The nfkb1 and nfkb2 genes encode closely related products regulating immune and inflammatory responses. Their role during development and differentiation remains unclear. The generation of nfkb1 null mice (p50-/-) resulted in altered immune responses, but had no effect on development. Similarly, nfkb2 knockout mice (p52-/-) did not show developmental defects (J.C. et al., manuscript submitted). We have investigated the potential for in vivo compensatory functions of these genes by generating double-knockout mice. The surprising result was that the animals developed osteopetrosis because of a defect in osteoclast differentiation, suggesting redundant functions of NF-kappaB1 and NF-kappaB2 proteins in the development of this cell lineage. The osteopetrotic phenotype was rescued by bone marrow transplantation, indicating that the hematopoietic component was impaired. These results define a new mouse osteopetrotic mutant and implicate NF-kappaB proteins in bone development, raising new directions in the treatment of bone disorders.

We demonstrate here that synthetic 22-mer peptide 46, corresponding to the carboxy-terminal amino acid residues 361-382 of p53, can activate specific DNA binding of wild-type p53 in vitro and can restore the transcriptional transactivating function of at least some mutant p53 proteins in living cells. Introduction of peptide 46 in Saos-2 cells carrying a Tet-regulatable His-273 mutant p53 construct caused growth inhibition and apoptosis in the presence of mutant p53 but not in its absence, confirming that the effect of the peptide is mediated by reactivation of mutant p53. Moreover, peptide 46 caused apoptosis in mutant as well as wild-type p53-carrying human tumor cell lines of different origin, whereas p53 null tumor cells were not affected. These findings raise possibilities for developing drugs that restore the tumor suppressor function of mutant p53 proteins, thus selectively eliminating tumor cells.

A synthetic 22-mer peptide (peptide 46) derived from the p53 C-terminal domain can restore the growth suppressor function of mutant p53 proteins in human tumor cells (G. Selivanova et al., Nat. Med. 3:632-638, 1997). Here we demonstrate that peptide 46 binds mutant p53. Peptide 46 binding sites were found within both the core and C-terminal domains of p53. Lys residues within the peptide were critical for both p53 activation and core domain binding. The sequence-specific DNA binding of isolated tumor-derived mutant p53 core domains was restored by a C-terminal polypeptide. Our results indicate that C-terminal peptide binding to the core domain activates p53 through displacement of the negative regulatory C-terminal domain. Furthermore, stabilization of the core domain structure and/or establishment of novel DNA contacts may contribute to the reactivation of mutant p53. These findings should facilitate the design of p53-reactivating drugs for cancer therapy.

Correspondence: J-J Curgy TD and CM made an equal contribution to this work.