Jui-He Tsai | PubMed Health

PubMed2005

HHR23A, a human homolog of Saccharomyces cerevisiae Rad23, regulates xeroderma pigmentosum C protein and is required for nucleotide excision repair.

HHR23A and hHR23B are the human homologs of Saccharomyces cerevisiae Rad23. hHR23B is associated with the nucleotide excision repair (NER) factor xeroderma pigmentosum C (XPC) protein and is required for global genome repair. The function of hHR23A is not yet clear. In this study, the potential function of the hHR23A protein was investigated using RNA interference techniques. The hHR23A knock-down (KD) construct diminished the RNA level of hHR23A protein by approximately 60%, and it did not interfere with expression of the hHR23B gene. Based on Southwestern immunoblot and host-cell reactivation assays, hHR23A(KD) cells were found to be deficient in DNA repair activity against the DNA damage caused by UVC irradiation. In these hHR23A(KD) cells, the XPC gene was not normally induced by UVC irradiation, indicating that the hHR23A protein is involved in NER through regulation of the DNA damage recognition protein XPC. Co-immunoprecipitation experiments revealed that hHR23A was associated with a small portion of hHR23B and the majority of p53 protein, indicating that hHR23A regulates the function of XPC by its association with the NER activator p53.

Cell Line, Tumor↗

PubMed2002

Two UVC-induced stress response pathways in HeLa cells identified by cDNA microarray.

Environmental toxins induce multiple effects in vivo, involving various molecular pathways. The ultraviolet C (UVC, 254 nm) component of sunlight can cause strong cytotoxic and genotoxic effects. In this study, UVC-induced stress response factors were analyzed by cDNA microarray, using the Millennium(R) Nylon membrane chip system. HeLa cells were irradiated with 30 Joule/m(2)/sec UVC, incubated for 30 or 60 minutes and then subjected to the analysis. Multiple chips were used for each experimental condition so that the data could be analyzed statistically. Principal component analysis (PCA) was used to identify groups of genes whose expression changed in a similar manner with time post-UVC irradiation. Three major factors were identified, depending on the directionality of expression changes in each gene. The factor loadings in all three identified gene groups were high, indicating that genes within each group were highly correlated. Two factors exhibited significantly changed expression patterns after 30 minutes of incubation but in the opposite direction. This indicates that the "immediate early" UVC-induced stress response was elicited by two major pathways. Interestingly, expression of the genomic damage-inducible GADD genes, as well as p53, was initially decreased, unlike the "immediate early" genes Fos/Jun and Egr-1, which were strongly increased after 30 minutes of incubation. The results indicate that PCA used in the analysis of pre-hypothesized, functionally related genes can identify the potential subpathways in a group. This method provides a novel approach for identifying functionally-related genes in microarray studies.

Enzymes↗