Role of Ribosomal Protein RPS2 in Controlling let-7a Expression in Human Prostate Cancer

Abstract

We discovered that an inverse relationship exists in the expression of ras/c-myc and ribosomal protein RPS2 with pre-let-7a-1/let-7a/let-7f miRNA and prostate tumor cell malignancy. Nonmalignant IBC-10a cells expressed low levels of ras/RPS2 and elevated pre-let-7a-1/let-7a/let-7f miRNA, whereas the reverse occurred in malignant PCa-20a and PC-3ML cells. Stable transfection of IBC-10a cells with pBABE.ras and pBABE.RPS2 induced ras, c-myc, and RPS2 expression, whereas the levels of let-7a/let-7f miRNA dropped to near zero. Conversely, in pBABE.pre-let-7a-1 transfected PCa-20a and PC-3ML clones, let-7a/let-7f increased whereas ras, RPS2, and c-myc dropped greater than 5-fold. Electrophoretic mobility shift assays, antibody "supershift" assays and immunoprecipitation assays revealed that RPS2 specifically binds pre-let-7a-1 to block RNA processing. Immunoflourescent studies and Northern blots confirmed that RPS2 complexes with pre-let-7a-1 (i.e., in episomal structures) to block processing to let-7a/let-7f, indicating RPS2 may prevent let-7a miRNA expression to indirectly promote oncogene expression. Functional studies further showed that the colony-forming ability (CFA) and invasive activities of IBC-10a cells were significantly enhanced in pBABE-ras.IBC-10a and pBABE-RPS2-IBC-10a clones. Conversely, with the "knockdown" of ras and RPS2 in malignant PC-3ML cells (i.e., in pLKO. TRC.shRNA.ras.PC3-ML, pLKO.TRC.shRNA.RPS2.PC-3ML transfected cells), there was both a loss of these functions and a loss of tumorigenesis in SCID mice. Likewise, with the overexpression of let-7a/let-7f in pBABE. pre-let-7a-1.PC-3ML clones (and PCa-20a clones), CFAs, invasive activities in vitro, and tumorigenesis in vivo were significantly reduced. These results show for the first time that RPS2 blocks pre-let-7a-1 processing to enable ras and c-myc expression and the transformation of primary tumor cells. Mol Cancer Res; 9(1); 36-50. Ó2011 AACR.

MicroRNAs en route to the clinic: progress in validating and targeting microRNAs for cancer therapy

“…88) or let-7g (REF. 89) to the lungs at the same time as Kras G12D expression reduced tumour burden by as much as 66%. The burden of preformed xenografts was reduced by intratumoral delivery of let-7b (REF.…”

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Over-expressed RPL34 promotes malignant proliferation of non-small cell lung cancer cells

“…The main function of ribosomal proteins is participating in the self-assembly of ribosomes and protein synthesis. Recently, ribosomal proteins were found to be involved in other cell functions besides ribosomal functions, including regulation of cell cycle (Nosrati et al, 2015;Gou et al, 2010) and even malignant transformation of normal cells (Wang et al, 2011). Some ribosomal proteins were found to play important roles in the development and progress of cancer cells (Khalaileh et al, 2013;Donati et al, 2011).…”

Polymeric nanoparticle-based delivery of microRNA-199a-3p inhibits proliferation and growth of osteosarcoma cells

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