MDM2 Is a Negative Regulator of p21 , Independent of p53

Abstract

The MDM2 oncogene has both p53-dependent and p53-independent activities. We have previously reported that antisense MDM2 inhibitors have significant anti-tumor activity in multiple human cancer models with various p53 statuses (Zhang, Z., Li, M., Wang, H., Agrawal, S., and Zhang, R. (2003) Proc. Natl. Acad. Sci. U. S. A. 100, 11636–11641). We have also provided evidence that MDM2 has a direct role in the regulation of p21, a cyclin-dependent kinase inhibitor. Here we provide evidence supporting functional interaction between MDM2 and p21 in vitro and in vivo. The inhibition of MDM2 with anti-MDM2 antisense oligonucleotide or Short Interference RNA targeting MDM2 significantly elevated p21 protein levels in PC3 cells (p53 null). In contrast, overexpression of MDM2 diminished the p21 level in the same cells by shortening the p21 half-life, an effect reversed by MDM2 antisense inhibition. MDM2 facilitates p21 degradation independent of ubiquitination and the E3 ligase function of MDM2. Instead, MDM2 promotes p21 degradation by facilitating binding of p21 with the proteasomal C8 subunit. The physical interaction between p21 and MDM2 was demonstrated both in vitro and in vivo with the binding region in amino acids 180–298 of the MDM2 protein. In summary, we provide evidence supporting a physical interaction between MDM2 and p21. We also demonstrate that, by reducing p21 protein stability via proteasome-mediated degradation, MDM2 functions as a negative regulator of p21, an effect independent of both p53 and ubiquitination. The MDM2 oncogene has both p53-dependent and p53-independent activities. We have previously reported that antisense MDM2 inhibitors have significant anti-tumor activity in multiple human cancer models with various p53 statuses (Zhang, Z., Li, M., Wang, H., Agrawal, S., and Zhang, R. (2003) Proc. Natl. Acad. Sci. U. S. A. 100, 11636–11641). We have also provided evidence that MDM2 has a direct role in the regulation of p21, a cyclin-dependent kinase inhibitor. Here we provide evidence supporting functional interaction between MDM2 and p21 in vitro and in vivo. The inhibition of MDM2 with anti-MDM2 antisense oligonucleotide or Short Interference RNA targeting MDM2 significantly elevated p21 protein levels in PC3 cells (p53 null). In contrast, overexpression of MDM2 diminished the p21 level in the same cells by shortening the p21 half-life, an effect reversed by MDM2 antisense inhibition. MDM2 facilitates p21 degradation independent of ubiquitination and the E3 ligase function of MDM2. Instead, MDM2 promotes p21 degradation by facilitating binding of p21 with the proteasomal C8 subunit. The physical interaction between p21 and MDM2 was demonstrated both in vitro and in vivo with the binding region in amino acids 180–298 of the MDM2 protein. In summary, we provide evidence supporting a physical interaction between MDM2 and p21. We also demonstrate that, by reducing p21 protein stability via proteasome-mediated degradation, MDM2 functions as a negative regulator of p21, an effect independent of both p53 and ubiquitination. p21WAF1/CIP1, which belongs the of cyclin-dependent kinase has as an of evidence that a role in and of The regulation of p21 also previously p53-dependent R. and degradation also by and via proteasome-mediated MDM2 antisense antisense R. a negative regulator of p53 R. that functions activity S. and proteasome-mediated degradation R. A. MDM2 has with A. S. protein and S. that has p53-independent R. The in the of the E3 ligase p53 ubiquitination and degradation S. E3 ligase has also the degradation of the S. MDM2 in human and MDM2 levels with a R. The MDM2 also have a role in cancer We have MDM2 antisense that have in vitro and in vivo human cancer models S. R. Proc. Natl. Acad. Sci. U. S. A. S. R. S. R. S. R. S. R. Proc. Natl. Acad. Sci. U. S. A. MDM2 of p21 was in human cancer cells or of p53 S. R. S. R. S. R. S. R. Proc. Natl. Acad. Sci. U. S. A. a role of MDM2 in p21 In the we a of the interaction between MDM2 and p21. We demonstrated that MDM2 has direct activity in the degradation of p21 protein by binding and facilitating interaction with the C8 of independent of both p53 and ubiquitination. We also have that p21 has an role in the of MDM2 and and the of human MDM2 and p53 provided by The human MDM2 was with and and the same of and The was a of of MDM2 protein by of and by the with the same The was provided by and the p21 protein was with in which the a the the p21 protein in human p21 was with and and the same of and of and The the of was provided by RNA the of the and of in vivo. and of MDM2 and p21 and The of the MDM2 the MDM2 The of the p21 and and and MDM2 antisense oligonucleotide and previously S. R. Proc. Natl. Acad. Sci. U. S. A. cells as previously S. R. Proc. Natl. Acad. Sci. U. S. A. cells in and p21, and MDM2 p21 PC3 PC3 cells with with and by the MDM2 PC3 PC3 cells with by the of a The by and in in and by the with as in the The was by protein which with The by and by the in the and p21 in vitro in the and or and with in and and The and protein with with and with a protein a direct physical binding between MDM2 protein and p21 protein in or protein was with in vitro and p21 or MDM2 protein in the binding The by which with with and with p21 or MDM2 The same p21 protein binding protein. The with the same of with of or protein The protein also was by p21 cells with various in the with p21 or p53 and the with protein and by in The with of was by the of with and The by with and by the and previously S. R. Proc. Natl. Acad. Sci. U. S. A. with or various with cells with or and with was by with cells in a p21 of p53 and effect of MDM2 p21 protein was in PC3 (p53 cells by anti-MDM2 antisense oligonucleotide or MDM2 MDM2 p21 was and was an between the level of MDM2 and that of p21 and In contrast, MDM2 a in p21 protein p21 degradation and p21 degradation reversed by inhibition of PC3 cells MDM2 with the inhibitors or In cells with the level of p21 protein was inhibitors The effect of MDM2 overexpression p21 degradation was reversed by inhibitors or by the anti-MDM2 antisense oligonucleotide In a with the protein overexpression of MDM2 the of p21 by the and MDM2 facilitates p21 ubiquitination E3 ligase PC3 cells with MDM2 and levels of p21 In MDM2 the ubiquitination of which was as a that MDM2 p21 ubiquitination and of PC3 cells with p21 and MDM2 and with in in by the with p21 was by and by p21 with the MDM2 p21 ubiquitination p53 was in PC3 cells with MDM2 p21 protein the C8 of the of the and by in vitro R. S. we that MDM2 has a direct effect of MDM2 p21 PC3 cells with in p21 C8 in the of cells with MDM2 and p21 supporting the that MDM2 facilitates that the effect of MDM2 p21 protein stability independent of E3 ligase an MDM2 protein the E3 ligase activity was protein the p21 by the p53 protein level facilitates p21 degradation independent of E3 ligase MDM2 ubiquitination of p53 protein p21 protein. PC3 cells with MDM2 The by p21 and with or p21 PC3 cells with MDM2 and with or p53 and by p53 was by with or p53 PC3 cells with of p21, or or in various of the was by with an with and with p21 or MDM2 PC3 cells with MDM2 and with or p53 with and and MDM2 or p53 was by MDM2 or p53 MDM2 protein facilitates p21 protein binding the C8 in PC3 cells with MDM2 with or p21 and the with of protein. The p21 protein was by and by p21 The p21 protein levels in the also by of PC3 cells with MDM2 and p21 with of protein or protein. The p21 protein was and by p21 in with the p21 protein level in the the of MDM2 protein p21 protein stability independent of E3 ligase the the of the of MDM2 protein and protein p21 protein level in PC3 cells with MDM2 or MDM2 by the with was by PC3 cells with MDM2 or MDM2 with p53 and by between MDM2 and p21 the with of PC3 cells by p21 or MDM2 which was by with MDM2 or p21 demonstrate a direct physical interaction between p21 and MDM2. the with or The by or that the interaction of the was and physical interaction between p21 and MDM2 physical binding between MDM2 and p21 was in PC3 or with the p21 and MDM2 in with with the was with or cells with protein with or protein or with the or was with or the MDM2 protein and the p21 protein in the of MDM2 and cells with or with MDM2 protein or by with The protein was and by with MDM2 the binding p21 acids of p21 PC3 cells with MDM2 or which was by the with an by MDM2 protein the p21 protein in or in with and by MDM2 or p21 or was with in vitro and p21 protein or MDM2 protein The by and by p21 or MDM2 binding the MDM2 protein by with and a of MDM2 The region between amino acids and was in MDM2 binding the p21 protein and the of the binding between MDM2 and p21 in the of p21 degradation, the MDM2 was MDM2 protein was of p21 degradation the that the interaction between p21 and MDM2 in a multiple protein in the a was by or protein and in vitro p21 or MDM2 binding between the was that the binding of an in MDM2 and demonstrated that, in and in models of human MDM2 inhibition in significant anti-tumor activity and S. R. S. R. S. R. S. R. Proc. Natl. Acad. Sci. U. S. A. In a p21 was elevated as a of MDM2 In we the role that p21 in the activity of MDM2 The and p21 PC3 cells with the anti-MDM2 antisense oligonucleotide The p21 cells the MDM2 antisense a of the was that of cells has a role in the and by MDM2 p21 PC3 cells the of MDM2 inhibition with p21 and PC3 cells with various of by or and in MDM2 and p21 PC3 cells with MDM2 PC3 The p21 and MDM2 protein levels in MDM2 p21 MDM2 and p21 and PC3 cells with or by or in or and p21 MDM2 and MDM2 and p21 role of p21 in by MDM2 was by p21 MDM2 MDM2 and p21 and PC3 cells that with various of or PC3 which the p21 level the as by and reversed by p21 that p21 a role in MDM2 of p21 MDM2 by antisense in cells with p53 or an role of MDM2 in the regulation of p21 independent of We have provided evidence that MDM2 a negative regulator of p21, In the we have and the MDM2 protein p21 protein and facilitates interaction with the C8 of MDM2 facilitates proteasome-mediated p21 protein degradation, independent of both and p21 has an role in inhibition and by MDM2 that p21 of the p53-independent MDM2 the p21 protein as both a negative and regulator of regulation both and the of p21 has the of p21 protein proteasome-mediated has that the ubiquitination of p21 degradation the A. was evidence supporting the of E3 ligase in p21 protein Proc. Natl. Acad. Sci. U. S. A. p21 a protein in the of In the of evidence that MDM2 promotes p21 proteasome-mediated The direct physical binding between as in in vivo and in vitro the The of MDM2 protein the binding p21 protein the E3 ligase activity of MDM2 protein a role in p53 degradation, p21 We also have that proteasome-mediated p21 protein degradation was by which MDM2 promotes p21 p21 protein and Proc. Natl. Acad. Sci. U. S. A. and ubiquitination proteasome-mediated degradation that the p21 protein by the A. The p21 protein the C8 of the and by in vitro A. the C8 In the the binding between p21 and C8 in vitro was in of cells with MDM2 and p21, that MDM2 promotes p21 interaction with the a p53 protein degradation and functions R. in which MDM2 as a p53 negative evidence that MDM2 has p53-independent with R. p21 by protein degradation a role in MDM2 that p21 a the role of p21 in that p21 S. R. and cells Sci. The independent of p53 S. R. and has demonstrated in cancer cells A. S. in with In S. R. S. R. S. R. Proc. Natl. Acad. Sci. U. S. A. we that MDM2 by antisense in p21 and in various cancer of p53 S. R. Proc. Natl. Acad. Sci. U. S. A. In the we have p21 MDM2 and MDM2 p21 PC3 We have that p21 cells the and by antisense MDM2 that p21 has a role in the of MDM2 inhibition. MDM2 cells the the as and with the MDM2 of p21 the the level of the of p21 in the by MDM2 p21WAF1/CIP1, which belongs the of cyclin-dependent kinase has as an of evidence that a role in and of The regulation of p21 also previously p53-dependent R. and degradation also by and via proteasome-mediated The MDM2 antisense antisense R. a negative regulator of p53 R. that functions activity S. and proteasome-mediated degradation R. A. MDM2 has with A. S. protein and S. that has p53-independent R. The in the of the E3 ligase p53 ubiquitination and degradation S. E3 ligase has also the degradation of the S. The MDM2 in human and MDM2 levels with a R. The MDM2 also have a role in cancer We have MDM2 antisense that have in vitro and in vivo human cancer models S. R. Proc. Natl. Acad. Sci. U. S. A. S. R. S. R. S. R. S. R. Proc. Natl. Acad. Sci. U. S. A. MDM2 of p21 was in human cancer cells or of p53 S. R. S. R. S. R. S. R. Proc. Natl. Acad. Sci. U. S. A. a role of MDM2 in p21 In the we a of the interaction between MDM2 and p21. We demonstrated that MDM2 has direct activity in the degradation of p21 protein by binding and facilitating interaction with the C8 of independent of both p53 and ubiquitination. We also have that p21 has an role in the of MDM2 and and the of human MDM2 and p53 provided by The human MDM2 was with and and the same of and The was a of of MDM2 protein by of and by the with the same The was provided by and the p21 protein was with in which the a the the p21 protein in human p21 was with and and the same of and of and The the of was provided by RNA the of the and of in vivo. and of MDM2 and p21 and The of the MDM2 the MDM2 The of the p21 and and and MDM2 antisense oligonucleotide and previously S. R. Proc. Natl. Acad. Sci. U. S. A. cells as previously S. R. Proc. Natl. Acad. Sci. U. S. A. cells in and p21, and MDM2 p21 PC3 PC3 cells with with and by the MDM2 PC3 PC3 cells with by the of a The by and in in and by the with as in the The was by protein which with The by and by the in the and p21 in vitro in the and or and with in and and The and protein with with and with a protein a direct physical binding between MDM2 protein and p21 protein in or protein was with in vitro and p21 or MDM2 protein in the binding The by which with with and with p21 or MDM2 The same p21 protein binding protein. The with the same of with of or protein The protein also was by p21 cells with various in the with p21 or p53 and the with protein and by in The with of was by the of with and The by with and by the and previously S. R. Proc. Natl. Acad. Sci. U. S. A. with or various with cells with or and with was by with cells in a and and the of human MDM2 and p53 provided by The human MDM2 was with and and the same of and The was a of of MDM2 protein by of and by the with the same The was provided by and the p21 protein was with in which the a the the p21 protein in human p21 was with and and the same of and of and The the of was provided by RNA the of the and of in vivo. and of MDM2 and p21 and The of the MDM2 the MDM2 The of the p21 and and and MDM2 antisense oligonucleotide and previously S. R. Proc. Natl. Acad. Sci. U. S. A. cells as previously S. R. Proc. Natl. Acad. Sci. U. S. A. cells in and p21, and MDM2 p21 PC3 PC3 cells with with and by the MDM2 PC3 PC3 cells with by the of a The by and in in and by the with as in the The was by protein which with The by and by the in the In and p21 in vitro in the and or and with in and and The and protein with with and with a protein a direct physical binding between MDM2 protein and p21 protein in or protein was with in vitro and p21 or MDM2 protein in the binding The by which with with and with p21 or MDM2 The same p21 protein binding protein. The with the same of with of or protein The protein also was by p21 cells with various in the with p21 or p53 and the with protein and by in The with of was by the of with and The by with and by the and previously S. R. Proc. Natl. Acad. Sci. U. S. A. with or various with cells with or and with was by with cells in a p21 of p53 and effect of MDM2 p21 protein was in PC3 (p53 cells by anti-MDM2 antisense oligonucleotide or MDM2 MDM2 p21 was and was an between the level of MDM2 and that of p21 and In contrast, MDM2 a in p21 protein p21 degradation and p21 degradation reversed by inhibition of PC3 cells MDM2 with the inhibitors or In cells with the level of p21 protein was inhibitors The effect of MDM2 overexpression p21 degradation was reversed by inhibitors or by the anti-MDM2 antisense oligonucleotide In a with the protein overexpression of MDM2 the of p21 by the and MDM2 facilitates p21 ubiquitination E3 ligase PC3 cells with MDM2 and levels of p21 In MDM2 the ubiquitination of which was as a that MDM2 p21 ubiquitination and of PC3 cells with p21 and MDM2 and with in in by the with p21 was by and by p21 with the MDM2 p21 ubiquitination p53 was in PC3 cells with MDM2 p21 protein the C8 of the of the and by in vitro R. S. we that MDM2 has a direct effect of MDM2 p21 PC3 cells with in p21 C8 in the of cells with MDM2 and p21 supporting the that MDM2 facilitates that the effect of MDM2 p21 protein stability independent of E3 ligase an MDM2 protein the E3 ligase activity was protein the p21 by the p53 protein level between MDM2 and p21 the with of PC3 cells by p21 or MDM2 which was by with MDM2 or p21 demonstrate a direct physical interaction between p21 and MDM2. the with or The by or that the interaction of the was and physical interaction between p21 and MDM2 physical binding between MDM2 and p21 was in PC3 or with the p21 and MDM2 in with with the was with or cells with protein with or protein or with the or was with or the MDM2 protein and the p21 protein in the of MDM2 and cells with or with MDM2 protein or by with The protein was and by with MDM2 the binding p21 acids of p21 PC3 cells with MDM2 or which was by the with an by MDM2 protein the p21 protein in or in with and by MDM2 or p21 or was with in vitro and p21 protein or MDM2 protein The by and by p21 or MDM2 binding the MDM2 protein by with and a of MDM2 The region between amino acids and was in MDM2 binding the p21 protein and the of the binding between MDM2 and p21 in the of p21 degradation, the MDM2 was MDM2 protein was of p21 degradation the that the interaction between p21 and MDM2 in a multiple protein in the a was by or protein and in vitro p21 or MDM2 binding between the was that the binding of an in MDM2 and demonstrated that, in and in models of human MDM2 inhibition in significant anti-tumor activity and S. R. S. R. S. R. S. R. Proc. Natl. Acad. Sci. U. S. A. In a p21 was elevated as a of MDM2 In we the role that p21 in the activity of MDM2 The and p21 PC3 cells with the anti-MDM2 antisense oligonucleotide The p21 cells the MDM2 antisense a of the was that of cells has a role in the and by MDM2 p21 PC3 cells the of MDM2 inhibition with p21 and PC3 cells with various of by or and in MDM2 and p21 PC3 cells with MDM2 PC3 The p21 and MDM2 protein levels in MDM2 p21 MDM2 and p21 and PC3 cells with or by or in or and p21 MDM2 and MDM2 and p21 role of p21 in by MDM2 was by p21 MDM2 MDM2 and p21 and PC3 cells that with various of or PC3 which the p21 level the as by and reversed by p21 that p21 a role in MDM2 inhibition. MDM2 p21 of p53 and effect of MDM2 p21 protein was in PC3 (p53 cells by anti-MDM2 antisense oligonucleotide or MDM2 MDM2 p21 was and was an between the level of MDM2 and that of p21 and In contrast, MDM2 a in p21 protein p21 degradation and p21 degradation reversed by inhibition of PC3 cells MDM2 with the inhibitors or In cells with the level of p21 protein was inhibitors The effect of MDM2 overexpression p21 degradation was reversed by inhibitors or by the anti-MDM2 antisense oligonucleotide In a with the protein overexpression of MDM2 the of p21 by the and MDM2 facilitates p21 ubiquitination E3 ligase PC3 cells with MDM2 and levels of p21 In MDM2 the ubiquitination of which was as a that MDM2 p21 ubiquitination and of PC3 cells with p21 and MDM2 and with in in by the with p21 was by and by p21 with the MDM2 p21 ubiquitination p53 was in PC3 cells with MDM2 p21 protein the C8 of the of the and by in vitro R. S. we that MDM2 has a direct effect of MDM2 p21 PC3 cells with in p21 C8 in the of cells with MDM2 and p21 supporting the that MDM2 facilitates that the effect of MDM2 p21 protein stability independent of E3 ligase an MDM2 protein the E3 ligase activity was protein the p21 by the p53 protein level between MDM2 and p21 the with of PC3 cells by p21 or MDM2 which was by with MDM2 or p21 demonstrate a direct physical interaction between p21 and MDM2. the with or The by or that the interaction of the was and The binding the MDM2 protein by with and a of MDM2 The region between amino acids and was in MDM2 binding the p21 protein and the of the binding between MDM2 and p21 in the of p21 degradation, the MDM2 was MDM2 protein was of p21 degradation the that the interaction between p21 and MDM2 in a multiple protein in the a was by or protein and in vitro p21 or MDM2 binding between the was that the binding of p21 an in MDM2 and demonstrated that, in and in models of human MDM2 inhibition in significant anti-tumor activity and S. R. S. R. S. R. S. R. Proc. Natl. Acad. Sci. U. S. A. In a p21 was elevated as a of MDM2 In we the role that p21 in the activity of MDM2 The and p21 PC3 cells with the anti-MDM2 antisense oligonucleotide The p21 cells the MDM2 antisense a of the was that of cells The role of p21 in by MDM2 was by p21 MDM2 MDM2 and p21 and PC3 cells that with various of or PC3 which the p21 level the as by and reversed by p21 that p21 a role in MDM2 inhibition. of p21 MDM2 by antisense in cells with p53 or an role of MDM2 in the regulation of p21 independent of We have provided evidence that MDM2 a negative regulator of p21, In the we have and the MDM2 protein p21 protein and facilitates interaction with the C8 of MDM2 facilitates proteasome-mediated p21 protein degradation, independent of both and p21 has an role in inhibition and by MDM2 that p21 of the p53-independent MDM2 the p21 protein as both a negative and regulator of regulation both and the of p21 has the of p21 protein proteasome-mediated has that the ubiquitination of p21 degradation the A. was evidence supporting the of E3 ligase in p21 protein Proc. Natl. Acad. Sci. U. S. A. p21 a protein in the of In the of evidence that MDM2 promotes p21 proteasome-mediated The direct physical binding between as in in vivo and in vitro the The of MDM2 protein the binding p21 protein the E3 ligase activity of MDM2 protein a role in p53 degradation, p21 We also have that proteasome-mediated p21 protein degradation was by which MDM2 promotes p21 p21 protein and Proc. Natl. Acad. Sci. U. S. A. and ubiquitination proteasome-mediated degradation that the p21 protein by the A. The p21 protein the C8 of the and by in vitro A. the C8 In the the binding between p21 and C8 in vitro was in of cells with MDM2 and p21, that MDM2 promotes p21 interaction with the a p53 protein degradation and functions R. in which MDM2 as a p53 negative evidence that MDM2 has p53-independent with R. p21 by protein degradation a role in MDM2 that p21 a the role of p21 in that p21 S. R. and cells Sci. The independent of p53 S. R. and has demonstrated in cancer cells A. S. in with In S. R. S. R. S. R. Proc. Natl. Acad. Sci. U. S. A. we that MDM2 by antisense in p21 and in various cancer of p53 S. R. Proc. Natl. Acad. Sci. U. S. A. In the we have p21 MDM2 and MDM2 p21 PC3 We have that p21 cells the and by antisense MDM2 that p21 has a role in the of MDM2 inhibition. MDM2 cells the the as and with the MDM2 of p21 the the level of the of p21 in the by MDM2 of p21 MDM2 by antisense in cells with p53 or an role of MDM2 in the regulation of p21 independent of We have provided evidence that MDM2 a negative regulator of p21, In the we have and the MDM2 protein p21 protein and facilitates interaction with the C8 of MDM2 facilitates proteasome-mediated p21 protein degradation, independent of both and p21 has an role in inhibition and by MDM2 that p21 of the p53-independent MDM2 the p21 protein as both a negative and regulator of regulation both and the of p21 has the of p21 protein proteasome-mediated has that the ubiquitination of p21 degradation the A. was evidence supporting the of E3 ligase in p21 protein Proc. Natl. Acad. Sci. U. S. A. p21 a protein in the of In the of evidence that MDM2 promotes p21 proteasome-mediated The direct physical binding between as in in vivo and in vitro the The of MDM2 protein the binding p21 protein the E3 ligase activity of MDM2 protein a role in p53 degradation, p21 We also have that proteasome-mediated p21 protein degradation was by which MDM2 promotes p21 p21 protein and Proc. Natl. Acad. Sci. U. S. A. and ubiquitination proteasome-mediated degradation that the p21 protein by the A. The p21 protein the C8 of the and by in vitro A. the C8 In the the binding between p21 and C8 in vitro was in of cells with MDM2 and p21, that MDM2 promotes p21 interaction with the The a p53 protein degradation and functions R. in which MDM2 as a p53 negative evidence that MDM2 has p53-independent with R. p21 by protein degradation a role in MDM2 that p21 a the role of p21 in that p21 S. R. and cells Sci. The independent of p53 S. R. and has demonstrated in cancer cells A. S. in with In S. R. S. R. S. R. Proc. Natl. Acad. Sci. U. S. A. we that MDM2 by antisense in p21 and in various cancer of p53 S. R. Proc. Natl. Acad. Sci. U. S. A. In the we have p21 MDM2 and MDM2 p21 PC3 We have that p21 cells the and by antisense MDM2 that p21 has a role in the of MDM2 inhibition. MDM2 cells the the as and with the MDM2 of p21 the the level of the of p21 in the by MDM2 We R. and A. and