Oral Presentation 6th Australian Health and Medical Research Congress 2012

Site-specific phosphorylation of MCC impacts upon diverse cellular functions in the colon. (#151)

Laurent Pangon 1 , Roger Daly 1 2 , Elizabeth A Musgrove 1 2 , Maija Kohonen-Corish 1 2 3
  1. Garvan Institute of Medical Research, Darlinghurst, Sydney, NSW, Australia
  2. St Vincent’s Clinical School, Faculty of Medicine, University of NSW, Sydney, NSW, Australia
  3. School of Medicine, University of Western Sydney, Sydney, NSW, Australia

The ‘Mutated in Colorectal Cancer’ (MCC) gene was initially discovered due to its linkage with APC. However, MCC was overlooked for many years until it was discovered that it is frequently silenced by methylation in colorectal cancer (1) and that mutated MCC is a driver of carcinogenesis in the mouse (2). MCC is emerging as a multifunctional protein. We aim to determine the cellular mechanisms whereby a MCC defect can promote colorectal carcinogenesis. We have identified several phosphorylated serines in the MCC protein by mass spectrometry, such as S118, S120 and S828. We mutated these serines to either alanine (A, nonphosphorylable) or aspartic acid (D, phosphomimetic) and analysed their effect on MCC function in several cellular pathways in vitro. We found that MCC phosphomutants S118A and S120A impaired the ability of MCC to induce cell cycle arrest at G2/M phase following UV radiation (3). This suggests that phosphorylation of S118/S120 is important for the DNA damage response to single-strand DNA breaks. Phosphorylated S828 is located in the highly conserved PDZ-binding motif of MCC (ETSL, 826-829), which binds the polarity/migration protein Scrib and regulates epithelial cell migration (4). We found that MCC also binds the non-muscle motor protein Myosin-IIB and that the S828D phosphomimetic substitution alters Myosin-IIB subcellular localisation. Formation of lamellipodia was reduced in S828D expressing Caco2 cells compared to wild-type MCC, indicating that dephosphorylation of MCC-S828 is important for lamellipodia formation (5). The PDZ-binding motif is one of the most common protein-protein interaction motifs, but this is the first evidence of phosphorylation at the -1 residue, allowing another level of regulation. Healthy epithelial cells in the gut need to ‘turn on’ lamellipodia and migrate short distances, when required to rapidly seal damage in the epithelial layer. These protective functions may be impaired by MCC silencing, thus promoting colorectal carcinogenesis.

  1. Kohonen-Corish et al 2007. Oncogene 26:4435-41
  2. Starr et al 2009. Science 323: 1747-50
  3. Pangon et al 2010. Genes Cancer 1: 917-926
  4. Arnaud et al 2009. FEBS Lett 583: 2326-32
  5. Pangon et al 2012. BBA – Mol Cell Res 1823: 1058–67