The overall goal of this recombinant HBV reporter system is to make it easy to conduct mass screening for anti-Hepatitis B virus, or HBV agents. This method can help answer key questions in the HBV field, such as screening for anti-HBV agents and identification HBV factors. The main advantage of this technique is that the HBV reporter system can monitor the earlier stages of the HBV replication cycle.
After preparing cell culture medium, the day before transvection, place four times 10 to the six HepG2 cells in medium, on a 10 cm collagen coated dish. Incubate the cells at 37 degrees C in a humidifed 5%CO2 incubator. Using a transvectionary agent according to the manufacturer's instructions, transvect the cells with 5 mcg of pUC1 2HBV delta epsilon, and 5 mcg of pUC1 2HBV/NL.
The next day, remove the culture medium and add 10 mL of fresh culture medium. Then, one week after transvection, transfer the culture medium containing the recombinant HBV to a 50 mL tube. Next, add 10 mL of fresh culture medium to the plate containing transvected cells.
Then collect and centrifuge the culture medium at 2, 300 x g for five minutes to remove the cell debris containing the recombinant HBV. Pass the supernatant through a 45 mcm membrane filter. Then add an equal volume of 25%PEG, 1.5 molar NaCl, to the filtrate, and gently mix.
Incubate the sample overnight at four degrees C.The following day, spin the solution at 2, 300 x g and four degrees C, for 20 minutes. Discard the supernatant and dissolve the pellet in 5 mL of TNE buffer. Now centrifuge the sample again to remove cell debris, then load 5 mL of the TNE-containing recombinant HBV onto 8 mL of 20%sucrose in TNE.
Centrifuge the two at 100, 000 x g and 15 degrees celsius for three hours. Discard as much of the supernatant as possible and use 1 mL of serum-free DMEM per 40 mL of starting culture to re-suspend the pellet. Incubate the suspension at four degrees celsius overnight.
The following morning, filter the suspension through a 45 mcm filter. Then prepare 5 mL aliquots and store the tubes at minus 80 degrees celsius. Plate HepG2 cells, stably expressing sodium taurocholate cotransporting polypeptide, or NTCP, that are susceptible to HBV infection, and incubate at 37 degrees celsius and 5%CO2.
One day before infection, plate approximately five times 10 to the fourth HepG2 NTCP cells into the wells of a 96-well collagen coated plate, in 1 mL of culture medium. Thaw recombinant HBV in a 37 degree celsius water bath, until there is a small bit of ice remaining in the vial. Prepare medium for infection by combining 78 mcL of fresh culture medium, 2 mcL of DMSO, 10 mcL of 40%PEG 8000, in 1x PBS, and 10 mcL of recombinant HPV.
Add 100 mcL of recombinant HBV solution to each well of a 96-well plate. One day after infection, use 300 mcL of PBS to wash the cell three times to remove the contaminating reporter protein from the virus fraction. Add 200 mcL of culture medium, containing 2%DMSO, to the infected cells, and incubate for one week or less.
To carry out analysis of the HBV infection, one week after infection, use PBS to wash the infected cells three times. Add 50 mcL of Lysis Buffer to the infected cells. Rock the culture plate for five minutes then centrifuge at 2, 000 x g for five minutes.
Add 50 mcL of the reporter substrate to a Luminometer plate. Then add 20 mcL of the cell lysate to the plate and mix by briefly shaking. Finally, place the plate in the Luminometer and initiate reading.
This gel shows digestion of the constructed pUC1 2HBVNL reporter plasmid, and the pUC1 2HBV delta helper plasmid with HindII and EcoRI. Both samples produce the expected band sizes. In this western blot, lysates from HepG2 cells, or HepG2 cells expressing recombinant myc-tagged NTCP and infected with recombinant HBV, were probed with an anti-myc antibody that recognizes the 34 kDa unglycosylated and the 65 kDa glycosolated recombinant proteins.
The graphs shown here illustrate the kinetics of the reporter gene. RNA and DNA levels in recombinant HBV infected HepG2 NTCP myc-clone 22, or human primary hepatocyte cells. The levels of HBV RNA in the reporter activity were elevated at three days after infection, in both the infected cells and the primary hepatocytes.
In contrast, there was no change in DNA levels at nine days post-infection, because recombinant HBV is deficient for functional core and pole, that play important roles in the intracellular DNA replication pathway. In this figure, inhibition of recombinant HBV by Hepatitis B Immune Globulin, or HBIG, Heparin, and IFN-beta, are illustrated. HBIG and Heparin strongly suppressed the reporter activity to less than 10%at 75 U/mL, and 150 U/mL, respectively.
IFN-beta on the other hand, suppressed reporter activity to less than 50%at 1000 U/mL. Once mastered, this technique can be done in one week for preparation of recombinant HBV, in six days for infection recombinant HBV, and in summary, means for measurement of the reporter protein, if it is performed properly. While attempting this procedure, it's important to remember the washing step that removes the contaminating reporter protein from the bias fraction.
Following this procedure, other results like infection with wide HBV can be performed in order to answer additional question to that the recombinant HBV did not produce first positive results. After its development, this technique paved the way for researchers in the field of HBV to explore the development of anti-HBV agent in a cell culture model. After watching this video, you should have a good understanding of how to purify and infect cells with recombinant HBV.
Don't forget that working with recombinant HBV can be extremely hazardous and precautions such as wearing gloves should always be taken while performing this procedure.
