Because of its C-terminal HDEL ER retention signal, RCN1 is localized to the ER lumen in most cells.32 However, plasma membrane distribution of RCN1 has been observed in bone endothelial cells and prostate cancer cells and has been found to increase after treatment with tumor necrosis factor α (TNF-α).33 Here, we report that the mRNA and protein levels of RCN1 increase after treatment with TNF-α, which may override the ability of KDEL receptors to transport proteins with ER retention signals to the ER lumen43 and result in increased RCN1 membrane distribution. Here, RCN1 is linked to prostate cancer.