SETDB1 Inhibits p53-Mediated Apoptosis and Is Required for Formation of Pancreatic Ductal Adenocarcinomas in Mice

Abstract

Setdb1 p53 P ancreatic ductal adenocarcinoma (PDAC) is one of the most dismal malignancies, with an extremely poor prognosis. 1 In order to further improve the prognosis, it is crucial to elucidate the molecular mechanisms underlying PDAC initiation and progression. Recent studies have revealed that epigenetic abnormalities exhibit a great influence on the characteristics of cancer development in addition to genetic abnormalities. 2-4 One form of epigenetic regulation, known as histone modification, contributes to tumorigenesis by affecting the expression of oncogenes/tumor suppressor genes. In fact, previous reports have shown that histone methyltransferases suppress pancreatic cancer by regulating glucose/fatty acid metabolism and promoting pancreatic regeneration. 5,6 Setdb1 serves as a histone 3 lysine 9 trimethyltransferase. Trimethylation of histone 3 lysine 9 (H3K9me3) is a repressive chromatin modification. 7 Setdb1 plays different functional roles through gene silencing. It helps to control heterochromatin formation 8 and contributes to stem cell maintenance, 9 embryonic development, and endogenous proviral silencing. 10 Recently, an in vivo study revealed that the amplification of Setdb1 accelerates the development of melanoma, 11 and SETDB1 has been shown to promote tumorigenesis in various human cancers, including lung, 12 liver, 13,14 and breast cancers. 15 Furthermore, a wholeexome sequencing study revealed a copy number amplification mutation of SETDB1 in PDAC patients. 16 These findings indicate a role of Setdb1 in PDAC initiation and progression. However, the functional role of Setdb1 in PDAC remains elusive. Therefore, in this study, we aimed to investigate the impact of Setdb1 deletion on Kras-induced pancreatic tumorigenesis and elucidate the in vivo role of Setdb1 in PDAC formation in mouse models. Materials and Methods Mice Experimental animals were generated by crossing Ptf1a Cre (gift from Y. Kawaguchi, Kyoto University, Kyoto, Japan), 17 Kras G12D (gift from D. Tuveson, Cold Spring Harbor Laboratory, Cold Spring Harbor, NY), 18 Setdb1 flox (gift from Y. Shinkai, Riken, Saitama, Japan), 10 and p53 flox (purchase from Jackson Laboratory, Bar Harbor, ME; JAX strain 008462). Acute pancreatitis was induced at 6 weeks of age by injecting cerulein (2 mg/injection diluted in phosphate-buffered saline; Sigma-Aldrich, St Louis, MO) intraperitoneally on 2 consecutive days once every hour for 8 hours each day. 19 Clinical Samples Forty-eight surgically resected specimens of pancreatic cancer tissues were obtained from patients who had been admitted to Kyoto University Hospital. Written informed consent was obtained from all patients and the protocol was approved by the Ethics Committee of Kyoto University.

A New SET Piece in Cancer Development

“…The authors provide robust and rigorous data to support this and other concepts, including a paradox in early stage lesion development, where Setdb1 deletion accelerated ADM and PanIN formation. This work was further evaluated in human pancreatic cancer cells both in culture, in mice and in silico to further support the main premise of Ogawa et al 13 Perhaps a primary limitation of this work and this sphere of research in general is the lack of effective DNA methyltransferase inhibitors, as several reports including this one used mithramycin A, which does decrease Setdb1 expression, 18,19 but is predominantly considered a DNA and RNA polymerase inhibitor. So these analyses are fraught with background from this antibiotic, but there is no real alternative and indeed no specific SETDB1 inhibitor to date.…”

“…These results generated by Ogawa et al 13 extend SETDB1 as a potential pivotal causative agent and targetable piece in the riddle of improving therapeutic efficacy for pancreatic cancer and expand our understanding of SETDB1 function in the backdrop of cancer etiology. The investigative team employed autochthonous models of pancreatic neoplasia (KC) and cancer (KPC with floxed loss of p53) to evaluate complete loss of Setdb1 in the presence and absence of p53 in vivo and generated KCS and KPCS mice in the process.…”

“…16 In a more classical setting, SETDB1 catalyzes histone lysine methylation to ultimately silence p53 leading to growth of hepatocellular carcinoma cells with a similar effect in colon cancer cells. 17 These findings set the stage for the seminal work described by Ogawa et al 13 in pancreatic cancer.…”

“…Indeed, this may explain the occasional reports that SETDB1 has tumor promoting and suppressing activities in the same cancer, as demonstrated in the lung. 4,5 However, most published findings report that SETDB1 serves to promote tumorigenesis in a variety of cancers including breast, 6,7 prostate, 8 colon, [9][10][11] liver, 12 and now pancreatic cancer, as described by Ogawa et al 13 in this edition of Gastroenterology.…”

A multilayered post-GWAS assessment on genetic susceptibility to pancreatic cancer

“…Two variants in high LD (r 2 = 0.92) and potentially relevant at the functional level are in 1q21.3 (SETDB1-rs17661062 and FAM63A-rs59942146). SETDB1 has recently been reported to be required for formation of PC in mice by inhibiting p53-mediated apoptosis [48], and FAM63A/MINDY1 has been found to interact significantly with diabetes (duration ≥ 3 years) in a metaanalysis on PC risk conducted within the PanC4 and PanScan consortia [49]. Interestingly, these two variants were also associated with an increased methylation of the cg17724175 in MCL1.…”