角质层主要由角质细胞组成，形成对外界侵袭和脱水的保护屏障。角质层稳态是通过角质细胞增殖和分化之间微妙平衡的维持。在这个过程的调节中，角质细胞特异性miR-203微RNA的作用至关重要，它通过直接靶向和下调参与角质细胞增殖的基因mRNA表达，如ΔNp63、Skp2和Msi2等，来促进细胞分化。我们旨在鉴定与角质细胞增殖/分化平衡调节相关的新miR-203靶点。为此，我们对过表达miR-203的人类原代角质细胞进行了转录组分析，结果显示miR-203的过表达抑制了增殖、有丝分裂和细胞周期等功能，激活了分化、凋亡和细胞死亡等过程。在这些下调基因中，我们鉴定了24个潜在的miR-203靶向mRNA，其中8个与增殖有关。我们证明了SRC和RAPGEF1是miR-203的直接靶点。此外，在3D重建皮肤模型中，SRC和RAPGEF1在表皮形态发生过程中被下调，而miR-203被上调。最后，沉默实验表明SRC或RAPGEF1参与了角质细胞的增殖并调节其分化。初步结果表明它们在皮肤癌细胞过增殖中具有参与作用。总之，这些数据表明RAPGEF1和SRC可能是miR-203在表皮稳态调节中的新的介质物。© 2023. Springer Nature Limited.

The epidermis is mostly composed of keratinocytes and forms a protecting barrier against external aggressions and dehydration. Epidermal homeostasis is maintained by a fine-tuned balance between keratinocyte proliferation and differentiation. In the regulation of this process, the keratinocyte-specific miR-203 microRNA is of the outmost importance as it promotes differentiation, notably by directly targeting and down-regulating mRNA expression of genes involved in keratinocyte proliferation, such as ΔNp63, Skp2 and Msi2. We aimed at identifying new miR-203 targets involved in the regulation of keratinocyte proliferation/differentiation balance. To this end, a transcriptome analysis of human primary keratinocytes overexpressing miR-203 was performed and revealed that miR-203 overexpression inhibited functions like proliferation, mitosis and cell cycling, and activated differentiation, apoptosis and cell death. Among the down-regulated genes, 24 putative target mRNAs were identified and 8 of them were related to proliferation. We demonstrated that SRC and RAPGEF1 were direct targets of miR-203. Moreover, both were down-regulated during epidermal morphogenesis in a 3D reconstructed skin model, while miR-203 was up-regulated. Finally silencing experiments showed that SRC or RAPGEF1 contributed to keratinocyte proliferation and regulated their differentiation. Preliminary results suggest their involvement in skin carcinoma hyperproliferation. Altogether this data indicates that RAPGEF1 and SRC could be new mediators of miR-203 in epidermal homeostasis regulation.© 2023. Springer Nature Limited.