Biomedical subjects

Joseph Cheung

Publications and source records attributed to Joseph Cheung.

22 records · Page 2Linked to original sources

PubMed2002

A novel gene encoding a TIG multiple domain protein is a positional candidate for autosomal recessive polycystic kidney disease.

Autosomal recessive polycystic kidney disease (ARPKD) is a common hereditary renal cystic disease in infants and children. By genetic linkage analyses, the gene responsible for this disease, termed polycystic kidney and hepatic disease 1 (PKHD1), was mapped on human chromosome 6p21.1-p12, and has been further localized to a 1-cM genetic interval flanked by the D6S1714/D6S243 (telomeric) and D6S1024 (centromeric) markers. We recently identified a novel gene in this genetic interval from kidney cDNA, using cloning strategies. The gene PKHD1 (PKHD1-tentative) encodes a novel 3396-amino-acid protein with no apparent homology with any known proteins. We named its gene product "tigmin" because it contains multiple TIG domains, which usually are seen in proteins containing immunoglobulin-like folds. PKHD1 encodes an 11.6-kb transcript and is composed of 61 exons spanning an approximately 365-kb genomic region on chromosome 6p12-p11.2 adjacent to the marker D6S1714. Northern blot analyses demonstrated that the gene has discrete bands with one peak signal at approximately 11 kb, indicating that PKHD1 is likely to have multiple alternative transcripts. PKHD1 is highly expressed in adult and infant kidneys and weakly expressed in liver in northern blot analysis. This expression pattern parallels the tissue involvement observed in ARPKD. In situ hybridization analysis further revealed that the expression of PKHD1 in the kidney is mainly localized to the epithelial cells of the collecting duct, the specific tubular segment involved in cyst formation in ARPKD. These features of PKHD1 make it a strong positional candidate gene for ARPKD.

Amino Acid Sequence↗

PubMed2002

The RAY1/ST7 tumor-suppressor locus on chromosome 7q31 represents a complex multi-transcript system.

We recently identified a novel gene, RAY1 (FAM4A1), which spans a translocation breakpoint at 7q31 in a patient with autism. This gene has more recently been reported to be a suppressor of tumorigenicity, ST7, although controversy surrounds this observation because subsequent reports have failed to corroborate these findings. Our further analysis of this locus reveals that it is composed of a multigene system that includes two noncoding sense strand genes (ST7OT3 and ST7OT4) that overlap with many alternative forms of the coding RAY1/ST7 transcript, and two noncoding genes on the antisense strand (ST7OT1 and ST7OT2). RAY1/ST7 was determined to have at least three different 5' exons with alternative start codons, one of which seems to be used almost exclusively in the brain. We have also identified a third alternative 3' end of RAY1/ST7 that uses exons from ST7OT3. ST7OT3 spans from intron 10 to exon 14 of RAY1/ST7 and includes several exons. ST7OT4 has at least seven exons and is transcribed on the sense strand between RAY1/ST7 exon 1 and a tropomyosin-like sequence, TPM3L2. ST7OT1 overlaps with the RAY1/ST7 exon 1 and promoter. ST7OT2 spans from RAY1/ST7 intron 9 to intron 1, and has multiple isoforms. We screened the exons of RAY1/ST7 and ST7OT1-3 for sequence variants in 90 unrelated autism probands and identified several rare variants, including a Ile361Val substitution. Although these variants were not observed in a control population, it is unclear whether they contribute to the autistic phenotype. We postulate that the apparent noncoding genes at the RAY1/ST7 locus may be regulatory RNAs. The RAY1/ST7 may generate at least 18 possible isoforms, with many more arising if other sense-strand exons from ST7OT3 and ST7 OT4 are used in a selective and possibly tissue-specific manner.

Alternative Splicing↗

PubMed2002

The apolipoprotein E2 allele modulates activity and maximal velocity of the sodium-lithium countertransporter.

BACKGROUND: Alterations in erythrocyte sodium-lithium countertransport (SLC) activity and its maximal velocity (Vmax) are associated with hypertension and hypertriglyceridemia. The presence of apolipoprotein (apo) E variants is associated with hypertriglyceridemia. This study investigated the relationship between apoE phenotype and SLC kinetics. METHODS: Cardiovascular risk factors and SLC kinetics were measured in 171 subjects and 69 controls. Apolipoprotein E phenotypes were determined by Western blotting. RESULTS: Patients were 51% male, aged 56+/-13 years, with a blood pressure (BP) of 134+/-22/81+/-11 mm Hg, total cholesterol of 6.71+/-1.57 (256+/-61 mg/dL); median triglycerides 1.65 mmol/L (146 mg/dL) (range, 0.31 to 9.85 mmol/L; 27 to 872 mg/dL) and high-density lipoprotein (HDL) 1.39+/-0.43 mmol/L (54+/-16.6 mg/dL); fasting glucose 4.91+/-0.61 mmol/L (88.5+/-11.0 mg/dL); median insulin 11.7 IU/L (range, 3.7 to 39.8 IU/L). Phenotype frequencies were E3/E3 56%, E2/E3 14%, E2/E2 1%, E3/E4 27%, and E4/E4 2%. The SLC activity, Vmax, and sodium affinity (Km) were not significantly different with respect to apoE phenotype in simple analysis by Kruskal Wallis test. However, in multiple regression analysis after exclusion of BP, a strong co-correlate of SLC activity, the presence of an apoE2 allele was associated reduced activity (beta = -0.061; P = .01) along with HDL:apoA1 ratio (beta = -0.170; P < .001), whereas for the kinetic parameter Vmax, associations were found with triglyceride (beta = 0.029; P = .04), HDL:apoA1 ratio (beta = -0.186; P = .03) and the presence of an apoE2 allele (beta = -0.089; P = .04). CONCLUSIONS: These findings suggest that the apoE phenotype may modulate SLC activity and that the presence of an apoE2 allele phenotype is associated with lower SLC activity and Vmax.

Adult↗

PubMed2002

A role for common fragile site induction in amplification of human oncogenes.

Oncogene amplification is an important process in human tumorigenesis, but its underlying mechanism is currently unknown. Cytogenetic analysis indicates that amplification of drug-selected genes in rodent cells is driven by recurrent breaks within chromosomal common fragile sites (CFSs), via the breakage-fusion-bridge (BFB) mechanism. Here we show that BFB cycles drive the intrachromosomal amplification of the MET oncogene in a human gastric carcinoma. Our molecular evidence includes a "ladder-like" structure and inverted repeat organization of the MET amplicons. Furthermore, we show that the breakpoints, setting the centromeric amplicon boundaries, are within the CFS FRA7G region. Upon replication stress, this region showed perturbed chromatin organization, predisposing it to breakage. Thus, in vivo induction of CFSs can play an important role in human oncogenesis.

Centromere↗