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Induction of DNA damage and expression of heat shock protein HSP70 by polychlorinated biphenyls in the marine sponge Suberites domuncula Olivi

The effects of different polychlorinated biphenyls (PCBs) including toxic coplanar non-ortho (PCB77) and non-planar mono-ortho (PCB118) and di-ortho (PCB153) congeners on the extent of DNA damage as well as on the expression of heat shock protein 70 (HSP70) were investigated in the marine sponge Suberites domuncula Olivi (Porifera; Demospongiae). A time-dependent increase in the number of DNA single-strand breaks, expressed as strand scission factor (SSF), was found after injection of a single dose of 25 mu g of PCB 118 or PCB 153 per gram wet mass of S. domuncula, using Fast Micromethod assay, which is based on the unwinding of DNA under alkaline conditions. The number of strand breaks induced by PCB153 was about two-fold higher than that observed for PCB118 after an incubation period of six days. Unexpectedly, a strong reduction in the rate of DNA unwinding compared to untreated control, that could be indicative for the formation of DNA crosslinks, was found following treatment of S. domuncula with PCB77, which is, in vertebrate systems, the most toxic among the PCB congeners studied. The three selected PCB congeners are able to induce the expression of both "constitutive" (HSP73; M-r 73 kDa) and "inducible" (HSP75; M-r 75 kDa) HSP70 proteins. The expression of HSP75 was markedly lower than that observed for HSP73, and varied considerably among different sponge individuals exposed to PCB77. The results in this work demonstrate that: (1) marine sponges (S. domuncula) respond to distinct PCB congeners by induction of different degrees of DNA damage, and (2) expression of HSP is a potential (but not specific) biomarker for PCB exposure in sponges.

DNA damage; heat shock protein hsp70; polychlorinated biphenyls; environmental stress

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