Involvement of type 4 cAMP-phosphodiesterase in the myogenic differentiation of L6 cells

Myogenic cell differentiation is induced by Arg(8)-vasopressin, whereas hig h cAMP levels and protein kinase A (PKA) activity inhibit myogenesis. We in vestigated the role of type 4 phosphodiesterase (PDE4) during L6-C5 myoblas t differentiation. Selective PDE4 inhibition resulted in suppression of dif ferentiation induced by vasopressin. PDE4 inhibition prevented vasopressin- induced nuclear translocation of the muscle-specific transcription factor m yogenin without affecting: its overall expression level. The effects of PDE 4 inhibition could be attributed to an increase of cAMP levels and PKA acti vity. RNase protection,,reverse transcriptase PCR, immunoprecipitation, Wes tern blot, and enzyme activity assays demonstrated that the PDE4D3 isoform is the major PDE4 expressed in L6-C5 myoblasts and myotubes, accounting for 75% of total cAMP-hydrolyzing activity. Vasopressin cell stimulation cause d a biphasic increase of PDE4 activity, Which peaked at 2 and 15 min and re mained elevated for 48 h. In the continuous presence of vasopressin, cAMP l evels and PKA activity were lowered. PDE4D3 overexpression increased sponta neous and vasopressin-dependent differentiation of L6-C5 cells. These resul ts show that PDE4D3 plays a key role in the control of cAMP levels and: dif ferentiation of L6-C5 cells. Through the modulation of PDE4 activity, vasop ressin inhibits the cAMP signal transduction pathway, which regulates myoge nesis possibly by controlling the subcellular localization of myogenin.