The Wnt antagonist Frzb-1 regulates chondrocyte maturation and long bone development during limb skeletogenesis

Chondrosarcoma cell differentiation

A mixed population of lymphocytes from a healthy donor co-existed with an established culture of allogeneic chondrosarcoma cells, during which time the tumor cells changed from malignantly transformed to benign fibroblast-like morphology; from multilayered to a monolayered growth pattern; lost their potency to grow in colonies in soft agar; and showed signs of senescence. A discussion of possible molecular mechanisms for this event is offered. If there are as yet undiscovered lymphokines that can induce reversal of the malignant geno/phenotype, the cognate gene(s) should be cloned for genetic engineering and for the mass production of the corresponding molecular mediators for clinical trials.

Interpreting the molecular biology and clinical behavior of multiple myeloma in the context of global gene expression profiling

Multiple myeloma (MM) is a rare but uniformly fatal malignancy of antibody-secreting plasma cells (PCs). Although several key molecular events in disease initiation or progression have been confirmed (e.g. FGFR3/MMSET activation) or implicated (e.g. chromosome 13 deletion), the mechanisms of MM development remain enigmatic. Importantly, although generally being indistinguishable morphologically, MM exhibits a tremendous degree of variability in clinical course, with some patients surviving only months and others many years. However, current laboratory parameters can account for no more than 20% of this outcome variability. Furthermore, the means by which current drugs impart their anti-MM effect are also mostly unknown. In addition, the mechanisms by which MM cells contribute to serious comorbidities, such as osteopenia and/or focal lytic lesions of bone, are also poorly understood. Finally, very little knowledge exists concerning the molecular events leading to benign hyperplasia and/or overt malignancy of PCs. Given that abnormal gene expression lies at the heart of most, if not all, cancers, high-throughput global gene expression profiling has become a powerful tool for investigating molecular biology and clinical behavior of diseases. Here, we discuss recent progress made in addressing many of the above issues through the molecular dissection of the transcriptome of normal PCs and MM.

Activation of beta-catenin-LEF/TCF signal pathway in chondrocytes stimulates ectopic endochondral ossification

OBJECTIVE

Members of the Wnt signaling protein family are expressed during cartilage development and skeletogenesis, but their roles and mechanisms of action in those processes remain unclear. Recently, we found that beta-catenin-LEF/TCF-dependent Wnt signaling stimulates chondrocyte maturation and hypertrophy and extracellular matrix calcification in vitro, events normally associated with cartilage-to-bone transition during skeletogenesis. Thus, we tested here whether activation of this pathway promotes endochondral ossification.

DESIGN

Chick chondrocytes were infected with avian retroviral expression vectors encoding constitutive-active (CA) or dominant-negative (DN) forms of LEF, which activate or block beta-catenin-dependent Wnt signaling respectively. These cells and companion uninfected control cells were seeded into type I collagen gels and transplanted intramuscularly into nude mice. The resulting ectopic tissue masses forming over time in vivo were subjected to histological and molecular biological analyses.

RESULTS

Transplantation of chick chondrocytes induced de novo endochondral bone formation. In situ hybridization and RT-PCR using species-specific probes and primers showed that the ectopic cartilaginous tissue was avian and thus donor-derived, whereas the bone tissue was mouse and thus host-derived. CA-LEF-expressing ectopic tissue masses contained abundant bone and marrow, while DN-LEF-expressing masses contained little bone and lacked marrow.

CONCLUSIONS

Activation of beta-catenin-LEF/TCF-dependent Wnt signaling accelerates chondrocyte maturation and replacement of cartilage by bone.