Elevated DDX21 regulates c-Jun activity and rRNA processing in human breast cancers

Abstract

IntroductionThe DDX21 RNA helicase has been shown to be a nucleolar and nuclear protein involved in ribosome RNA processing and AP-1 transcription. DDX21 is highly expressed in colon cancer, lymphomas, and some breast cancers, but little is known about how DDX21 might promote tumorigenesis.MethodsImmunohistochemistry was performed on a breast cancer tissue array of 187 patients. In order to study the subcellular localization of DDX21 in both tumor tissue and tumor cell lines, indirect immunofluorescence was applied. The effect of DDX21 knockdown was measured by cellular apoptosis, rRNA processing assays, soft agar growth and mouse xenograft imaging. AP-1 transcriptional activity was analyzed with a luciferase reporter and bioluminescence imaging, as well as qRT-PCR analysis of downstream target, cyclin D1, to determine the mechanism of action for DDX21 in breast tumorigenesis.ResultsHerein, we show that DDX21 is highly expressed in breast cancer tissues and established cell lines. A significant number of mammary tumor tissues and established breast cancer cell lines exhibit nuclear but not nucleolar localization of DDX21. The protein expression level of DDX21 correlates with cell proliferation rate and is markedly induced by EGF signaling. Mechanistically, DDX21 is required for the phosphorylation of c-Jun on Ser73 and DDX21 deficiency markedly reduces the transcriptional activity of AP-1. Additionally, DDX21 promotes rRNA processing in multiple breast cancer cell lines. Tumor cells expressing high levels of endogenous DDX21 undergo apoptosis after acute DDX21 knockdown, resulting in significant reduction of tumorigenicity in vitro and in vivo.ConclusionsOur findings indicate that DDX21 expression in breast cancer cells can promote AP-1 activity and rRNA processing, and thus, promote tumorigenesis by two independent mechanisms. DDX21 could serve as a marker for a subset of breast cancer patients with higher proliferation potential and may be used as a therapeutic target for a subset of breast cancer patients.Electronic supplementary materialThe online version of this article (doi:10.1186/s13058-014-0449-z) contains supplementary material, which is available to authorized users.

Proteomic identification of nuclear processes manipulated by cytomegalovirus early during infection

“…Finally, we identified several RNA helicases to be significantly induced early during HCMV infection. This includes DDX21 that is highly expressed in several cancers [24] and contributes to coordinating transcription with ribosomal RNA processing [25]. Overall, our studies have identified new cellular proteins as well as processes that are manipulated by HCMV early during infection and represent possible targets of antiviral therapies.…”

Diverse Roles of DEAD/DEAH-Box Helicases in Innate Immunity and Diseases

“…DDX21 also interacts with mitotic regulator PP1 [161] and oncoprotein DEK [162]. Additionally, upregulated DDX21 has been found to promote tumorigenesis in breast cancer by phosphorylating c-Jun, a component of AP-1 transcription factor involved in cell survival pathways [163].…”

“…Finding those proteins would aid us in gaining a better insight into the pathways in which DEAD/DEAH-box helicases are known to participate. This is particularly intriguing for DDX3 [48,49] and DDX21 [60,158,163,165], as both helicases have shown to achieve two opposite effects through their regulatory activities, which possibly depends on the actual cellular conditions.…”

DEAD box RNA helicases crucial regulators of gene expression and oncogenesis

“…DDX21 in breast cancer cells promotes tumorigenesis by regulating the transcriptional activity of c-Jun, and also through rRNA processing. Depletion of DDX21 results in significant reduction of tumorigenicity in vitro and in vivo (168). In breast cancer tissues, DDX21 mRNA expression has been correlated with disease-free survival (169); overexpression of accumulation of DDX21 is reported in colon cancers and lymphomas (170,171).…”