STK11 and breast carcinoma: We found that LKB1 acts as the primary upstream kinase leading to activation of AMPK in breast cancer cells, as CAMKKβ could not be detected by Western blot (results not shown) and was therefore not analyzed further, and knock-down of TAK1 using an siRNA approach did not affect CPT1 enzyme activity or the phosphorylation status of AMPKα (results not shown).