Genetic abnormalities in cancers frequently result in activation of PKB, by loss of the tumor suppressor PTEN or by activating mutations of PI3KCα.
The MAPK pathway is deregulated in many human malignancies through aberrant signaling upstream of the protein and by activating mutations of the protein itself, both of which induce a proliferative advantage.
Many human breast cancers have PI3K activation as a consequence of Her-2/neu or Src oncogene expression [ 21], or by activating mutations of the PI3K p110α subunit [ 11], any of which could lead to NIS expression.
In 35% of follicular thyroid carcinomas, neoplastic transformation is triggered by activating mutations of the RAS gene or by the fusion of the PAX8 transcription factor with the gene encoding for peroxisome proliferator-activated receptor (Fagin, 2000; Kroll et al, 2000).
Inhibition of Smoothened (Smo), a seven-pass transmembrane receptor with similar topology to G-protein-coupled receptors (GPCRs), shows promise for the treatment of cancers driven by activating mutations to the Hh pathway and also for a subset of epithelial cancers that may require Hh for growth via a paracrine mechanism.
By contrast, activating mutation of AKT genes has not been widely reported in human cancers.
Akt is often activated in cancer cells by the activating mutation of PI3K [ 49], inactivation of PTEN [ 50] and, a recently demonstrated mechanism, by mutation of Akt itself [ 51].
Their recent research indicated that deletion of Zfp521 from chondrocytes rescued Jansen metaphyseal chondrodysplasia, a disorder caused by a constitutively activating mutation of PTH1R [ 47].
Hyperactivation of the PI3K pathway by activating mutations or loss of PTEN expression has been associated with resistance to trastuzumab-based chemotherapy (Esteva et al, 2010; Nagata et al, 2004).
Many components of this pathway are mutated, often by activating mutations and gene amplification, or loss of function of PTEN.
