Literally, all is depending on the data set that you want to achieve and explain in your paper. If you think only PCR data could be used to explain your research goal briefly, then it would be okay. However, based on my opinion, more data presented in paper is better, especially if they are integrated and could support each other, even it requires more efforts to achieve them.

As Intan said before: depends on what you want to show. If you want to show, that they are activated it is necessary to show phosphorylated proteins in a Western. More mRNA does not necessarily mean that there is more protein which is more active. But great antibodies for your SMADs are available (at least for human samples; for the other species I cannot tell) and it is not hard to do.

Thank you very much

I think it is more solid by adding protein data by either western blot or IHC. However, you may get inconsistent results in mRNA and protein studies as the changes observed are depend on the time points you chose.

As my experience of paper reading, generally when you are studying any signalling mechanism, its always better to give western blot results with RTPCR results. I think they both are important as RT PCR shows RNA expression and western directly relates protein level and as Teresa said you can not detect if your protein phosphorylation by RT PCR so its always better to go for western as well. SMADs antibodeis are available so i think it would be better to go for western to avoid reviewers concern while writing paper in the end of your work.

Activity of SMADs depends on phosphorylation. Thus, measuring RNA expression is only of limited value. Of course you can publish a paper with the qPCR values, but it will largely depend on luck and the journal you choose. The method you use also depends on your experimental setting. If you have cells in culture, as a reviewer I would not accept the qPCR conclusion. If you isolate 3 primary cells from a rare source, I would agree that the qPCR is is best you can do with it.