Quantitative proteomics and transcriptomics exploration of primary myeloid cells: importance of β tubulin isotypes for bone resorption.

In the hematopoietic lineage, osteoclasts (Oc) and immature dendritic cells (Dc) are closely related myeloid cell types that fulfill very distinct biological functions; Oc participate in maintaining skeleton health while Dc sample the environment for foreign antigens. These morphological and functional specificities are based on the profound modification of gene and protein expression that occur during Oc and Dc differentiation. Here we provide global proteomic and transcriptomic analysis of primary mouse Oc, Dc and bone marrow macrophages based on original SILAC and RNAseq data obtained in a homogeneous experimental system. In particular, we established specific signatures for Oc and Dc that contain species of unknown functions, on top of the expected differentiation markers of each cell type. By siRNA screening, we highlighted potential new regulators of Oc biology. We also show that Oc, Dc and Mo have the same repertoire of 4 α and 4 β tubulin isotypes, but that Oc express much higher levels of Tubb6. We demonstrate that elevated expression of Tubb6 in Oc is necessary for the correct organization of podosomes into a belt, which is the backbone of the bone resorption apparatus, and that this function is conserved in human Oc. Consistently, we found that lowering Tubb6 expression hinders Oc resorption activity. Overall, our study highlights potential new regulators of Oc and Dc biology and it illustrates the functional importance of the tubulin isotype repertoire in the biology of differentiated cells.