S Subbaiah | PubMed Health

PubMed1998

A lambda 3' enhancer drives active and untemplated somatic hypermutation of a lambda 1 transgene.

Somatic hypermutation is a highly regulated process that targets mutations to the rearranged Ig genes. Little is known about the cis-elements required for somatic hypermutation of the lambda light chain gene. We have studied somatic hypermutation of a rearranged lambda 1 transgene under the control of either a lambda 2-4 or kappa 3' enhancer. The mutations in the transgenes were analyzed by sequencing DNA amplified from hypermutating Peyer's patch B cells. The results indicate that the lambda 3' enhancer can drive active hypermutation of a lambda 1 transgene in Peyer's patch cells. The lambda 1 transgene under analysis carried two marked V lambda 2 genes immediately upstream that could serve as sequence donors in possible gene conversion events. There was no evidence of sequence transfer to the hypermutated lambda 1 gene, suggesting that gene conversion is not a major mechanism for somatic hypermutation in mice.

Animals↗

PubMed1990

Proteoglycan synthesis by normal and neoplastic human transitional epithelial cells.

Metabolically 35S-labeled proteoglycans were isolated from cell-associated matrices and media of confluent cultures of human normal transitional epithelial cells and HCV-29T transitional carcinoma cells. On Sepharose CL-4B columns, the cell-associated proteoglycans synthesized from both cell types separated into three identical size classes, termed CI, CII, and CIII. Normal epithelial cell C-fractions eluted in a 22:34:45 proportion and contained 64%, 64%, and 72% heparan sulfate, whereas corresponding HCV-29T fractions eluted in a 29:11:60 proportion, and contained 91%, 77%, and 70% heparan sulfate, respectively. Medium proteoglycans from normal cells separated into two size classes in a proportion of 6:94 and were composed of 35% and 50% heparan sulfate. HCV-29T medium contained only one size class of proteoglycans consisting of 23% heparan sulfate. The remaining percentages were accounted for by chondroitin/dermatan sulfate. On isopycnic CsCl gradients, proteoglycan fractions from normal cells had buoyant densities that were higher than the corresponding fractions from HCV-29T cells. DEAE-Sephacel chromatography showed that cell and medium associated heparan sulfate from HCV-29T cells was consistently of lower charge density (undersulfated) than that from normal epithelial cells. In contrast, the chondroitin/dermatan sulfate of HCV-29T was of a charge density similar to that of normal cells. These as well as other structural and compositional differences in the proteoglycan may account, at least in part, for the altered behavioral traits of highly invasive carcinoma cells.

Carcinoma, Transitional Cell↗