We next determined the ability of these mutated receptors to respond to the synthetic ligand THIQ, a selective MC4R agonist that potently stimulates cAMP production in the wild-type receptor in vitro [21] (EC50 = 3.5 nM) and the inhibition of food intake in vivo.
In particular, a significant number of PI3K-mutated tumors failed to respond, whereas a proportion of tumors lacking PI3K and PTEN alterations benefited from the treatment.
Reliable identification of KRAS mutations has become impelling given the recent finding that also tumours harbouring only a few KRAS-mutated cells fail to respond to cetuximab (Bando et al, 2011; Molinari et al, 2011).
Discrimination of coactivator involvement was assessed using two SRF-dependent luciferase reporter constructs, based on the c-fos SRE, considered to be specific for TCF coactivation, and on a mutated SRE (3D.A), considered to respond preferentially to MRTF coactivation.
Concerning the higher expression of BRCA1 mRNA observed in the poor-prognosis tumors, we could hypothesize that patients expressing high levels of BRCA1 would present a lower response to chemotherapy because TNBC BRCA1 mutated patients are known to respond better to chemotherapy [ 37].
H3.1-mutated tumours were found to respond better to the treatment, mainly radiotherapy, have a less aggressive course and metastasize less frequently.
Nevertheless, BRAFV600E CRCs fail to respond to mutated BRAF inhibitors as single agents.
Interestingly, an in vitro analysis of signal competence reveals that unmutated CLL cells generally continue to respond, whereas mutated CLL cells are anergised [ 63].
Among B-cell malignancies, this phenotypic feature is unique to CLL and correlates with a defective tyrosine kinase activity resulting in reduced tyrosine phosphorylation upon stimulation through the BCR pathway, although a majority of UM cases (2/3), which exhibit a low response, appear to respond better than mutated ones.
Transgenic animals expressing either wild type or mutated GATA constructs were analyzed for their ability to respond to both physiological activation by high salt (Figure 4B,C) and genetic activation by osr mutants (Figure 4D,E).
