RBM14 prevents assembly of centriolar protein complexes and maintains mitotic spindle integrity. (2015)
Figure 3

RBM14 interacts with STIL and prevents a complex formation of STIL and CPAP

A HeLa cells immunoprecipitated with control IgG or STIL antibodies. Soluble cytosolic fractions (input) and immunoprecipitates (IPs) were analyzed by Western blotting using RBM14, STIL or CPAP antibodies.

B GST pull-down assay testing interactions between purified STIL[N] (˜5 μg, aa1–1018) and GST-RBM14 [N] or [C]. The asterisks indicate non-specific bands.

C Schematic of our analyses of Y2H, GST pull-down and co-immunoprecipitation of the interaction between RBM14 and STIL (see also Supplementary Fig S3). Brackets indicate the fragments tested in this study, and the interaction detected is shown with arrows. A previous study reported that the C-terminus of CPAP interacts with the fragment of STIL aa231–781, as indicated (Tang et al, 2011).

D Mitotic U2OS cells treated with control or RBM14 siRNA were stained with antibodies against centrin-2 (green) and STIL (magenta). Insets show approximately twofold magnified views of fluorescent foci around the centrosome. Scale bar, 5 μm. Histograms represent frequency of mitotic cells with excess STIL foci co-localized with centrin foci. Values are mean percentages ± SEM from three independent samples (n = 30 for each condition). **P < 0.01 (one-tailed t-test).

E In vitro competitive binding assay. GST pull-down experiment was performed as in (B), with purified STIL[N] and GST-RBM14[C] in the presence of the indicated amount of purified His-CPAP[SBD], His-tagged STIL-Binding Domain of CPAP. The fraction of STIL[N] bound to GST-RBM14[C] in such conditions was monitored by Western blotting using STIL antibodies which recognize the N-terminal region of STIL. Input materials were analyzed by Western blotting using the STIL or CPAP antibodies. The precipitated GST-RBM14[C] was analyzed by SDS–PAGE, stained with SimplyBlue™ Safe (Invitrogen).

F Interaction between STIL and GFP-CPAP in the presence of FLAG-RBM14 FL or fragments. U2OS cells expressing GFP-CPAP were transfected with empty vector as a control, FLAG-RBM14[N], FLAG-RBM14[C] or FLAG-RBM14 FL constructs, immunoprecipitated with STIL antibodies, and the resulting IPs were analyzed by Western blotting using STIL, CPAP or FLAG antibodies. Quantification of relative protein amounts of co-immunoprecipitated GFP-CPAP in each STIL-IP fraction, normalized with the amount of STIL precipitated, is shown below the panels. Means ± SEM were calculated from three independent experiments. **P < 0.01 (one-tailed t-test). Note that we did not find any significant effect of exogenous expression of RBM14 full-length protein or deletion mutants on the expression levels of GFP-CPAP or endogenous STIL proteins in this experiment.

G U2OS cells treated with the indicated siRNAs were stained with antibodies against centrin-2 (green) and C-Nap1 (magenta). Histograms represent frequency of mitotic cells with excess centrin foci at spindle poles in each condition. Values are mean percentages ± SEM from three independent experiments (n = 30 for each condition). **P < 0.01 (one-tailed t-test). Representative mitotic cells treated with siRNAs against RBM14 alone, RBM14 + STIL or RBM14 + CPAP are shown below. Insets show approximately twofold magnified views of fluorescent foci around the centrosome. Scale bar, 5 μm.