Hsp70 is required for optimal cell proliferation in mouse A6 mesoangioblast stem cells

Mouse Hsp70 (70 kDa heat shock protein) is preferentially induced by heat orstress stimuli. We previously found that Hsp70 is constitutively expressed in A6 mouse mesoangioblast stem cells, but its possible role in these cells and thecontrol of its basal transcription remained unexplored. Here we report that inthe absence of stress, Ku factor is able to bind the HSE (heat shock element)consensus sequence in vitro, and in vivo it is bound to the proximal hsp70promoter. In addition, we show that constitutive hsp70 transcription depends onthe co-operative interaction of different factors such as Sp1 (specificityprotein 1) and GAGA-binding protein with Ku factor, which binds the HSE consensussequence. We used mRNA interference assays to select knockdown cell clones. Thesecells were able to respond to heat stress by producing a large amount of Hsp70,and produced the same amount of Hsp70 as that synthesized by stressed A6 cells.However, severe Hsp70 knockdown cells had a longer duplication time, suggestingthat constitutive Hsp70 expression has an effect on the rate of proliferation.