Supplementary Figure 1 shows analysis of TRIB1 expression in clinical prostate cancer specimens using Oncomine and cBioPortal database. Supplementary Figure 2 shows TRIB1 expression in prostate cancer cell lines and the effect of TRIB1 knockdown on the morphology of the prostate cancer cells. Supplementary Figure 3 shows TRIB1 knockdown in prostate cancer cell lines and the effect of TRIB1 overexpression on anchorage-independent cell growth. Supplementary Figure 4 shows that TRIB1 does not affect ERK phosphorylation or the C/EBP proteins. Supplementary Figure 5 shows subcellular localization of TRIB1, role of GRP78 in 2D and 3D cell survival, and regulation of GRP78 expression by TRIB1. Supplementary Figure 6 shows typical staining patterns of TRIB1 and the ER chaperone in human prostate cancer tissues. Supplementary Figure 7 shows analysis of the tumor-propagating cell population in patient-derived prostate cancer primary cultures.
ARTICLE ABSTRACT
Endocrine therapy is the standard treatment for advanced prostate cancer; however, relapse occurs in most patients with few treatment options available after recurrence. To overcome this therapeutic hurdle, the identification of new molecular targets is a critical issue. The capability to proliferate in three-dimensional (3D) conditions is a characteristic property of cancer cells. Therefore, factors that regulate 3D growth are considered rational targets for cancer therapy. Here, we applied a functional genomic approach to the 3D spheroid cell culture model and identified TRIB1, a member of the Trib family of serine/threonine kinase-like proteins, as an essential factor for prostate cancer cell growth and survival. RNAi-mediated silencing of TRIB1 suppressed prostate cancer cell growth selectively under the 3D conditions. This effect was rescued by ectopic expression of an RNAi-resistant TRIB1 exogene. Gene signature–based analysis revealed that TRIB1 was related to endoplasmic reticulum (ER) pathways in prostate cancer and was required for expression of the ER chaperone GRP78, which is critical for prostate tumorigenesis. Of note, GRP78 was expressed preferentially in a subpopulation of prostate cancer cells that possess tumor-propagating potential, and these tumor-propagating cells were highly sensitive to TRIB1 and GRP78 depletion. In a xenograft model of human prostate cancer, TRIB1 depletion strongly inhibited tumor formation. Supporting these observations, we documented frequent overexpression of TRIB1 in clinical specimens of prostate cancer. Overall, our results indicated that the TRIB1–ER chaperone axis drives prostate tumorigenesis and the survival of the tumor-propagating cells. Cancer Res; 74(17); 4888–97. ©2014 AACR.
