IADR Abstract Archives
Calprotectin and Casein Kinase 2 Colocalize in Mitotic HNSCC Cells.
Objectives: Calprotectin, a heterodimeric complex of the calcium-binding proteins S100A8 and S100A9 (S100A8/A9), has intracellular and extracellular antimicrobial properties and also appears to regulate cell cycle progression, cell growth and survival. Down-regulated in head and neck squamous cell carcinoma (HNSCC), S100A8/A9 over-expression in vitro appears to suppress tumorigenesis by activating the G2/M DNA damage checkpoint. Cdc25C and Cdc2 inactivate and mitosis arrests in a PP2A-dependent manner. Casein kinase 2 (CK2), a ubiquitous serine/threonine kinase, is hypothesized to interact with S100A8/A9, forming an on/off switch mechanism with PP2A regulating the G2/M checkpoint. Objective: To identify changes in location of S100A8/A9 during the cell cycle and colocalization with CK2.
Methods: Methods: S100A8/A9-expressing TR146 SCC cells were used for in vitro studies. TR146 cells were established in non-synchronous and synchronous cultures at early S (double thymidine block) and G2/M (thymidine-nocodazole block) phases. Proteins were imaged using confocal immunofluorescence microscopy and analyzed using ImageJ software.
Results: Results: In non-mitotic TR146 cells, S100A8/A9 distributed in the cytoplasm and colocalized perinuclearly with CK2a. In early metaphase cells, S100A8/A9 and CK2a appear to colocalize at the microtubule-organizing centers (MTOCs). When released from thymidine-nocodazole block, synchronous metaphase TR146 cells showed S100A8/A9 and CK2a co-located and decorating mitotic spindles.
Conclusions: Conclusion: S100A8/A9 appears, therefore, to translocate from the cytoplasm into the nucleus during mitosis. First the centrosomes label with both S100A8/A9 and CK2 during early metaphase. Later during metaphase, mitotic spindle labeling strongly suggests colocalization of S100A8/A9 and CK2. These data are consistent with a role of S100A8/A9 in the control of the cell cycle checkpoint at G2/M and CK2 and PP2a serving as on-off controls.
Methods: Methods: S100A8/A9-expressing TR146 SCC cells were used for in vitro studies. TR146 cells were established in non-synchronous and synchronous cultures at early S (double thymidine block) and G2/M (thymidine-nocodazole block) phases. Proteins were imaged using confocal immunofluorescence microscopy and analyzed using ImageJ software.
Results: Results: In non-mitotic TR146 cells, S100A8/A9 distributed in the cytoplasm and colocalized perinuclearly with CK2a. In early metaphase cells, S100A8/A9 and CK2a appear to colocalize at the microtubule-organizing centers (MTOCs). When released from thymidine-nocodazole block, synchronous metaphase TR146 cells showed S100A8/A9 and CK2a co-located and decorating mitotic spindles.
Conclusions: Conclusion: S100A8/A9 appears, therefore, to translocate from the cytoplasm into the nucleus during mitosis. First the centrosomes label with both S100A8/A9 and CK2 during early metaphase. Later during metaphase, mitotic spindle labeling strongly suggests colocalization of S100A8/A9 and CK2. These data are consistent with a role of S100A8/A9 in the control of the cell cycle checkpoint at G2/M and CK2 and PP2a serving as on-off controls.