PARATHYROID-HORMONE REGULATES THE EXPRESSION OF THE NUCLEAR MITOTIC APPARATUS PROTEIN IN THE OSTEOBLAST-LIKE CELLS, ROS-17 2.8/

The parathyroid hormone (PTH) signaling pathways that effect changes i n osteoblast gene expression also alter the organization of the cytosk eletal proteins, PTH regulates the expression of nucleoskeletal protei ns, such as nuclear mitotic apparatus protein (NuMA) and topoisomerase II-alpha. NuMA is a structural component of the interphase nucleus an d organizes the microtubules of the mitotic spindle during mitogenesis , We propose that PTH-induced alterations in osteoblast cytoarchitectu re are accompanied by changes in osteoblast nuclear structure that con tribute to changes in gene expression, We used immunofluorescence and confocal microscopy to determine the effect of PTH on the expression a nd nuclear distribution of NuMA in the rat osteosarcoma cell line, ROS 17/2.8, Cells were treated with PTH or vehicle, then fixed and staine d with NuMA antibody, Optical sections of interphase naive cells revea led a diffuse distribution of NuMA, interspersed with speckles, in the central nuclear planes but not in nucleoli, During the metaphase and anaphase, NuMA localized at the mitotic spindle apparatus, The percent age of NuMA-immunopositive ROS 17/2.8 cells decreased with increasing confluence, but serum starvation did not attenuate NuMA expression, Ce ll density-dependent changes in cytoskeletal organization were observe d in these cells, PTH treatment induced changes in cytoskeletal organi zation and increased the percentage of NuMA-immunopositive ROS 17/2.8 cells, These data suggest that PTH effects changes in osteoblast nucle ar architecture by regulating NuMA, and that these alterations may be coupled to cytoskeletal organization, (C) 1998 by Elsevier Science Inc . All rights reserved.