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PURPOSE. Retinoblastoma (RB) is the most common primary intraocular tumor in children. Chemoresistance is the major obstacle for treatment of these tumors. This study aims to determine whether or not downregulating microRNA-222 (miR-222) could serve as a potential therapeutic target for preventing chemoresistance in RB treatment. METHODS. Differentially expressed miR-222 in RB samples and its downstream target genes were predicted using bioinformatics methods. The expression of miR-222 was altered by mimic or inhibitor to examine its role in RB cell in response to the chemotherapeutic agent vincristine (VCR). Further bioinformatic analysis predicted involvement of the stability of hypoxia-inducible factor 1α (HIF1α) protein in regulation of the von Hippel-Lindau (VHL) tumor suppressor, followed by characterization of the effect of VHL on the ubiquitin-proteasome degradation of HIF1α. Next, VHL or HIF1α was overexpressed to determine their effects on RB cell activities after VCR treatment. In vivo assays were performed on nude mice to further verify the in vitro results. RESULTS. miR-222 is highly expressed in RB tissues and cells and was found to facilitate resistance of RB cells to VCR. Of note, miR-222 specifically bound to and negatively regulated VHL. VHL could inhibit the stability of HIF1α and promote the degradation of ubiquitin-proteasome, thus reducing HIF1α expression to attenuate VCR resistance in RB cells. Moreover, inhibition of miR-222 in combination with VCR suppressed tumor formation in nude mice. CONCLUSIONS. miR-222 promotes the expression of HIF1α by targeting VHL, thus accelerating the resistance of RB cells to the chemotherapeutic agent VCR.

Diabetes-induced oxidative stress is the key factor that initiates neuronal damage in the diabetic retina leading to diabetic retinopathy. This study was to investigate the possible effects of coumestrol (CMS) on inflammation, apoptosis and oxidative stress of retinal cells in streptozotocin-nicotinamide (STZ)-induced DR. Initially, a rat model of STZ was established by intraperitoneal injection of streptozotocin, and the expression of SIRT1 in retina tissues was determined by RT-qPCR. Next, the regulatory roles of CMS in oxidative stress, inflammation, and apoptosis of retinal cells were analyzed through detecting the expression of ROS, MDA, SOD, NO, iNOS, IL-6, TNF-α, and CRP, apoptotic factors (Cyt-C and Caspase-3) after ARPE-19 cells were treated with CMS. Moreover, the relationship between CMS and SIRT1 was analyzed. SIRT1 was lowly expressed in retina tissues. CMS treatment suppressed expression of ROS, MDA, iNOS, NO, IL-6, TNF-α, and CRP, as well as expression of Cyt-C and Caspase-3, but induced SOD expression in retina cells. CMS activated the expression of SIRT1, thereby inhibited oxidative stress, inflammation and apoptosis of retinal cells induced by DR. Taken together, the present study defines that CMS ameliorated DR by inhibiting inflammation, apoptosis and oxidative stress of retinal cells through the activation of SIRT1.