p57Kip2 is induced by MyoD through a p73-dependent pathway.
The cyclin-dependent-kinase inhibitors p21 and p57 are highly expressed in skeletal muscle where they redundantly control cell cycle arrest during differentiation. We have previously shown that p57 is a target of the myogenic factor MyoD in cells lacking p21. Here we show that MyoD induces p57 at the transcriptional level through a mechanism different from that involved in p21 regulation, since it is E-box-independent and requires new synthesized protein(s). We have identified p73 family members as the factors that mediate the activation of p57 through a 165bp promoter region. The levels of p73 alpha, beta and delta isoforms increase during muscle differentiation both in MyoD-expressing fibroblasts and in spontaneously differentiating C2 myoblasts. Moreover, the expression of a p73 dominant negative mutant interferes with the induction of p57. Finally, each of the isoforms up-regulated by MyoD, even when over-expressed alone, is capable of inducing p57 in p21-lacking fibroblasts. In contrast, the same p73 isoforms, either induced by MyoD or exogenously over-expressed, are unable to activate the expression of p57 in p21-expressing fibroblasts. Our finding that a transfected p57 promoter-reporter construct, unlike the endogenous gene, is responsive to both MyoD and p73 even in these cells, suggests that a cis-acting mechanism, probably involving a repressive chromatin structure, prevents the induction of p57 in p21-expressing fibroblasts.
Vaccarello
Giovanna
G
Istituto Pasteur-Fondazione Cenci Bolognetti, Dipartimento di Biotecnologie Cellulari ed Ematologia, Sezione di Genetica Molecolare, Università di Roma La Sapienza, Viale Regina Elena 324, 00161 Roma, Italy.
Figliola
Rocco
R
Cramerotti
Sabrina
S
Novelli
Fabiana
F
Maione
Rossella
R
D000818:Animals; D002454:Cell Differentiation / Q000502:physiology; D002461:Cell Line, Transformed; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000096:biosynthesis / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D050761:Cyclin-Dependent Kinase Inhibitor p57 / Q000096:biosynthesis* / Q000235:genetics; D004268:DNA-Binding Proteins / Q000502:physiology*; D005347:Fibroblasts / Q000378:metabolism; D051379:Mice; D008809:Mice, Inbred C3H; D018345:Mice, Knockout; D017570:MyoD Protein / Q000502:physiology*; D009687:Nuclear Proteins / Q000502:physiology*; D011401:Promoter Regions, Genetic; D015398:Signal Transduction / Q000502:physiology*; D014158:Transcription, Genetic; D000072160:Tumor Protein p73; D025521:Tumor Suppressor Proteins / Q000502:physiology*; D015854:Up-Regulation / Q000235:genetics
C493957:Cdkn1a protein, mouse; C493965:Cdkn1c protein, mouse; D050759:Cyclin-Dependent Kinase Inhibitor p21; D050761:Cyclin-Dependent Kinase Inhibitor p57; D004268:DNA-Binding Proteins; D017570:MyoD Protein; D009687:Nuclear Proteins; C000606368:Trp73 protein, mouse; D000072160:Tumor Protein p73; D025521:Tumor Suppressor Proteins