RC/BTB2 is essential for formation of primary cilia in mammalian cells

RC/BTB2 is a binding partner of sperm associated antigen 16S (SPAG16S), which is a regulator of spermiogenesis in mice, a process during which sperm flagella are formed. The expression of Rc/btb2 is also regulated by multicilin, a protein that controls ciliogenesis. Given that mouse Rc/btb2 mRNA is not only expressed in tissues bearing motile cilia, but also in tissues without motile cilia, we investigated whether RC/BTB2 plays a role in the general process of ciliogenesis by studying two cell lines that have primary cilia, NIH3T3, and IMCD3. We discovered that the subcellular localization of RC/BTB2 in the NIH3T3 and IMCD3 cells encompasses the pathway for ciliogenesis. RC/BTB2 was found in the Golgi bodies and centrosomes, two key structures essential for normal ciliogenesis. Knockdown of Rc/btb2 gene expression in these cell lines disrupted ciliogenesis. The percentage of cells with primary cilia was significantly reduced in stable cell lines transduced with specific Rc/btb2 shRNA viruses as compared to the control cells. When cilia were formed in the knockdown cells, they were significantly shorter than those in the control cells. Knockdown of Rc/btb2 expression did not affect cell proliferation and the cell cycle. Exogenous expression of RC/BTB2 in these stable knockdown cells restored ciliogenesis. These findings suggest that RC/BTB2 is a necessary component of the process of formation of primary cilia in somatic cells, perhaps through the transportation of cargos from Golgi bodies to centrosomes for cilia assembling.