Cellular Levels of DNA Polymerase α and β Activities in Mouse Sarcoma Cells Trated with Benzo(a)pyrene Diolepoxide

Enzyme activities of DNA polymerase α and β have been analyzed in anti (+)-r-7, t-8-dihydroxy-t-9,10-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene (BPDE) treated mouse sarcoma cells. The time courses of repair synthesis following treatment of mouse sarcoma cells with 400 ng/ml of BPDE as measured by ³H-thymidine incorporation into the cells for 1 hr show biphasic curve, which indicates two apparent repair phases. Two distinct chromatographic elution profiles of DNA polymerases were observed when cells were treated with carcinogen and post incubated for 3 or 9 hrs, and cell homogenates were applied onto DEAE-52 anion exchange column. Cellular level of DNA polymerase α activity allowed to repair the DNA damage for 3 hrs was significantly higher than that of DNA polymerase β while DNA polymerase β activity was a predominant one in 9 hrs post incubated cells. Data presented here suggest that both DNA polymerase α and β are required to resynthesize the excised DNA damage, and that DNA polymerase α is the major enzyme involved in the resynthesis of DNA damage after endonuclease nicking step while DNA polymerase β is playing the major role in filling the rest of the gap thereafter

Elucidation of the Intestinal Zinc Transport mechanism

The effects of prostaglandin El [PGE1], testosterone, 17β-estradiol and indomethacin on the zinc flux rate across the jejunal segements isolated from rats of each sex were determined using the Ussing chamber technique. Addition of PGE1 [5.0 μM] to the segment bathing medium significantly stimulated the zinc flux rate from mucosa-to-serosa [J_(ms)] of the jejunal segements isolated from male rats and inhibited it in those from female rats. 17β-estradiol [10 nM] inhibited J_(ms) of jujunal segments isolated from male rats, but testosterone stimulated those from female rats. To confirm that testosterone stimulates and 17β-estradiol inhibits J_(ms), the effects of testosterone on the zinc flux rates of segments isolated from male rats and 17β-estradiol on those from female rats were determined. In those experiments, both testosterone and 17β-estradiol inhibited J_(ms) without affecting the zinc flux rate from serosa-to-mucosa [J_(sm)]. However, when rats were ovariectomized, both of these steroid hormones stimulated J_(ms). Interestingly neither PGE1 nor steroid sex hormones produced any effect on the J_(sm), although indomethacin stimulated the J_(sm) of segments from male rats. These results suggest that steroid sex hormones interact with PGs in influencing the intestinal zinc transport and that endogenous PGs and steroid sex hormones augment the effects of exogenous hormones and PGs