Differential expression of heat shock protein 90 isoforms in small cell lung cancer

Heat shock protein 90 (HSP90), a molecular chaperone, plays important roles in cellular protection against various stressful stimuli and in the regulation of cellular growth and apoptosis. HSP90 has 4 different types of human isoforms; HSP90α, HSP90β, glucose related protein 94 (GRP94) and tumor necrosis factor (TNF) receptor-associated protein 1 (TRAP1). We assessed the differential expression of these HSP90 isoforms in small-cell lung cancer (SCLC) and the correlation of their expression levels with clinicopathological factors and patient survival rates. This study included 117 SCLCs, comprised of 108 primary and 9 metastatic tumor tissues. We performed immunohistochemical staining for HSP90α, HSP90β, GRP94 and TRAP1 in 117 tumors and found that HSP90α and HSP90β were positive in 11 (9%) and 61 tumors (52%), respectively, most of which showed weak expression, whereas GRP94 and TRAP1 were positive in 115 (98%) and 117 tumors (100%), respectively, the majority of which showed moderate or strong expression. None of the HSP90 isoforms showed significant associations with clinicopathological factors or survival status in patients with SCLC. Our results indicate that GRP94 and TRAP1 might contribute more to the carcinogenesis or biology of SCLC than HSP90α and HSP90β, and that isoform selectivity should be considered when HSP90 inhibitors are studied or utilized for the treatment of SCLC.