The Small Heat Shock Protein 27 Is a Key Regulator of CD8+CD57+ Lymphocyte Survival

Abstract

Differences in CD8+CD57− and CD8+CD57+ lymphocyte lifespan have been documented. Lower numbers and shorter lifespan are characteristic of CD8+CD57+ in normal individuals. However, CD8+CD57+ are expanded in certain disease states including T cell large granular leukemia and other hematologic malignancies. The mechanisms responsible for the differences in CD8+CD57− and CD8+CD57+ lifespan remain elusive. In this study, we demonstrate that the small heat shock protein (Hsp) 27 is a key regulator of CD8+CD57+ lymphocyte lifespan. We found that Hsp27 expression is significantly lower in CD8+CD57+ than in CD8+CD57− lymphocytes. In contrast, Hsp60 and Hsp70 are expressed at comparable levels. Unlike other antiapoptotic Bcl-2–like molecules, the expression of Hsp27 tightly correlates with CD8+CD57+ and CD8+CD57− lifespan. We demonstrate that Hsp27 overexpression in CD8+CD57+ lymphocytes to levels found normally in CD8+CD57− lymphocytes decreased apoptosis. Accordingly, silencing of Hsp27 in CD8+CD57− lymphocytes increased apoptosis. Collectively these results demonstrate that Hsp27 is a critical regulator of normal CD8+CD57+ lifespan supporting its use as a marker of lifespan in this lineage, and suggest a mechanism responsible for the decreased apoptosis and clonal expansion characteristic of certain disease states.