Essential role of RSK2 in c-Fos–dependent osteosarcoma development
Jean-Pierre David, Denis Mehic, Latifa Bakiri, Arndt F. Schilling, Vice Mandic, Matthias Priemel, Maria Helena Idarraga, Markus O. Reschke, Oskar Hoffmann, Michael Amling, Erwin F. Wagner
Jean-Pierre David, Denis Mehic, Latifa Bakiri, Arndt F. Schilling, Vice Mandic, Matthias Priemel, Maria Helena Idarraga, Markus O. Reschke, Oskar Hoffmann, Michael Amling, Erwin F. Wagner
View: Text | PDF
Article Bone biology

Essential role of RSK2 in c-Fos–dependent osteosarcoma development

Abstract

Inactivation of the growth factor–regulated S6 kinase RSK2 causes Coffin-Lowry syndrome in humans, an X-linked mental retardation condition associated with progressive skeletal abnormalities. Here we show that mice lacking RSK2 develop a progressive skeletal disease, osteopenia due to impaired osteoblast function and normal osteoclast differentiation. The phenotype is associated with decreased expression of Phex, an endopeptidase regulating bone mineralization. This defect is probably not mediated by RSK2-dependent phosphorylation of c-Fos on serine 362 in the C-terminus. However, in the absence of RSK2, c-Fos–dependent osteosarcoma formation is impaired. The lack of c-Fos phosphorylation leads to reduced c-Fos protein levels, which are thought to be responsible for decreased proliferation and increased apoptosis of transformed osteoblasts. Therefore, RSK2-dependent stabilization of c-Fos is essential for osteosarcoma formation in mice and may also be important for human osteosarcomas.

Authors

Jean-Pierre David, Denis Mehic, Latifa Bakiri, Arndt F. Schilling, Vice Mandic, Matthias Priemel, Maria Helena Idarraga, Markus O. Reschke, Oskar Hoffmann, Michael Amling, Erwin F. Wagner

×

Figure 5

Options: View larger image (or click on image) Download as PowerPoint
Molecular and cellular analysis of RSK2 function in c-Fos–induced osteos...
Molecular and cellular analysis of RSK2 function in c-Fos–induced osteosarcomas. (A) In vivo analysis of RSK2 expression and c-Fos expression and phosphorylation on serine 362 in sections of osteosarcomas isolated from H2-c-fosLTR/Rsk2+/y and H2-c-fosLTR/Rsk2–/y mice. Top row: toluidine blue staining; second row, RSK2; third row, c-Fos; bottom row, P-Ser362. b, bone; arrows, osteoblasts. (B) Determination of proliferation and apoptotic indices in tumor section of H2-c-fosLTR/Rsk2+/y and H2-c-fosLTR/Rsk2–/y littermates. Proliferation was determined by counting of the proportion of Ki67-positive cells within the tumor, and the apoptotic indices were determined by counting of the proportion of TUNEL-positive cells (arrowheads) within the tumor. *P < 0.05. (C) Left: Western blot analysis of c-Fos expression and phosphorylation on serine 362 in primary osteoblasts (OBs) and in cell lines (P1.15, P1.4, P1, K11, R3, and C3) established from c-Fos–induced osteosarcomas of various origins (P, pelvis; K, long bone; R, ribs; C, calvaria). Right: Western blot analysis of c-Fos expression and phosphorylation in primary cells isolated from tumors of H2-c-fosLTR/Rsk2+/y and H2-c-fosLTR/Rsk2–/y littermates and Northern blot analysis of c-Fos expression in long bones of H2-c-fosLTR/Rsk2+/y and H2-c-fosLTR/Rsk2–/y littermates. Loading was controlled by analysis of β-actin and fox expression, respectively. Double asterisks indicate nonspecific bands. (D) Effect of inhibition of proteasome activity by MG132 on c-Fos expression in primary cells isolated from H2-c-fosLTR/Rsk2–/y tumors (left) and in a cell line established from H2-c-fosLTR/Rsk2–/y tumors (right). (E) Effect of RSK2 inhibitor (RO 31-8220) on c-Fos expression in primary cells isolated from tumors of H2-c-fosLTR/Rsk2+/y mice. (F) Effect of RSK2 inhibitor on apoptosis and proliferation of primary cells isolated from tumors of H2-c-fosLTR/Rsk2+/y mice.