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4.3.2 Heat shock proteins
All organisms, from bacteria to mammals, respond to different environmental stress
conditions by the synthesis of highly conserved proteins, known as heat shock proteins
(HSPs) (Hamer et al., 2004). They are so called because they were first described in cells of
Drosophila melanogaster during exposure to high temperatures. At the time, it was verified
that the exposure of cells to heat produced a new pattern of thickening of chromosomes,
which represented specific sites of transcription for the synthesis of proteins. The stress
induced the expression of certain genes, which led the cell to produce a certain class of
proteins, so-called heat shock proteins. Later, researchers observed that these proteins were
expressed in almost all living beings, and not only in response to heat, but also when the cell
was exposed to a series of other stressing factors (toxic concentrations of metals, organic
pollutants, temperature, osmolarity, hypoxia/anoxia and ultraviolet radiation), and then
they began to be called “stress proteins” or “anti-stress proteins” (Meyer & Silva, 1999).
Many toxicants affect the correct conformation and consequently, the function of different
proteins. In this condition, where the proteins are found incorrectly folded inside the cell, it
is initiated a stress response. The HSPs take action, acting as molecular chaperones, since
they bind to other proteins, regulating their conformation, movement through the
membrane or organelles and enzymatic activity (Calabrese et al., 2005). Therefore, they
avoid incorrect interactions between proteins, helping in their synthesis, folding and
degradation (Meyer & Silva, 1999).
According to Bierkens (2000), HSPs are one of the main cellular markers in the evaluation of
the toxicity of different compounds and are widely used to monitor ecosystems. Such
monitoring has shown high levels of HSPs in the tissues of invertebrates collected in
contaminated areas, when compared to those animals existent in uncontaminated
environments (Bierkens, 2000; Malaspina & Silva-Zacarin, 2006).
These proteins are found highly conserved in all the living organisms (Burdon, 1986) and
can be classified according their molecular weight into four families: HSP90 (90 kDa), HSP70
(70 kDa), HSP60 (60 kDa) and small HSPs. The family HSP70 is one of the most studied and
several studies have shown its induction in stress conditions by heavy metals (Köhler et al.,
1992, 1996b; Nadeau et al., 2001; Zanger et al., 1996).
Monari et al. (2011) worked with the mollusc species Chamelea gallina , observing an increase
in the expression of HSP70. The authors affirm that the induction of HSP70 can be
considered an adaptation mechanism associated with changes in the environmental
parameters.
Silva-Zacarin et al. (2006), using immune-histochemical methods, observed an increase in
the levels of the products of the positive reaction to HSP70 in the salivary glands of bees
treated with acaricides in comparison with the control group. Moreover, they also verified
alterations in the immune-reactivity between the nucleus and cytoplasm according to the
acaricide used and the treatment period. According to the authors, the determination and
location of HSP70 by immune-histochemistry can be useful to detect cellular responses to
chemical stressors.
Köhler et al. (1992) points out the HSP70 in invertebrates of soil as a possible tool in the
monitoring of environmental toxicants. In a study conducted by Zanger et al. (1996), the
authors exposed adult of the diplopod Julus scandinavius to substrates contaminated with
different concentrations of cadmium and investigated the expression levels of HSP70. The
analyses showed that an increase in the concentration of cadmium in the animals diet
resulted in high levels of HSP70.
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