###### Abstract
Hsp70 family members may be involved in passing the newly synthesized unfolded proteins to Hsp60 proteins under physiological conditions. Hsp70s are engaged in protein translocation, facilitating degradation, and control of the activity of a great number of proteins, mainly transcription factors [20; 21; 22]. Hsp60 is a highly conservative chaperonin that is primarily found in mitochondria. Mitochondrial Hsp60 functions as an oligomer of fourteen 60 kDa subunits. It cooperates with the heptameric 10 kDa Hsp10 complex, which forms a lid, closing the Hsp60 tetradecamer opening [23; 24]. This Hsp60/Hsp10 complex is responsible for mitochondrial protein homeostasis, including active folding of unfolded proteins and ATP-dependent proteolysis of denatured or misfolded proteins [25; 26]. It has been shown that mitochondrial production of Hsp60 is significantly increased under stress conditions. However, small amounts of Hsp60 protein have also been detected in the cytosol [26]. Cytosolic Hsp60 can be detected as a monomer, but only oligomers can be active [24]. The role of cytosolic Hsp60 is not clear; however, many studies have indicated its involvement in either pro- or anti-apoptotic processes [27; 28; 29; 30]. Extracellular release of Hsp60 either through secretion or as a result of cell necrosis has been reported as well [31; 32]. One of the best known small Hsps is Hsp27 with a molecular weight of 27 kDa. It is a multi-functional and ATP-independent protein that can be found in the nucleus and cytoplasm in nearly all tissues. However, the function of Hsp27 as a protein chaperone has not been extensively examined compared to other Hsps [33]. HSP27 is composed of the WDPF domain, \(\alpha\)-crystallain domain, PSRLFDQXFGEXLL sequence, and C-terminus. The \(\alpha\)-crystallain domain with an active structure is associated with oligomerization [34; 35]. Hsp27 is able to form multimeric aggregates (alone or with other small Hsps, e.g., Hsp20) and thus stabilize different proteins by facilitating the refolding of denatured proteins into active forms [36] and protect cells from death [37]. Hsp27 is also involved in regulation of apoptosis mediated by increasing antioxidant defense of cells and interactions with STAT3, cytochrome c-1 and pro-caspase 3 [38; 39; 40]. It was shown that Hsp27 is overexpressed in various physiological (cell development, differentiation, aging) and pathological conditions, including cancers. High expression of Hsp27 is associated with increased tumorigenic potential of neoplastic cells, leading to a poor prognosis in many cancer types [41; 42; 43; 44; 45; 46; 47; 48; 49]. Moreover, upregulated Hsp27 is associated with resistance to cytostatics in neoplastic cells [50; 51; 52; 53; 54; 55] and inhibits the apoptosis caused by radiation [56; 57; 58]. Hsp27, as a significant molecule involved in apoptosis, seems to be an interesting target in cancer therapy. The Hsp40 family is a large group of a co-chaperones. Hsp40 has been found in the cytosol, nucleus, mitochondria, ribosomes, endosome and endoplasmic reticulum. It is involved in protein translation, folding, unfolding, translocation, and degradation. There are three subclasses of Hsp40: A, B and C. Subclasses A and B work independently of ATP and reduce stress in cells by inhibition of protein aggregation. Moreover, subclass A of Hsp40 can bind proteins and prevent their aggregation without Hsp70. Subclass B binds protein independently of Hsp70; however, it must be connected with Hsp70 to prevent the aggregation of proteins [59]. Subclass C of Hsp40 is strictly dependent on Hsp70 [59; 60]. The complex of Hsp40-Hsp70 together with Hsp90 takes part in upregulation of the Akt pathway, associated with upregulation of cellular survival. However, the role of the Hsp40 family in cancers has not been extensively investigated and current data are rather controversial. Some authors underlined that Hsp40 co-chaperones are involved in tumor growth [61].