Field validation of hsp70 stress proteins as biomarkers in Asian clam (Potamocorbula amurensis): is downregulation an indicator of stress?

The focus of this paper is to consider the applicability of the hsp70 stres s protein response as a biomarker in field studies. Stress proteins (or hea t shock proteins, hsp) of the hsp70 family are induced by sublethal concent rations of a variety of environmental pollutants. However, few studies have applied these proteins as biomarkers of environmental stress under field c onditions. Our laboratory is investigating hsp70 proteins and other respons es of Asian clam (Potamocorbula amurensis) as potential biomarkers in labor atory and field studies. Our efforts include two studies presently being co nducted in northern San Francisco Bay: (1) monthly collection of clams from four sites along a cadmium contamination gradient; (2) 7 day in situ expos ure of clams at two selected sites at Mare Island Naval Shipyard. Here we p resent results on hsp70 proteins in P. amurensis in held-collected and outp lanted clams. Both held projects are ongoing, therefore the results present ed here do not represent completed studies; rather, they illustrate a porti on of our experience. For this workshop, we illustrate weaknesses and stren gths of these proteins as biomarkers, and we underscore where additional wo rk is needed. In field-collected clams (study no. 1), site-specific differe nces in levels of two hsp70 proteins, hsp70 and hsp76, were measured in May and June 1997. Although an inverse correlation exists between cadmium tiss ue concentrations and hsp70 protein levels, differences detected may be ref lective of a salinity gradient. Results from recent laboratory exposures to cadmium and a range of salinities are discussed. After in situ exposure fo r 7 days (study no. 2), both hsp70 and hsp76 levels were significantly redu ced in clams from site R. However, given a brief heat-shock in the laborato ry, hsp70 protein levels were significantly higher in clams from this site than in controls. Results indicate that downregulation as well as upregulat ion of hsp70 proteins may be indicators of stress in P. amurensis.