Induced pluripotent stem cells (iPSCs) can be generated from differentiated human and mouse somatic cells using transcription factors such as Oct4, Sox2, Klf4, and c-Myc. It is possible to augment the reprogramming process with chemical compounds, but issues related to low reprogramming efficiencies and, with a number of protocols, residual vector sequences, remain to be resolved. We show here that it is possible to reprogram mouse and human cells to pluripotency by direct transfection of mature double-stranded microRNAs (miRNAs). Our approaches use a combination of mir-200c plus mir-302 s and mir-369 s family miRNAs. Because this reprogramming method does not require vector-based gene transfer, it holds significant potential for biomedical research and regenerative medicine.

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Although cancer is a disease with genetic and epigenetic origins, the possible effects of reprogramming by defined factors remain to be fully understood. We studied the effects of the induction or inhibition of cancer-related genes and immature status-related genes whose alterations have been reported in gastrointestinal cancer cells. Retroviral-mediated introduction of induced pluripotent stem (iPS) cell genes was necessary for inducing the expression of immature status-related proteins, including Nanog, Ssea4, Tra-1-60, and Tra-1-80 in esophageal, stomach, colorectal, liver, pancreatic, and cholangiocellular cancer cells. Induced cells, but not parental cells, possessed the potential to express morphological patterns of ectoderm, mesoderm, and endoderm, which was supported by epigenetic studies, indicating methylation of DNA strands and the histone H3 protein at lysine 4 in promoter regions of pluripotency-associated genes such as NANOG . In in vitro analysis induced cells showed slow proliferation and were sensitized to differentiation-inducing treatment, and in vivo tumorigenesis was reduced in NOD/SCID mice. This study demonstrated that pluripotency was manifested in induced cells, and that the induced pluripotent cancer (iPC) cells were distinct from natural cancer cells with regard to their sensitivity to differentiation-inducing treatment. Retroviral-mediated introduction of iPC cells confers higher sensitivity to chemotherapeutic agents and differentiation-inducing treatment.

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