POPX2 phosphatase regulates cell polarity and centrosome placement

• Main Author: Hoon, Jing Ling
• Other Authors: Koh Cheng Gee
• Format: Theses and Dissertations
• Language: English
• Published: 2015
• Subjects: DRNTU::Science::Biological sciences::Molecular biology
• Online Access: https://hdl.handle.net/10356/62211
• Institution: Nanyang Technological University

The wound healing process involves fibroblasts orienting their centrosomes towards the wound edge, such that they are able to migrate into the wound to close it. There are two currently known pathways that regulate centrosome positioning. The first pathway lies under the control of Cdc42, and another pathway involves the localization of N-cadherin to cell-cell contacts as well as the activation of integrin signaling at the leading edge. It is currently unknown whether these pathways function in an independent or cooperative manner. Thus, it is of interest to study how these signaling pathways might function to regulate centrosome positioning, as well as identify other proteins that might regulate these pathways to control the position of the centrosome. In this study, we investigated how centrosome orientation is regulated in mouse fibroblasts, NIH3T3 cells, and have identified a serine-threonine phosphatase, POPX2, as a regulator of centrosome orientation. By measuring the positions of the centrosome and nucleus, we show that POPX2 negatively regulates multiple proteins that control centrosome positioning to inhibit centrosome centration, but not rearward nuclear movement. N-cadherin localization to cell-cell junctions is required for proper centrosome orientation. We observed that high POPX2 expression results in a reduced peripheral N-cadherin localization using immunofluorescence staining, and this is due to the inhibition of Kinesin-2 motor motility by POPX2. Consequently, this perturbs the localization of focal adhesions as well as Cdc42-Par6/PKCζ signaling, thus impairing proper centrosome orientation. Microtubule-based motors also play an important role in centrosome orientation by generating a force along the microtubules to position the centrosome, and this is perturbed in cells overexpressing POPX2. Overexpression of POPX2 results in reduced peripheral Par3 localization and reduced expression of LIC2 (cytoplasmic dynein 1 light intermediate chain 2), resulting in defects in microtubule tethering and perturbations in microtubule dynamics at cell-cell contacts. We thus propose that POPX2 modulates the position of centrosomes during wound healing by acting as an integrator and regulator of multiple signaling pathways.