WPF Shortcut Key not firing - wpf

Question

I have a prism delegate command setup for refresh the data in my application.
I also have setup shortcuts for close and about window using delegate command.
Using F5 also does not trigger the refresh in the view model. If I use Alt+F4, the application closes. But it does not execute the CloseApplication method in the view model. What is missing in the following code to execute the ViewModel using the Gesture Shorcuts?
UserControl:
<UserControl.InputBindings>
<KeyBinding Gesture="ALT+F4" Command="{Binding CloseCommand}" />
<KeyBinding Gesture="F5" Command="{Binding RefreshCommand}" />
</UserControl.InputBindings>
<DockPanel>
<Menu DockPanel.Dock="Top">
<MenuItem Header="_File">
<MenuItem Header="E_xit" Command="{Binding CloseCommand}" InputGestureText="Alt+F4" />
<MenuItem Header="Refresh" Command="{Binding RefreshCommand}" InputGestureText="F5" />
</MenuItem>
<MenuItem Header="_Help">
<MenuItem Header="_About" Command="{Binding AboutCommand}" />
</MenuItem>
</Menu>
<ToolBar ToolBarTray.IsLocked="True">
<Button Content="Home" MinHeight="50" MinWidth="80" VerticalContentAlignment="Bottom" />
<Button Content="Page 1" MinHeight="50" MinWidth="80" VerticalContentAlignment="Bottom" />
<Button Content="Page 2" MinHeight="50" MinWidth="80" VerticalContentAlignment="Bottom" />
</ToolBar>
</DockPanel>
ViewModel of the UserControl
public class TopMenuViewModel:NotificationObject
{
private DelegateCommand _closeCommand;
private DelegateCommand _aboutCommand;
private DelegateCommand _refreshCommand;
public TopMenuViewModel()
{
_closeCommand = new DelegateCommand(CloseApplication);
_aboutCommand = new DelegateCommand(ShowAboutWindow);
_refreshCommand = new DelegateCommand(RefreshApplication);
}
private void ShowAboutWindow()
{
Console.WriteLine("Show about window");
}
private void CloseApplication()
{
Application.Current.Shutdown();
}
private void RefreshApplication()
{
Console.WriteLine("Refreshing..");
}
public ICommand CloseCommand
{
get { return _closeCommand; }
}
public ICommand AboutCommand
{
get { return _aboutCommand; }
}
public ICommand RefreshCommand
{
get { return _refreshCommand; }
}
}
The view model methods are called if I use the mouse to click the menu or use the Alt+x or Alt+A. But not using the KeyBinding that I have put in. Thanks for your help.