Fig 6. GST-tagged Mo-MLV p12_M63I shows increased chromatin association and phosphorylation in mitosis.

(A) A representative immunoblot showing subcellular distribution of GST-p12 mutants. GST-tagged GST-p12_M63I (lanes 1–3) or GST-p12+hCBS (lanes 4–6) were expressed in 293T cells for ~40 h. Cells were then subjected to biochemical fractionation and equivalent amounts of fractions S2-cytosolic, S3-soluble nuclear and P3-chromatin pellet were analysed by SDS-PAGE and immunoblotting with anti-p12, anti-HSP90 (cytosolic marker) and anti-H2B (chromatin marker) antibodies. (B) Representative confocal microscopy images showing GST-p12 localisation in HeLa cells stably transduced with constructs expressing GST-p12_M63I and GST-p12+hCBS. Cells were stained for p12 (anti-p12, green) and H2B (anti-H2B, red). Blue boxes indicate mitotic cells and red boxes show interphase cells. (C) Representative silver stained gel (top) and immunoblot (bottom) comparing the interaction of GST-p12_M63I and GST-p12+hCBS with mitotic and interphase chromatin. 293T cells were transiently-transfected with expression constructs for GST-tagged Mo-MLV p12_WT, M63I or GST-p12+hCBS for ~24 h before being treated overnight with either nocodazole (to arrest in mitosis) or aphidicolin (to block in interphase). GST-p12 protein complexes were precipitated from normalised cell lysates with glutathione-sepharose beads and analysed by SDS-PAGE followed by silver-staining or immunoblotting with anti-CLTC and anti-H2B antibodies. Bands corresponding to core histones in the silver-stained gel are starred. (D) Quantitation of H2B pulled-down with GST-p12 from mitotic versus interphase cell lysates. Median H2B band intensities from immunoblots in (C) were measured using a Li-cor Odyssey imaging system. The increase in H2B precipitation from mitotic cell lysates relative to interphase cell lysates are plotted in the bar chart (mean ± SEM, three biological replicates). (E) GST-p12 phosphorylation in mitosis and interphase. Normalised, interphase or mitotic 293T cell lysates expressing GST-tagged Mo-MLV p12_WT, M63I or S61A were incubated with glutathione-sepharose beads. Bound proteins were separated by SDS-PAGE and the gel was sequentially stained with ProQ diamond (PQ, specifically stains phosphorylated proteins) and Sypro ruby (SR, stains all proteins) dyes. Band intensities were measured using a ChemiDoc imaging system and the bar chart shows PQ/SR ratios, plotted as mean ± SD of 3 technical replicates.