The DNA damage response (DDR) is a complex regulatory network that is critical for maintaining genome integrity. Posttranslational modifications are widely used to ensure strict spatiotemporal control of signal flow, but how the DDR responds to environmental cues, such as changes in ambient oxygen tension, remains poorly understood. We found that an essential component of the ATR/CHK1 signaling pathway, the human homolog of the Caenorhabditis elegans biological clock protein CLK-2 (HCLK2), associated with and was hydroxylated by prolyl hydroxylase domain protein 3 (PHD3). HCLK2 hydroxylation was necessary for its interaction with ATR and the subsequent activation of ATR/CHK1/p53. Inhibiting PHD3, either with the pan-hydroxylase inhibitor dimethyloxaloylglycine (DMOG) or through hypoxia, prevented activation of the ATR/CHK1/p53 pathway and decreased apoptosis induced by DNA damage. Consistent with these observations, we found that mice lacking PHD3 were resistant to the effects of ionizing radiation and had decreased thymic apoptosis, a biomarker of genomic integrity. Our identification of HCLK2 as a substrate of PHD3 reveals the mechanism through which hypoxia inhibits the DDR, suggesting hydroxylation of HCLK2 is a potential therapeutic target for regulating the ATR/CHK1/p53 pathway.
Liang Xie, Xinchun Pi, Ashutosh Mishra, Guohua Fong, Junmin Peng, Cam Patterson
Cancer is principally considered a genetic disease, and numerous mutations are thought essential to drive its growth. However, the existence of genomically stable cancers and the emergence of mutations in genes that encode chromatin remodelers raise the possibility that perturbation of chromatin structure and epigenetic regulation are capable of driving cancer formation. Here we sequenced the exomes of 35 rhabdoid tumors, highly aggressive cancers of early childhood characterized by biallelic loss of SMARCB1, a subunit of the SWI/SNF chromatin remodeling complex. We identified an extremely low rate of mutation, with loss of SMARCB1 being essentially the sole recurrent event. Indeed, in 2 of the cancers there were no other identified mutations. Our results demonstrate that high mutation rates are dispensable for the genesis of cancers driven by mutation of a chromatin remodeling complex. Consequently, cancer can be a remarkably genetically simple disease.
Ryan S. Lee, Chip Stewart, Scott L. Carter, Lauren Ambrogio, Kristian Cibulskis, Carrie Sougnez, Michael S. Lawrence, Daniel Auclair, Jaume Mora, Todd R. Golub, Jaclyn A. Biegel, Gad Getz, Charles W.M. Roberts
Inflammatory bowel disease (IBD) is a chronic illness caused by complex interactions between genetic and environmental factors that propagate inflammation and damage to the gastrointestinal epithelium. This state of chronic inflammation increases the risk for development of colitis-associated cancer in IBD patients. Thus, the development of targeted therapeutics that can disrupt the cycle of inflammation and epithelial injury is highly attractive. However, such biological therapies, including those targeting epidermal growth factor receptor pathways, pose a risk of increasing cancer rates. Using two mouse models of colitis-associated cancer, we found that epidermal growth factor receptor inactivation accelerated the incidence and progression of colorectal tumors. By modulating inflammation and epithelial regeneration, epidermal growth factor receptor optimized the response to chronic inflammation and limited subsequent tumorigenesis. These findings provide important insights into the pathogenesis of colitis-associated cancer and suggest that epidermal growth factor–based therapies for IBD may reduce long-term cancer risk.
Philip E. Dubé, Fang Yan, Shivesh Punit, Nandini Girish, Steven J. McElroy, M. Kay Washington, D. Brent Polk
Squamous cell carcinomas (SCCs) are heterogeneous and aggressive skin tumors for which innovative, targeted therapies are needed. Here, we identify a p53/TACE pathway that is negatively regulated by FOS and show that the FOS/p53/TACE axis suppresses SCC by inducing differentiation. We found that epidermal Fos deletion in mouse tumor models or pharmacological FOS/AP-1 inhibition in human SCC cell lines induced p53 expression. Epidermal cell differentiation and skin tumor suppression were caused by a p53-dependent transcriptional activation of the metalloprotease TACE/ADAM17 (TNF-α–converting enzyme), a previously unknown p53 target gene that was required for NOTCH1 activation. Although half of cutaneous human SCCs display p53-inactivating mutations, restoring p53/TACE activity in mouse and human skin SCCs induced tumor cell differentiation independently of the p53 status. We propose FOS/AP-1 inhibition or p53/TACE reactivating strategies as differentiation-inducing therapies for SCCs.
Juan Guinea-Viniegra, Rainer Zenz, Harald Scheuch, María Jiménez, Latifa Bakiri, Peter Petzelbauer, Erwin F. Wagner
The histone methyltransferase WHSC1 (also known as MMSET) is overexpressed in multiple myeloma (MM) as a result of the t(4;14) chromosomal translocation and in a broad variety of other cancers by unclear mechanisms. Overexpression of WHSC1 did not transform wild-type or tumor-prone primary hematopoietic cells. We found that ACA11, an orphan box H/ACA class small nucleolar RNA (snoRNA) encoded within an intron of WHSC1, was highly expressed in t(4;14)-positive MM and other cancers. ACA11 localized to nucleoli and bound what we believe to be a novel small nuclear ribonucleoprotein (snRNP) complex composed of several proteins involved in postsplicing intron complexes. RNA targets of this uncharacterized snRNP included snoRNA intermediates hosted within ribosomal protein (RP) genes, and an RP gene signature was strongly associated with t(4;14) in patients with MM. Expression of ACA11 was sufficient to downregulate RP genes and other snoRNAs implicated in the control of oxidative stress. ACA11 suppressed oxidative stress, afforded resistance to chemotherapy, and increased the proliferation of MM cells, demonstrating that ACA11 is a critical target of the t(4;14) translocation in MM and suggesting an oncogenic role in other cancers as well.
Liang Chu, Mack Y. Su, Leonard B. Maggi Jr., Lan Lu, Chelsea Mullins, Seth Crosby, Gaofeng Huang, Wee Joo Chng, Ravi Vij, Michael H. Tomasson
Identification of the cellular mechanisms that mediate cancer cell chemosensitivity is important for developing new cancer treatment strategies. Several chemotherapeutic drugs increase levels of the posttranslational modifier ISG15, which suggests that ISGylation could suppress oncogenesis. However, how ISGylation of specific target proteins controls tumorigenesis is unknown. Here, we identified proteins that are ISGylated in response to chemotherapy. Treatment of a human mammary epithelial cell line with doxorubicin resulted in ISGylation of the p53 family protein p63. An alternative splice variant of p63, ΔNp63α, suppressed the transactivity of other p53 family members, and its expression was abnormally elevated in various human epithelial tumors, suggestive of an oncogenic role for this variant. We showed that ISGylation played an essential role in the downregulation of ΔNp63α. Anticancer drugs, including doxorubicin, induced ΔNp63α ISGylation and caspase-2 activation, leading to cleavage of ISGylated ΔNp63α in the nucleus and subsequent release of its inhibitory domain to the cytoplasm. ISGylation ablated the ability of ΔNp63α to promote anchorage-independent cell growth and tumor formation in vivo as well to suppress the transactivities of proapoptotic p53 family members. These findings establish ISG15 as a tumor suppressor via its conjugation to ΔNp63α and provide a molecular rationale for therapeutic use of doxorubicin against ΔNp63α-mediated cancers.
Young Joo Jeon, Mi Gyeong Jo, Hee Min Yoo, Se-Hoon Hong, Jung-Mi Park, Seung Hyeun Ka, Kyu Hee Oh, Jae Hong Seol, Yong Keun Jung, Chin Ha Chung
Natural killer (NK) cells are primary effectors of innate immunity directed against transformed tumor cells. In response, tumor cells have developed mechanisms to evade NK cell–mediated lysis through molecular mechanisms that are not well understood. In the present study, we used a lentiviral shRNA library targeting more than 1,000 human genes to identify 83 genes that promote target cell resistance to human NK cell–mediated killing. Many of the genes identified in this genetic screen belong to common signaling pathways; however, none of them have previously been known to modulate susceptibility of human tumor cells to immunologic destruction. Gene silencing of two members of the JAK family (JAK1 and JAK2) increased the susceptibility of a variety of tumor cell types to NK-mediated lysis and induced increased secretion of IFN-γ by NK cells. Treatment of tumor cells with JAK inhibitors also increased susceptibility to NK cell activity. These findings may have important clinical implications and suggest that small molecule inhibitors of tyrosine kinases being developed as therapeutic antitumor agents may also have significant immunologic effects in vivo.
Roberto Bellucci, Hong-Nam Nguyen, Allison Martin, Stefan Heinrichs, Anna C. Schinzel, William C. Hahn, Jerome Ritz
In prostate cancer, the signals that drive cell proliferation change as tumors progress from castration-sensitive (androgen-dominant) to castration-resistant states. While the mechanisms underlying this change remain uncertain, characterization of common signaling components that regulate both stages of prostate cancer proliferation is important for developing effective treatment strategies. Here, we demonstrate that paxillin, a known cytoplasmic adaptor protein, regulates both androgen- and EGF-induced nuclear signaling. We show that androgen and EGF promoted MAPK-dependent phosphorylation of paxillin, resulting in nuclear translocation of paxillin. We found nuclear paxillin could then associate with androgen-stimulated androgen receptor (AR). This complex bound AR-sensitive promoters, retaining AR within the nucleus and regulating AR-mediated transcription. Nuclear paxillin also complexed with ERK and ELK1, mediating c-FOS and cyclin D1 expression; this was followed by proliferation. Thus, paxillin is a liaison between extranuclear MAPK signaling and nuclear transcription in response to androgens and growth factors, making it a potential regulator of both castration-sensitive and castration-resistant prostate cancer. Accordingly, paxillin was required for normal growth of human prostate cancer cell xenografts, and its expression was elevated in human prostate cancer tissue microarrays. Paxillin is therefore a potential biomarker for prostate cancer proliferation and a possible therapeutic target for prostate cancer treatment.
Aritro Sen, Ismary De Castro, Donald B. DeFranco, Fang-Ming Deng, Jonathan Melamed, Payel Kapur, Ganesh V. Raj, Randall Rossi, Stephen R. Hammes
More than 15% of cancer deaths worldwide are associated with underlying infections or inflammatory conditions, therefore understanding how inflammation contributes to cancer etiology is important for both cancer prevention and treatment. Inflamed tissues are known to harbor elevated etheno-base (ε-base) DNA lesions induced by the lipid peroxidation that is stimulated by reactive oxygen and nitrogen species (RONS) released from activated neutrophils and macrophages. Inflammation contributes to carcinogenesis in part via RONS-induced cytotoxic and mutagenic DNA lesions, including ε-base lesions. The mouse alkyl adenine DNA glycosylase (AAG, also known as MPG) recognizes such base lesions, thus protecting against inflammation-associated colon cancer. Two other DNA repair enzymes are known to repair ε-base lesions, namely ALKBH2 and ALKBH3; thus, we sought to determine whether these DNA dioxygenase enzymes could protect against chronic inflammation-mediated colon carcinogenesis. Using established chemically induced colitis and colon cancer models in mice, we show here that ALKBH2 and ALKBH3 provide cancer protection similar to that of the DNA glycosylase AAG. Moreover, Alkbh2 and Alkbh3 each display apparent epistasis with Aag. Surprisingly, deficiency in all 3 DNA repair enzymes confers a massively synergistic phenotype, such that animals lacking all 3 DNA repair enzymes cannot survive even a single bout of chemically induced colitis.
Jennifer A. Calvo, Lisiane B. Meira, Chun-Yue I. Lee, Catherine A. Moroski-Erkul, Nona Abolhassani, Koli Taghizadeh, Lindsey W. Eichinger, Sureshkumar Muthupalani, Line M. Nordstrand, Arne Klungland, Leona D. Samson
Coordinated translation initiation is coupled with cell cycle progression and cell growth, whereas excessive ribosome biogenesis and translation initiation often lead to tumor transformation and survival. Hepatocellular carcinoma (HCC) is among the most common and aggressive cancers worldwide and generally displays inherently high resistance to chemotherapeutic drugs. We found that RACK1, the receptor for activated C-kinase 1, was highly expressed in normal liver and frequently upregulated in HCC. Aberrant expression of RACK1 contributed to in vitro chemoresistance as well as in vivo tumor growth of HCC. These effects depended on ribosome localization of RACK1. Ribosomal RACK1 coupled with PKCβII to promote the phosphorylation of eukaryotic initiation factor 4E (eIF4E), which led to preferential translation of the potent factors involved in growth and survival. Inhibition of PKCβII or depletion of eIF4E abolished RACK1-mediated chemotherapy resistance of HCC in vitro. Our results imply that RACK1 may function as an internal factor involved in the growth and survival of HCC and suggest that targeting RACK1 may be an efficacious strategy for HCC treatment.
Yuanyuan Ruan, Linlin Sun, Yuqing Hao, Lijing Wang, Jiejie Xu, Wen Zhang, Jianhui Xie, Liang Guo, Lei Zhou, Xiaojing Yun, Hongguang Zhu, Aiguo Shen, Jianxin Gu