H3K9 methyltransferases and demethylases control lung tumor-propagating cells and lung cancer progression

Epigenetic regulators are attractive anticancer targets, but the promise of therapeutic strategies inhibiting some of these factors has not been proven in vivo or taken into account tumor cell heterogeneity. Here we show that the histone methyltransferase G9a, reported to be a therapeutic target in many cancers, is a suppressor of aggressive lung tumor-propagating cells (TPCs). Inhibition of G9a drives lung adenocarcinoma cells towards the TPC phenotype by de-repressing genes which regulate the extracellular matrix. Depletion of G9a during tumorigenesis enriches tumors in TPCs and accelerates disease progression metastasis. Depleting histone demethylases represses G9a-regulated genes and TPC phenotypes. Demethylase inhibition impairs lung adenocarcinoma progression in vivo. Therefore, inhibition of G9a is dangerous in certain cancer contexts, and targeting the histone demethylases is a more suitable approach for lung cancer treatment. Understanding cellular context and specific tumor populations is critical when targeting epigenetic regulators in cancer for future therapeutic development.

Is oncogene addiction angiogenesis-dependent?

Does an activated oncogene that initiates tumor growth need to remain activated to maintain the cancer phenotype? This question has been answered affirmatively by experiments in which doxycycline-regulated oncogene activation induces growth of large tumors that regress completely upon oncogene inactivation--a phenomenon called oncogene addiction. We assemble here the evidence that oncogene addiction is angiogenesis-dependent. Although activated oncogenes increase tumor cell proliferation and decrease their apoptosis, these activities are not sufficient to expand tumor mass beyond a microscopic size. Oncogenes must also induce tumor angiogenesis for expansion of tumor mass. We propose experiments to validate the "endothelial centric" hypothesis of oncogene addiction.