PDZRN3 protects against apoptosis in myoblasts by maintaining cyclin A2 expression

Abstract

PDZRN3 is a PDZ domain-containing RING-finger family protein that functions in various developmental processes. We previously showed that expression of PDZRN3 is induced together with that of MyoD during the early phase of skeletal muscle regeneration in vivo. We here show that PDZRN3 suppresses apoptosis and promotes proliferation in myoblasts in a manner dependent on cyclin A2. Depletion of PDZRN3 in mouse C2C12 myoblasts by RNA interference reduced the proportion of Ki-67-positive cells and the level of Akt phosphorylation, implicating PDZRN3 in regulation of both cell proliferation and apoptosis. Exposure of C2C12 cells as well as of C3H10T1/2 mesenchymal stem cells and NIH-3T3 fibroblasts to various inducers of apoptosis including serum deprivation resulted in a greater increase in the amount of cleaved caspase-3 in PDZRN3-depleted cells than in control cells. The abundance of cyclin A2 was reduced in PDZRN3-depleted C2C12 myoblasts, as was that of Mre11, which contributes to the repair of DNA damage. Overexpression of cyclin A2 restored the expression of Mre11 and Ki-67 as well as attenuated caspase-3 cleavage in PDZRN3-depleted cells deprived of serum. These results indicate that PDZRN3 suppresses apoptosis and promotes proliferation in myoblasts and other cell types by maintaining cyclin A2 expression.PDZ domain-containing RING-finger protein 3 (PDZRN3 or LNX3) was originally identified in silico as a homolog of LNX1 (PDZRN2), whose function as E3 ubiquitin ligase for NUMB is thought to contribute to cell fate determination at the level of inhibition of Notch signaling 1 . Although both LNX1 and PDZRN3 contain an NH 2 -terminal RING domain and a COOH-terminal consensus binding motif for the PDZ domain, LNX1 possesses four PDZ domains in its central region whereas PDZRN3 has only two. We first cloned PDZRN3 cDNA from human heart, and we showed that the protein is also expressed in various other human tissues including skeletal muscle, brain, and liver 2 . Subsequent studies implicated PDZRN3 in developmental processes such as the differentiation of myoblasts 2 , osteoblasts 3 , and adipocytes 4 , neurogenesis 5 , vascular morphogenesis 6 , maintenance of endothelial intercellular junctions 7 , and control both of paracellular Mg 2+ flux in renal tubular epithelial cells 8 and of the spatial arrangement of neurons 9 . Mutations of the PDZRN3 gene have also been identified in several tumor types 10-15 .Regeneration of skeletal muscle is initiated by the activation of satellite cells (myogenic stem cells) in response to injury. These cells give rise to myoblasts that express the transcription factor MyoD, proliferate (early phase of differentiation), and subsequently differentiate into myocytes that express the transcription factor myogenin and fuse to form myotubes (late phase of differentiation). We previously showed that depletion of PDZRN3 inhibited the late phase of differentiation of myocytes into myotubes 2,16 , and that the expression of PDZRN3 is induced together with that of MyoD during regeneration...

Lower expression of PDZRN3 induces endometrial carcinoma progression via the activation of canonical Wnt signaling

“…Previous studies reported that PDZRN3 and its E3 ubiquitin ligase domain serve an important role in ubiquitination function and in promoting cell differentiation (26,27), which confirms the hypothesis that it may be involved in promoting tumor progression. Following analysis of the public database TCGA, significant differences in PDZRN3 expression were identified in EC tissues.…”