Bone morphogenetic protein 2 and casein kinase 2 regulate the differentiation of osteoblasts

Abstract

The objective of this research is to study the shuttling and localization of BMP2 receptors on the cell membrane during signaling leading to osteoblast differentiation. Signaling is initiated by the binding of bone morphogenetic protein 2 (BMP2) to transmembrane BMP receptors type Ia (BMPRIa) and type II (BMPRII). Intracellularly, the protein casein kinase II (CK2) is associated with BMPRIa at three binding sites, denoted 2.1, 2.2, and 2.3. CK2 is a negative regulator of BMP2 signaling. Its dissociation, in response to BMP2 binding or blockage of CK2 binding sites, leads to signal transduction. As a location of BMP receptors, the membrane domains caveolae are known to be involved in signaling. To study the localization of BMP receptors in response to BMP2 and blockage of CK2 binding sites with blocking peptides, mesenchymal stem cells of the mouse cell line C2C12 were labeled for caveolin 1 (marker for caveolae), BMPRIa, and CK2 and imaged. The technique of image cross correlation spectroscopy determined the spatial similarity (colocalization) of the proteins to establish where BMP receptors were located on the membrane. The results showed that BMP2 stimulation and blockage of CK2 binding site 2.3, led to increased colocalization of BMPRIa with caveolin 1. This indicates that BMP receptors are localizing to caveolae with these particular treatments. Funding provided through the Howard Hughes Medical Institute (HHMI)