Plays a role as negative regulator of myoblast differentiation, in part through effects on MTOR signaling. Has no detectable enzymatic activity.PPAPDC3, also known as nuclear envelope transmembrane protein 39 (NET39), was initially discovered in an in silico screen for secreted or membrane proteins. It is a member of the PAP2 superfamily of phosphatases and haloperoxidases. PPAPDC3 has recently been shown to act as a negative regulator of myoblast differentiation by diminishing the activity of the mammalian target of rapamycin TOR. PPAPDC3 is highly expressed in cardiac and skeletal muscle and becomes strongly upregulated during cultured myoblast differentiation tissues. Overexpression of PPAPDC3 in myoblasts repressed myogenesis while knockdown by RNA interference promoted differentiation indicating its part in the regulatory mechanism for myogenesis.