miR-34 miRNAs provide a barrier for somatic cell reprogramming

Abstract

Somatic reprogramming induced by defined transcription factors is a low efficiency process that is enhanced by p53 deficiency 1-5. To date, p21 is the only p53 target shown to contribute to p53 repression of iPSC (induced pluripotent stem cell) generation 1, 3, suggesting additional p53 targets may regulate this process. Here, we demonstrated that mir-34 microRNAs (miRNAs), particularly miR-34a, exhibit p53-dependent induction during reprogramming. mir-34a deficiency in mice significantly increased reprogramming efficiency and kinetics, with miR-34a and p21 cooperatively regulating somatic reprogramming downstream of p53. Unlike p53 deficiency, which enhances reprogramming at the expense of iPSC pluripotency, genetic ablation of mir-34a promoted iPSC generation without compromising self-renewal and differentiation. Suppression of reprogramming by miR-34a was due, at least in part, to repression of pluripotency genes, including Nanog, Sox2 and Mycn (N-Myc). This post-transcriptional gene repression by miR-34a also regulated iPSC differentiation kinetics. miR-34b and c similarly repressed reprogramming; and all three mir-34 miRNAs acted cooperatively in this process. Taken together, our findings identified mir-34 miRNAs as novel p53 targets that play an essential role in restraining somatic reprogramming.

The p53-induced lincRNA-p21 derails somatic cell reprogramming by sustaining H3K9me3 and CpG methylation at pluripotency gene promoters

“…This finding reinforces the notion that p53 impairs reprogramming not exclusively through apoptosis or cell senescence [26]. Mechanistically, lincRNA-p21 blocks reprogramming by preserving high levels of H3K9me3 and CpG methylation at pluripotency genes.…”

“…We selected 51 lincRNAs previously reported to regulate embryonic stem cell (ESC) pluripotency (26) or differentiation (25) [22] and 16 p53-regulated lincRNAs [18] (Figure 1A). The rationale for choosing the latter group is that p53 is an important regulator of ESC differentiation and a major barrier for reprogramming [8].…”

ΔNp63 regulates select routes of reprogramming via multiple mechanisms

“…[21][22][23][24][25][26][27][28][29] Thus, we asked whether p53 is also activated in p63 À / À MEFs. However, neither p53 protein nor its sensitive targets p21 and miR34a/b/c, also known reprogramming barriers, [40][41][42][43] (Figure 5g). Moreover, the tumor suppressors p19-Arf and p16-Ink4A, which are known reprogramming barriers in mouse and human fibroblasts, 23,24 were shown to partially mediate skin and limb defects of p63 À / À mice.…”

Upregulated sirtuin 1 by miRNA-34a is required for smooth muscle cell differentiation from pluripotent stem cells

“…24 Members of the miR-34 family have been suggested as critical regulators in regulation of cancer cell apoptosis and cell cycle arrest. 16,25,26 It has been recently reported that suppression of somatic cell reprogramming into pluripotent cells by miR-34a was due to their repression of pluripotency genes, 27 implying that miR-34a could have an important role in stem cell differentiation. Indeed, recent studies show that miR-34a has a role in neural 28 and megakaryocytic differentiation 29 and is a critical cell-fate determinant in early-stage dividing colon cancer stem cells.…”