May 2, 2003;
Links between tumor suppressors: p53 is required for TGF-beta gene responses by cooperating with Smads.
tumor suppressor belongs to a family of proteins that sense multiple cellular inputs to regulate cell proliferation, apoptosis, and differentiation. Whether and how these functions of p53
intersect with the activity of extracellular growth factors is not understood. Here, we report that key cellular responses to TGF-beta signals rely on p53
family members. During Xenopus embryonic development, p53
promotes the activation of multiple TGF-beta target genes. Moreover, mesoderm
differentiation is inhibited in p53
-depleted embryos. In mammalian cells, the full transcriptional activation of the CDK inhibitor p21(WAF1) by TGF-beta requires p53
-deficient cells display an impaired cytostatic response to TGF-beta signals. Smad and p53
protein complexes converge on separate cis binding elements on a target promoter and synergistically activate TGF-beta induced transcription. p53
can physically interact in vivo with Smad2
in a TGF-beta-dependent fashion. The results unveil a previously unrecognized link between two primary tumor suppressor pathways in vertebrates.
[+] show captions
Figure 2. In Vivo Requirement of p53 in TGF-β Gene Responses(A) p53 morpholino oligonucleotides (MO, 20 ng) specifically knockdown the translation of both endogenous (left) and overexpressed (right) Xp53 mRNA (100 pg) in animal halves explanted at gastrula stage. β-catenin protein serves as specificity control.(B) Animal caps, injected with the indicated MO, were explanted and treated with Activin protein (50 pM). Lane 4: p53 MO selectively blocks Activin inductions of Mixer, Mix.2, Eomes, and Xbra, but not of goosecoid (Gsc). Lane 5: mp53AS mRNA injection rescues Activin inductions in p53 MO injected animal caps.(C) Whole-mount in situ hybridizations on control- and p53 morphant embryos showing severe phenotypes. Control MO or p53 MO (10 ng each), together with lacZ mRNA (200 pg), were injected at the 4-cell stage in a single blastomere. Embryos shown in the upper panels were collected at gastrula, stained for β-gal activity (red staining), and processed for in situ hybridization. Embryos shown in the lower panels were radially injected (20 ng per embryo) and collected at stage 13. Note that upon p53 knockdown, staining for Chordin, Xbra, and XmyoD, but not for Vent-1, is reduced.(D and E) Phenotypes of p53-depleted embryos. Embryos were injected as in (C) and cultured until siblings reached the tailbud stage.(F–I) Embryos were injected on the right side at the 2-cell stage with 15 ng of control MO (F) or p53 MO either alone (G) or in combination with mp53AS mRNA ([H], 30 pg; [I], 100 pg). Embryos were collected at stage 26 and processed for in situ hybridization with the XmyoD probe.
p53 and TGF-beta in development: prelude to tumor suppression?