Worm Breeder's Gazette 13(3): 69 (June 1, 1994)
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
P-glycoproteins can cause Multi Drug Resistance in mammalian tumor cells by active export of a variety of cytotoxic drugs. Drugs that are generally transported are large hydrophobic molecules of plant or microbial origin, e.g. plant alkaloids. P-glycoproteins belong to the evolutionary well conserved family of membrane bound ATP binding transport proteins. Wild type C. elegans is very resistant to most anti cancer drugs, we want to determine whether the nematode P-glycoproteins are involved in resistance. In C. elegans four P-glycoprotein gene homologs are identified, pgp-1 ,-2, -3 and -4 (C.R. Lincke et al., J.Mol.Biol.1992; 266:5303-5310). So far pgp-1 and pgp-3 are analyzed in detail, pgp-4 has been analyzed partially and the pgp-2 nucleotide sequence determination is in progress. Based on lacZ fusion experiments it has been determined that both pgp-1 and pgp-3 are expressed in intestinal cells (C.R. Lincke et al., EMB0 J. 1993; 12:1620-1625).
With immunohistochemistry, using a mouse monoclonal antibody (C219) that recognizes a highly conserved epitope present in almost all P-glycoprotein isoforms, the expression was analyzed in transgenic strains that overexpress PGP1 or PGP3 .Indeed both proteins are expressed in the intestinal cell membrane, at the site of the lumen and PGP3 is also expressed in the membrane of the large H-shaped excretory cell, probably in the apical membrane. The expression in the membrane of the intestinal cells and of the excretory cell suggests a function in protecting the animal against dietary and environmental toxins.
To investigate the biological function we have isolated Tc1 induced deletion mutants (R. Zwaal et al.,PNAS 1993; 90:7431-7435, C. elegans 1993 meeting abstract p.188). Also a mutant strain was obtained in which both pgp-1 and pgp-3 are deleted, a double knock-out. We investigated whether P-glycoproteins are involved in detoxification. The double knock-out, single knock-out and wild type strains were tested for sensitivity to drugs that are known substrates for P-glycoproteins in other organisms. So far we obtained clear results with the drugs colchicine and chloroquine. Adult animals were counted that could survive and grow on the drug plates. Both the double and the pgp-3 single knock-out mutant were sensitive for both drugs. The pgp-1 single knock-out is not sensitive (fig; chloroquine sensitivity, colchicine data not shown). These results indicate
that pgp-3 is responsible for resistance to colchicine and chloroquine.
Plant alkaloids are not made by plants to be used in chemotherapy, and P-glycoproteins are not made by human cells to interfere with cancer therapy. We here describe what seems to be a more natural combination: plants make compounds to protect themselves against nematodes and other organism, and P-glycoproteins are made by these various organisms to excrete these drugs.