SPSite site = new SPSite("http://localhost/site");
SPWeb web = site.OpenWeb();
SPList list = web.Lists["nameList"];
list.BreakRoleInheritance(false);
SPUser user = new SPFieldUserValue(web, properties.ListItem["AssignedTo"].ToString()).User;
SPRoleDefinition role = web.RoleDefinitions["nameRole"];
SPPrincipal PrincipalEmployees = user;
SPRoleAssignment RoleAssignmentEmp = new SPRoleAssignment(PrincipalEmployees);
RoleAssignmentEmp.RoleDefinitionBindings.Add(role);
list.RoleAssignments.Add(RoleAssignmentEmp);
list.Update();