Impairment of K‐Ras signaling networks and increased efficacy of epidermal growth factor receptor inhibitors by a novel synthetic miR‐143

Abstract

Despite considerable research on K‐Ras inhibitors, none had been established until now. We synthesized nuclease‐resistant synthetic miR‐143 (miR‐143#12), which strongly silenced K‐Ras, its effector signal molecules AKT and ERK, and the K‐Ras activator Sos1. We examined the anti‐proliferative effect of miR‐143#12 and the mechanism in human colon cancer DLD‐1 cell (G13D) and other cell types harboring K‐Ras mutations. Cell growth was markedly suppressed in a concentration‐dependent manner by miR‐143#12 (IC50: 1.32 nmol L−1) with a decrease in the K‐Ras mRNA level. Interestingly, this mRNA level was also downregulated by either a PI3K/AKT or MEK inhibitor, which indicates a positive circuit of K‐Ras mRNA expression. MiR‐143#12 silenced cytoplasmic K‐Ras mRNA expression and impaired the positive circuit by directly targeting AKT and ERK mRNA. Combination treatment with miR‐143#12 and a low‐dose EGFR inhibitor induced a synergistic inhibition of growth with a marked inactivation of both PI3K/AKT and MAPK/ERK signaling pathways. However, silencing K‐Ras by siR‐KRas instead of miR‐143#12 did not induce this synergism through the combined treatment with the EGFR inhibitor. Thus, miR‐143#12 perturbed the K‐Ras expression system and K‐Ras activation by silencing Sos1 and, resultantly, restored the efficacy of the EGFR inhibitors. The in vivo results also supported those of the in vitro experiments. The extremely potent miR‐143#12 enabled us to understand K‐Ras signaling networks and shut them down by combination treatment with this miRNA and EGFR inhibitor in K‐Ras‐driven colon cancer cell lines.

MicroRNA‐143/Musashi‐2/KRAS cascade contributes positively to carcinogenesis in human bladder cancer

“…Furthermore, we demonstrated previously that syn‐miR‐143 functions as a tumor suppressor in BC cells . In an earlier study, we also showed that miR‐143 directly targets KRAS signaling networks . Furthermore, it was reported that miR‐143 also directly targets MSI2 in cervical cancer .…”

“…Previously, we have clarified the signaling networks. The “positive circuit” through the constitutive KRAS activation‐stimulation of effector signaling pathways (PI3K/AKT and MAPK) occurs in colorectal cancer, resulting in enhanced nuclear KRAS transcription . As shown in Figure , this cascade was also seen in BC cell lines and, again, the “positive circuit” also occurred in HRAS signaling networks.…”

“…We were also able to show that the expression of KRAS was affected by MSI2 through binding of the latter to KRAS mRNA, the finding of which was validated by RNA‐IP, SPR, and the expression profiles of the genes involved. Previously, we showed that miR‐143 directly silences KRAS signaling networks; and Dong et al reported that miR‐143 also targets RNA‐binding protein MSI2. However, the association between these targets of miR‐143, KRAS and MSI2 had not been previously reported.…”

“…Recently, we developed a chemically modified miR‐143 that has potent RNase‐resistant anticancer activity (Figure ). This syn‐miR‐143 silences not only KRAS but also KRAS effector signaling molecules, AKT and ERK …”

“…In addition, microRNAs (miR) that directly target KRAS signaling impede KRAS‐driven tumorigenesis . Previous studies including ours demonstrated that miR‐143 suppresses KRAS‐mediated tumorigenesis . Moreover, miR‐143 is strongly downregulated in several cancers, including BC; and it inhibits cell proliferation by suppressing both signaling pathways of PI3K/AKT and MAPK, which are downstream of KRAS effector signaling pathways, as well as KRAS in BC …”