Feedback Regulation PIP5K1C By Smurf1 Is Important To Lung Cancer Tumorgenesis And Metastasis

Protein ubiquitination is a highly controlled reversible posttranslational modification that regulates various cellular function including cell proliferation, migration, and apoptosis. It is an enzymatic cascade that requires ubiquitin-activating enzyme E1, ubiquitin conjugating enzyme E2, and ubiquitin ligase E3. Ubiquitination requires binding of substrate to the specific E3 ubiquitin ligase which promotes the ubiquitination of the target proteins. Smurfl is a homologous to E6AP carboxyl Terminus (HECT) E3 ubiquitin ligase and has critical roles in cell polarity, cell migration, and development via targeting various substrates such as Smad, RhoA, and Talin. Smurfl is required for osteoblast function via degradation of MEKK2. Recent study indicated that the homolog Smurf2 is tumor suppressor protein. However, the role of Smurfl in tumorgenesis is still unclear.Smurfl contains a C2 domain, WW domain, and HECT domain. WW domain is required for binding of Smurfl to the PY motif of substrates. C2 domain is also involved in direct binding to some substrates such as RhoA. Moreover, C2 domain of Smurf determines the specificity towards its substrates including RhoA, Smad, and GEF of CDC42. Binding of C2 domain to the HECT promotes the formation of homodimer of Smurfl and thus inhibits its E3 activity. Moreover, C2 domain is essential for Smurfl membrane localization and induction of cell migration. However, the extract mechanism underlying the membrane localization of Smurfl and its function in cell proliferation and migration remains elusive.Phosphotidylinositol 4,5-biphosphate (herein referred to as PIP2) plays essential role in numerous cell processes, including migration, proliferation, and gene expression. Phosphotidylinositol phosphate kinase 1C(PIP5K1C) is a phosphotidylinositol kinase that generates PIP2 through phosphorylation of phosphotidylinositol 4-phosphate (PI4P) in vivo. Two major isoforms of human PIP5K1C have been well studied:short form PIP5K1C87 and long form PIP5K1C90. PIP5K1C plays an important role in cell polarity and migration of both adherent cells and leukocytes. As a critical lipid kinase, the subcellular localization, activity, and function of PIP5K1C are precisely regulated by its binding protein partners. For example, adaptor protein AP2 increases its activity and regulates the endocytosis of EGFR and AMPA by direct interaction with the COOH terminus of PIP5K1C90. Binding of small G protein ARF6 regulates its subcellular localization. Binding of Talin re-localizes PIP5K1C90 to the focal adhesion and regulates the localized PIP2 level and cell migration. PIP5K1C is also regulated by posttranslational modification, including phosphorylation and acetylation. PIP5K1C was shown to be overexpressed in breast cancers patients correlated with poor survival. However, the mechanism by which regulates the PIP5K1C protein level in cells remains unknown.In this study, we identified that PIP5K1C is highly expressed in lung cancers and its protein level is regulated by E3 ubiquitin ligase Smurf1. On the other hand, Smurfl C2 efficiently binds to PIP2, which is required for smurf1 membrane recruitment and cell migration.