Hsp70 localizes differently from chaperone Hsc70 in mouse mesoangioblasts under physiological growth conditions.

Mouse A6 mesoangioblasts express Hsp70even in the absence of cellular stress. Its expression and itsintracellular localization were investigated under normalgrowth conditions and under hyperthermic stress. Immunofluorescenceassays indicated that without any stress afraction of Hsp70 co-localized with actin microfilaments,in the cell cortex and in the contractile ring of dividingcells, while the Hsc70 chaperone did not. Hsp70 immunoprecipitationassays confirmed that a portion of Hsp70binds actin. Immunoblot assays showed that both proteinswere present in the nucleus. After heat treatment Hsp70and actin continued to co-localize in the leading edge of A6cells but not on microfilaments. Although Hsp70 andHsc70 are both basally synthesized they showed differentcellular distribution, suggesting an Hsp70 different activityrespect to the Hsc70 chaperone. Moreover, we foundHsp70 in the culture medium as it has been described inother cell types.