Long Yu

Genetic variants in STAT4 and HLA-DQ genes confer risk of hepatitis B virus–related hepatocellular carcinoma

To identify genetic susceptibility loci for hepatitis B virus (HBV)-related hepatocellular carcinoma (HCC) in the Chinese population, we carried out a genome-wide association study (GWAS) in 2,514 chronic HBV carriers (1,161 HCC cases and 1,353 controls) followed by a 2-stage validation among 6 independent populations of chronic HBV carriers (4,319 cases and 4,966 controls). The joint analyses showed that HCC risk was significantly associated with two independent loci: rs7574865 at STAT4, Pmeta = 2.48 × 10−10, odds ratio (OR) = 1.21; and rs9275319 at HLA-DQ, Pmeta = 2.72 × 10−17, OR = 1.49. The risk allele G at rs7574865 was significantly associated with lower mRNA levels of STAT4 in both the HCC tissues and nontumor tissues of 155 individuals with HBV-related HCC (Ptrend = 0.0008 and 0.0002, respectively). We also found significantly lower mRNA expression of STAT4 in HCC tumor tissues compared with paired adjacent nontumor tissues (P = 2.33 × 10−14).

Identification and characterization of nine novel human small GTPases showing variable expressions in liver cancer tissues

Digestion and detoxification are the two most important functions of the liver, and liver cells always keep a high metabolism level and active vesicular traffic. The malfunction of the vesicular traffic system might be a cause of the abnormal biological behavior of cancerous liver cells. The Ras superfamily is known to regulate various steps of vesicular traffic in eukaryotic cells. It would be significant to determine the change of vesicular transport molecules such as the members of Ras superfamily in carcinogenesis of liver cells. In the present study, we have cloned nine novel genes encoding human small GTPases: RAB1B, RAB4B, RAB10, RAB22A, RAB24, RAB25 ARL5, SARA1, and SARA2, among which the former six belong to the RAB family and the latter three belong to the ARF/SAR1 family. The identification of these new genes has greatly enlarged the pool of the Ras superfamily. It is interesting to find that they are upregulated in most of the 11 hepatocellular carcinoma and 1 cholangiohepatoma cases. Furthermore, the expression in 16 normal human adult tissues, the chromosome loci, and the gene structures of the nine genes are also described. The above findings could be valuable for understanding the vesicular transport system and elucidating the molecular basis of liver cancer carcinogenesis.

Destruction of Full-Length Androgen Receptor by Wild-Type SPOP, but Not Prostate-Cancer-Associated Mutants

SUMMARY The SPOP E3 ubiquitin ligase gene is frequently mutated in human prostate cancers. Here, we demonstrate that SPOP recognizes a Ser/Thr-rich degron in the hinge domain of androgen receptor (AR)and induces degradation of full-length AR and inhibition of AR-mediated gene transcription and prostate cancer cell growth. AR splicing variants, most of which lack the hinge domain, escape SPOP-mediated degradation. Prostate-cancer-associated mutants of SPOP cannot bind to and promote AR destruction. Furthermore, androgens antagonize SPOP-mediated degradation of AR, whereas antiandrogens promote this process. This study identifies AR as a bona fide substrate of SPOP and elucidates a role of SPOP mutations in prostate cancer, thus implying the importance of this pathway in resistance to antiandrogen therapy of prostate cancer.

Human tumor microRNA signatures derived from large‐scale oligonucleotide microarray datasets

The expression profiles of microRNAs (miRNAs) are associated with the initiation and progression of human tumors. DNA microarrays are widely used to explore the expression patterns of miRNAs. Because of the limited sample size and experimental expense, the statistical power of individual research projects is not sufficient to yield a robust conclusion. However, collected microarray datasets of expression profiles provide opportunities to compile the information of individual studies. Our study carried out a comprehensive meta‐analysis of miRNA expression microarray datasets from 28 published tumor studies; it comprises 33 comparisons and nearly 4,000 tumor and corresponding nontumorous samples. This work reports 52 miRNAs as common signatures that are dysregulated in tumors. In addition to the commonly altered miRNAs, five solid cancers displayed specific tissue patterns of altered miRNAs as well. The meta‐analysis also revealed some novel tumor‐related miRNAs such as hsa‐miR‐144, hsa‐miR‐130b, hsa‐miR‐132, hsa‐miR‐154, hsa‐miR‐192 and hsa‐miR‐345. We further validated the expression pattern of hsa‐miR‐154 in human hepatocellular carcinoma by RT‐PCR. Restoration of intracellular miR‐154 inhibited tumor cell malignance and the G1/S transition in cancer cells. Both bioinformatic prediction and western blotting demonstrated that miR‐154 could target CCND2. In addition, expression patterns of miR‐154 were inversely correlated with those of CCND2 in hepatocellular carcinoma. Overall, this study used a large‐scale data analysis to identify a qualified list of miRNAs that are consistently changed in tumors, which could lead to a better understanding of human tumor etiology.

Iron Metabolism Regulates p53 Signaling through Direct Heme-p53 Interaction and Modulation of p53 Localization, Stability, and Function

SUMMARY Iron excess is closely associated with tumorigenesis in multiple types of human cancers, with underlying mechanisms yet unclear. Recently, iron deprivation has emerged as a major strategy for chemotherapy, but it exerts tumor suppression only on select human malignancies. Here, we report that the tumor suppressor protein p53 is downregulated during iron excess. Strikingly, the iron polyporphyrin heme binds to p53 protein, interferes with p53-DNA interactions, and triggers both nuclear export and cytosolic degradation of p53. Moreover, in a tumorigenicity assay, iron deprivation suppressed wild-type p53-dependent tumor growth, suggesting that upregulation of wild-type p53 signaling underlies the selective efficacy of iron deprivation. Our findings thus identify a direct link between iron/heme homeostasis and the regulation of p53 signaling, which not only provides mechanistic insights into iron-excess-associated tumorigenesis but may also help predict and improve outcomes in iron-deprivation-based chemotherapy.

The Ubiquitin Ligase Itch Regulates Apoptosis by Targeting Thioredoxin-interacting Protein for Ubiquitin-dependent Degradation

Thioredoxin interacting protein (TXNIP) was originally characterized as an endogenous inhibitor of thioredoxin, a key regulator in cellular redox homeostasis. TXNIP is also known to play important roles in tumor growth and metastasis, glucose and lipid metabolism. TXNIP expression is induced by various stress stimuli. However, it has been unclear how TXNIP is down-regulated. Here, we report that TXNIP undergoes proteasomal degradation in cells. We identify Itch as the E3 ubiquitin ligase for TXNIP. We demonstrate that Itch mediates polyubiquitination of TXNIP both in vitro and in vivo. Overexpression of Itch leads to TXNIP proteasomal degradation. Knockdown of Itch by small interfering RNA causes an accumulation of the steady-state level of TXNIP. We also show that the PPXY motifs of TXNIP and the WW domains of Itch mediate their interaction. Furthermore, the Itch-TXNIP interaction regulates intracellular reactive oxygen species levels and apoptosis. These findings establish a new mechanism for the negative regulation of TXNIP by Itch and shed new light on the regulation of cellular redox homeostasis.

Cloning and identification of the human LPAAT-zeta gene, a novel member of the lysophosphatidic acid acyltransferase family

AbstractLysophosphatidic acid (LPA) is a naturally occurring component of phospholipid and plays a critical role in the regulation of many physiological and pathophysiological processes including cell growth, survival, and pro-angiogenesis. LPA is converted to phosphatidic acid by the action of lysophosphatidic acid acyltransferase (LPAAT). Five members of the LPAAT gene family have been detected in humans to date. Here, we report the identification of a novel LPAAT member, which is designated as LPAAT-ζ. LPAAT-ζ was predicted to encode a protein consisting of 456 amino acid residues with a signal peptide sequence and the acyltransferase domain. Northern blot analysis showed that LPAAT-ζ was ubiquitously expressed in all 16 human tissues examined, with levels in the skeletal muscle, heart, and testis being relatively high and in the lung being relatively low. The human LPAAT-ζ gene consisted of 13 exons and is positioned at chromosome 8p11.21.

An Insertion/Deletion Polymorphism within RERT-lncRNA Modulates Hepatocellular Carcinoma Risk

The Prolyl hydroxylase 1 (EGLN2) is known to affect tumorigenesis by regulating the degradation of hypoxia-inducible factor. Polymorphisms in EGLN2 may facilitate cancer cell survival under hypoxic conditions and directly associate with cancer susceptibility. Here, we examined the contribution of a 4-bp insertion/deletion polymorphism (rs10680577) within the distal promoter of EGLN2 to the risk of hepatocelluar carcinoma (HCC) in Chinese populations. The contribution of rs10680577 to HCC risk was investigated in 623 HCC cases and 1,242 controls and replicated in an independent case-control study consisting of 444 HCC cases and 450 controls. Logistic regression analysis showed that the deletion allele of rs10680577 was significantly associated with increased risk for HCC occurrence in both case-control studies [OR = 1.40; 95% confidence interval (CI) = 1.18-1.66, P < 0.0001; OR = 1.49; 95% CI = 1.18-1.88, P = 0.0007]. Such positive association was more pronounced in current smokers (OR = 3.49, 95% CI = 2.24-5.45) than nonsmokers (OR = 1.24, 95% CI = 1.03-1.50; heterogeneity P = 0.0002). Genotype-phenotype correlation studies showed that the deletion allele was significantly correlated with higher expression of both EGLN2 and RERT-lncRNA [a long noncoding RNA whose sequence overlaps with Ras-related GTP-binding protein 4b (RAB4B) and EGLN2)] in vivo and in vitro. Furthermore, RERT-lncRNA expression was also significantly correlated with EGLN2 expression in vivo, consistent with in vitro gain-of-function study that showed overexpressing RERT-lncRNA upregulated EGLN2. Finally, in silico prediction suggested that the insertion allele could disrupt the structure of RERT-lncRNA. Taken together, our findings provided strong evidence for the hypothesis that rs10680577 contributes to hepatocarcinogenesis, possibly by affecting RERT-lncRNA structure and subsequently EGLN2 expression, making it a promising biomarker for early diagnosis of HCC.

Nuclear Export of NF90 to Stabilize IL-2 mRNA Is Mediated by AKT-Dependent Phosphorylation at Ser647 in Response to CD28 Costimulation

IL-2 is one of the most important cytokines required for T cell-mediated immune responses. Costimulation of CD28 in T cells up-regulates IL-2 mRNA levels via transcription activation and mRNA stabilization. Upon T cell activation, NF90, an AU-rich element (ARE)-binding protein, translocates from the nucleus into the cytoplasm, where it binds to the ARE-containing 3′ untranslated regions of IL-2 mRNA and slows down degradation of IL-2 mRNA. The translocation of NF90 is mediated through a nuclear export signal at its N terminus, but how it is triggered is still unclear. Phosphorylation of ARE-binding proteins has been reported as a signal transduction pathway to stabilize ARE-containing transcripts. In this study, we demonstrate that AKT phosphorylates NF90 on Ser647 upon CD28 costimulation. This phosphorylation is necessary for nuclear export of NF90 and IL-2 mRNA stabilization by this protein, because a mutation at Ser647 abolished both functions. We observed that treatment of cells with CD28 costimulation induced distinct increase in phosphorylation of AKT and NF90 at Ser647 concomitantly. Phosphorylation at Ser647 of NF90 up-regulated IL-2 production in response to CD28 costimulation. In vivo and in vitro data support a model in which CD28 costimulation activates AKT to phosphorylate NF90 at Ser647 and phosphorylation triggers NF90 to relocate to the cytoplasm and stabilize IL-2 mRNA.

Identification of two novel human dynein light chain genes, DNLC2A and DNLC2B, and their expression changes in hepatocellular carcinoma tissues from 68 Chinese patients.

Two full-length cDNAs, DNLC2A and DNLC2B, were cloned and characterized. Their open reading frames respectively encode 96 amino acids which are most closely homologous to roadblock/LC7, one member of an ancient dynein light chain protein family, conserved in nematode, fruit fly, mouse and rat. The DNLC2A was expressed in 12 of 16 human tissues examined, with especially strong expression in heart, liver and brain, whereas there was weak expression in lung, prostate, testis, small intestine and colon. The expression of DNLC2B was generally high compared with that of DNLC2A except in liver. Northern blotting and/or semi-quantitative RT-PCR analysis examined the expression changes of DNLC2A and DNLC2B in 68 hepatocellular carcinoma tissue samples. It was revealed that DNLC2A was up-regulated (45 out of the 68 cases) while DNLC2B was down-regulated (44 out of 68 cases), compared with their adjacent tumor-free liver tissues. Interestingly, among the total 68 liver cancer samples tested, DNLC2A was up-regulated while DNLC2B was down-regulated in 28 cases; DNLC2A was up-regulated while no obvious change was observed for DNLC2B in 10 cases; no obvious change was observed for DNLC2A while DNLC2B was down-regulated in 14 cases. Although the underlying mechanism is not clear to date, the apparent up-regulation of DNLC2A and down-regulation of DNLC2B suggest that these genes might be involved in tumor progression. On the other hand, the different expression changes of the two homologous genes indicate that hepatocellular carcinomas are caused by different pathological mechanisms. In addition, DNLC2A was assigned to human chromosome 20q12-q13.11 near the marker D20S106 by radiation hybrid mapping.