Life begins with information in the genome. Thus, maintaining the genomic integrity during cell proliferation is essential for survival of living organisms. In order to ensure accurate chromosome segregation of mitosis, eukaryotic cells develop the sophisticated mitotic machinery and checkpoint mechanism, and their detailed molecular mechanisms have been intensively studied in recent decades.
- Chromosome segregation in human cells and its regulation by SAC
In eukaryotic cells, chromosome segregation is carried out by the mitotic spindle apparatus (Godek et al., 2014; Kang and Yu, 2009; Lara-Gonzalez et al., 2012). Microtubules originated from the centrosome bind each chromosome specifically through the kinetochore, a proteineous complex structure assembled on the centromere and segregate exact half copies of sister chromatids to each daughter cell. The Spindle Assembly Checkpoint (SAC) consisting of Bub1, Bub3, BubR1, Mad1, Mad2, Mps1, and Aurora B is a surveillance mechanism to monitor kinetochore-microtubule attachment errors (Godek et al., 2014; Musacchio, 2015; Sacristan and Kops, 2014). In response to unattached or erroneously attached kinetochore, the SAC initiates its signaling cascade to synthesize Mitotic Checkpoint Complex (MCC) at the kinetochore. The MCC in turn inhibits Anaphase Promoting Complex/Cyclosome (APC/C) to arrest cell cycle for repair of erroneous kinetochore-microtubule attachments.
Any defect in this process leads to aneuploidy which is a hallmark of cancer (Hanahan and Weinberg, 2011). Furthermore, increased chromosome instability of cancer cells has been shown to closely correlate with their poor prognosis and drug resistance (McGranahan et al., 2012). On the other hand, however, cellular stress of aneuploidy has been used as a chemotherapeutic target of cancer because cancer cells cannot segregate chromosomes properly and trigger apoptotic cell death upon further insult of segregation machinery by mitotic cancer drugs. Spindle assembly checkpoint kinases has been recently investigated as new targets of mitotic cancer drugs.
In our lab, we study the functional roles of spindle assembly checkpoint kinases in eukaryotic chromosome segregation. Although a great number of studies revealed how the spindle assembly checkpoint kinases function spatially and temporally in a detail, their downstream targets are still largely unknown. Thus, we will focus on what their downstream targets are and how the deregulation of the kinases on these targets contributes genetic instability of cancer. Furthermore, we study how normal cells sense aneuploidy stress, how they relay the signal to arrest cell cycle or trigger apoptosis, and whether they can be exploited as new targets of cancer chemotherapy.
- High-content analysis of single cell response in cancer
One of the major difficulties in cancer studies is that tumors consist of heterogeneous populations and population average studies often miss minor populations which may develop to more aggressive tumors. One good way to tackle this problem is a single cell analysis which receives much attention recently. The single cell high-content (HC) image analysis has been used for high-dimensional phenotypic profiling of cell cultures, tissues, or organisms (Feng et al., 2009). It analyzes whole cell responses using reporter proteins and generates systematic profiles of cellular responses to understand functional connectivity of the genes (Boutros et al., 2015). Several recent studies have applied this approach to search new genes controlling mitosis by using mitotic structure reporters (Neumann et al., 2010; Perlman et al., 2005). We have also successfully employed single cell HC image analysis for phenotypic profiling of small molecule compound libraries (Kang et al., 2016).
In our lab, we would like to continue to study drug responses of cancer cells with established HC image analysis pipeline. Functional connectivity of the mitotic kinases in human cells or even screening genetic library for new regulators of aneuploidy in normal or cancer cells will be explored by this method. In this regard, previously established central-dogma (CD) tagged cell library will be a useful tool as a collection of live bio-reporters.