Emerging studies indicated that cancer stem cells represent a subpopulation of cells within the tumor that is responsible for chemotherapeutic resistance. However, the underlying mechanism is still not clarified yet. Here we report that miR-196b-5p is dramatically upregulated in CRC tissues and high expression of miR-196b-5p correlates with poor survival in CRC patients. Moreover, recurrent gains (amplification) contribute to the miR-196b-5p overexpression in CRC tissues. Silencing miR-196b-5p suppresses spheroids formation ability, the fraction of SP cells, expression of stem cell factors and the mitochondrial potential, and enhances the apoptosis induced by 5-fluorouracil in CRC cells; while ectopic expression of miR-196b-5p yields an opposite effect. In addition, downregulation of miR-196b-5p resensitizes CRC cells to 5-fluorouracil in vivo. Our results further demonstrate that miR-196b-5p promotes stemness and chemoresistance of CRC cells to 5-fluorouracil via targeting negative regulators SOCS1 and SOCS3 of STAT3 signaling pathway, giving rise to activation of STAT3 signaling. Interestingly, miR-196b-5p is highly enriched in the serum exosomes of patients with CRC compared to the healthy control subjects. Thus, our results unravel a novel mechanism of miR-196b-5p implicating in the maintenance of stem cell property and chemotherapeutic resistance in CRC, offering a potential rational registry of anti-miR-196b-5p combining with conventional chemotherapy against CRC.

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Ultraviolet (UV) irradiation is the most important factor contributing to the development of skin cancer. The use of chemopreventive agents, especially naturally occurring plant products, to prevent skin cancer caused by UV might an effective therapeutic or preventive intervention. Using in silico virtual screening of the Chinese Medicine Library, we identified norathyriol as a potential ERK2 inhibitor. Norathyriol is a metabolite of mangiferin, which is found in mango, Hypericum elegans, and Tripterospermum lanceolatum, and has potent anticancer-promoting activity. Here, we show that norathyriol inhibits ERK1/2 kinase activities and attenuates UVB-induced phosphorylation of the mitogen-activated protein kinase (MAPK) cascades. Direct binding of norathyriol with ERK2 was confirmed by a co-crystal structure. The norathyriol xanthone moiety acts as an adenine mimeric and anchors the compound by hydrogen bonds to the hinge region of the protein ATP-binding site. Norathyriol inhibited cell growth in mouse skin epidermal JB6 P+ cells by inducing G2-M phase arrest. Mouse skin tumorigenesis data clearly showed that treatment with norathyriol significantly suppressed solar UV-induced skin carcinogenesis in vivo. Results also indicated that norathyriol exhibits a potent chemopreventive activity through the inhibition of transcription factor AP-1 and NF-κB by targeting ERKs in UV-induced skin carcinogenesis.