## 3 Hsp60 in Carcinogenesis
### Hsp60 and miRNAs Correlations and Implications for Carcinogenesis  
MicroRNAs (miRNAs) are a class of small non-coding RNAs that regulate gene expression post-transcriptionly by translational inhibition and/or mRNAs destabilization [140]. MiRNAs regulate most protein coding genes, and thus they virtually control all biological processes [141; 142]. MiRNAs dysregulation following amplification or deletion of miRNA genes, abnormal transcriptional control of miRNAs, dysregulated epigenetic changes, or defects in the miRNA biogenesis process, are associated with pathological conditions, including cancer [143; 144]. Dysregulated, abnormal miRNAs can affect all hallmarks of cancer (e.g., continued proliferative signalling, evasion of growth suppressors, cell death resistance, invasiveness and metastasization, and angiogenesis) by acting either as oncocmiRNAs or tumor suppressors, with inhibition of tumor suppressive mRNAs or oncogenic mRNAs, respectively [145; 146]. For this reason, miRNAs are considered for use not only as diagnostic and prognostic biomarkers, but also as potential targets or agents in anti-cancer treatment [147]. MiR-9 and miR-221 have been classified as onco-miR8 because an increase in their levels paralleled increased risk for tumorigenesis and resistance to chemotherapeutics in primary cancers [148; 149; 150; 151]. In breast cancer, miR-9 and miR-221 increased levels correlated with poor outcome and promoted tumor progression and aggressiveness by favoring epithelial-mesenchymal transition (EMT) and breast cancer stem cell phenotypes [152]. Therefore, they have been suggested as potential biomarkers for breast cancer progression and targets for treatment. miR-30 was found decreased in prostate cancer and acted as tumor suppressor by targeting the EMT-associated gene ERG (Ets-related gene) [153]. Conversely, when increased, miR-30 suppressed EMT and inhibited cell migration and invasion, suggesting it could be used as a therapeutic agent (Table 3) [153]. Hsps, including Hsp60, are also targets for regulation by miRNAs and this has been investigated in various cancers [154; 155; 156; 157]. miR-1 and miR-206 increase in rat cardiomyocytes contributes to glucose-mediated apoptosis by diminishing Hsp60 and IGF-1 expression and inhibiting the IGF-1/IGF-1/PI3 K/Akt pathway [158]. Conversely, treatment of cardiomyocytes with carvedilol, a non-selective \(\beta\)-adrenergic receptor antagonist, inhibited miR-1, which resulted in increased levels of Hsp60 and apoptosis prevention (Table 3) [159]. MiR-29a was found augmented in the serum of breast cancer patients [155]. Downregulation of miR-29a in a breast cancer cell line promoted apoptosis by causing an increase in the level of Hsp60 and a decrease of Hsp27, Hsp40, Hsp70, and Hsp90, suggesting that downregulation of this miRNA is a promising strategy to sensitize cancer cells to chemotherapy [155]. It is likely that the anti-cancer effects observed with the increase  
Figure 2: Diagram representing the Hsp60 secreting mechanism. Hsp60 (pink cylinder) is encoded in a single nuclear gene (1). After translation (2), Hsp60 is translocated to the mitochondrion matrix, in which it performs its canonical chaperoning function (3). In tumor cells, Hsp60 accumulates in the cytosol (4), and/or reaches the plasma-cell membrane, near lipid rafts (yellow) (5). The membrane-associated Hsp60 is internalized through a mechanism of endocytosis into early endosomes (6), and then secreted via exosomes after the fusion of multivesicular bodies (MVBs) with the plasma-cell membrane (7). Hsp60 is also exported extracellularly via the classic Golgi-mediated secretion pathway (8). Exosomal Hsp60 (9) and free Hsp60 (10) can reach other cells, e.g., tumor cells and immune cells, nearby or in distant sites via circulation. of Hsp60 were related to the known pro-apoptotic role of the chaperonin [56; 57], or to its ability to stimulate an anti-tumor immune response when exposed on cell surface or released extracellularly [53; 54; 121].