EVALUATION OF STRESS-INDUCIBLE HSP90 GENE-EXPRESSION AS A POTENTIAL MOLECULAR BIOMARKER IN XENOPUS-LAEVIS

In this study we have evaluated stress-inducible hsp90 mRNA accumulati on as a potential molecular biomarker in Xenopus laevis. In order to o btain a probe for Northern blot analysis we employed a PCR-based appro ach using degenerate primers for the amplification and cloning of an h sp90 gene sequence from Xenopus laevis. The deduced amino acid sequenc e is 102 amino acids in length and exhibited the highest degree of ide ntity with zebrafish and human hsp90 beta genes, Furthermore, the puta tive intron and exon boundaries of this fragment are the same as hsp90 beta in chicken, mouse and human, indicating that the fragment repres ents a Xenopus hsp90 beta-like gene. Northern blot analyses revealed t hat this gene was constitutively expressed in cultured A6 cells. While heat shock and sodium arsenite exposure resulted in the increased acc umulation of hsp90 mRNA in A6 cells, treatment with cadmium chloride a nd zinc chloride did not. Also, exposure of A6 cells to concurrent hea t shock and sodium arsenite produced a mild synergistic response with respect to hsp90 mRNA levels in contrast to hsp70 mRNA levels which di splayed a strong synergistic effect. Finally, hsp90 mRNA was detected constitutively throughout early embryogenesis but was heat-inducible o nly in late blastula and later stages of development. Given the normal abundance and limited stress-induced accumulation of hsp90 mRNA, it m ay not have a great deal of potential as a molecular biomarker compare d to hsp70 and hsp30 mRNA. However, it may be useful in conjunction wi th other stress protein mRNAs to establish a set of biomarker profiles to characterize the cellular response to a stressful or toxic agent.