Yeong-Shiau Pu

Aristolochic acid-associated urothelial cancer in Taiwan

Aristolochic acid, a potent human carcinogen produced by Aristolochia plants, is associated with urothelial carcinoma of the upper urinary tract (UUC). Following metabolic activation, aristolochic acid reacts with DNA to form aristolactam (AL)-DNA adducts. These lesions concentrate in the renal cortex, where they serve as a sensitive and specific biomarker of exposure, and are found also in the urothelium, where they give rise to a unique mutational signature in the TP53 tumor-suppressor gene. Using AL-DNA adducts and TP53 mutation spectra as biomarkers, we conducted a molecular epidemiologic study of UUC in Taiwan, where the incidence of UUC is the highest reported anywhere in the world and where Aristolochia herbal remedies have been used extensively for many years. Our study involves 151 UUC patients, with 25 patients with renal cell carcinomas serving as a control group. The TP53 mutational signature in patients with UUC, dominated by otherwise rare A:T to T:A transversions, is identical to that observed in UUC associated with Balkan endemic nephropathy, an environmental disease. Prominent TP53 mutational hotspots include the adenine bases of 5′AG (acceptor) splice sites located almost exclusively on the nontranscribed strand. A:T to T:A mutations also were detected at activating positions in the FGFR3 and HRAS oncogenes. AL-DNA adducts were present in the renal cortex of 83% of patients with A:T to T:A mutations in TP53, FGFR3, or HRAS. We conclude that exposure to aristolochic acid contributes significantly to the incidence of UUC in Taiwan, a finding with significant implications for global public health.

Resistance to Paclitaxel Is Proportional to Cellular Total Antioxidant Capacity

Paclitaxel, one of the most commonly prescribed chemotherapeutic agents, is active against a wide spectrum of human cancer. The mechanism of its cytotoxicity, however, remains controversial. Our results indicate that paclitaxel treatment increases levels of superoxide, hydrogen peroxide, nitric oxide (NO), oxidative DNA adducts, G2-M arrest, and cells with fragmented nuclei. Antioxidants pyruvate and selenium, the NO synthase inhibitor N(omega)-nitro-L-arginine methyl ester, and the NO scavenger manganese (III) 2-(4-carboxyphenyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide all decreased paclitaxel-mediated DNA damage and sub-G1 cells. In contrast, the glutamylcysteine synthase inhibitor buthionine sulfoximine (BSO) and the superoxide dismutase (SOD) inhibitor 2-methoxyestradiol (2-ME) increased the sub-G1 fraction in paclitaxel-treated cells. These results suggest that reactive oxygen and nitrogen species are involved in paclitaxel cytotoxicity. This notion is further supported with the observation that concentrations of paclitaxel required to inhibit cell growth by 50% correlate with total antioxidant capacity. Moreover, agents such as arsenic trioxide (As2O3), BSO, 2-ME, PD98059, U0126 [mitogen-activated protein/extracellular signal-regulated kinase inhibitors], and LY294002 (phosphatidylinositol 3-kinase/Akt inhibitor), all of which decrease clonogenic survival, also decrease the total antioxidant capacity of paclitaxel-treated cells, regardless whether they are paclitaxel sensitive or paclitaxel resistant. These results suggest that paclitaxel chemosensitivity may be predicted by taking total antioxidant capacity measurements from clinical tumor samples. This, in turn, may then improve treatment outcomes by selecting out potentially responsive patients.

Mutational Signature of Aristolochic Acid Exposure as Revealed by Whole-Exome Sequencing

The mutational signature of aristolochic acid exemplifies how genome-wide sequencing can be used to identify environmental exposures leading to cancer. Carcinogen AAlert Aristolochic acid (AA) is a natural compound derived from plants in the Aristolochia genus. For centuries, Aristolochia has been used throughout Asia to treat a variety of ailments as a component of traditional Chinese medicine. In recent years, however, a more sinister side of this herb has come to light when it was linked to kidney damage and cancers of the urinary tract. Now, two studies by Poon et al. and Hoang et al. present a “molecular signature” of AA-induced DNA damage, which helps to explain the mutagenic effects of AA and may also be useful as a way to detect unsuspected AA exposure as a cause of cancer. The molecular signature seen in AA-associated tumors is characterized by a predominance of A:T-to-T:A transversions, a relatively unusual type of mutation that is infrequently seen in other types of cancer, including those caused by other carcinogens. These mutations concentrate at splice sites, causing the inappropriate inclusion or exclusion of entire exons in the resulting mRNA. The overall mutation rate is another notable feature of AA-associated cancers, because it is several times higher than the rate of mutations caused by other carcinogens such as tobacco and ultraviolet light. In both studies, the authors also used the molecular signature to discover that AA was a likely cause of tumors previously attributed to other carcinogens. In one case, a urinary tract cancer that had been attributed to smoking and, in the other case, a liver cancer previously attributed to a chronic hepatitis infection were both identified as having the telltale signature of AA mutagenesis. The identification of a specific molecular signature for AA has both clinical and public health implications. For individual patients, the molecular signature could help physicians identify which tumors were caused by AA. Although this information cannot yet be used to optimize the treatment of individual patients, those who are diagnosed with AA-associated cancers could be monitored more closely for the appearance of additional tumors. Meanwhile, a better understanding of the mutagenic effects of AA should also help to strengthen public health efforts to decrease exposure to this carcinogenic herb. In humans, exposure to aristolochic acid (AA) is associated with urothelial carcinoma of the upper urinary tract (UTUC). Exome sequencing of UTUCs from 19 individuals with documented exposure to AA revealed a remarkably large number of somatic mutations and an unusual mutational signature attributable to AA. Most of the mutations (72%) in these tumors were A:T-to-T:A transversions, located predominantly on the nontranscribed strand, with a strong preference for deoxyadenosine in a consensus sequence (T/CAG). This trinucleotide motif overlaps the canonical splice acceptor site, possibly accounting for the excess of splice site mutations observed in these tumors. The AA mutational fingerprint was found frequently in oncogenes and tumor suppressor genes in AA-associated UTUC. The AA mutational signature was observed in one patient’s tumor from a UTUC cohort without previous indication of AA exposure. Together, these results directly link an established environmental mutagen to cancer through genome-wide sequencing and highlight its power to reveal individual exposure to carcinogens.

Changing trends of prostate cancer in Asia

Although Asian people have the lowest incidence and mortality rates of prostate cancer in the world, these rates have risen rapidly in the past two decades in most Asian countries. Prostate cancer has become one of the leading male cancers in some Asian countries. In 2000, the age-adjusted incidence was over 10 per 100 000 men in Japan, Taiwan, Singapore, Malaysia, the Philippines and Israel. Although some of the increases may result from enhanced detection, much of the increased incidence may be associated with westernization of the lifestyle, with increasing obesity and increased consumption of fat. The differences in incidences between native Americans and Asian immigrants are getting smaller, reflecting a possible improvement of diagnostic efforts and changes of environmental risk factors in Asian immigrants. Nevertheless, the huge variations in incidences among ethnic groups imply that there are important genetic risk factors. The stage distributions of prostate cancer in Asian populations are still unfavorable compared to those of Western developed countries. However, a trend towards diagnosing cancer with more favorable prognosis is seen in most Asian countries. Both genetic and environmental risk factors responsible for elevated risks in Asian people are being identified, which may help to reduce prostate cancer incidence in a chemopreventive setting.

Negative modulation of androgen receptor transcriptional activity by Daxx.

ABSTRACT The transcriptional activity of the androgen receptor (AR) modulated by positive or negative regulators plays a critical role in controlling the growth and survival of prostate cancer cells. Although numerous positive regulators have been identified, negative regulators of AR are less well understood. We report here that Daxx functions as a negative AR coregulator through direct protein-protein interactions. Overexpression of Daxx suppressed AR-mediated promoter activity in COS-1 and LNCaP cells and AR-mediated prostate-specific antigen expression in LNCaP cells. Conversely, downregulation of endogenous Daxx expression by RNA interference enhances androgen-induced prostate-specific antigen expression in LNCaP cells. In vitro and in vivo interaction studies revealed that Daxx binds to both the amino-terminal and the DNA-binding domain of the AR. Daxx proteins interfere with the AR DNA-binding activity both in vitro and in vivo. Moreover, sumoylation of AR at its amino-terminal domain is involved in Daxx interaction and trans-repression. Together, these findings not only provide a novel role of Daxx in controlling AR transactivation activity but also uncover the mechanism underlying sumoylation-dependent transcriptional repression of the AR.

A Cullin3-KLHL20 Ubiquitin Ligase-Dependent Pathway Targets PML to Potentiate HIF-1 Signaling and Prostate Cancer Progression

Tumor hypoxia is associated with disease progression and treatment failure, but the hypoxia signaling mechanism is not fully understood. Here, we show that KLHL20, a Cullin3 (Cul3) substrate adaptor induced by HIF-1, coordinates with the actions of CDK1/2 and Pin1 to mediate hypoxia-induced PML proteasomal degradation. Furthermore, this PML destruction pathway participates in a feedback mechanism to maximize HIF-1α induction, thereby potentiating multiple tumor hypoxia responses, including metabolic reprogramming, epithelial-mesenchymal transition, migration, tumor growth, angiogenesis, and chemoresistance. In human prostate cancer, overexpression of HIF-1α, KLHL20, and Pin1 correlates with PML down-regulation, and hyperactivation of the PML destruction pathway is associated with disease progression. Our study indicates that the KLHL20-mediated PML degradation and HIF-1α autoregulation play key roles in tumor progression.

Stopping smoking might reduce tumour recurrence in nonmuscle-invasive bladder cancer

To evaluate effects of stopping smoking on the outcome of nonmuscle‐invasive bladder cancer, as cigarette smoking is a risk factor for bladder cancer and little is known about whether stopping smoking reduces the risk of recurrence or progression.

Risk factors for prostate carcinoma in Taiwan

Although prostate carcinoma remains a rare disease among Chinese men, its incidence is on the rise. The authors conducted a hospital‐based case–control study to identify risk factors for prostate carcinoma in northern Taiwan.

Genetic polymorphisms of N-acetyltransferase 1 and 2 and risk of cigarette smoking-related bladder cancer

SummaryAromatic amines from cigarette smoking or occupational exposure, recognized risk factors for bladder cancer, are metabolized by N-acetyltransferases (NAT). This study examined the association of (NAT) 1 and 2 genotypes with the risk of smoking-related bladder cancer. A total of 74 pathologically confirmed bladder cancer patients and 184 controls were serially recruited from the National Taiwan University Hospital. History of cigarette smoking and other risk factors for bladder cancer was obtained through standardized questionnaire interview. Peripheral blood lymphocytes were collected from each subject and genotyped for NAT1 and NAT2 by DNA sequencing and polymerase chain reaction-restriction fragment length polymorphism methods. Allele frequency distributions of NAT1 and NAT2 were similar between cases and controls. There was a significant dose–response relationship between the risk of bladder cancer and the quantity and duration of cigarette smoking. The biological gradients were significant among subjects carrying NAT1*10 allele or NAT2 slow acetylators, but not among NAT2 rapid acetylators without NAT1*10 allele. The results are consistent with the hypothesis that NAT1 and NAT2 might modulate the susceptibility to bladder cancer associated with cigarette smoking.

Podocalyxin EBP50 ezrin molecular complex enhances the metastatic potential of renal cell carcinoma through recruiting Rac1 guanine nucleotide exchange factor ARHGEF7.

Podocalyxin was initially identified in glomerular podocytes to critically maintain the structural and functional integrity of the glomerular ultrafiltrative apparatus. Lately, it has emerged as a malignant marker in tumors arising from a variety of tissue origins. By immunohistochemistry, we identified that 9.6% of renal cell carcinoma patients overexpress this protein. This subset of patients had significantly shorter disease-specific and overall survivals, and, importantly, we established podocalyxin overexpression as an independent prognostic factor for latent distant metastasis with multivariate analysis. Podocalyxin down-regulation by small interfering RNA led to defective migration in model renal tubular cells, which was corrected by re-expression of podocalyxin. The activity of the small GTPase Rac1, a well-characterized modulator of cell migration, was diminished by podocalyxin knock-down. Conversely, podocalyxin overexpression in human embryonic kidney cells up-regulated Rac1 activity, which depended on a complex formed by podocalyxin, ERM-binding phosphoprotein 50, ezrin, and ARHGEF7, a Rac1 activator. Therefore, podocalyxin can serve as a biomarker to identify renal cell carcinoma patients with higher metastatic potential for more aggressive intervention at earlier clinical stages.