Stathmin interaction with HSC70 family proteins

Stathmin is a ubiquitous cytosolic phosphoprotein participating in the rela y and integration of diverse intracellular signaling pathways involved in t he control of cell proliferation, differentiation, and activities. It is ph osphorylated in response to diverse extracellular signals including hormone s and growth factors, and it is highly expressed during development and in diverse tumoral cells and tissues. Stathmin interacts with tubulin and othe r potential protein partners such as BiP, KlS, CC1 and CC2/tsg101. In our p resent search for further functional partners of stathmin, we identified pr oteins in the Hsp70 family, and in particular Hsc70, as interacting with st athmin in vitro. Hsc70 is among the proteins coimmunoprecipitated with stat hmin, and it is the main protein retained specifically on stathmin-Sepharos e beads identified by one- and two-dimensional electrophoresis and immunobl ots. Bovine serum albumin (BSA)-Sepharose did not bind Hsc70, and anti-stat hmin antisera specifically inhibited the interaction of Hsc70 with stathmin -Sepharose. The binding of Hsc70 to stathmin is dependent on the phosphoryl ation status of stathmin, as it did not occur with a "pseudophosphorylated" mutant form of stathmin. This interaction is further dependent on the ATP status of Hsc70. It was inhibited in the presence of ATP-Mg++ but not in th e presence of ATP-Mg++ and ethylenediaminetetraacetic acid (EDTA) or of ADP . Our results suggest that the interaction of stathmin with Hsc70 is specif ic in both proteins and most likely biologically relevant in the context of their functional implication in the control of numerous intracellular sign aling and regulatory pathways, and hence of normal cell growth and differen tiation.