Functional Analysis of RUNX2 Mutations in Japanese Patients with Cleidocranial Dysplasia Demonstrates Novel Genotype-Phenotype Correlations

Abstract

Cleidocranial dysplasia (CCD) is an autosomal dominant heritable skeletal disease caused by heterozygous mutations in the osteoblast-specific transcription factor RUNX2. We have performed mutational analysis of RUNX2 on 24 unrelated patients with CCD. In 17 patients, 16 distinct mutations were detected in the coding region of RUNX2: 4 frameshift, 3 nonsense, 6 missense, and 2 splicing mutations, in addition to 1 polymorphism. The missense mutations were all clustered within the Runt domain, and their protein products were severely impaired in DNA binding and transactivation. In contrast, two RUNX2 mutants had the Runt domain intact and remained partially competent for transactivation. One criterion of CCD, short stature, was much milder in the patients with the intact Runt domain than in those without. Furthermore, a significant correlation was found between short stature and the number of supernumerary teeth. On the one hand, these genotype-phenotype correlations highlight a general, quantitative dependency, by skeleto-dental developments, on the gene dosage of RUNX2, which has hitherto been obscured by extreme clinical diversities of CCD; this gene-dosage effect is presumed to manifest on small reductions in the total RUNX2 activity, by approximately one-fourth of the normal level at minimum. On the other hand, the classic CCD phenotype, hypoplastic clavicles or open fontanelles, was invariably observed in all patients, including those with normal height. Thus, the cleidocranial bone formation, as mediated by intramembranous ossification, may require a higher level of RUNX2 than does skeletogenesis (mediated by endochondral ossification), as well as odontogenesis (involving still different complex processes). Overall, these results suggest that CCD could result from much smaller losses in the RUNX2 function than has been envisioned on the basis of the conventional haploinsufficiency model.

Prolyl Isomerase Pin1-mediated Conformational Change and Subnuclear Focal Accumulation of Runx2 Are Crucial for Fibroblast Growth Factor 2 (FGF2)-induced Osteoblast Differentiation

“…The genotype-phenotype correlation regarding various RUNX2 mutations revealed that the Runx2 protein was differentially distributed between the nucleus and the cytosol in different mutants, demonstrating the importance of nuclear localization in bone development (48). This result suggests that the nuclear positioning of Runx2 in the nucleus promotes its transactivation activity, which provides an alternative molecular etiology for CCD development.…”

Aurora kinase-induced phosphorylation excludes transcription factor RUNX from the chromatin to facilitate proper mitotic progression

“…4A). Interestingly, the T173I mutation was found in RUNX3 in the colon carcinoma cell line LS411, whereas its equivalent mutation in RUNX1 (T196I) was detected in chronic myelomonocytic leukemia (cancer.sanger.ac.uk/cosmic) (23)(24)(25); the equivalent residue in RUNX2 was found to be mutated, also to isoleucine, in the disease cleidocranial dysplasia (CCD) (26). This finding indicates that the T173 residue is important for the function of the Runt domain.…”

TEL-AML1 preleukemic activity requires the DNA binding domain of AML1 and the dimerization and corepressor binding domains of TEL

“…In addition, a construct containing a point mutation within the RHD of TEL-AML1 was generated (MSCV-R201Q). R201Q is the most frequent mutation in the RHD of AML1 in human patients, found in familial platelet disorder with predisposition to AML (Song et al, 1999), AML (Preudhomme et al, 2000) and cleidocranial dysplasia (Quack et al, 1999;Zhou et al, 1999;Otto et al, 2002;Yoshida et al, 2002). Conservative mutation of this amino acid, at the corresponding position in mouse AML1 (R174), reduces the affinity of the AML1 RHD domain for DNA by 1000-fold, without disrupting heterodimerization with the corebinding factor (CBF)b cofactor or perturbing the RHD fold (Li et al, 2003).…”