The human ARF tumor suppressor senses blastema activity and suppresses epimorphic tissue regeneration

Abstract

The control of proliferation and differentiation by tumor suppressor genes suggests that evolution of divergent tumor suppressor repertoires could influence species’ regenerative capacity. To directly test that premise, we humanized the zebrafish p53 pathway by introducing regulatory and coding sequences of the human tumor suppressor ARF into the zebrafish genome. ARF was dormant during development, in uninjured adult fins, and during wound healing, but was highly expressed in the blastema during epimorphic fin regeneration after amputation. Regenerative, but not developmental signals resulted in binding of zebrafish E2f to the human ARF promoter and activated conserved ARF-dependent Tp53 functions. The context-dependent activation of ARF did not affect growth and development but inhibited regeneration, an unexpected distinct tumor suppressor response to regenerative versus developmental environments. The antagonistic pleiotropic characteristics of ARF as both tumor and regeneration suppressor imply that inducing epimorphic regeneration clinically would require modulation of ARF –p53 axis activation.DOI: http://dx.doi.org/10.7554/eLife.07702.001

A redox mechanism underlying nucleolar stress sensing by nucleophosmin

“…The interaction of ribosomal proteins with HDM2 is required for the activation of p53 induced by nucleolar stress414243. ARF can also bind to HDM2, to stabilize p53 in diverse cellular events48636465. Our findings emphasize that the nucleoplasmic localization of NPM1 alone allows it to induce p53 stabilization under stress.…”

Zebrafish fin and heart: what's special about regeneration?

“…Interestingly, only p16 but not Arf can be found in the genomes of zebrafish and salamanders [82 ]. In a transgenic zebrafish reporter line, the human ARF promoter has been shown to be silent during embryonic development and at skin injury sites, but highly active in the blastema of regenerating fins [82 ]. These results imply that the signaling environment in the regeneration context is similar to that in mammalian tumors, resulting in activation of ARF.…”

“…In mammals, the cyclin-dependent kinase 2a (Cdkn2a) locus codes for two independent proteins, p16Ink4a and Arf. Interestingly, only p16 but not Arf can be found in the genomes of zebrafish and salamanders [82 ]. In a transgenic zebrafish reporter line, the human ARF promoter has been shown to be silent during embryonic development and at skin injury sites, but highly active in the blastema of regenerating fins [82 ].…”

“…These results imply that the signaling environment in the regeneration context is similar to that in mammalian tumors, resulting in activation of ARF. Expression of human ARF protein from the ARF promoter impairs fin regeneration, since it inhibits cell proliferation and induces apoptosis [82 ]. Thus, it's possible that the evolution of some tumor suppressor mechanisms in mammals came at the expense of the ability to regenerate.…”

“…One possible hint comes from an intriguing study indicating that tumor suppressor mechanisms evolved by mammals are incompatible with regeneration [82 ]. Under conditions of loss of G1/S checkpoints, the tumor suppressor Arf can stabilize and activate p53 and thus promote cell cycle arrest and apoptosis [83].…”