I dont know if it works or not but i think there is a probability of the following process. after cell lysis you can try RTqPCR where you can quantify the amount of mRNA encoding your protein produces.

Thank you Leila and Walter for your input. I do what Walter said, in fact: to use a parallel culture to quantify protein and hen normalize the data obtained from the fixed wells. I was just curious if it would be possible to "decross-link" the fixed proteins to get same-cells data. SDS 2% + boiling has been used to get proteins out of paraffinized sections, but it did not work well for my fixed cells.

v.