TRAP1 is Involved in Cell Cycle Regulated by Retinoblastoma Susceptibility Gene (RB1) in Early Hypoxia and has Variable Expression Patterns in Human Tumors

Tumor necrosis factor receptor associated protein 1(TRAP1) is a member of the Hsp90 family that acts as a molecular chaperon to the tumor suppressor retinoblastoma susceptibility gene (RB1). We have previously demonstrated that TRAP1-positive cells contain a high level of cell proliferating genes, whilst TRAP1-negative cells contain a high level of genes involved in cell cycles and metastases. In this study, we performed a functional analysis of TRAP1 which focused on its regulation within a cell cycle in relation to RB1. Following a heat shock, TRAP1 translocates to the nucleus and chaperons RB1. When TRAP1 is silenced by siRNA, or prevented from entering the nucleus in hypoxic cells, formation of RB1/E2F1 complexes is impaired and cell cycle activity is promoted by deregulating the G1/S transition. Inhibition of the nuclear translocation of TRAP1 with geldanamycin abrogates its ability to maintain RB1 in a form that associates with E2F1. Restoration of TRAP1 expression reverses these effects. We analysed TRAP1/RB1 expression on 630 tumors by immunohistochemical staining and found TRAP1 lost in some types of cancer, such as non-small cell lung cancer and breast cancer, and the positive correlation of TRAP1 expression in nuclear and cytoplasm with RB1 was observed. Clinico-pathological data showed that breast carcinoma patients lacking nuclear TRAP1 have a shorter disease free survival. Our data suggests that nuclear translocation of TRAP1 is crucial for its function as a chaperon. The loss of TRAP1 expression in certain types of cancer may provide the growth advantage due to the lost control at cell cycle check point.