Expression Patterns and Corepressor Function of Retinoic Acid-induced 2 in Prostate Cancer.

BACKGROUND: Revealing molecular mechanisms linked to androgen receptor activity can help to improve diagnosis and treatment of prostate cancer. Retinoic acid-induced 2 (RAI2) protein is thought to act as a transcriptional coregulator involved in hormonal responses and epithelial differentiation. We evaluated the clinical relevance and biological function of the RAI2 protein in prostate cancer. METHODS: We assessed RAI2 gene expression in the Cancer Genome Atlas prostate adenocarcinoma PanCancer cohort and protein expression in primary tumors (n = 199) by immunohistochemistry. We studied RAI2 gene expression as part of a multimarker panel in an enriched circulating tumor cell population isolated from blood samples (n = 38) of patients with metastatic prostate cancer. In prostate cancer cell lines, we analyzed the consequences of androgen receptor inhibition on RAI2 protein expression and the consequences of RAI2 depletion on the expression of the androgen receptor and selected target genes. RESULTS: Abundance of the RAI2 protein in adenocarcinomas correlated with the androgen receptor; keratins 8, 18, and 19; and E-cadherin as well as with an early biochemical recurrence. In circulating tumor cells, detection of RAI2 mRNA significantly correlated with gene expression of FOLH1, KLK3, RAI2, AR, and AR-V7. In VCaP and LNCaP cell lines, sustained inhibition of hormone receptor activity induced the RAI2 protein, whereas RAI2 depletion augmented the expression of MME, STEAP4, and WIPI1. CONCLUSIONS: The RAI2 protein functions as a transcriptional coregulator of the androgen response in prostate cancer cells. Detection of RAI2 gene expression in blood samples from patients with metastatic prostate cancer indicated the presence of circulating tumor cells.

Targeting circulating monocytes with CCL2-loaded liposomes armed with an oncolytic adenovirus.

Oncolytic viruses (OVs) selectively replicate in and destroy cancer cells resulting in anti-tumor immunity. However, clinical use remains a challenge because of virus clearance upon intravenous delivery. OV packaging using a nanomedicine approach could overcome this. Here we encapsulate an oncolytic adenovirus (Ad[I/PPT-E1A]) into CCL2-coated liposomes in order to exploit recruitment of CCR2-expressing circulating monocytes into tumors. We demonstrate successful encapsulation of Ad[I/PPT-E1A] into CCL2-coated liposomes that were preferentially taken up by CCR2-expressing monocytes. No complex-related toxicities were observed following incubation with prostate tumor cells and the encapsulation did not affect virus oncolytic activity in vitro. Furthermore, intravenous administration of our nanomedicine resulted in a significant reduction in tumor size and pulmonary metastasis in prostate cancer-bearing mice whereby a 1000-fold less virus was needed compared to Ad[I/PPT-E1A] alone. Taken together our data provide an opportunity to target OVs via circulation to inaccessible tumors using liposome-assisted drug delivery.

Master corepressor inactivation through multivalent SLiM-induced polymerization mediated by the oncogene suppressor RAI2.

While the elucidation of regulatory mechanisms of folded proteins is facilitated due to their amenability to high-resolution structural characterization, investigation of these mechanisms in disordered proteins is more challenging due to their structural heterogeneity, which can be captured by a variety of biophysical approaches. Here, we used the transcriptional master corepressor CtBP, which binds the putative metastasis suppressor RAI2 through repetitive SLiMs, as a model system. Using cryo-electron microscopy embedded in an integrative structural biology approach, we show that RAI2 unexpectedly induces CtBP polymerization through filaments of stacked tetrameric CtBP layers. These filaments lead to RAI2-mediated CtBP nuclear foci and relieve its corepressor function in RAI2-expressing cancer cells. The impact of RAI2-mediated CtBP loss-of-function is illustrated by the analysis of a diverse cohort of prostate cancer patients, which reveals a substantial decrease in RAI2 in advanced treatment-resistant cancer subtypes. As RAI2-like SLiM motifs are found in a wide range of organisms, including pathogenic viruses, our findings serve as a paradigm for diverse functional effects through multivalent interaction-mediated polymerization by disordered proteins in healthy and diseased conditions.