Physical and Functional Interactions between ELL2 and RB in the Suppression of Prostate Cancer Cell Proliferation, Migration, and Invasion

Abstract

Elongation factor, RNA polymerase II, 2 (ELL2) is expressed and regulated by androgens in the prostate. ELL2 and ELL-associated factor 2 (EAF2) form a stable complex, and their orthologs in Caenorhabditis elegans appear to be functionally similar. In C. elegans, the EAF2 ortholog eaf-1 was reported to interact with the retinoblastoma (RB) pathway to control development and fertility in worms. Because RB loss is frequent in prostate cancer, ELL2 interaction with RB might be important for prostate homeostasis. The present study explored physical and functional interaction of ELL2 with RB in prostate cancer. ELL2 expression in human prostate cancer specimens was detected using quantitative polymerase chain reaction coupled with laser capture microdissection. Co-immunoprecipitation coupled with deletion mutagenesis was used to determine ELL2 association with RB. Functional interaction between ELL2 and RB was tested using siRNA knockdown, BrdU incorporation, Transwell, and/or invasion assays in LNCaP, C4-2, and 22Rv1 prostate cancer cells. ELL2 expression was downregulated in high–Gleason score prostate cancer specimens. ELL2 could be bound and stabilized by RB, and this interaction was mediated through the N-terminus of ELL2 and the C-terminus of RB. Concurrent siRNA knockdown of ELL2 and RB enhanced cell proliferation, migration, and invasion as compared to knockdown of ELL2 or RB alone in prostate cancer cells. ELL2 and RB can interact physically and functionally to suppress prostate cancer progression.

Regulation of ELL2 stability and polyubiquitination by EAF2 in prostate cancer cells

“…The major signaling pathways altered in the mouse ELL2 knockout prostate are likely conserved and are also involved in ELL2 action in human prostate cancer cell lines. We have previously reported downregulation of ELL2 mRNA in high‐Gleason score prostate cancer specimens . The downregulation of ELL2 protein in clinical prostate cancer specimens is consistent with its mRNA downregulation.…”

“…Our previous studies showed that the ELL2 mRNA was downregulated in prostate cancer specimens, particularly in high Gleason grade prostate cancer specimens . ELL2 mutation is not frequent in prostate cancer .…”

“…Our recent studies suggest that ELL2 plays an important role in prostate carcinogenesis. ELL2 mRNA expression was downregulated in high Gleason grade prostate cancer specimens . Knockdown of ELL2 by siRNA resulted in increased proliferation, migration, and invasion in prostate cancer cell lines .…”

Conditional deletion of ELL2 induces murine prostate intraepithelial neoplasia

“…ELL2 was previously identified as androgen responsive gene in the prostate cancer cell line LNCaP [17]. We also recently showed that knockdown of ELL2 in C4-2 and LNCaP cells significantly enhanced invasion and migration and induced a slight increase in BrdU incorporation (Qiu et al 2017). Here, knockdown of ELL2 in LNCaP prostate cancer cells induced an increase in cellular proliferation (Figure 3D).…”

“…Eaf2 knockout mice developed high-grade murine prostatic intraepithelial neoplasia and increased vascularity in several murine strains (mPIN) (Xiao, et al 2008; Pascal et al 2013). Recently, we reported that siRNA knockdown of ELL2 in combination with RB enhanced proliferation, migration and invasion in prostate cancer cell lines LNCaP, C4-2 and 22RV1, while ELL2 knockdown alone enhanced migration and invasion but did not induce a statistically significant increased proliferation (Qiu, et al 2017). ELL2 expression was down-regulated in high Gleason score prostate cancer specimens.…”