In contrast to normal OCL precursors, pagetic OCL precursors express MVNP and form OCL at physiologic concentrations of 1,25(OH)2D3, as do normal OCL precursors transfected with the MVNP gene. Using a GST-VDR chimeric protein, we identified TAFII-17 as VDR binding protein expressed by pagetic OCL precursors and MVNP transduced normal OCL precursors. TAF(II)-17 was in part responsible for the increased 1,25(OH)2D3 responsivity of pagetic OCL precursors.
Introduction: Pagetic osteoclasts (OCLs) and their precursors express measles virus nucleocapsid protein (MVNP) and form large numbers of OCLs at low concentrations of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3]. Similarly, normal OCL precursors transfected with MVNP also form OCLs at low concentrations of 1,25(OH)2D3. These results suggest that expression of MVNP in OCL precursors enhances vitamin D receptor (VDR)-mediated gene transcription.
Materials and methods: To determine the mechanism for the increased OCL formation capacity of pagetic OCL precursors in response to 1,25(OH)2D3, lysates from pagetic and MVNP-transduced normal OCL precursors were incubated with a GST-VDR chimeric protein.
Results: A 17-kDa peptide that bound VDR was detected in MVNP-transduced cells and pagetic OCL precursors treated with 1,25(OH)2D3. This peptide was identified as TAFII-17, a component of the TFIID transcription complex. Expression of increased levels of TAFII-17 in cells allowed TAFII-17 to bind to VDR at low concentrations of 1,25(OH)2D3. An antisense oligonucelotide (AS-ODN) to TAFII-17 significantly decreased OCL formation in response to 1,25(OH)2D3 in pagetic but not normal marrow cultures by approximately 40%. Transfection of TAFII-17 or MVNP into NIH3T3 cells increased VDR transcriptional activity as measured by DR-3 reporter assays.
Conclusion: These data show that expression of the MVNP gene in OCL precursors results in increased levels of TAFII-17. TAFII-17 can bind VDR at low concentrations of 1,25(OH)2D3. These results suggest that MVNP expression in Paget's OCL precursors increases expression of a component(s) of the VDR transcription complex that can increase OCL formation.