Antibody suppliers routinely conjugate protein marker antibodies for their catalogues. These target specific proteins and show up abnormalities in cells. For example, some marker proteins are expressed in above-normal amounts in tumour cells; they are therefore used as markers in cancer studies, identified via the relevant antibody conjugated with a fluorescent dye.
We at Novus Biologicals recently added a new PCNA antibody to our database, derived from the PC10 clone. PCNA (proliferating cell nuclear antigen) has long been suggested as a marker for replicating cells. It acts as a processivity factor to DNA-polymerase delta, acting by encircling the DNA to create a link to the genome.
PCNA plays a role in mismatch repair pathways and DNA excision, and is thought to be essential to cell proliferation, as its levels directly correlate to the rate of DNA synthesis and cellular reproduction rate. Nuclear levels are elevated in the late G1 phase, just prior to protein synthesis, and decline during the G2 and M phases. It binds to several other proteins.
PCNA has potential as a tumour cell marker, and antibodies could be used therapeutically to detect the proliferation status of tumour cells in vivo. However, a major problem is that the antibodies would not be tumour-specific, as the protein is also found in cells that are adjacent to tumours, but not showing any activity themselves (i.e. quiescent). This is thought to be due to PCNA’s role in the nucleotide excision repair mechanism.
For this reason, Ki-67 antibodies are often used in cancer studies. Ki-67 is expressed by proliferating cells at all stages of the cell cycle, and is thought to play an important role in cell cycle regulation. However, unlike PCNA it is absent in quiescent cells, and is not expressed in DNA excision repair. However, it has a disadvantage in having a short biological half-life, being degraded in less than an hour.
Marker antibodies are essential to cancer research, and antibody catalogues are continually being revised to take account of the latest findings.
