ARF Promotes MDM2 Degradation and Stabilizes p53: ARF-INK4a Locus Deletion Impairs Both the Rb and p53 Tumor Suppression Pathways

AbstractThe INK4a-ARF locus encodes two unrelated proteins that both function in tumor suppression. p16 INK4a binds to and inhibits the activity of CDK4 and CDK6, and ARF arrests the cell cycle in a p53-dependent manner. We show here that ARF binds to MDM2 and promotes the rapid degradation of MDM2. This interaction is mediated by the exon 1β–encoded N-terminal domain of ARF and a C-terminal region of MDM2. ARF-promoted MDM2 degradation is associated with MDM2 modification and concurrent p53 stabilization and accumulation. The functional consequence of ARF-regulated p53 levels via MDM2 proteolysis is evidenced by the ability of ectopically expressed ARF to restore a p53-imposed G1 cell cycle arrest that is otherwise abrogated by MDM2. Thus, deletion of the ARF-INK4a locus simultaneously impairs both the INK4a–cyclin D/CDK4-RB and the ARF-MDM2-p53 pathways

Evaluation of patient-reported delays and affordability-related barriers to care in head and neck cancer

OBJECTIVE: To examine the prevalence and predictors of patient-reported barriers to care among survivors of head and neck squamous cell carcinoma and the association with health-related quality of life (HRQOL) outcomes. STUDY DESIGN: Retrospective cohort study. SETTING: Outpatient oncology clinic at an academic tertiary care center. METHODS: Data were obtained from the UNC Health Registry/Cancer Survivorship Cohort. Barriers to care included self-reported delays in care and inability to obtain needed care due to cost. HRQOL was measured with validated questionnaires: general (PROMIS) and cancer specific (FACT-GP). RESULTS: The sample included 202 patients with head and neck squamous cell carcinoma with a mean age of 59.6 years (SD, 10.0). Eighty-two percent were male and 87% were White. Sixty-two patients (31%) reported at least 1 barrier to care. Significant predictors of a barrier to care in unadjusted analysis included age ≤60 years ( CONCLUSION: Delay- and affordability-related barriers are common among survivors of head and neck cancer and appear to be associated with significantly worse HRQOL outcomes. Certain sociodemographic groups appear to be more at risk of patient-reported barriers to care

Direct Comparison of HPV16 Viral Genomic Integration, Copy Loss, and Structural Variants in Oropharyngeal and Uterine Cervical Cancers Reveal Distinct Relationships to E2 Disruption and Somatic Alteration

Squamous cell carcinoma of the oropharynx caused by HPV type 16 (HPV16+ OPSCC) is the most common HPV-associated malignancy in the USA and has many molecular differences from uterine cervical squamous cell carcinoma (UCSCC). Our understanding of HPV oncogenesis relied on studies of UCSCC revealing a consensus model reliant on HPV integration with a loss of E2. Here, we compare patterns of HPV integration in UCSCC and OPSCC by analysis of affinity capture sequencing of the HPV16 genome in 104 OPSCC and 44 UCSCC tumors. These cohorts were contemporaneously sequenced using an identical strategy. Integration was identified using discordant read pair clustering and assembly-based approaches. Viral integration sites, structural variants, and copy losses were examined. While large-scale deep losses of HPV16 genes were common in UCSCC and were associated with E2 loss, deep copy losses of the HPV16 genome were infrequent in HPV16+ OPSCC. Similarly, structural variants within HPV16 favored E2 loss in UCSCC but not OPSCC. HPV16 integration sites were non-random, with recurrent integration hot-spots identified. OPSCC tumors had many more integration sites per tumor when compared to UCSCC and had more integration sites in genomic regions with high gene density. These data show that viral integration and E2 disruption are distinct in UCSCC and OPSCC. Our findings also add to growing literature suggesting that HPV tumorigenesis in OPSCC does not follow the model developed based on UCSCC

Global Genome Demethylation Causes Transcription-Associated DNA Double Strand Breaks in HPV-Associated Head and Neck Cancer Cells

High levels of DNA methylation at CpG loci are associated with transcriptional repression of tumor suppressor genes and dysregulation of DNA repair genes. Human papilloma virus (HPV)-associated head and neck squamous cell carcinomas (HNSCC) have high levels of DNA methylation and methylation has been associated with dampening of an innate immune response in virally infected cells. We have been exploring demethylation as a potential treatment in HPV+ HNSCC and recently reported results of a window clinical trial showing that HNSCCs are particularly sensitive to demethylating agent 5-azacytidine (5-aza). Mechanistically, sensitivity is partially due to downregulation of HPV genes expression and restoration of tumor suppressors p53 and Rb. Here, for the first time, we show that 5-azaC treatment of HPV+ HNSCC induces replication and transcription-associated DNA double strand breaks (DSBs) that occur preferentially at demethylated genomic DNA. Blocking replication or transcription prevented formation of DNA DSBs and reduced sensitivity of HPV-positive head and neck cancer cells to 5-azaC, demonstrating that both replication and active transcription are required for formation of DSBs associated with 5-azaC

Molecular classification of head and neck squamous cell carcinomas using patterns of gene expression

The prognostication of head and neck squamous cell carcinoma (HNSCC) is largely based upon the tumor size and location and the presence of lymph node metastases. Here we show that gene expression patterns from 60 HNSCC samples assayed on cDNA microarrays allowed categorization of these tumors into four distinct subtypes. These subtypes showed statistically significant differences in recurrence-free survival and included a subtype with a possible EGFR-pathway signature, a mesenchymal-enriched subtype, a normal epithelium-like subtype, and a subtype with high levels of antioxidant enzymes. Supervised analyses to predict lymph node metastasis status were approximately 80% accurate when tumor subsite and pathological node status were considered simultaneously. This work represents an important step toward the identification of clinically significant biomarkers for HNSCC

LZAP Inhibits p38 MAPK (p38) Phosphorylation and Activity by Facilitating p38 Association with the Wild-Type p53 Induced Phosphatase 1 (WIP1)

LZAP (Cdk5rap3, C53) is a putative tumor suppressor that inhibits RelA, Chk1 and Chk2 and activates p53. LZAP is lost in a portion of human head and neck squamous cell carcinoma and experimental loss of LZAP expression is associated with enhanced invasion, xenograft tumor growth and angiogenesis. p38 MAPK can increase or decrease proliferation and cell death depending on cellular context. LZAP has no known enzymatic activity, implying that its biological functions are likely mediated by its protein-protein interactions. To gain further insight into LZAP activities, we searched for LZAP-associated proteins (LAPs). Here we show that the LZAP binds p38, alters p38 cellular localization, and inhibits basal and cytokine-stimulated p38 activity. Expression of LZAP inhibits p38 phosphorylation in a dose-dependent fashion while loss of LZAP enhances phosphorylation and activation with resultant phosphorylation of p38 downstream targets. Mechanistically, the ability of LZAP to alter p38 phosphorylation depended, at least partially, on the p38 phosphatase, Wip1. Expression of LZAP increased both LZAP and Wip1 binding to p38. Taken together, these data suggest that LZAP activity includes inhibition of p38 phosphorylation and activation

A novel ARF-binding protein (LZAP) alters ARF regulation of HDM2

The tumour suppressor ARF (alternative reading frame) is encoded by the INK4a (inhibitor of cyclin-dependent kinase 4)/ARF locus, which is frequently altered in human tumours. ARF binds MDM2 (murine double minute 2) and releases p53 from inhibition by MDM2, resulting in stabilization, accumulation and activation of p53. Recently, ARF has been found to associate with other proteins, but, to date, little is known about ARF-associated proteins that are implicated in post-translational regulation of ARF activity. Using a yeast two-hybrid screen, we have identified a novel protein, LZAP (LXXLL/leucine-zipper-containing ARF-binding protein), that interacts with endogenous ARF in mammalian cells. In the present study, we show that LZAP reversed the ability of ARF to inhibit HDM2's ubiquitin ligase activity towards p53, but simultaneously co-operated with ARF, maintaining p53 stability and increasing p53 transcriptional activity. Expression of LZAP, in addition to ARF, increased the percentage of cells in the G(1) phase of the cell cycle. Expression of LZAP also caused activation of p53 and a p53-dependent G(1) cell-cycle arrest in the absence of ARF. Taken together, our data suggest that LZAP can regulate ARF biochemical and biological activity. Additionally, LZAP has p53-dependent cell-cycle effects that are independent of ARF

Lymphatic Mapping Patterns in Early Oral Squamous Cell Carcinoma

Objectives: Correlate location of sentinel nodes on lymphoscintigraphy versus sentinel lymph node biopsy (SLNB) and lymphatic metastases for T1 and T2 N0 oral cavity cancer. Methods: This was a prospective cooperative group trial of 140 patients with untreated T1 and T2 N0 oral cancers at academic medical centers. Interventions were lymphoscintigraphy, resection of the primary, SLNB, and immediate neck dissection. The outcome measures were location of sentinel nodes by lymphoscintigraphy versus SLNB, and location of metastases. Results: Lymph nodes located by lymphoscintigraphy and SLNB were found predominately in levels I through IV. There was heterogeneity in the number of the lymph nodes found at lymphoscintigraphy and at SLNB, which was significantly different in levels II and III ( P < 0.0001). In 6 of 28 cases with bilateral drainage on imaging, SLNB detected only unilateral sentinel nodes. Sensitivity of lymphoscintigraphy in predicting the levels of sentinel nodes ranged from 42% to 63%, and specificity from 71% to 95%, for each level. Comparison of locations of nodal metastases to historical data showed fewer metastases to level I in our study ( P = 0.0295). Metastases occurred predominantly in levels I, II, and III. In one case of a lateral tongue cancer, a contralateral node was the only positive node. Conclusions: Lymphatic drainage patterns and lymph node metastases involved predominantly levels I, II, and III. Lymphoscintigraphy is not very sensitive for predicting the levels of sentinel nodes. In levels II and III, the rate of detection of lymph nodes between the two modalities is significantly different