Cell autonomous angiotensin II signaling controls the pleiotropic functions of oncogenic K-Ras.

Oncogenic K-Ras (K-Ras) promotes senescence in normal cells but fuels transformation of cancer cells after the senescence barrier is bypassed. The mechanisms regulating this pleiotropic function of K-Ras remain to be fully established and bear high pathological significance. We find that K-Ras activates the angiotensinogen (AGT) gene promoter and promotes AGT protein expression in a Kruppel-like factor 6-dependent manner in normal cells. We show that AGT is then converted to angiotensin II (Ang II) in a cell-autonomous manner by cellular proteases. We show that blockade of the Ang II receptor type 1 (AT-R) in normal cells inhibits oncogene-induced senescence. We provide evidence that the oncogenic K-Ras-induced synthesis of Ang II and AT-R activation promote senescence through caveolin-1-dependent and nicotinamide adenine dinucleotide phosphate oxidase 2-mediated oxidative stress. Interestingly, we find that expression of AGT remains elevated in lung cancer cells but in a Kruppel-like factor 6-independent and high-mobility group AT-hook 1-dependent manner. We show that Ang II-mediated activation of the AT-R promotes cell proliferation and anchorage-independent growth of lung cancer cells through a STAT3-dependent pathway. Finally, we find that expression of AGT is elevated in lung tumors of K-Ras mice, a mouse model of lung cancer, and human lung cancer. Treatment with the AT-R antagonist losartan inhibits lung tumor formation in K-Ras mice. Together, our data provide evidence of the existence of a novel cell-autonomous and pleiotropic Ang II-dependent signaling pathway through which oncogenic K-Ras promotes oncogene-induced senescence in normal cells while fueling transformation in cancer cells.