There is increasing evidence that cancers contain their own stem-like cells called cancer stem cells (CSCs). A small subset of cells, termed side population (SP), has been identified using flow cytometric analysis. The SP cells have the ability to exclude the DNA binding dye, Hoechst33342, and are highly enriched for stem cells in many kinds of normal tissues. Because CSCs are thought to be drug resistant, SP cells in cancers might contain CSCs. We initially examined the presence of SP cells in several human thyroid cancer cell lines. A small percentage of SP cells were found in ARO (0.25%), FRO (0.1%), NPA (0.06%), and WRO (0.02%) cells but not TPC1 cells. After sorting, the SP cells generated both SP and non-SP cells in culture. The clonogenic ability of SP cells was significantly higher than that of non-SP cells. Moreover, the SP prevalence was dependent on cell density in culture, suggesting that SP cells preferentially survived at lower cell density. Microarray experiment revealed differential gene expression profile between SP and non-SP cells, and several genes related to stemness were up-regulated. However, non-SP population also contained cells that were tumorigenic in nude mice, and non-SP cells generated a small number of SP cells. These results suggest that cancer stem-like cells are partly, but not exclusively, enriched in SP population. Clarifying the key tumorigenic population might contribute to the establishment of a novel therapy for thyroid cancer.

Runx2 and Sp7 are essential transcription factors for osteoblast differentiation. However, the molecular mechanisms responsible for the proliferation of osteoblast progenitors remain unclear. The early onset of Runx2 expression caused limb defects through the Fgfr1–3 regulation by Runx2. To investigate the physiological role of Runx2 in the regulation of Fgfr1–3, we compared osteoblast progenitors in Sp7−/− and Runx2−/− mice. Osteoblast progenitors accumulated and actively proliferated in calvariae and mandibles of Sp7−/− but not of Runx2−/− mice, and the number of osteoblast progenitors and their proliferation were dependent on the gene dosage of Runx2 in Sp7−/− background. The expression of Fgfr2 and Fgfr3, which were responsible for the proliferation of osteoblast progenitors, was severely reduced in Runx2−/− but not in Sp7−/− calvariae. Runx2 directly regulated Fgfr2 and Fgfr3, increased the proliferation of osteoblast progenitors, and augmented the FGF2-induced proliferation. The proliferation of Sp7−/− osteoblast progenitors was enhanced and strongly augmented by FGF2, and Runx2 knockdown reduced the FGF2-induced proliferation. Fgfr inhibitor AZD4547 abrogated all of the enhanced proliferation. These results indicate that Runx2 is required for the proliferation of osteoblast progenitors and induces proliferation, at least partly, by regulating Fgfr2 and Fgfr3 expression.

Sixty-four patients with adult T-cell leukemia/lymphoma (ATL; 18 patients with indolent subtype and 46 with aggressive subtype) associated with human T-lymphotropic virus type 1 (HTLV-1) were analyzed using comparative genomic hybridization (CGH). The most frequent observations were gains at chromosomes 14q, 7q, and 3p and losses at chromosomes 6q and 13q. Chromosome imbalances, losses, and gains were more frequently observed in aggressive ATL than in indolent ATL, with significant differences between the 2 ATL subtypes at gains of 1q and 4q. An increased number of chromosomal imbalances was associated with a significantly shorter survival in all patients. A high number of chromosomal losses was associated with a poor prognosis in indolent ATL, whereas the presence of 7q؉ was marginally associated with a good prognosis in aggressive ATL. Paired samples (ie, samples obtained at different sites from 4 patients) and sequential samples from 13 patients (from 6 during both chronic disease and acute crisis and from 7 during both acute onset and relapse) were examined by CGH and Southern blotting for HTLV-1. All but 2 paired samples showed differences on CGH assessment. Two chronic/crisis samples showed distinct results regarding both CGH and HTLV-1 integration sites, indicating clonal changes in ATL at crisis. In 11 patients, the finding of identical HTLV-1 sites and clonally related CGH results suggested a common origin of sequential samples. In contrast to chronic/ crisis samples, CGH results with all acute/ relapse sample pairs showed the presence of clonally related but not evolutional subclones at relapse, thereby suggesting marked chromosomal instability. In summary, clonal diversity is common during progression of ATL, and CGH alterations are associated with clinical course. (Blood. 2001;97:3875-3881)