Harold D. Love

GTP hydrolysis by arf-1 mediates sorting and concentration of Golgi resident enzymes into functional COP I vesicles

Upon addition of GTPγS to in vitro budding reactions, COP I vesicles form but retain their coat, making them easy to isolate and analyze. We have developed an in vitro budding assay that reconstitutes the formation of COP I‐derived vesicles under conditions where GTP hydrolysis can occur. Once formed, vesicles are uncoated and appear functional as they fuse readily with acceptor membranes. Electron microscopy shows a homogeneous population of uncoated vesicles that contain the medial/trans Golgi enzyme α1,2‐mannosidase II. Biochemical quantitation of vesicles reveals that resident Golgi enzymes are up to 10‐fold more concentrated than in donor membranes, but vesicles formed in the presence of GTPγS show an average density of resident Golgi enzymes similar to that seen in donor membranes. We show that the sorting process is mediated by the small GTPase arf‐1 as addition of a dominant, hydrolysis‐deficient arf‐1 Q71L mutant produced results similar to that of GTPγS. Strikingly, the average density of the anterograde cargo protein, polymeric IgA receptor, in COP I‐derived vesicles was similar to that found in starting membranes and was independent of GTP hydrolysis. We conclude that hydrolysis of GTP bound to arf‐1 promotes selective segregation and concentration of Golgi resident enzymes into COP I vesicles.

Hypoxia and the metabolic phenotype of prostate cancer cells.

Many cancer cells have an unusual ability to grow in hypoxia, but the origins of this metabolic phenotype remain unclear. We compared the metabolic phenotypes of three common prostate cancer cell models (LNCaP, DU145, PC3), assessing energy metabolism, metabolic gene expression, and the response to various culture contexts (in vitro and xenografts). LNCaP cells had a more oxidative phenotype than PC3 and DU145 cells based upon respiration, lactate production, [ATP], metabolic gene expression, and sensitivity of these parameters to hypoxia. PC3 and DU145 cells possessed similar Complex II and mtDNA levels, but lower Complex III and IV activities, and were unresponsive to dinitrophenol or dichloroacetate, suggesting that their glycolytic phenotype is due to mitochondrial dysfunction rather than regulation. High passage under normoxia converted LNCaP from oxidative to glycolytic cells (based on respiration and lactate production), and altered metabolic gene expression. Though LNCaP-derived cells differed from the parental line in mitochondrial enzyme activities, none differed in mitochondrial content (assessed as cardiolipin levels). When LNCaP-derived cells were grown as xenografts in immunodeficient mice, there were elements of a hypoxic response (e.g., elevated VEGF mRNA) but line-specific changes in expression of select glycolytic, mitochondrial and fatty acid metabolic genes. Low oxygen in vitro did not influence the mRNA levels of SREBP axis, nor did it significantly alter triglyceride production in any of the cell lines suggesting that the pathway of de novo fatty acid synthesis is not directly upregulated by hypoxic conditions. Collectively, these studies demonstrate important differences in the metabolism of these prostate cancer models. Such metabolic differences would have important ramifications for therapeutic strategies involving metabolic targets.

Tissue-specific consequences of cyclin D1 overexpression in prostate cancer progression.

The cyclin D1 oncogene encodes the regulatory subunit of a holoenzyme that phosphorylates and inactivates the Rb protein and promotes progression through G(1) to S phase of the cell cycle. Several prostate cancer cell lines and a subset of primary prostate cancer samples have increased cyclin D1 protein expression. However, the relationship between cyclin D1 expression and prostate tumor progression has yet to be clearly characterized. This study examined the effects of manipulating cyclin D1 expression in either human prostatic epithelial or stromal cells using a tissue recombination model. The data showed that overexpression of cyclin D1 in the initiated BPH-1 cell line increased cell proliferation rate but did not elicit tumorigenicity in vivo. However, overexpression of cyclin D1 in normal prostate fibroblasts (NPF) that were subsequently recombined with BPH-1 did induce malignant transformation of the epithelial cells. The present study also showed that recombination of BPH-1 + cyclin D1-overexpressing fibroblasts (NPF(cyclin D1)) resulted in permanent malignant transformation of epithelial cells (BPH-1(NPF-cyclin D1) cells) similar to that seen with carcinoma-associated fibroblasts (CAF). Microarray analysis showed that the expression profiles between CAFs and NPF(cyclin D1) cells were highly concordant including cyclin D1 up-regulation. These data indicated that the tumor-promoting activity of cyclin D1 may be tissue specific.

Androgen Regulated Genes in Human Prostate Xenografts in Mice: Relation to BPH and Prostate Cancer

Benign prostatic hyperplasia (BPH) and prostate carcinoma (CaP) are linked to aging and the presence of androgens, suggesting that androgen regulated genes play a major role in these common diseases. Androgen regulation of prostate growth and development depends on the presence of intact epithelial-stromal interactions. Further, the prostatic stroma is implicated in BPH. This suggests that epithelial cell lines are inadequate to identify androgen regulated genes that could contribute to BPH and CaP and which could serve as potential clinical biomarkers. In this study, we used a human prostate xenograft model to define a profile of genes regulated in vivo by androgens, with an emphasis on identifying candidate biomarkers. Benign transition zone (TZ) human prostate tissue from radical prostatectomies was grafted to the sub-renal capsule site of intact or castrated male immunodeficient mice, followed by the removal or addition of androgens, respectively. Microarray analysis of RNA from these tissues was used to identify genes that were; 1) highly expressed in prostate, 2) had significant expression changes in response to androgens, and, 3) encode extracellular proteins. A total of 95 genes meeting these criteria were selected for analysis and validation of expression in patient prostate tissues using quantitative real-time PCR. Expression levels of these genes were measured in pooled RNAs from human prostate tissues with varying severity of BPH pathologic changes and CaP of varying Gleason score. A number of androgen regulated genes were identified. Additionally, a subset of these genes were over-expressed in RNA from clinical BPH tissues, and the levels of many were found to correlate with disease status. Our results demonstrate the feasibility, and some of the problems, of using a mouse xenograft model to characterize the androgen regulated expression profiles of intact human prostate tissues.

Hypertension Is a Major Contributor to 20-Hydroxyeicosatetraenoic Acid–Mediated Kidney Injury in Diabetic Nephropathy

In the kidney, 20-hydroxyeicosatetraenoic acid (20-HETE) is a primary cytochrome P450 4 (Cyp4)-derived eicosanoid that enhances vasoconstriction of renal vessels and induces hypertension, renal tubular cell hypertrophy, and podocyte apoptosis. Hypertension and podocyte injury contribute to diabetic nephropathy and are strong predictors of disease progression. In this study, we defined the mechanisms whereby 20-HETE affects the progression of diabetic nephropathy. We used Cyp4a14KO male mice that exhibit androgen-sensitive hypertension due to increased Cyp4a12-mediated 20-HETE production. We show that, upon induction of diabetes type 1 via streptozotocin injection, Cyp4a14KO male mice developed worse renal disease than streptozotocin-treated wild-type mice, characterized by increased albuminuria, mesangial expansion, glomerular matrix deposition, and thickness of the glomerular basement membranes. Castration blunted androgen-mediated Cyp4a12 synthesis and 20-HETE production, normalized BP, and ameliorated renal damage in diabetic Cyp4a14KO mice. Notably, treatment with a 20-HETE antagonist or agents that normalized BP without affecting Cyp4a12 expression and 20-HETE biosynthesis also ameliorated diabetes-mediated renal damage and albuminuria in Cyp4a14KO male mice. Taken together, these results suggest that hypertension is the major contributor to 20-HETE-driven diabetes-mediated kidney injury.

Glyoxalase 2 Is Involved in Human Prostate Cancer Progression as Part of a Mechanism Driven By PTEN/PI3K/AKT/mTOR Signaling With Involvement of PKM2 and ERα

Glyoxalase 2 (Glo2), together with glyoxalase 1 (Glo1), forms the main scavenging system of methylglyoxal, a potent pro‐apoptotic agent mainly generated by glycolysis. An increased rate of glycolysis is a well known signature of cancer cells. As a survival strategy, Glo1 is overexpressed in many human malignant cells, including prostate cancer (PCa), where it plays a crucial role in progression. No information is available on the role of Glo2 in the same ambit. PCa is the most common malignancy affecting men in the western world. Progression to a lethal hormone‐refractory PCa represents the major concern in this pathology. Therefore, a deeper understanding of the molecular mechanisms underlying PCa invasiveness and metastasis is urgently needed in order to develop novel therapeutic targets for this incurable state of the malignancy.

Glyoxalase 2 drives tumorigenesis in human prostate cells in a mechanism involving androgen receptor and p53-p21 axis

Glyoxalase 2 (Glo2), a metabolic enzyme, is overexpressed in some human cancers which suggests this enzyme may play a role in human tumorigenesis. In prostate cancer (PCa), the role of Glo2 has been scarcely investigated and there are no studies addressing a causative involvement of this protein in this neoplasia. Here, we examined the immunohistochemical profile of Glo2 in human PCa and benign adjacent tissues and investigated Glo2 involvement in PCa development in human prostate cell lines. PCa and matched adjacent normal tissues were obtained from paraffin sections of primary PCa from 20 patients who had undergone radical prostatectomy. Histopathological diagnosis was confirmed for each sample. Glo2 expression analysis was performed by immunohistochemistry in prostate tissues, and by qRT‐PCR and immunoblotting in prostate cell lines. The causative and mechanistic role of Glo2 in prostate tumorigenesis was demonstrated by Glo2 ectopic expression/silencing and employing specific activators/inhibitors. Our results showed that Glo2 was selectively expressed in PCa but not in the luminal compartment of the adjacent benign epithelium consistently in all the examined 20 cases. Glo2 expression in PCa was dependent on androgen receptor (AR) and was aimed at stimulating cell proliferation and eluding apoptosis through a mechanism involving the p53‐p21 axis. Glo2 was intensely expressed in the basal cells of benign glands but was not involved in PCa genesis. Our results demonstrate for the first time that Glo2 drives prostate tumorigenesis and suggest that it may represent a novel adjuvant marker in the pathological diagnosis of early PCa.

TPX2 as a prognostic indicator and potential therapeutic target in clear cell renal cell carcinoma

OBJECTIVES Our aims were to determine if targeting protein for Xklp2 (TPX2) is correlated with clear cell renal cell carcinoma (ccRCC) histology and oncologic outcomes using The Cancer Genome Atlas (TCGA) and an institutional tissue microarray (TMA). METHODS Clinicopathological data obtained from the TCGA consisted of 415 samples diagnosed with ccRCC. A TMA was constructed from tumors of 207 patients who underwent radical nephrectomy for ccRCC. TPX2 expression by immunohistochemistry on TMA was assessed by a genitourinary pathologist. Clinical data were extracted and linked to TMA cores. TPX2 and Aurora-A mRNA coexpression were evaluated in the TCGA cohort. Overall survival (OS), cancer-specific survival, and recurrence-free survival (RFS) were analyzed using the Kaplan-Meier method and log-rank statistics. Univariate and multivariate analyses were conducted using Cox proportional hazard models. RESULTS Median follow-up time for the TCGA cohort was 3.07 years. Aurora-A and TPX2 mRNA coexpression were significantly correlated (Pearson correlation = 0.918). High TPX2 mRNA expression was associated with advanced stage, metastasis, poor OS, and RFS. Median follow-up time for the TMA cohort was 5.3 years. Elevated TPX2 protein expression, defined as greater than 75th percentile staining intensity, was identified in 47/207 (22.7%) patients. Increased TPX2 immunostaining was associated with poor OS (P = 0.0327, 53% 5-year mortality), cancer-specific survival (P<0.01, 47.8% 5-year cancer-specific mortality), RFS (P = 0.0313, 73.6%, 5-year recurrence rate), grade, T stage, and metastasis. Multivariate analysis demonstrated elevated expression served as an independent predictor of RFS (hazard ratio = 3.62 (1.13-11.55), P = 0.029). CONCLUSIONS We show TPX2, a regulator of Aurora-A, is associated with high grade and stage of ccRCC, and is an independent predictor of recurrence. Future studies are warranted testing its role in ccRCC biology, and its potential as a therapeutic target.

Pharmacologic Inhibition of ß-catenin With Pyrvinium Inhibits Murine and Human Models of Wilms Tumor.

Wilms tumor (WT) is the most common renal malignancy in children and the fourth most common pediatric solid malignancy in the US. Although the mechanisms underlying the WT biology are complex, these tumors most often demonstrate activation of the canonical Wnt/β-catenin pathway. We and others have shown that constitutive activation of β-catenin restricted to the renal epithelium is sufficient to induce primitive renal epithelial tumors, which resemble human WT. Here we demonstrate that pharmacologic inhibition of β-catenin gene transcription with pyrvinium inhibits tumor growth and metastatic progression in a murine model of WT. Cellular invasion is significantly inhibited in both murine WT-like and human WT cells and is accompanied by downregulation of the oncogenes Myc and Birc5 (survivin). Our studies provide proof of the concept that the canonical Wnt/β-catenin pathway may be a novel therapeutic target in the management of WT.

Functional KRAS mutations and a potential role for PI3K/AKT activation in Wilms tumors

Wilms tumor (WT) is the most common renal neoplasm of childhood and affects 1 in 10 000 children aged less than 15 years. These embryonal tumors are thought to arise from primitive nephrogenic rests that derive from the metanephric mesenchyme during kidney development and are characterized partly by increased Wnt/β‐catenin signaling. We previously showed that coordinate activation of Ras and β‐catenin accelerates the growth and metastatic progression of a murine WT model. Here, we show that activating KRAS mutations can be found in human WT. In addition, high levels of phosphorylated AKT are present in the majority of WT. We further show in a mouse model and in renal epithelial cells that Ras cooperates with β‐catenin to drive metastatic disease progression and promotes in vitro tumor cell growth, migration, and colony formation in soft agar. Cellular transformation and metastatic disease progression of WT cells are in part dependent on PI3K/AKT activation and are inhibited via pharmacological inhibition of this pathway. Our studies suggest both KRAS mutations and AKT activation are present in WT and may represent novel therapeutic targets for this disease.