Identification, tissue distribution and characterization of two heat shock factors (HSFs) in goldfish (Carassius auratus)

Heat shock proteins (HSPs) are synthesized rapidly in response to a variety of physiological or environmental stressors, whereas the transcriptional activation of HSPs is regulated by a family of heat shock factors (HSFs). In vertebrates, multiple HSFs (HSF1-4) have been reported to have different roles in response to a range of stresses. This paper reports the cDNA cloning of two goldfish (Carassius auratus) HSF gene families, HSF1 and three isoforms of HSF2. Both HSF1 and HSF2s showed high homology to the known HSFs from other organisms, particularly the zebrafish. Different patterns of HSF1 and HSF2 mRNA expression were detected in several goldfish tissues, highlighting their distinct roles. In cadmium (Cd)-treated tissues, the responses of HSP70 showed less difference. However, the increase in HSF1 and HSF2 in these tissues differs considerable. In particular, HSF2 was induced strongly in the heart and liver. On the other hand, in heart tissue, HSF1 showed the smallest increment. These results suggest the potential role of HSF2 in assisting HSF1 in these tissues. In another in vitro experiment of hepatocyte cultures, Cd exposure caused similar patterns of goldfish HSF1 and HSF2 mRNA expression and induction of the HSP70 protein. On the other hand, an examination of the characterization of recombinant proteins showed that HSF1 undergoes a conformation change induced by heat shock above 30 °C and approaches each other in the trimer, whereas HSF2 could not sense thermal stress directly. Furthermore, immune-blot analysis of HSFs showed that both monomers and trimmers of HSF1 were observed in cadmium-induced tissues, whereas HSF2 were all in monomeric. These results show that HSF1 and HSF2 play different roles in the transcription of heat shock proteins.