Research On The Self-polymerization Sequence Of Exo70 And Its Role In Breast Cancer Cell Migration

Breast cancer is the most common female malignancy in the world.Distant metastasis and recurrence are the main causes of death in patients with breast cancer.Therefore,it is of great significance to study the regulatory mechanisms of breast cancer metastasis.Exo70,a key component of the Exocyst complex,promotes breast cancer metastasis via facilitating the assembly of Exocyst complex.Self-polymerization of Exo70 protein can also affect the migration of breast cancer cells,independent of the Exocyst complex.However,there are still some problems that need to be further clarified,for example,the key sequences for Exo70 polymerization remains unclear.Is Exo70 polymerization just an ancillary role or equally important to cancer metastasis when compared to the formation of the Exocyst complex?In the present study,we found that Exo70 was obviously more capable of forming self-polymerization than binding to the other seven subunits of Exocyst complex,suggesting the importance of its self-polymerization.Then we constructed a set of truncation mutants of Exo70 in order to determine the core sequence for its dimerization.With co-immunoprecipitation analysis,we identified two identical protein sequences "SLEKS" located at amino acid 31?35 and 505?509 as critical sequences for the self-polymerization of Exo70.Using transwell migration assay,we further found that the full length Exo70 significantly promotes breast cancer metastasis,while Exo70 mutant with deletion of these two sequences(?31?35/A505?509)don't process such ability,indicating that these two "SLEKS"sequences play pivotal role in breast cancer cell migration.Together,these results provide fundamental basis for researches on novel functions of Exo70 besides its well-known role in Exocyst complex formation,and offer a potential drug target for treating breast cancer and its metastasis.