H3K9me3-Governed Senescence In Tumor Development and Lymphoma Treatment

Premature senescence, a terminal cell-cycle arrest condition of viable cells in response to acute cellular stresses such as oncogenic activation or DNA-damaging anticancer therapy, is characterized by S-phase entry-controlling histone H3 lysine 9 trimethylation (H3K9me3). Previously, we reported an essential, tumor-suppressive role for the H3K9 histone methyltransferase Suv39h1 in oncogene-induced senescence (OIS) as a barrier to lymphoma development in vivo (Braig-M et al., Nature, 2005). In the current study, we focused, in addition to Suv39h1, on the H3K9-active demethylases LSD1 and JMJD2C in both OIS and therapy-induced senescence (TIS).

Human diploid fibroblasts (HDFs) and mouse embryo fibroblasts (MEFs) were stably transfected with H-Ras^G12V to induce OIS. S-phase-promoting E2F target gene control by H3K9me3 was analyzed by chromatin immunoprecipitation. Transformation was assessed by anchorage-independent colony formation in vitro and tumor development in nude mice. To establish TIS, primary Eµ-myc transgenic mouse lymphoma cells, retrovirally transduced with bcl2 to block apoptosis, were exposed to adriamycin in vitro or cyclophosphamide in vivo. Senescence was analyzed by staining for senescence-associated b-galactosidase activity (SA-b-gal), Ki67 and BrdU incorporation. Lymphoma formation and treatment in vivo were monitored by luciferase and GFP imaging, SA-b-gal/Ki67 staining in situ, and overall survival was assessed by Kaplan Meier analysis.

H3K9-active demethylases – like overexpression of a dysfunctional H3R9 mutant – blocked cellular senescence, and permitted direct transformation under oncogenic Ras. In Myc-driven lymphomas, either loss of Suv39h1 or overexpression of LSD1 or JMJD2C cancelled TIS in vitro and in vivo. Notably, H3K9me3-impaired lymphomas resembled control lymphomas in their proliferation rate and sensitivity to drug-induced apoptosis, but displayed significantly shorter progression-free and overall survival after chemotherapy. Extended data sets on LSD1 and JMJD2C expression in human diffuse large B-cell lymphoma samples and their correlation to treatment outcome will be presented at the meeting.

The data underscore the essential albeit dynamic role of the H3K9me3 mark in OIS and TIS, and unveil the oncogenic potential of H3K9 demethylases, thereby providing a mechanistic basis for JMJD2C- or LSD1-targeting strategies in lymphoma therapy.

No relevant conflicts of interest to declare.