The BMP2/7 heterodimer inhibits the human breast cancer stem cell subpopulation and bone metastases formation.

Accumulating evidence suggests that a subpopulation of breast cancer cells, referred to as cancer stem cells (CSCs), have the ability to propagate a tumor and potentially seed new metastases. Furthermore, stimulation of an epithelial-to-mesenchymal transition by factors like transforming growth factor-ß (TGFß) is accompanied with the generation of breast CSCs. Previous observations indicated that bone morphogenetic protein-7 (BMP7) antagonizes the protumorigenic and prometastatic actions of TGFß, but whether BMP7 action is mechanistically linked to breast CSCs has remained elusive. Here, we have studied the effects of BMP7, BMP2 and a BMP2/7 heterodimer on the formation of human breast CSCs (ALDH(hi)/CD44(hi)/CD24(-/low)) and bone metastases formation in a preclinical model of intra-cardiac injection of MDA-MB-231 cells in athymic nude (Balb/c nu/nu) mice. The BMP2/7 heterodimer was the most efficient stimulator of BMP signaling and very effectively reduced TGFß-driven Smad signaling and cancer cell invasiveness. The tested BMPs-particularly the heterodimeric BMP2/7-strongly reduced the size of the ALDH(hi)/CD44(hi)/CD24(-/low) CSC subpopulation. In keeping with these in vitro observations, pretreatment of cancer cells with BMPs for 72 h prior to systemic inoculation of the cancer cells inhibited the formation of bone metastases. Collectively, our data support the notion that breast CSCs are involved in bone metastasis formation and describe heterodimeric BMP2/7 as a powerful TGFß antagonist with anti-metastatic potency.

Possible phenotypic dosage effect in patients compound heterozygous for FSHD-sized 4q35 alleles.

OBJECTIVE: Autosomal dominant facioscapulohumeral muscular dystrophy (FSHD) is associated with a contraction of the D4Z4 repeat array on chromosome 4. So far, homozygosity or compound heterozygosity for FSHD alleles has not been described, and it has been debated whether the absence of such subjects is because of the rarity or the lethality of the disorder. METHODS: Two unrelated families in which the probands are compound heterozygous for two FSHD-sized alleles were studied. Clinical examination, pulsed-field gel electrophoresis (PFGE) studies of DNA with probes proximal and distal to D4Z4, and cytogenetic analysis of metaphase chromosomes by FISH were performed. RESULTS: Complementary molecular and cytogenetic approaches confirmed the chromosome 4qA origin of all FSHD-sized repeat arrays that segregate in the families. CONCLUSIONS: Heterozygosity for FSHD-sized alleles is compatible with life in men and women. A possible dosage effect was observed in both probands in whom each 4qA allele contributed to the FSHD phenotype. Because at least one of the FSHD alleles in both families showed an unusual low penetrance, the authors propose that susceptibility for FSHD is partly determined by intrinsic properties of the disease allele other than the residual D4Z4 repeat size alone.

Interchromosomal repeat array interactions between chromosomes 4 and 10: a model for subtelomeric plasticity.

Chromosomal rearrangements occur more frequently in subtelomeric domains than in other regions of the genome and are often associated with human pathology. To further elucidate the plasticity of subtelomeric domains, we examined the 3.3 kb D4Z4 repeat array on chromosome 4 and its homologue on chromosome 10 in 208 Dutch blood donors by pulsed field gel electrophoresis. These subtelomeric repeats are known to rearrange and partial deletions of this polymorphic array on chromosome 4 are associated with facioscapulohumeral muscular dystrophy (FSHD), an autosomal dominant myopathy. Our results show that mitotic rearrangements occur frequently as 3% of individuals display somatic mosaicism for a repeat expansion or contraction explaining the high variability of subtelomeric repeat array sizes. Translocated 4-type repeat arrays on chromosome 10 and the reverse configuration of 10-type repeat arrays on chromosome 4 are observed in 21% of individuals. The translocated repeat arrays on chromosome 4 tend to be more heterogeneous than 4-type repeats on chromosome 10. The repeat length on chromosome 4 is on average larger than on chromosome 10. But on both chromosomes we observe a multi-modal repeat length distribution with equidistant peaks at intervals of 65 kb, possibly reflecting a higher-order chromatin structure. Interestingly, in as many as six random blood donors (3%) we identified FSHD-sized 4-type repeat arrays. Assuming that these individuals are clinically unaffected, these results imply an incomplete penetrance in the upper range of FSHD alleles. Overall, the observed dynamic characteristics of these homologous domains may serve as a model for subtelomeric plasticity.

De novo facioscapulohumeral muscular dystrophy: frequent somatic mosaicism, sex-dependent phenotype, and the role of mitotic transchromosomal repeat interaction between chromosomes 4 and 10.

Autosomal dominant facioscapulohumeral muscular dystrophy (FSHD) is caused by deletion of most copies of the 3.3-kb subtelomeric D4Z4 repeat array on chromosome 4q. The molecular mechanisms behind the deletion and the high proportion of new mutations have remained elusive. We surveyed 35 de novo FSHD families and found somatic mosaicism in 40% of cases, in either the patient or an asymptomatic parent. Mosaic males were typically affected; mosaic females were more often the unaffected parent of a nonmosaic de novo patient. A genotypic-severity score, composed of the residual repeat size and the degree of somatic mosaicism, yields a consistent relationship with severity and age at onset of disease. Mosaic females had a higher proportion of somatic mosaicism than did mosaic males. The repeat deletion is significantly enhanced by supernumerary homologous repeat arrays. In 10% of normal chromosomes, 4-type repeat arrays are present on chromosome 10. In mosaic individuals, 4-type repeats on chromosome 10 are almost five times more frequent. The reverse configuration, also 10% in normal chromosomes, was not found, indicating that mutations may arise from transchromosomal interaction, to which the increase in 4-type repeat clusters is a predisposing factor. The somatic mosaicism suggests a mainly mitotic origin; mitotic interchromosomal gene conversion or translocation between fully homologous 4-type repeat arrays may be a major mechanism for FSHD mutations.