The L1 genes of two human papillomavirus type 16 (HPV16) isolates derived from condylomata acuminata were used to express the L1 major capsid protein in insect cells via recombinant baculoviruses. Both L1 major capsid proteins self-assembled into virus-like particles (VLP) with high efficiency and could be purified in preparative amounts on density gradients. The yield of VLP was 3 orders of magnitude higher than what has been obtained previously, using L1 derived from the prototype HPV16. DNA sequence comparison identified a single nonconserved amino acid change to be responsible for the inefficient self-assembly of the prototype L1. VLP were also obtained by expressing L1 of HPV6, HPV11, and cottontail rabbit papillomavirus, indicating that L1 from a variety of papillomaviruses has the intrinsic capacity to self-assemble into VLP. Coexpression of HPV16 L1 plus L2 by using a baculovirus double-expression vector also resulted in efficient self-assembly of VLP, and the average particle yield increased about fourfold in comparison to when L1 only was expressed. Coimmunoprecipitation of L1 and L2 and cosedimentation of the two proteins in a sucrose gradient demonstrated that L2 was incorporated into the particles. The ability to generate preparative amounts of HPV16 L1 and L1-L2 VLP may have implications for the development of a serological assay to detect anti-HPV16 virion immune responses to conformational epitopes and for immunoprophylaxis against HPV16 infection.

No abstract

The binding of aflatoxin B1, AFB1, a potent hepatocarcinogen, to various high molecular weight (HMW) DNAs from human normal liver and two liver cancer cell lines, Alexander primary liver carcinoma (PLC) and Mahlavu hepatocellular carcinoma (hHC) and from NIH/3T3 cell have been investigated. The kinetics of AFB1 binding to these DNAs showed similar initial rates but the extents of binding to the PLC and hHC DNAs seemed to be slightly higher. Preferential AFB1 bindings were identified in both PLC and hHC DNAs compared to normal liver DNA when analyzed by restriction endonuclease digestions and agarose gel electrophoresis. A critical AFB1 binding dosage, ranging 100 to 460 fmole/,Lg DNA, was found to activate the carcinogenic effect of the Mahlavu hHC HMW DNA, but not normal liver HMW DNA, rendering it capable of inducing focal transformation in NIH/3T3 cell. Excessive AFB1 binding on the hHC and PLC HMW DNAs resulted in an "over-kill" of both cell transformation capability and templating activity of the DNA.

The binding of aflatoxin B1, AFB1, a potent hepatocarcinogen, to various high molecular weight (HMW) DNAs from human normal liver and two liver cancer cell lines, Alexander primary liver carcinoma (PLC) and Mahlavu hepatocellular carcinoma (hHC) and from NIH/3T3 cell have been investigated. The kinetics of AFB1 binding to these DNAs showed similar initial rates but the extents of binding to the PLC and hHC DNAs seemed to be slightly higher. Preferential AFB1 bindings were identified in both PLC and hHC DNAs compared to normal liver DNA when analyzed by restriction endonuclease digestions and agarose gel electrophoresis. A critical AFB1 binding dosage, ranging 100 to 460 fmole/,Lg DNA, was found to activate the carcinogenic effect of the Mahlavu hHC HMW DNA, but not normal liver HMW DNA, rendering it capable of inducing focal transformation in NIH/3T3 cell. Excessive AFB1 binding on the hHC and PLC HMW DNAs resulted in an "over-kill" of both cell transformation capability and templating activity of the DNA.

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