Casein kinase 2 regulates in vivo bone formation through its interaction with bone morphogenetic protein receptor type Ia

Approximately 7.9 million fractures occur annually in the United States with 5–10% of these resulting in delayed or impaired healing. Nearly half of the trauma cost of $56 billion per year is used for the treatment of fractures. More importantly, fracture results in a substantial reduction in the quality of life. New approaches and therapies are needed to enhance fracture healing. Only a limited number of treatments are available including bone grafting, allogeneic and autologous bone marrow transplantation, and bone morphogenetic protein (BMP).We previously identified Protein Kinase CK2 to interact with BMP receptor type Ia (BMPRIa) and as a key protein for signal activation. Peptides approximately 30 AA were developed that mimicked BMP2 action in vitro by blocking this interaction. In this paper we extended our studies to investigate if the most promising peptide could induce in vivo bone formation in mice and to elucidate this mechanism of action. The CK2 blocking peptide activated the Wnt pathway. To identify the optimal peptide concentration and peptide concentration curves for mineralization studies were performed. We designed BMPRIa mutants with a point mutation in the CK2 phosphorylation site to establish a specific effect. Mineralization was initiated with the overexpression of the BMPRIa mutants indicating CK2 is a negative regulatory protein for osteoblast differentiation. Osteoclast differentiation and activity was decreased with the CK2 blocking peptide. Further, subcutaneous calvarial bone injections of a CK2 blocking peptide increased bone area, areal bone mineral density, and bone growth. These results indicate CK2 is crucial for osteoblast differentiation and could be a target for future therapeutics of fracture healing.

► Calvarial injection of a CK2 blocking peptide induced in vivo bone growth.
► The CK2 blocking peptides initiate Smad signaling through a BMP receptor type Ia dependent mechanism.
► Specificity of the CK2 blocking peptides were verified by mutations of the BMP receptor type Ia.
► The CK2 blocking peptide, CK2.3, decreased osteoclast number and activity.
► The Wnt pathway is activated by peptide CK2.3.