I want to treat cells with TGF beta and try to find out some of those proteins are generally upregulate upon its treatment. Like alpha-SMA is upregualte in protein level for 24 Hrs. induction of TGF-beta in serum starved environment.

But alpha-SMA is a late marker of this pathway. I am looking for a marker which can show changes in protein levels in early hours, lets say in 3-4 hrs. after treatment.

You should think about the signaling molecules downstream of the TGF beta receptor. The immediate molecules that pop up are SMADs and PKCs in those early time-points. You will be able to see phosphorylation and even increase in the protein levels!

TGFbeta has feedback loop. So most easy way is  to try QPCR for TGFb1, b2 and TGFbR1 and TGFbR2 after 2 days