LSD1 and PHF2 are lysine de-methylases that can de-methylate both histone proteins, influencing gene expression and non-histone proteins, affecting their activity or stability. Functional approaches using Lsd1 or Phf2 inactivation in mouse have demonstrated the involvement of these enzymes in the engagement of progenitor cells into differentiation.
One of the best-characterized examples of how progenitor cells multiply and differentiate to form functional organ is myogenesis. It is initiated by the specific timing expression of the specific regulatory genes; among these factors, MYOD is a key regulator of the engagement into differentiation of muscle progenitor cells. Although the action of MYOD during muscle differentiation has been extensively studied, still little is known about the chromatin remodeling events associated with the activation of MyoD expression. Among the regulatory regions of MyoD expression, the Core Enhancer region (CE), which transcribes for a non-coding enhancer RNA (CEeRNA), has been demonstrated to control the initiation of MyoD expression during myoblast commitment.
We identified LSD1 and PHF2 as key activators of the MyoD CE. In vitro and in vivo ablation of LSD1 or inhibition of LSD1 enzymatic activity impaired the recruitment of RNA PolII on the CE, resulting in a failed expression of the CEeRNA. According to our results, forced expression of the CEeRNA efficiently rescue MyoD expression and myoblast fusion in the absence of LSD1. Moreover PHF2 interacts with LSD1 regulating its protein stability. Indeed in vitro ablation of PHF2 results in a massive LSD1 degradation and thus absence of CEeRNA expression. However, all the histone modifications occurring on the CE region upon activation cannot be directly attributed to LSD1 or PHF2 enzymatic activity.
These results raise the question of the identity of LSD1 and PHF2 partners, which co-participate to CEeRNA expression and thus to the engagement of myoblast cells into differentiation.