Small Heat Shock Protein αB-Crystallin Controls Shape and Adhesion of Glioma and Myoblast Cells in the Absence of Stress

Abstract

Cell shape and adhesion and their proper controls are fundamental for all biological systems. Mesenchymal cells migrate at an average rate of 6 to 60 μm/hr, depending on the extracellular matrix environment and cell signaling. Myotubes, fully differentiated muscle cells, are specialized for power-generation and therefore lose motility. Cell spreading and stabilities of focal adhesion are regulated by the critical protein vinculin from immature myoblast to mature costamere of differentiated myotubes where myofibril Z-band linked to sarcolemma. The Z-band is constituted from microtubules, intermediate filaments, cell adhesion molecules and other adapter proteins that communicate with the outer environment. Mesenchymal cells, including myoblast cells, convert actomyosin contraction forces to tension through mechano-responsive adhesion assembly complexes as Z-band equivalents. There is growing evidence that microtubule dynamics are involved in the generation of contractile forces; however, the roles of microtubules in cell adhesion dynamics are not well determined. Here, we show for the first time that αB-crystallin, a molecular chaperon for tubulin/microtubules, is involved in cell shape determination. Moreover, knockdown of this molecule caused myoblasts and glioma cells to lose their ability for adhesion as they tended to behave like migratory cells. Surprisingly, αB-crystallin knockdown in both C6 glial cells and L6 myoblast permitted cells to migrate more rapidly (2.7 times faster for C6 and 1.3 times faster for L6 cells) than dermal fibroblast. On the other hand, overexpression of αB-crystallin in cells led to an immortal phenotype because of persistent adhesion. Position of matured focal adhesion as visualized by vinculin immuno-staining, stress fiber direction, length, and density were clearly αB-crystallin dependent. These results indicate that the small HSP αB-crystallin has important roles for cell adhesion, and thus microtubule dynamics are necessary for persistent adhesion.

Small heat-shock proteins and their role in mechanical stress

“…In striated muscle, many also colocalize with the sarcomere, the basic unit of muscle contraction (Mercer et al 2018;Golenhofen et al 2004). These interactions have been reported under basal conditions as well as following oxidative, thermal, and mechanical stress (Koh and Escobedo 2004;Pivovarova et al 2007;Golenhofen et al 1999;Shimizu et al 2016;Ke et al 2011). They are not yet understood with enough clarity at the molecular level to know whether the sHSPs are targeting native-like proteins in a client-based mechanism, or misfolding proteins in a substratebased mechanism (Seit-Nebi et al 2013).…”

“…HspB5 knockdown causes both glial and myoblast cells to migrate faster in 2D culture as a result of being less adherent. The phenotype is sensitive to actin and tubulin depolymerization, and features changes in the position and possibly the turnover of vinculin, a critical protein linking cell adhesion complexes to actin stress fibers (Shimizu et al 2016). Thus future work will delineate the direct and downstream mechanisms by which HspB5 affects adhesiveness, and how these may overlap with HspB1, which has a similar effect on the migration of NIH3T3 fibroblasts (Lee et al 2008).…”

HSPB8 promotes cancer cell growth by activating the ERK‑CREB pathway and is indicative of a poor prognosis in gastric cancer patients

“…The small heat shock protein (sHsp) superfamily consists of a series of 15-30 kDa proteins with a common α-crystallin domain at the C-terminal. The most well-studied role of sHsp is acting as molecular chaperones (32,33), i.e. preventing the aggregation of enzymes under heat shock conditions and stabilizing the proteins.…”

The functional roles of the unstructured N- and C-terminal regions in αB-crystallin and other mammalian small heat-shock proteins

“…A common theme emerges from these studies: the assembly and dynamics of all three major cytoskeletal elements in the cell are modulated by sHsps, including Hsp27, αBc, HspB7 and Hsp22. Whilst studies sometimes focus on one specific element of the cytoskeleton (Almeida-Souza et al 2011;Shimizu et al 2016), it is obvious that both the competence and the integration of the different elements of the cytoskeleton rely on sHsps.…”