minus sign in datagrid

I am using a datagrid to display a data table filled with positive and negative integers.

When I use a custom column style for color by inheriting the from DataGridTextBoxColumn, all the negative integers appear with the negative sign after the intger (1-). If I do not use column styles the integer appears correctly (-1).

I have tried to setting the NumberNegativePattern to 1. I have tried converting to a string and adding a "-". I am able to make parentheses appear around the integer in lieu of a sign but no matter what I try, I cannot make the "-" sign appear in front of the integer. Help!!

Jason