Small heat shock proteins in cellular adhesion and migration: evidence from Plasmodium genetics

Cellular locomotion and adhesion critically depend on regulated turnover of filamentous actin. Biochemical data from diverse model systems support a role for the family of small heat shock proteins (HSPBs) in microfilament regulation. The small chaperones could either act directly, through competition with the motor myosin, or indirectly, through modulation of actin depolymerizing factor/cofilin activity. However, a direct link between HSPBs and actin-based cellular motility remained to be established. In a recent experimental genetics study, we provided evidence for regulation of Plasmodium motility by HSPB6/Hsp20. The infectious forms of malaria parasites, termed sporozoites, display fast and continuous substrate-dependent motility, which is largely driven by turnover of actin microfilaments. Sporozoite gliding locomotion is essential to avoid destruction by host defense mechanisms and to ultimately reach a hepatocyte, the target cell, where to transform and replicate. Genetic ablation of Plasmodium HSP20 dramatically changed sporozoite speed and substrate adhesion, resulting in impaired natural malaria transmission. In this article, we discuss the function of Hsp20 in this fast-moving unicellular protozoan and implications for the roles of HSPBs in adhesion and migration of eukaryotic cells.