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Biomedical subjects

John M Luk

Publications and source records attributed to John M Luk.

At least 19 recordsLinked to original sources

Clinicopathological roles of alterations of tumor suppressor gene p16 in papillary thyroid carcinoma.

BACKGROUND: Alterations of the p16 gene are common in human cancers, but their roles in thyroid cancers have not been clearly defined. The aim of the present study was to investigate the clinicopathological roles of the p16 gene in papillary thyroid carcinoma (PTC). METHODS: p16 gene alterations were investigated in 44 patients with PTC (9 men, 35 women) by immunohistochemistry, reverse transcriptase-polymerase chain reaction and methylation-specific polymerase chain reaction. The findings were correlated with their clinicopathological features. RESULTS: p16 protein expression, mRNA alterations, and promoter methylation were detected in 89% (n = 39), 77% (n = 33), and 41% (n = 18) of patients with PTC, respectively. There was no marked relationship between p16 protein expression, mRNA alteration, and promoter methylation. In follicular variant of PTC (FVPTC), there was a frequent lack of p16 protein expression and promoter methylation. PTCs showing p16 promoter methylation were often associated with a high AMES (age, metastasis to distant sites, extrathyroidal invasion, size) risk group and advanced pTNM (tumor-lymph node-metastasis) stages. CONCLUSIONS: p16 gene alterations are common and correlate with histological features and biological aggressiveness in PTC, suggesting that they might play an important role in its pathogenesis.

Adenocarcinoma, Follicular↗

Mutations in the tight-junction gene claudin 19 (CLDN19) are associated with renal magnesium wasting, renal failure, and severe ocular involvement.

Claudins are major components of tight junctions and contribute to the epithelial-barrier function by restricting free diffusion of solutes through the paracellular pathway. We have mapped a new locus for recessive renal magnesium loss on chromosome 1p34.2 and have identified mutations in CLDN19, a member of the claudin multigene family, in patients affected by hypomagnesemia, renal failure, and severe ocular abnormalities. CLDN19 encodes the tight-junction protein claudin-19, and we demonstrate high expression of CLDN19 in renal tubules and the retina. The identified mutations interfere severely with either cell-membrane trafficking or the assembly of the claudin-19 protein. The identification of CLDN19 mutations in patients with chronic renal failure and severe visual impairment supports the fundamental role of claudin-19 for normal renal tubular function and undisturbed organization and development of the retina.

Adolescent↗

Liver intestine-cadherin (CDH17) haplotype is associated with increased risk of hepatocellular carcinoma.

PURPOSE: Hepatocellular carcinoma (HCC), the most common form of liver cancer, is a leading cause of cancer death worldwide. We previously showed that aberrant mRNA splicing of the liver intestine-cadherin gene CDH17 in liver tissues was triggered by the specific constellation of two CDH17 single nucleotide polymorphisms (651T and IVS6+35G). CDH17 aberrant splicing was highly associated with tumor dissemination and shorter survival of HCC patients. Consequently, it is highly relevant to assess whether the presence of these single nucleotide polymorphisms in the general population represents a risk to the development of HCC. EXPERIMENTAL DESIGN: We conducted a case-control study including 164 HCC and 99 cirrhosis patients and 293 healthy controls. Genotyping was done by PCR and direct sequencing. Odds ratio (OR) and chi2 analysis were used to analyze genotypes and haplotypes. RESULTS: Genotypes 651TT [OR, 2.62; 95% confidence interval (95% CI), 1.34-5.03] and IVS6+35 GG (OR, 1.95; 95% CI, 1.04-3.62) were highly associated with HCC disease. The 651T (C>T) and IVS6+35G (A>G) alleles were also overrepresented in HCC patients and, in particular, the T-G haplotype was the most prevalent in HCC patients when compared with healthy controls (OR, 1.57; 95% CI, 1.167-2.109; P=0.004), which was in agreement with the aberrant splicing observed in tumor tissues. There was no significant difference in genotype and allele frequencies between cirrhosis patients and controls. CONCLUSION: The functional T-G haplotype of CDH17 (651 C>T and IVS6+35A>G) is a genetic susceptibility factor for the development of HCC in a Chinese population.

Alleles↗

Identification and validation of oncogenes in liver cancer using an integrative oncogenomic approach.

The heterogeneity and instability of human tumors hamper straightforward identification of cancer-causing mutations through genomic approaches alone. Herein we describe a mouse model of liver cancer initiated from progenitor cells harboring defined cancer-predisposing lesions. Genome-wide analyses of tumors in this mouse model and in human hepatocellular carcinomas revealed a recurrent amplification at mouse chromosome 9qA1, the syntenic region of human chromosome 11q22. Gene-expression analyses delineated cIAP1, a known inhibitor of apoptosis, and Yap, a transcription factor, as candidate oncogenes in the amplicon. In the genetic context of their amplification, both cIAP1 and Yap accelerated tumorigenesis and were required to sustain rapid growth of amplicon-containing tumors. Furthermore, cIAP1 and Yap cooperated to promote tumorigenesis. Our results establish a tractable model of liver cancer, identify two oncogenes that cooperate by virtue of their coamplification in the same genomic locus, and suggest an efficient strategy for the annotation of human cancer genes.

Adaptor Proteins, Signal Transducing↗

Kidney claudin-19: localization in distal tubules and collecting ducts and dysregulation in polycystic renal disease.

Tight junction (TJ) constitutes the barrier by controlling the passage of ions and molecules via paracellular pathway and the movement of proteins and lipids between apical and basolateral domains of the plasma membrane. Claudins, occludin, and junctional adhesion molecules are the major three transmembrane proteins at TJ. This study focuses a newly identified mammalian TJ gene, claudin-19, in kidneys. Mouse claudin-19 composes of 224 amino acids and shares 98.2% and 95% amino acid homology with rat and human, respectively; the most evolutionary-related claudins are claudin-1 and -7, which share approximately 75% DNA sequence homology with claudin-19. Claudin-19 is abundantly expressed in the mouse and rat kidneys among the organs examined by Northern blots, and to a much less extent, also found in brain by RT-PCR. Claudin-19 and zonula occludens-1 (ZO-1) are localized at junctional regions of Madin-Darby canine kidney (MDCK) cells by immunofluorescent microscopy. In addition, ZO-1 is found in the claudin-19-associated protein complexes in MDCK cells by co-immunoprecipitation. Using aquaporin-1 and aquaporin-2 antibodies as markers for different renal segment, strong expression of claudin-19 was observed in distal tubules of the cortex as well as in the collecting ducts of the medulla. To less extent, claudin-19 is also present in the proximal tubules (cortex) and in the loop of Henle (medulla). Furthermore, intense claudin-19 immunoreactivity is found co-localized with the ZO-1 in kidneys from postnatal day 15, day 45, and adult rats and mice. Similar localizations of claudin-19 and ZO-1 are also observed in human kidneys. Since these renal segments are mainly for controlling the paracellular cation transport, it is suggested that claudin-19 may participate in these processes. In human polycystic kidneys, decreased expression and dyslocalization of claudin-19 are noticed, suggesting a possible correlation between claudin-19 and renal disorders. Taken together, claudin-19 is a claudin isoform that is highly and specifically expressed in renal tubules with a putative role in TJ homeostasis in renal physiology.

Animals↗

TNP-470 blockage of VEGF synthesis is dependent on MAPK/COX-2 signaling pathway in PDGF-BB-activated hepatic stellate cells.

Angiogenesis is a key pathogenic event in hepatic fibrogenesis, which is mediated by activated hepatic stellate cells (HSCs). TNP-470 is a known anti-angiogenic agent in cancer, and in this study, we investigated the regulatory mechanisms of TNP-470 blockage of vascular endothelial growth factor (VEGF) synthesis in activated HSCs. Primary HSCs were isolated from rat liver, cultured in vitro, and activated with platelet-derived growth factor-BB (PDGF-BB). After treatment with TNP-470, Nimesulide, PD98059, SB203580 or SP600125, activated HSCs were analyzed by immunoblotting, quantitative RT-PCR, and ELISA for mitogen-activated protein kinase (MAPK) family [ERKs, JNK, and p38], cyclooxygenase-2 (COX-2), and VEGF levels. Phosphorylation of p44/42 MAPK, which was followed by increased expressions of COX-2 and VEGF, was observed in PDGF-BB-activated HSCs; these events could be ameliorated by addition with TNP-470 in time- and dose-dependent manners. TNP-470 also inhibited the secretion of VEGF from activated HSCs into culture supernatant. Furthermore, TNP-470 blockage of VEGF production in activated HSCs could be nullified by exogenous inoculation with prostaglandin E(2). In summary, our findings suggest that TNP-470 exhibits the observed anti-angiogenic properties in activated HSCs by targeting the COX-2/phospho-p44/42 MAPK pathway to inhibit VEGF production.

Angiogenesis Inhibitors↗

Acrosome-specific gene AEP1: identification, characterization and roles in spermatogenesis.

Spermatogenesis is a tightly regulated process leading to the development of spermatozoa. To elucidate the molecular spermatogenic mechanisms, we identified an acrosome-specific gene AEP1 in spermatids, which is located in rat chromosome 17p14 with a transcript size of 3,091 bp encoding a signal peptide, zinc finger-like motif, coiled-coil region, several predicted glycosylation and phosphorylation sites. Northern blot and RT-PCR analyses revealed the restricted expression of AEP1 to the testis only. In postnatal rat testes, AEP1 mRNA became detectable from postnatal 25 dpp (round spermatids) and onwards. By using in situ hybridization (ISH) and flow cytometry-fluorescent ISH, only the haploid spermatids yielded the positive AEP1 signal. Immunohistochemistry showed that AEP1 was expressed in the acrosomal cap of late-staged germ cells in rat testis, and co-localized with the acrosomal marker, peanut agglutinin. The spatial expression of AEP1 immunoreactivity in testis was conserved among diverse mammalian species (rat, pig, monkey, human). To further study its roles in spermatogenesis, we showed AEP1 and beta-actin was associated together in complex by co-immunoprecipitation in adult germ cells and by immunofluorescence assay in isolated spermatozoon. In human testes diagnosed with hypospermatogenesis, lower expression of AEP1 was observed, whereas there was no detectable signal in undescended testes. In short, AEP1 is an evolutionary-conserved acrosome-specific gene and likely functions in acrosome-cap formation.

Acrosome↗

Proteomic profiling of hepatocellular carcinoma in Chinese cohort reveals heat-shock proteins (Hsp27, Hsp70, GRP78) up-regulation and their associated prognostic values.

To facilitate the identification of candidate molecular biomarkers that are linked to the pathogenesis of hepatocellular carcinoma (HCC), we investigated protein-expression profiles of 146 tissue specimens including 67 pairs of tumors and adjacent non-tumors resected from HCC patients as well as 12 normal livers by 2-DE. Among the 1800 spots displayed in the liver proteome, a total of 90 protein species were found to be significantly different between the three groups (P < 0.05). Three of the top candidate markers up-regulated in HCC, with high receiver operating characteristic (ROC) curves, were identified by MS/MS analysis and belonged to the chaperone members: heat-shock protein (Hsp)27, Hsp70 and glucose-regulated protein (GRP)78. Over-expression of these chaperone proteins in HCC tissues was confirmed by Western blotting and immunohistochemistry. In correlation with clinico-pathological parameters, expression of Hsp27 was linked to alpha-fetoprotein level (P = 0.007) whereas up-regulation of GRP78 was associated with tumor venous infiltration (P = 0.035). No significant association of Hsp70 with any pathologic features was observed. The present HCC proteome analysis revealed that in response to the stressful cancerous microenvironment, tumor cells strived to increase the expression of chaperone proteins for cyto-protective function and to enhance tumor growth and metastasis.

Adolescent↗

Blockage of testicular connexins induced apoptosis in rat seminiferous epithelium.

Spermatogenesis, a tightly regulated developmental process of male germ cells in testis, is associated with temporal and spatial expression of gap junction proteins, such as the connexin family members. Perturbation of their expressions may lead to spermatogenic arrest as manifested by disruption of cell-cell interaction. To explore the role(s) of connexins during spermatogenesis, we utilized the small peptide antagonistic approach to specifically deplete connexin 31, connexin 33, and pan-connexin. Three connexin peptides corresponding to the extracellular binding domain of connexin 31 and connexin 33 and to the extracellular conserved domain of connexins were designed and synthesized commercially. Peptides (at single dosage of 0.5, 1, or 2 mg per animal) were injected into rat testes and testes were collected on day 0, 1, 3, 5, 10, 15, and 30 after microinjection. In situ TUNEL assay demonstrated the induction of apoptosis in the testes after pan-connexin peptide treatment in a dose-dependent manner from day 3 and onward. Unlike the pan-connexin peptide, connexin 31 and connexin 33 peptides appeared to have little effect on inducing apoptosis and germ cell loss. CD45 staining also detected the occasional presence of infiltrating lymphocytes in the seminiferous tubules. Accompanied with the apoptotic events, two apoptotic markers, NF-kappaB and caspase 3, demonstrated a general up-regulation in their expressions. In adjacent testis sections, eliminations of connexin 31, 32, and 43 were observed. However, an induction of connexin 33 expression was detected. This suggests the versatility and functional diversity of connexins in the testis. The expression of ZO-1, the only known adaptor of connexins in the testis, was reduced and remained in a low level in the seminiferous epithelium. As such, the alterations of connexins in seminiferous epithelium may induce apoptotic signaling in the testis via the caspase 3 and the NF-kappaB pathway. This demonstrates the significant role of testicular connexins to maintain the survival of germ cells by regulating inter-cellular communications among germ cells and adjacent supporting cells during spermatogenesis. In addition, the inter-relationship between connexins and other junction proteins and associated signaling protein were investigated. After pan-connexin peptide treatment, a dys-localization of N-cadherin, an adherens junction protein, and diminution of occludin, a tight junction protein, level were detected. In addition, inductions of junction regulatory protein, cathepsin L, was observed during the course of peptide-mediated germ cell loss in the testes. In summary, pan-connexin peptide treatment triggered apoptosis and germ cell loss in the testes. This event influenced the localization and expression of different junction proteins and junction-associated protein in the testes.

Animals↗

Kinetics and risk of de novo hepatitis B infection in HBsAg-negative patients undergoing cytotoxic chemotherapy.

BACKGROUND & AIMS: De novo hepatitis B virus (HBV)-related hepatitis after chemotherapy results in high morbidity and mortality. We evaluate the clinical course of de novo HBV-related hepatitis after chemotherapy. METHODS: Two hundred forty-four consecutive hepatitis B surface antigen (HBsAg)-negative lymphoma patients treated with chemotherapy were followed up for a median of 12.4 (range, 0.1-65.0) months. Serially collected serum samples were analyzed for hepatitis, serum HBV DNA, and HBsAg seroreversion. RESULTS: Eight of the 244 patients (3.3%) developed de novo HBV-related hepatitis. A 100-fold increase in serum HBV DNA preceded de novo HBV-related hepatitis by a median of 18.5 (range, 12-28) weeks. All 8 patients had normal serum alanine aminotransaminase level when the 100-fold increase in serum HBV DNA occurred. Patients with de novo HBV-related hepatitis were more likely to have occult HBV infection before chemotherapy. Direct sequencing results showed that these 8 patients had de novo HBV-related hepatitis from reactivation of occult HBV infection. Three of the 8 patients with de novo HBV-related hepatitis compared with 6 of the 236 patients without de novo HBV-related hepatitis developed fulminant hepatic failure (37.5% vs 2.5%, respectively, P < .001). On multivariate Cox analysis, de novo HBV-related hepatitis was independently associated with a higher risk of fulminant hepatic failure (relative risk, 29.854; 95% confidence interval: 4.844-183.980; P < .001). CONCLUSIONS: Close surveillance for a 100-fold increase in HBV DNA is recommended for HBsAg-negative patients treated with chemotherapy so that early commencement of antiviral therapy can be initiated before the occurrence of de novo HBV-related hepatitis.

Adult↗

Comparison of real-time PCR assays for monitoring serum hepatitis B virus DNA levels during antiviral therapy.

The performance characteristics of the RealART and Molecular Beacons assays were compared with those of the Digene Hybrid Capture II assay (ultrasensitive). The results of the RealART and Digene Hybrid assays were related (r = 0.94; P < 0.001) and diverged by 2 orders of magnitude. The RealART assay can be used to effectively monitor serum hepatitis B virus DNA levels.

DNA, Viral↗

Increased solubility of integrin betaA domain using maltose-binding protein as a fusion tag.

In proteomics research, generation of recombinant proteins in their native, soluble form with large quantity is often a challenging task. To tackle the expression difficulties, different expression vectors with distinct affinity fusion tags, i.e. pET-43.1a (N-utilization substance A tag), pMAL-cRI (maltose binding protein tag) (MBP tag), pGEX-4T-2 (glutathione S-transferase tag), and pET-15b (hexahistidine tag) were compared for their effects on the productivity and solubility, which were assessed by SDS-PAGE and immunoblotting, of the integrin betaA domain. The incubation temperatures were tested for its effects on these parameters. Our data suggested that MBP tag enhanced the yield and solubility of the betaA domain protein, which can also be recognized using an anti-CD18 antibody, at room temperature incubation. Thus, the nature of fusion partner chosen for expression in bacteria and its incubation temperature would significantly affect the yield and solubility of the recombinant target protein.

Animals↗

Tumor necrosis factor-alpha-induced protein 1 and immunity to hepatitis B virus.

AIM: To compare the gene expression profile in a pair of HBV-infected twins. METHODS: The gene expression profile was compared in a pair of HBV-infected twins. RESULTS: The twins displayed different disease outcomes. One acquired natural immunity against HBV, whereas the other became a chronic HBV carrier. Eighty-eight and forty-six genes were found to be up- or down-regulated in their PBMCs, respectively. Tumor necrosis factor-alpha-induced protein 1 (TNF-alphaIP1) that expressed at a higher level in the HBV-immune twins was identified and four pairs of siblings with HBV immunity by RT-PCR. However, upon HBV core antigen stimulation, TNF-alphaIP1 was downregulated in PBMCs from subjects with immunity, whereas it was slightly upregulated in HBV carriers. Bioinformatics analysis revealed a K+ channel tetramerization domain in TNF-alphaIP1 that shares a significant homology with some human, mouse, and C elegan proteins. CONCLUSION: TNF-alphaIP1 may play a role in the innate immunity against HBV.

Adaptor Proteins, Signal Transducing↗

Increased expression of vascular endothelial growth factor C in papillary thyroid carcinoma correlates with cervical lymph node metastases.

PURPOSE: Despite recent studies showing that vascular endothelial growth factor C (VEGF-C) mRNA is up-regulated in papillary thyroid carcinoma (PTC), the role of VEGF-C in lymph node metastasis is still unclear. The aim of this study is to investigate the expression pattern of VEGF-C immunoreactive protein in PTC and its relationship with cervical lymph node metastasis. EXPERIMENTAL DESIGN: Tissue samples were obtained from 39 specimens of PTC (20 with and 19 without lymph node metastasis) as well as 20 benign thyroid nodules. Overexpression of the VEGF-C protein was evaluated by immunoblotting with specific anti-VEGF-C antibody in paired tumor and nontumor tissues from PTC. The data were compared with patients' clinicopathologic features and lymph node metastasis. Immunohistochemical staining was done on selected paraffin sections to determine cellular localization of VEGF-C and to assess flt-4 (or VEGFR-3)-positive vessel density in PTC lesions. RESULTS: Overexpression of VEGF-C was detected in 69% of the PTC and in 5% of the benign thyroid specimens. When comparing between the metastatic and nonmetastatic groups of PTC, a higher expression level of VEGF-C was detected in both the tumor (P = 0.004) and adjacent nontumor tissues (P = 0.011). Positive immunostaining for VEGF-C was confirmed in PTC tumor tissues and metastatic lymph nodes, which correlated with flt-4-positive vessel density in tumor and peritumor tissues. The increased expression of VEGF-C protein in PTC is associated with lymph node metastasis (P = 0.004) and lymphovascular permeation (P = 0.001) but is independent of other clinicopatholgic variables. CONCLUSIONS: The VEGF-C immunoreactive protein is overexpressed in PTC lesions, which correlates with lymph node metastases. VEGF-C expression may play a role in lymphangiogenesis of PTC and further study is necessary to evaluate the clinical application of VEGF-C as a molecular marker for tumor metastases to cervical lymph nodes.

Adolescent↗

Hepatic potential of bone marrow stromal cells: development of in vitro co-culture and intra-portal transplantation models.

Bone marrow comprises heterogeneous cell populations and is thought to contain certain progenitors with the ability to differentiate into multiple mesenchymal cell lineages. To identify any differentiation plasticity of adult bone marrow stromal cells (BMSCs) into hepatocyte-like phenotypes, we developed a co-culture model with damaged liver tissue and an animal model of engraftment in cirrhotic liver via intra-portal transplantation. After 10 days of co-culture with injured liver tissues, BMSC expressed specific markers for hepatocytes by RT-PCR and Western blot. The two animal models for liver injury employed used carbon tetrachloride (CCl4) induction or bile duct ligation. For tracing BMSC resident in the liver after intra-portal transplantation, green fluorescent protein (GFP)-positive BMSCs or in situ hybridization of Y-chromosome Sry gene in male BMSC were used in a cross-sex transplantation model. Expression of hepatocyte-specific markers in recipients' liver tissues was determined by fluorescence immunohistochemistry. Our findings demonstrated that about 16% parenchyma cells were GFP-positive cells derived from infused BMSCs, and expression of albumin was detected in these cells in engrafted liver tissues. In conclusion, BMSCs exhibited hepatocyte-like phenotypes after co-cultivation with liver tissue and transplanted into the injured liver. The presented evidence indicated the trans differentiation potential of BMSC developing to the hepatocytes.

Albumins↗

Fibrosis progression in chronic hepatitis C patients with occult hepatitis B co-infection.

Occult hepatitis B virus (HBV) infection in individuals without hepatitis B surface antigen (HBsAg) can be identified in hepatitis C virus (HCV) infected patients. However, its role in fibrosis progression remains uncertain. This retrospective study compared the fibrosis progression (defined as fibrosis progression by at least one stage) and progression to severe fibrosis (fibrosis stage 3 or 4) in HCV patients with occult HBV infection. Occult HBV infection was diagnosed by the detection of HBV DNA in the serum of 74 consecutive anti-HCV positive patients by PCR. Thirty-one patients (41.9%) had occult HBV infection. All 74 patients had a median of 2 (range 2-3) liver biopsies. The median time between the first and last liver biopsy was 57.7 (range 15.0-132.8) months. Eleven of the 31 patients with occult HBV infection compared with 12 of the 43 patients without occult HBV infection had fibrosis progression (35.5% versus 27.9%, respectively, p=0.608). Six of the 31 patients with occult HBV infection compared with 8 of the 43 patients without occult HBV infection developed severe fibrosis (19.4% versus 18.6%, respectively, p=0.946). In conclusion, chronic HCV patients with occult HBV co-infection does not seem to progress more than patients without occult HBV infection. However, more large-scale studies are needed before a definite conclusion can be obtained.

DNA, Viral↗

Alternative mRNA splicing of liver intestine-cadherin in hepatocellular carcinoma.

PURPOSE: To identify alternative splicing of the liver intestine-cadherin (LI-cadherin) gene in hepatocellular carcinoma (HCC) and correlate its aberrant expression with clinical outcomes. EXPERIMENTAL DESIGN: Reverse transcription-PCR (RT-PCR) and quantitative real-time RT-PCR were used to examine alternative mRNA splicing and mRNA level of LI-cadherin in 50 paired tumor-peritumor tissues of 50 HCC and 8 normal liver specimens. The minigene exon-trapping strategy was employed to investigate the splicing mechanism introduced by nucleotide polymorphisms. Association of LI-cadherin splicing with tumor venous infiltration, first-year tumor recurrence, and overall survival after partial hepatectomy were determined. RESULTS: Alternative mRNA splicing of LI-cadherin was identified in half of the HCC specimens. Sequencing analysis indicated the loss of exon 7 in the spliced LI-cadherin gene. LI-cadherin mRNA was up-regulated from 2.58-fold to 800-fold in over 80% of HCC samples when compared with normal liver by quantitative PCR. Furthermore, nucleotide polymorphisms were identified in putative branch point at IVS6 + 35 (intron 6) as well as in coding sequence 651 (exon 6) in HCC tissues, which may affect alternative mRNA splicing. Clinically, those patients who harbored the alternative splicing of LI-cadherin were strongly associated with shorter overall survival time (P < 0.01) as well as higher incidences of tumor recurrences and venous infiltration (both P < 0.05) after hepatectomy. CONCLUSIONS: Over-expression of LI-cadherin was frequently detected in liver cancer patients. Aberrant alternative splicing of LI-cadherin was detected in 50% of HCC specimens and its clinical significance hinted at early tumor recurrence and poor overall survival of HCC patients.

Alternative Splicing↗