, WT or 985A > M45 significantly improved survival in Hsp70 null PTEC that expressed a cytosol-restricted NPM mutant, more effectively bound NPM, and also reduced NPM-Bax complex formation required for mitochondrial injury and cell death. Hsp70 knockout prevented the cytoprotective effect of suppressing NPM in ischemic PTEC and also increased cytosolic NPM accumulation after acute renal ischemia in vivo, emphasizing the inhibitory effect of Hsp70 on NPM-mediated toxicity. Distinct cytoprotective mechanisms by wild type and mutant Hsp70 proteins identify dual nuclear and cytosolic events that mediate NPM toxicity during stress-induced apoptosis and are rational targets for therapeutic AKI interventions. Antagonizing these early events in regulated cell death promotes renal cell survival during experimental AKI.

T95 nucleophosmin phosphorylation as a novel mediator and marker of regulated cell death in acute kidney injury.

The function of site-specific phosphorylation of nucleophosmin (NPM), an essential Bax chaperone, in stress-induced cell death is unknown. We hypothesized that NPM threonine 95 (T95) phosphorylation both signals and promotes cell death. In resting cells, NPM exclusively resides in the nucleus and T95 is nonphosphorylated. In contrast, phosphorylated T95 NPM (pNPM T95) accumulates in the cytosol after metabolic stress, in multiple human cancer cell lines following γ-radiation, and in postischemic human kidney tissue. Based on the T95 phosphorylation consensus sequence, we hypothesized that glycogen synthase kinase-3ß (GSK-3ß) regulates cytosolic NPM translocation by phosphorylating T95 NPM. In a cell-free system, GSK-3ß phosphorylated a synthetic NPM peptide containing T95. In vitro, bidirectional manipulation of GSK-3ß activity substantially altered T95 phosphorylation, cytosolic NPM translocation, and cell survival during stress, mechanistically linking these lethal events. Furthermore, GSK-3ß inhibition in vivo decreased cytosolic pNPM T95 accumulation in kidney tissue after experimental ischemia. In patients with acute kidney injury, both cytosolic NPM accumulation in proximal tubule cells and NPM-rich intratubular casts were detected in frozen renal biopsy tissue. These observations show, for the first time, that GSK-3ß promotes cell death partly by phosphorylating NPM at T95, to promote cytosolic NPM accumulation. T95 NPM is also a rational therapeutic target to ameliorate ischemic renal cell injury and may be a universal injury marker in mammalian cells.

Nucleophosmin Phosphorylation as a Diagnostic and Therapeutic Target for Ischemic AKI.

Background Ischemic AKI lacks a urinary marker for early diagnosis and an effective therapy. Differential nucleophosmin (NPM) phosphorylation is a potential early marker of ischemic renal cell injury and a therapeutic target.Methods Differential NPM phosphorylation was assessed by mass spectrometry in NPM harvested from murine and human primary renal epithelial cells, fresh kidney tissue, and urine before and after ischemic injury. The biologic behavior and toxicity of NPM was assessed using phospho-NPM mutant proteins that either mimic stress-induced or normal NPM phosphorylation. Peptides designed to interfere with NPM function were used to explore NPM as a therapeutic target.Results Within hours of stress, virtually identical phosphorylation changes were detected at distinct serine/threonine sites in NPM harvested from primary renal cells, tissue, and urine. A phosphomimic NPM protein that replicated phosphorylation under stress localized to the cytosol, formed monomers that interacted with Bax, a cell death protein, coaccumulated with Bax in isolated mitochondria, and significantly increased cell death after stress; wild-type NPM or a phosphomimic NPM with a normal phosphorylation configuration did not. Three renal targeted peptides designed to interfere with NPM at distinct functional sites significantly protected against cell death, and a single dose of one peptide administered several hours after ischemia that would be lethal in untreated mice significantly reduced AKI severity and improved survival.Conclusions These findings establish phosphorylated NPM as a potential early marker of ischemic AKI that links early diagnosis with effective therapeutic interventions.

Blocking peptides and molecular mimicry as treatment for kidney disease.

Protein mimotopes, or blocking peptides, are small therapeutic peptides that prevent protein-protein interactions by selectively mimicking a native binding domain. Inexpensive technology facilitates straightforward design and production of blocking peptides in sufficient quantities to allow preventive and therapeutic trials in both in vitro and in vivo experimental disease models. The kidney is an ideal peptide target, since small molecules undergo rapid filtration and efficient bulk absorption by tubular epithelial cells. Because the half-life of peptides is markedly prolonged in the kidneys compared with the bloodstream, blocking peptides are an attractive tool for treating diverse renal diseases, including ischemia, proteinuric states, such as membranous nephropathy and focal and segmental glomerulosclerosis, and renal cell carcinoma. Therapeutic peptides represent one of the fastest-growing reagent classes for novel drug development in human disease, partly because of their ease of administration, high binding affinity, and minimal off-target effects. This review introduces the concepts of blocking peptide design, production, and administration and highlights the potential use of therapeutic peptides to prevent or treat specific renal diseases.

Proteinuria causes dysfunctional autophagy in the proximal tubule.

Proteinuria is a major risk factor for chronic kidney disease progression. Furthermore, exposure of proximal tubular epithelial cells to excess albumin promotes tubular atrophy and fibrosis, key predictors of progressive organ dysfunction. However, the link between proteinuria and tubular damage is unclear. We propose that pathological albumin exposure impairs proximal tubular autophagy, an essential process for recycling damaged organelles and toxic intracellular macromolecules. In both mouse primary proximal tubule and immortalized human kidney cells, albumin exposure decreased the number of autophagosomes, visualized by the autophagosome-specific fluorescent markers monodansylcadaverine and GFP-LC3, respectively. Similarly, renal cortical tissue harvested from proteinuric mice contained reduced numbers of autophagosomes on electron micrographs, and immunoblots showed reduced steady-state LC3-II content. Albumin exposure decreased autophagic flux in vitro in a concentration-dependent manner as assessed by LC3-II accumulation rate in the presence of bafilomycin, an H+-ATPase inhibitor that prevents lysosomal LC3-II degradation. In addition, albumin treatment significantly increased the half-life of radiolabeled long-lived proteins, indicating that the primary mechanism of degradation, autophagy, is dysfunctional. In vitro, mammalian target of rapamycin (mTOR) activation, a potent autophagy inhibitor, suppressed autophagy as a result of intracellular amino acid accumulation from lysosomal albumin degradation. mTOR activation was demonstrated by the increased phosphorylation of its downstream target, S6K, with free amino acid or albumin exposure. We propose that excess albumin uptake and degradation inhibit proximal tubule autophagy via an mTOR-mediated mechanism and contribute to progressive tubular injury.

Conditional knockout of proximal tubule mitofusin 2 accelerates recovery and improves survival after renal ischemia.

Proximal tubule (PT) cells are critical targets of acute ischemic injury. Elimination of the mitochondrial fusion protein mitofusin 2 (Mfn2) sensitizes PT cells to apoptosis in vitro. However, the role of PT Mfn2 in ischemic AKI in vivo is unknown. To test its role, we evaluated the effects of conditional KO of PT Mfn2 (cKO-PT-Mfn2) on animal survival after transient bilateral renal ischemia associated with severe AKI. Forty-eight hours after ischemia, 28% of control mice survived compared with 86% of cKO-PT-Mfn2 animals (P<0.001 versus control). Although no significant differences in histologic injury score, apoptosis, or necrosis were detected between genotypes, cKO-PT-Mfn2 kidneys exhibited a 3.5-fold increase in cell proliferation restricted to the intrarenal region with Mfn2 deletion. To identify the signals responsible for increased proliferation, primary PT cells with Mfn2 deficiency were subjected to stress by ATP depletion in vitro. Compared with normal Mfn2 expression, Mfn2 deficiency significantly increased PT cell proliferation and persistently activated extracellular signal-regulated kinase 1/2 (ERK1/2) during recovery from stress. Furthermore, stress and Mfn2 deficiency decreased the interaction between Mfn2 and Ras detected by immunoprecipitation, and purified Mfn2 dose-dependently decreased Ras activity in a cell-free assay. Ischemia in vivo also reduced the Mfn2-RAS interaction and increased both RAS and p-ERK1/2 activity in the renal cortical homogenates of cKO-PT-Mfn2 mice. Our results suggest that, in contrast to its proapoptotic effects in vitro, selective PT Mfn2 deficiency accelerates recovery of renal function and enhances animal survival after ischemic AKI in vivo, partly by increasing Ras-ERK-mediated cell proliferation.

Recapturing time: a practical approach to time management for physicians.

Increasing pressures on physicians demand effective time management and jeopardise professional satisfaction. Effective time management potentially increases productivity, promotes advancement, limits burnout and improves both professional and personal satisfaction. However, strategies for improving time management are lacking in the current medical literature. Adapting time management techniques from the medical and non-medical literature may improve physician time management habits. These techniques can be divided into four categories: (1) setting short and long-term goals; (2) setting priorities among competing responsibilities; (3) planning and organising activities; and (4) minimising 'time wasters'. Efforts to improve time management can increase physician productivity and enhance career satisfaction.

Intractable hyponatremia complicated by a reset osmostat: a case report.

BACKGROUND: Hyponatremia associated with a low serum osmolality is a common and confounding electrolyte disorder. Correcting hyponatremia is also complicated, especially in the setting of chronic hyponatremia. Here, we provide a rational approach to accurately detecting and safely treating acute on chronic euvolemic hyponatremia in the setting of acute polydipsia with a chronic reset osmostat. CASE PRESENTATION: A 71-year-old hispanic gentleman with chronic hyponatremia presented with hiccups, polydipsia, and a serum sodium concentration of 120 mEq/L associated with diffuse weakness, inattentiveness, and suicidal ideation. Symptomatic euvolemic hyponatremia warranted hypertonic saline treatment in the acute phase and water restriction in the chronic phase. Both interventions resulted in improvement in symptoms and/or the serum sodium concentration, but to a serum sodium level that persistently remained below the normal range. Remarkably, the urine osmolality appropriately fell when the serum sodium concentration fell below 126 mEq/L. Also remarkable was the appropriate increase in urine osmolality when the serum sodium concentration exceeded 126 mEq/L. The preservation of both concentration and dilution, albeit at a lower-than-normal serum osmolality, shows that the osmostat regulating antidiuretic hormone release had been "reset." Both physiologic and pharmacologic resetting of the osmostat are discussed. CONCLUSIONS: Preservation of urinary concentrating and diluting ability at a lower-than-normal serum sodium concentration, especially in the setting of chronic hyponatremia, is diagnostic of a reset osmostat. The presence of a reset osmostat often confounds the treatment of concomitant acute hyponatremia. Early recognition of a reset osmostat avoids the need to normalize serum sodium concentration, expedites hospital discharge, and limits potential harm from overcorrecting acute hyponatremia.

Apoptosis and acute kidney injury.

Improved mechanistic understanding of renal cell death in acute kidney injury (AKI) has generated new therapeutic targets. Clearly, the classic lesion of acute tubular necrosis is not adequate to describe the consequences of renal ischemia, nephrotoxin exposure, or sepsis on glomerular filtration rate. Experimental evidence supports a pathogenic role for apoptosis in AKI. Interestingly, proximal tubule epithelial cells are highly susceptible to apoptosis, and injury at this site contributes to organ failure. During apoptosis, well-orchestrated events converge at the mitochondrion, the organelle that integrates life and death signals generated by the BCL2 (B-cell lymphoma 2) protein family. Death requires the 'perfect storm' for outer mitochondrial membrane injury to release its cellular 'executioners'. The complexity of this process affords new targets for effective interventions, both before and after renal insults. Inhibiting apoptosis appears to be critical, because circulating factors released by the injured kidney induce apoptosis and inflammation in distant organs including the heart, lung, liver, and brain, potentially contributing to the high morbidity and mortality associated with AKI. Manipulation of known stress kinases upstream of mitochondrial injury, induction of endogenous, anti-apoptotic proteins, and improved understanding of the timing and consequences of renal cell apoptosis will inevitably improve the outcome of human AKI.

Induction of heat shock protein 70 inhibits ischemic renal injury.

Heat shock protein 70 (Hsp70) is a potent antiapoptotic agent. Here, we tested whether it directly regulates renal cell survival and organ function in a model of transient renal ischemia using Hsp70 knockout, heterozygous, and wild-type mice. The kidney cortical Hsp70 content inversely correlated with tubular injury, apoptosis, and organ dysfunction after injury. In knockout mice, ischemia caused changes in the activity of Akt and glycogen synthase kinase 3-ß (kinases that regulate the proapoptotic protein Bax), increased active Bax, and activated the proapoptotic protease caspase 3. As these changes were significantly reduced in the wild-type mice, we tested whether Hsp70 influences ischemia-induced apoptosis. An Hsp70 inducer, geranylgeranylacetone, increased Hsp70 expression in heterozygous and wild-type mice, and reduced both ischemic tubular injury and organ dysfunction. When administered after ischemia, this inducer also decreased tubular injury and organ failure in wild-type mice but did not protect the knockout mice. ATP depletion in vitro caused greater mitochondrial Bax accumulation and death in primary proximal tubule cells harvested from knockout compared with wild-type mice and altered serine phosphorylation of a Bax peptide at the Akt-specific target site. In contrast, lentiviral-mediated Hsp70 repletion decreased mitochondrial Bax accumulation and rescued Hsp70 knockout cells from death. Thus, increasing Hsp70 either before or after ischemic injury preserves renal function by attenuating acute kidney injury.

Hexokinase regulates Bax-mediated mitochondrial membrane injury following ischemic stress.

Hexokinase (HK), the rate-limiting enzyme in glycolysis, controls cell survival by promoting metabolism and/or inhibiting apoptosis. Since HK isoforms I and II have mitochondrial targeting sequences, we attempted to separate the protective effects of HK on cell metabolism from those on apoptosis. We exposed renal epithelial cells to metabolic stress causing ATP depletion in the absence of glucose and found that this activated glycogen synthase kinase 3ß (GSK3ß) and Bax caused mitochondrial membrane injury and apoptosis. ATP depletion led to a progressive HK II dissociation from mitochondria, released mitochondrial apoptosis inducing factor and cytochrome c into the cytosol, activated caspase-3, and reduced cell survival. Compared with control, adenoviral-mediated HK I or II overexpression improved cell survival following stress, but did not prevent GSK3ß or Bax activation, improve ATP content, or reduce mitochondrial fragmentation. HK I or HK II overexpression increased mitochondria-associated isoform-specific HK content, and decreased mitochondrial membrane injury and apoptosis after stress. In vivo, HK II localized exclusively to the proximal tubule. Ischemia reduced total renal HK II content and dissociated HK II from proximal tubule mitochondria. In cells overexpressing HK II, Bax and HK II did not interact before or after stress. While the mechanism by which HK antagonizes Bax-mediated apoptosis is unresolved by these studies, one possible scenario is that the two proteins compete for a common binding site on the outer mitochondrial membrane.

GSK3beta promotes apoptosis after renal ischemic injury.

The mechanism by which the serine-threonine kinase glycogen synthase kinase-3beta (GSK3beta) affects survival of renal epithelial cells after acute stress is unknown. Using in vitro and in vivo models, we tested the hypothesis that GSK3beta promotes Bax-mediated apoptosis, contributing to tubular injury and organ dysfunction after acute renal ischemia. Exposure of renal epithelial cells to metabolic stress activated GSK3beta, Bax, and caspase 3 and induced apoptosis. Expression of a constitutively active GSK3beta mutant activated Bax and decreased cell survival after metabolic stress. In contrast, pharmacologic inhibition (4-benzyl-2-methyl-1,2,4-thiadiazolidine-3,5-dione [TDZD-8]) or RNA interference-mediated knockdown of GSK3beta promoted cell survival. Furthermore, RNA interference-mediated knockdown of Bax abrogated the cell death induced by constitutively active GSK3beta. In a cell-free assay, TDZD-8 inhibited the phosphorylation of a peptide containing the Bax serine(163) site targeted by stress-activated GSK3beta. In rats, TDZD-8 inhibited ischemia-induced activation of GSK3beta, Bax, and caspase 3; ameliorated tubular and epithelial cell damage; and significantly protected renal function. Taken together, GSK3beta-mediated Bax activation induces apoptosis and tubular damage that contribute to acute ischemic kidney injury.

HSP72 inhibits Smad3 activation and nuclear translocation in renal epithelial-to-mesenchymal transition.

Although heat shock protein 72 (HSP72) ameliorates renal tubulointerstitial fibrosis by inhibiting epithelial-to-mesenchymal transition (EMT), the underlying mechanism is unknown. Because Smad proteins transduce TGF-beta signaling from the cytosol to the nucleus and HSP72 assists in protein folding and facilitates nuclear translocation, we investigated whether HSP72 inhibits TGF-beta-induced EMT by modulating Smad expression, activation, and nuclear translocation. To evaluate the roles of distinct HSP72 structural domains in these processes, we constructed vectors that expressed wild-type HSP72 or mutants lacking either the peptide-binding domain (HSP72-DeltaPBD), which is responsible for substrate binding and refolding, or the nuclear localization signal (HSP72-DeltaNLS). Overexpression of wild-type HSP72 or HSP72-DeltaNLS inhibited TGF-beta1-induced EMT, but HSP72-DeltaPBD did not, suggesting a critical role for the PBD in this inhibition. HSP72 overexpression inhibited TGF-beta1-induced phosphorylation and nuclear translocation of Smad3 and p-Smad3, but not Smad2; these inhibitory effects required the PBD but not the NLS. Coimmunoprecipitation assays suggested a physical interaction between Smad3 and the PBD. siRNA knockdown of endogenous HSP72 enhanced both TGF-beta1-induced Smad3 phosphorylation and EMT and confirmed the interaction of HSP72 with both Smad3 and p-Smad3. In vivo, induction of HSP72 by geranylgeranylacetone suppressed Smad3 phosphorylation in renal tubular cells after unilateral ureteral obstruction. In conclusion, HSP72 inhibits EMT in renal epithelial cells primarily by exerting domain-specific effects on Smad3 activation and nuclear translocation.

Effective Medical Lecturing: Practice Becomes Theory: A Narrative Review.

Effective lecturing stimulates learning, creates a verbal history for our profession, and is a central basis for evaluating academic promotion. Unfortunately, few resources exist in the medical literature to guide the academician toward success as an effective lecturer. Using evidence-based principles, this review fosters adult learning in academic venues by incorporating the latest innovations in educational theory for both online and traditional teaching. The novice or advanced academic teacher will be guided toward critical self-evaluation of current teaching practices and encouraged to replace ineffective methods with ones more likely to be both rewarding and rewarded. By introducing literature-based learning techniques, emphasizing audience targeting, truncating content to an appropriate level of detail, effectively linking images and text, and accepting the brevity of learners' attentiveness, we show that the audience, not the speaker, is the primary educational focus.

Beta-catenin promotes survival of renal epithelial cells by inhibiting Bax.

Ischemia activates Bax, a proapoptotic BCL2 protein, as well as the prosurvival beta-catenin/Wnt signaling pathway. To test the hypothesis that beta-catenin/Wnt signaling regulates Bax-mediated apoptosis after induction of metabolic stress, which occurs during renal ischemia, we infected immortalized and primary proximal tubular epithelial cells with adenovirus to express either constitutively active or dominant negative beta-catenin constructs. Constitutively active beta-catenin significantly decreased apoptosis and improved cell survival after metabolic stress. Furthermore, active beta-catenin decreased Bax activation, oligomerization, and translocation to mitochondria, and reduced both organelle membrane injury and apoptosis. Dominant negative beta-catenin had the opposite effects. Because Akt regulates Bax, we examined the effects of the beta-catenin mutants on Akt expression and activation. Constitutively active beta-catenin increased Akt-1 expression and activation before and after stress, and treatment with a phosphatidylinositol-3 kinase inhibitor antagonized the protective effects of beta-catenin on Akt activation, Bax inhibition, and cell survival. In addition, beta-catenin significantly increased the rate of phosphorylation at Bax serine(184), an Akt-specific target. Taken together, these results suggest that beta-catenin/Wnt signaling promotes survival of renal epithelial cells after metabolic stress, in part by inhibiting Bax in a phosphatidylinositol-3 kinase/Akt-dependent manner.

Cross organelle stress response disruption promotes gentamicin-induced proteotoxicity.

Gentamicin is a nephrotoxic antibiotic that causes acute kidney injury (AKI) primarily by targeting the proximal tubule epithelial cell. The development of an effective therapy for gentamicin-induced renal cell injury is limited by incomplete mechanistic insight. To address this challenge, we propose that RNAi signal pathway screening could identify a unifying mechanism of gentamicin-induced cell injury and suggest a therapeutic strategy to ameliorate it. Computational analysis of RNAi signal screens in gentamicin-exposed human proximal tubule cells suggested the cross-organelle stress response (CORE), the unfolded protein response (UPR), and cell chaperones as key targets of gentamicin-induced injury. To test this hypothesis, we assessed the effect of gentamicin on the CORE, UPR, and cell chaperone function, and tested the therapeutic efficacy of enhancing cell chaperone content. Early gentamicin exposure disrupted the CORE, evidenced by a rise in the ATP:ADP ratio, mitochondrial-specific H2O2 accumulation, Drp-1-mediated mitochondrial fragmentation, and endoplasmic reticulum-mitochondrial dissociation. CORE disruption preceded measurable increases in whole-cell oxidative stress, misfolded protein content, transcriptional UPR activation, and its untoward downstream effects: CHOP expression, PARP cleavage, and cell death. Geranylgeranylacetone, a therapeutic that increases cell chaperone content, prevented mitochondrial H2O2 accumulation, preserved the CORE, reduced the burden of misfolded proteins and CHOP expression, and significantly improved survival in gentamicin-exposed cells. We identify CORE disruption as an early and remediable cause of gentamicin proteotoxicity that precedes downstream UPR activation and cell death. Preserving the CORE significantly improves renal cell survival likely by reducing organelle-specific proteotoxicity during gentamicin exposure.

Hsp27 inhibits sublethal, Src-mediated renal epithelial cell injury.

Disruption of cell contact sites in renal epithelial cells contributes to organ dysfunction after ischemia. We hypothesized that heat shock protein 27 (Hsp27), a known cytoprotectant protein, preserves cell architecture and cell contact site function during ischemic stress. To test this hypothesis, renal epithelial cells were subjected to transient ATP depletion, an in vitro model of ischemia-reperfusion injury. Compared with control, selective Hsp27 overexpression significantly preserved cell-cell junction function during metabolic stress as evidenced by reduced stress-mediated redistribution of the adherens junction protein E-cadherin, higher transepithelial electrical resistance, and lower unidirectional flux of lucifer yellow. Hsp27 overexpression also preserved paxillin staining within focal adhesion complexes and significantly decreased cell detachment during stress. Surprisingly, Hsp27, an F-actin-capping protein, only minimally reduced stress induced actin cytoskeleton collapse. In contrast to Hsp27 overexpression, siRNA-mediated knockdown had the opposite effect on these parameters. Since ischemia activates c-Src, a tyrosine kinase that disrupts both cell-cell and cell-substrate interactions, the relationship between Hsp27 and c-Src was examined. Although Hsp27 and c-Src did not coimmunoprecipitate and Hsp27 overexpression failed to inhibit whole cell c-Src activation during injury, manipulation of Hsp27 altered active c-Src accumulation at cell contact sites. Specifically, Hsp27 overexpression reduced, whereas Hsp27 knockdown increased active p-(416)Src detected at contact sites in intact cells as well as in a purified cell membrane fraction. Together, this evidence shows that Hsp27 overexpression prevents sublethal REC injury at cell contact sites possibly by a c-Src-dependent mechanism. Further exploration of the biochemical link between Hsp27 and c-Src could yield therapeutic interventions for ameliorating ischemic renal cell injury and organ dysfunction.

Peroxisome proliferator-activated receptor gamma inhibition prevents adhesion to the extracellular matrix and induces anoikis in hepatocellular carcinoma cells.

Activation of the nuclear transcription factor peroxisome proliferator-activated receptor gamma (PPARgamma) inhibits growth and survival of hepatocellular carcinoma (HCC) cell lines. To further investigate the function of PPARgamma in HCC, PPARgamma expression patterns in primary tumors were examined, and the responses of two HCC cell lines to PPARgamma activation and inhibition were compared. PPARgamma expression was increased in HCC and benign-appearing peritumoral hepatocytes compared with remote benign hepatocytes. Both compound PPARgamma inhibitors and PPARgamma small interfering RNAs prevented HCC cell lines from adhering to the extracellular matrix. Loss of adhesion was followed by caspase-dependent apoptosis (anoikis). PPARgamma inhibitors had no effect on initial beta1 integrin-mediated adhesion, or on total focal adhesion kinase levels but did reduce focal adhesion kinase phosphorylation. The PPARgamma inhibitor T0070907 was significantly more efficient at causing cancer cell death than the activators troglitazone and rosiglitazone. T0070907 caused cell death by reducing adhesion and inducing anoikis, whereas the activators had no direct effect on adhesion and caused cell death at much higher concentrations. In conclusion, PPARgamma overexpression is present in HCC. Inhibition of PPARgamma function causes HCC cell death by preventing adhesion and inducing anoikis-mediated apoptosis. PPARgamma inhibitors represent a potential novel treatment approach to HCC.

The Role of BCL-2 Family Members in Acute Kidney Injury.

B-cell lymphoma 2 (BCL-2) family proteins gather at the biologic cross-roads of renal cell survival: the outer mitochondrial membrane. Despite shared sequence and structural features, members of this conserved protein family constantly antagonize each other in a life-and-death battle. BCL-2 members innocently reside within renal cells until activated or de-activated by physiologic stresses caused by common nephrotoxins, transient ischemia, or acute glomerulonephritis. Recent experimental data not only illuminate the intricate mechanisms of apoptosis, the most familiar form of BCL-2-mediated cell death, but emphasizes their newfound roles in necrosis, necroptosis, membrane pore transition regulated necrosis, and other forms of acute cell demise. A major paradigm shift in non-cell death roles of the BCL-2 family has occurred. BCL-2 proteins also regulate critical daily renal cell housekeeping functions including cell metabolism, autophagy (an effective means for recycling cell components), mitochondrial morphology (organelle fission and fusion), as well as mitochondrial biogenesis. This article considers new concepts in the biochemical and structural regulation of BCL-2 proteins that contribute to membrane pore permeabilization, a universal feature of cell death. Despite these advances, persistent BCL-2 family mysteries continue to challenge cell biologists. Given their interface with many intracellular functions, it is likely that BCL-2 proteins determine cell viability under many pathologic circumstances relevant to the nephrologist and, as a consequence, represent an ideal therapeutic target.