mRNA increase and protein expression
Posted 25 October 2011 - 01:59 PM
I am just wondering if anyone of you have ever tried corresponding increases in mRNA transcript with changes in protein level? I was using one of those targeted real time PCR assay that basically uses control vs treatment samples and I could screen for the modulation of 84 enzymes at the same time. I went ahead and tried to detect changes in protein expression of some of the genes that were upregulated by at least 15 times or so, but I could barely see changes in the protein expression. And not only for one of them, but for at least four of the proteins I tried. I am therefore wondering, just because the mRNA is upregulated, does it always mean that the protein has to be upregulated as well?
Posted 26 October 2011 - 05:54 AM
The bottom line is that if RNA and protein levels were directly correlated there should be a well fit straight line through all data points, but the points are all over the place, which is why you always need to be careful how far you take your conclusions from mRNA levels alone.
Best of Luck.
Edited by allynspear, 26 October 2011 - 05:59 AM.
Posted 26 October 2011 - 08:35 AM
Thank you again!
Posted 27 October 2011 - 06:08 AM
This, and all the variations of this question, have been debated A LOT in the battle of the -omics (genomics vs transcriptomics vs proteomics) and the real answer is:
We don't know
I have been trying to find one specific paper, but I can't seem to find it now, where they actually showed that in cells growing under two different growth conditions, cells responded differently to treatment with some drug. In both cases the mRNA levels went up 4-5 fold, but in one media, the protein levels stayed almost the same, and in the other media, the protein levels went up 8-9 fold. I think they showed that this was due to the presence of some microRNA that was continuously repressing translation in one case but not the other. The bottom line is that mRNA levels are relevant, but they are not the only thing controlling expression. Just like in signalling cascades, just because the receptor is activated, doesn't mean that other things downstream can't be blocked.
Good luck with your project!
Posted 27 October 2011 - 04:50 PM
Thank you again.
Posted 10 January 2012 - 08:45 PM
The only time I see HUGE differences is during major inflammatory or apoptotic stress. Homeostatic pathway proteins and mRNA levels are down regulated and stress response mediators, both protein and RNA go up.
Posted 09 March 2012 - 12:12 PM
I have the same problem, so I'm really interested in this topic!!!
I have two questions:
1) How can I be sure that the proteins remain unchanged and it is not an artefact? How do you discarded it?
2) allynspear: did you find the paper you cited? can you send it to me?
Thanks a lot!
Posted 11 March 2012 - 03:04 PM
Posted 13 March 2012 - 04:00 PM
Posted 13 March 2012 - 04:06 PM
Would it be a good idea, if you want to measure both mRNA and protein expression upon a certain stimulus, to first perform qPCR for mRNA-Levels and have a look at the protein expression at a later time point (depending on the respective half-life of the protein), instead of measuring both at the same time point ?
Posted 14 March 2012 - 05:36 AM
Thanks a lot for your comments!
Regarding the half-life, I can´t measure at a different time, because I work with human placenta obtained at birth!!! I know that i have only a "photograph" of this time...
Also, I would expect that different mRNA-proteins have different half-life, but I've these results in at least 4 different mRNA-proteins...
Edited by lauxi, 14 March 2012 - 05:41 AM.