Potential multidrug resistance gene POHL: An ecologically relevant indicator in marine sponges

Sponges are sessile filter feeders found in all aquatic habitats from the t ropics to the arctic. Against potential environmental hazards, they are pro vided with efficient defense systems, e.g., protecting chaperones and/or th e P-170/multidrug resistance pump system. Here we report on a further multi drug resistance pathway that is related to the pad one homologue (POH1) mec hanism recently identified in humans. It is suggested that proteolysis is i nvolved in the inactivation of xenobiotics by the POH1 system. Two cDNAs we re cloned, one from the demosponge Geodia cydonium and a second from the he xactinellid sponge Aphrocallistes vastus. The cDNA from G. cydonium, termed GCPOHL, encodes a deduced polypeptide with a size of 34,591 Da and that fr om A. vastus, AVPOHL, a protein of a calculated M-r of 34,282. The two spon ge cDNAs are highly similar to each other as well as to the known sequences from fungi (Schizosaccharomyces pombe and Saccharomyces cerevisiae) and ot her Metazoa (from Schistosoma mansoni to humans). Under controlled laborato ry conditions, the expression of the potential multidrug resistance gene PO HL is, in G. cydonium, strongly upregulated in response to the toxins staur osporin (20 muM) or taxol (50 muM); the first detectable transcripts appear after 1 d and reach a maximum after 3 to 5 d of incubation. The relevance of the expression pattern of the G. cydonium gene POHL for the assessment o f pollution in the field was determined at differently polluted sites in th e area around Rovinj (Croatia; Mediterranean Sea, Adriatic Sea). The load o f the selected sites was assessed by measuring the potency of XAD-7 concent rates of water samples taken from those places to induce the level of benzo [a]pyrene monooxygenase (BaPMO) in fish and to impair the multidrug resista nce (MDR)/P-170 extrusion pump in clams. These field experiments revealed t hat the levels of inducible BaPMO activity in fish and of the MDR potential by the water concentrates are highly correlated with the level of expressi on of the potential multidrug resistance gene POHL in G. cydonium. This rep ort demonstrates that the detoxification POH pathway, here mediated by the G. cydonium GCPOHL gene, is an additional marker for the assessment of the environmental load in a given marine area.