I want to do the following, but no idea how to... anyone has idea? Thanks!

Define a new work item attribute, named "QC Status". And enumeration value setting is: "new, open, assigned, fixed, closed".
What I want to do is, defect value set to "new" (i am ok for this part), and  when value of QC Status is "new", only value: "open" and "assigned" are available for chosen in the drop down list;

After select one value , for example, "assinged", then save it. Then at this moment, current value is "assigned", and only "fixed" and "closed" are avilabe fo chosen.

It is quite similar about the 2 attribute dependency enumeration, but here it is for one attribute only...the available list depends on the current value of the attribute.

Thanks a lot!