The Role Of MiR-424in The Metabolic Switch Of Cancer-associated Fibroblast And Tumor Resistance To Chemotherapy

Tumor growth not only depends on malignant cancer cells, but also on tumor stroma. Acertain group of fibroblasts named cancer associated fibroblasts (CAFs) in stroma, is believedto actively promote the growth and progression of tumor. Recent reports show that CAFactivates a metabolic switch that favors glycolysis and attenuates the mitochondrial activity,and thus leads to the significant tumor growth. However，the mechanisms that underline theshift of aerobic metabolism are unknown.In this study, we found that isocitrate dehydrogenase3subunit alpha (IDH3α) can triggerthe aerobic metabolic shift in CAF induced by transforming growth factor-β1(TGF-β1). Thedownregulation of IDH3α in CAF leads to the accumulation of hypoxia inducible factor1α(HIF1α), a well-known transcriptional factor in regulating glycolysis, resulting in theincreasing of glucose transport and lactate extracellular secretion. The inhibition of IDH3αinduces the expression of NDUFA4L2, mediated by HIF1-α. The induction of NDUFA4L2decreases the maximal and basal rates of oxygen consumption of fibroblasts. We confirmedthe expression of IDH3α also decreased in CAFs isolated from colon samples. IHC analysisshowed that IDH3α protein level is decreased in colon sample section and melanoma samplesection. Functionally, the metabolic reprogram in CAF can promote tumor growth in vitro andin vivo.We further found that miR-424regulates the expression of IDH3α in CAF.Overexpression of miR-424in CAF inhibits the protein level of IDH3α via binding its3’-untranslated region (3’UTR). We also observed that miR-424regulate glycolysis throughinhibiting IDH3α expression and functionally promote the tumor growth in vitro and in vivo.Chemotherapy resistance of tumor cells is a big challenge to all oncologists. Adaption tohypoxia is an essential cellular response that is controlled by the master oxygen-sensitivetranscription factor HIF1(hypoxia-inducible factor1). The mechanism by which tumor cellsacquire resistance to chemotherapy under hypoxic conditions is not fully understood. In thisstudy, we found that hypoxia induces miR-424expression which in turn suppresses thePDCD4expression, a tumor suppressor regulating apoptosis, by targeting its3’UTR.Functionally, overexpression of miR-424decreased the sensitivity of cancer cells (HCT116 and A375) to doxorubicin and etoposide. In contrast, the inhibition of miR-424enhancedapoptosis and increased the sensitivity of cancer cells to doxorubicin. In a xenograft tumormodel, miR-424overexpression promoted tumor growth following doxorubicin treatment,suggesting that miR-424promotes tumor cell resistance to doxorubicin. Furthermore,miR-424levels are inversely correlated with PDCD4expression in clinical colon cancersamples. These results suggest that miR-424is a potential molecular target for tumor therapy.