Smurf1 Regulates PIP5K1C Stability And Biological Functions

Smad ubiquitylation regulatory factor-1 (Smurfl) has been identified as a HECT type E3, and, it belongs to the Nedd4 subfamily. Smurfl contains a catalytic HECT domain in the C terminal, two WW domains (WW1 and WW2), and a phospholipid binding C2 domain in the N terminal region. It can involve many kinds of signal pathways, including BMP pathway, the non-canonical Wnt pathway, and the mitogen-activated protein kinase pathway. Smurfl has critical roles in cell growth, osteoblast differentiation, cell development, cell polarity, cell migration, and immune responses via targeting various substrates such as Smads, RunX2, RunX3, Tbx6, MEKK2, RhoA, Par6, Talin, STAT1.Phosphatidylinositol phosphate kinase 1C(PIP5K1C) is an important phosphate kinase that generates phosphatidylinositol (4,5)-bisphosphate (PIP2). Through which PIP5K1C plays an essential role in various biological functions:such as cell migration, focal adhesion, endocytosis and other cellular processes. Human PIP5K1C has two major isforms:short form PIP5K1C-87 and long form PIP5K1C-90. Through bind other proteins, functions of PIP5K1C can be regulated. In addition, PIP5K1C is also regulated by posttranslational modification, including phosphorylation and acetylation. However, whether PIP5K1C is regulated by ubiquitination remains unknown.In this study, we identified that PIP5K1C is highly expressed in lung cancer tissues; and PIP5K1C protein is regulated by the ubiquitin-dependent protein degradation pathway; using siRNA knock down and overexpression approach, we have identified E3 ubiquitin ligase Smurfl, which can directly target PIP5K1Cfor ubiquitination and degradation. Using immunoprecipitation and GST-Pull Down assays, we detect the interaction between Smurfl and PIP5K1C in vivo and in vitro. We confirm that Smurfl promotes PIP5K1C ubiquitination and targets PIP5K1C degradation. And K255 in PIP5K1C is the major site required for Smurfl-mediated ubiquitination. In addition, Smurfl can inhibit the PIP5K1C-mediated cell growth and other biological process. We conducted a exploration on the mechanism by which regulates Smurfl-mediated PIP5K1C degradation.In summary, we identified that Smurfl can regulate PIP5K1C stability, and Smurfl can inhibit PIP5K1C-mediated biological functions. It helps further study to explore the biological functions of the two proteins.