Ambiguity of HSP70 Functions in Proteostasis: Health and Disease

Maintenance of proteostasis is crucial in cell survival, whereas its violation underlies numerous pathologies. 70 kDa heat shock proteins (Hsp70) are known actors of proteostasis, although their effects can vary greatly between in vivo and in vitro studies, as well as between different isoforms. Depending on the type of interaction and localization of HSP70 with other components of PQC, it can both counteract and promote the progression of pathological processes. Here, we review Hsp70 role in proteostasis with respect to these differences. The structural arrangement of the Hsp70 molecule dictates its mode of binding to target proteins (also referred to as client proteins) and to its partners, such as co-chaperones and other members of the Hsp family. Depending on certain isoform and on these partners, Hsp70 can act in two ways, directing client proteins either into refolding or degradation via ubiquitin-proteasome system or autophagy. In disease, different isoforms of Hsp70 play an essential role in the progression of pathology. We briefly summarize key findings about Hsp70 involvement into neurodegeneration, ischemic injury, diabetes mellitus, viral infections and skin diseases. Potential clinical application of Hsp70 modulators depends on both with a need for selectivity for certain isoforms and a proper extrapolation between pools of data from in vitro and in vivo studies.