Pharmacologic dissection of the overlapping impact of heat shock protein family members on platelet function

BACKGROUND: Platelets play a pivotal role in hemostasis, wound healing, and inflammation, and are thus implicated in a variety of diseases, including cancer. Platelet function is associated with release of granule content, cellular shape change, and upregulation of receptors that promote establishment of a thrombus and maintenance of hemostasis. OBJECTIVES: The role of heat shock proteins (Hsps) in modulating platelet function has been studied for a number of years, but comparative roles of individual Hsps has not been thoroughly examined. METHODS: We utilized a panel of specific inhibitors of Hsp40, Hsp70, Hsp90, and Grp94 (the endoplasmic reticulum homolog of Hsp90) to assess their impact on several aspects of platelet function. RESULTS: Inhibition of each of the aforementioned Hsps reduced alpha granule release. In contrast, there was some selectivity in impacts on dense granule release. Thromboxane synthesis was impaired after exposure to inhibitors of Hsp40, Hsp90 and Grp94, but not after inhibition of Hsp70. Both expression of active glycoprotein IIb/IIIa (GpIIb/IIIa) and fibrinogen-induced platelet shape change were diminished by our inhibitors. In contrast, aggregation was selectively abrogated after inhibition of Hsp40 or Hsp90. Lastly, activated platelet - cancer cell interactions were reduced by inhibition of both Hsp70 and Grp94. CONCLUSIONS: These data suggests the importance of Hsp networks in regulating platelet activity.