Ribosomal Protein L23 Negatively Regulates Cell Apoptosis Via Its Suppression of Miz1 and Activation c-Myc in Higher-Risk Myelodysplastic Syndromes

Ribosomal protein (RP) L23 has been suggested to be a negative regulator of cell apoptosis. Previously, we reported that RPL23 is over-expressed in higher -risk myelodysplastic syndromes (MDS), which is negatively correlated with apoptosis of bone marrow CD34⁺ cells and predicts poor prognosis. However, the mechanism of the negative regulation of cell apoptosis by RPL23 in higher- risk MDS remains unclear. In the present study, lentiviral transfection of a RPL23-RNAi vector led to generate RPL23-knockdown (KD) in MDS cell line (SKM-1). Gene microarray was performed in RPL23-KD and control (NC) cells. We employed Gene Set Enrichment Analysis (GSEA) to identify functional gene sets and pathways differentially expressed between the two groups. The results showed that RPL23 knockdown induced remarkable proliferation inhibition, distinct pro-apoptosis and cell cycle arrest when compared with NC. Global gene expression profile showed, by comparison to NC samples, 306 genes upregulated while 448 genes downregulated. Among genes varying wildly, increased expression of Miz-1 (FC = 3.79, p=1.19E-20) and lowered expression of c-Myc (FC= -2.613, p=1.49E-05) were identified in RPL23-KD cell, which were verified both by qRT-PCR and western-blot. mRNA and protein levels of p15and p21significantly increased in RPL23-KD cells. In bone marrow sample from 46 patients with higher risk MDS, the mRNA level of Miz1 was remarkably lower than normal controls, which was negatively correlated to RPL23 expression level (r= -0.252, p = 0.048). The mRNA expression level of c-Myc in higher-risk MDS was significantly higher than normal control, which is positively correlated to the RPL23 expression level (r = 0.70, p = 0.004). IHC showed equidirectionally increased c-Myc and RPL23 and lowered expression of Miz1 in patients with higher-risk MDS compared to normal control. In conclusion, the negative regulation of cell apoptosis by RPL23 in higher-risk MDS might be through its suppression of Miz1 and activation of c-Myc.