Embracing cancer complexity: Hallmarks of systemic disease

The last 50 years have witnessed extraordinary developments in understanding mechanisms of carcinogenesis, synthesized as the hallmarks of cancer. Despite this logical framework, our understanding of the molecular basis of systemic manifestations and the underlying causes of cancer-related death remains incomplete. Looking forward, elucidating how tumors interact with distant organs and how multifaceted environmental and physiological parameters impinge on tumors and their hosts will be crucial for advances in preventing and more effectively treating human cancers. In this perspective, we discuss complexities of cancer as a systemic disease, including tumor initiation and promotion, tumor micro- and immune macro-environments, aging, metabolism and obesity, cancer cachexia, circadian rhythms, nervous system interactions, tumor-related thrombosis, and the microbiome. Model systems incorporating human genetic variation will be essential to decipher the mechanistic basis of these phenomena and unravel gene-environment interactions, providing a modern synthesis of molecular oncology that is primed to prevent cancers and improve patient quality of life and cancer outcomes.

Abstract 4679: Investigating the role of cryptochrome 2 in human cancer

Through numerous epidemiological studies, The World Health Organization (WHO) deemed disruption of circadian rhythms a probable carcinogen. Circadian rhythms regulate many physiological and cellular processes, while maintaining a ~24hr period. The molecular mechanisms by which disrupted circadian rhythms promote tumorigenesis remain unclear. Recently, our lab found that Cryptochrome 2 (CRY2) acts as an adapter to recruit c-MYC to the E3 ligase complex SKP-CULLIN-FBXL3 (SCFFBXL3) to promote degradation of c-MYC, a known proto-oncogene transcription factor. We identified five recurrent CRY2 mutations (CRY2 D347H, S436R, R460C, D467N and S532L) in a variety of human cancers from The Cancer Genome Atlas (TCGA) (referred to as CRY2 TCGA mutations). We hypothesized that these mutations may disrupt the interactions between CRY2, FBXL3, and c-MYC and thereby promote c-MYC accumulation. We performed several biochemical and functional assays in parallel to investigate the impact of these mutations on CRY2 activities. While three of the mutants tested reduce the association of CRY2 with FBXL3 as expected, we unexpectedly found that one of the CRY2 TCGA mutants abolishes interaction between CRY2, CLOCK, and BMAL1 without affecting its ability to interact with FBXL3 or c-MYC. Thus, this mutation prevents the normal function of CRY2 within the circadian clock and affects two-dimensional colony formation, which could impact cellular transformation as well.

Citation Format: Alanna Chan, Katja Lamia. Investigating the role of cryptochrome 2 in human cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4679.

Vulnerability to helpless behavior is regulated by the circadian clock component CRYPTOCHROME in the mouse nucleus accumbens

The nucleus accumbens (NAc), a central component of the midbrain dopamine reward circuit, exhibits disturbed circadian rhythms in the postmortem brains of depressed patients. We hypothesized that normal mood regulation requires proper circadian timing in the NAc, and that mood disorders are associated with dysfunctions of the NAc cellular circadian clock. In mice exhibiting stress-induced depression-like behavior (helplessness), we found altered circadian clock function and high nighttime expression of the core circadian clock component CRYPTOCHROME (CRY) in the NAc. In the NAc of helpless mice, we found that higher expression of CRY is associated with decreased activation of dopamine 1 receptor-expressing medium spiny neurons (D1R-MSNs). Furthermore, D1R-MSN-specific CRY-knockdown in the NAc reduced susceptibility to stress-induced helplessness and increased NAc neuronal activation at night. Finally, we show that CRY inhibits D1R-induced G protein activation, likely by interacting with the Gs protein. Altered circadian rhythms and CRY expression were also observed in human fibroblasts from major depressive disorder patients. Our data reveal a causal role for CRY in regulating the midbrain dopamine reward system, and provide a mechanistic link between the NAc circadian clock and vulnerability to depression.

Guidelines for Genome-Scale Analysis of Biological Rhythms

Genome biology approaches have made enormous contributions to our understanding of biological rhythms, particularly in identifying outputs of the clock, including RNAs, proteins, and metabolites, whose abundance oscillates throughout the day. These methods hold significant promise for future discovery, particularly when combined with computational modeling. However, genome-scale experiments are costly and laborious, yielding “big data” that are conceptually and statistically difficult to analyze. There is no obvious consensus regarding design or analysis. Here we discuss the relevant technical considerations to generate reproducible, statistically sound, and broadly useful genome-scale data. Rather than suggest a set of rigid rules, we aim to codify principles by which investigators, reviewers, and readers of the primary literature can evaluate the suitability of different experimental designs for measuring different aspects of biological rhythms. We introduce CircaInSilico, a web-based application for generating synthetic genome biology data to benchmark statistical methods for studying biological rhythms. Finally, we discuss several unmet analytical needs, including applications to clinical medicine, and suggest productive avenues to address them.

Circadian Amplitude Regulation via FBXW7-Targeted REV-ERBα Degradation

Defects in circadian rhythm influence physiology and behavior with implications for the treatment of sleep disorders, metabolic disease, and cancer. Although core regulatory components of clock rhythmicity have been defined, insight into the mechanisms underpinning amplitude is limited. Here, we show that REV-ERBα, a core inhibitory component of clock transcription, is targeted for ubiquitination and subsequent degradation by the F-box protein FBXW7. By relieving REV-ERBα-dependent repression, FBXW7 provides an unrecognized mechanism for enhancing the amplitude of clock gene transcription. Cyclin-dependent kinase 1 (CDK1)-mediated phosphorylation of REV-ERBα is necessary for FBXW7 recognition. Moreover, targeted hepatic disruption of FBXW7 alters circadian expression of core clock genes and perturbs whole-body lipid and glucose levels. This CDK1-FBXW7 pathway controlling REV-ERBα repression defines an unexpected molecular mechanism for re-engaging the positive transcriptional arm of the clock, as well as a potential route to manipulate clock amplitude via small molecule CDK1 inhibition.

[Histologic and prognostic study of nephroblastoma in central Tunisia]

Nephroblastoma is a common malignant tumour in childhood that benefited from therapeutic progress. This is a retrospective study of 35 nephroblastoma diagnosed and treated in the central region of Tunisia within the last 8 years (1991-1999). We report and compare clinical features, therapeutic results and prognostic factors with those reported in the literature. The mean age was 3-years and 9 months, and the main clinical symptom was abdominal mass. Pre-operative chemotherapy was done in 32 cases and the objective response rate was 58%. Thirty-three patients had radical nephrectomy and only one had partial nephrectomy. Histologic analysis concluded to an anaplastic nephroblastoma in 2 cases. Using the classification of the international society of pediatric oncology, 11.4% of tumours were stage I, 48.6% stage II, 5.7% stage III, 11.4% stage IV and 2.9% stage V. The overall 5 years survival was 80%; tumour relapse was only independent prognosis factor in multivariate analysis (P < 0.01). Prognosis of nephroblastoma has been improved with chemotherapy and the pluridisciplinar treatment.