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Endogenous APOBEC3B overexpression characterizes HPV-positive and HPV-negative oral epithelial dysplasias and head and neck cancers.

ABSTRACT: The DNA cytosine deaminase APOBEC3B (A3B) is a newly recognized endogenous source of mutations in a range of human tumors, including head/neck cancer. A3B inflicts C-to-T and C-to-G base substitutions in 5'-TCA/T trinucleotide motifs, contributes to accelerated rates of tumor development, and affects clinical outcomes in a variety of cancer types. High-risk human papillomavirus (HPV) infection causes A3B overexpression, and HPV-positive cervical and head/neck cancers are among tumor types with the highest degree of APOBEC signature mutations. A3B overexpression in HPV-positive tumor types is caused by the viral E6/E7 oncoproteins and may be an early off-to-on switch in tumorigenesis. In comparison, less is known about the molecular mechanisms responsible for A3B overexpression in HPV-negative head/neck cancers. Here, we utilize an immunohistochemical approach to determine whether A3B is turned from off-to-on or if it undergoes a more gradual transition to overexpression in HPV-negative head/neck cancers. As positive controls, almost all HPV-positive oral epithelial dysplasias and oropharyngeal cancers showed high levels of nuclear A3B staining regardless of diagnosis. As negative controls, A3B levels were low in phenotypically normal epithelium adjacent to cancer and oral epithelial hyperplasias. Interestingly, HPV-negative and low-grade oral epithelial dysplasias showed intermediate A3B levels, while high-grade oral dysplasias showed high A3B levels similar to oral squamous cell carcinomas. A3B levels were highest in grade 2 and grade 3 oral squamous cell carcinomas. In addition, a strong positive association was found between nuclear A3B and Ki67 scores suggesting a linkage to the cell cycle. Overall, these results support a model in which gradual activation of A3B expression occurs during HPV-negative tumor development and suggest that A3B overexpression may provide a marker for advanced grade oral dysplasia and cancer.

SUBMITTER: Argyris PP

PROVIDER: S-EPMC8261524 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Human papillomaviruses (HPVs) are associated with nearly all cervical cancers (CCs), 20-30% of head and neck cancers (HNCs), and other cancers. Because HNCs also arise in HPV-negative patients, this type of cancer provides unique opportunities to define similarities and differences of HPV-positive versus HPV-negative cancers arising in the same tissue. Here, we describe genome-wide expression profiling of 84 HNCs, CCs and site-matched normal epithelial samples in which we used laser capture microdissection to enrich samples for tumor-derived versus normal epithelial cells. This analysis revealed that HPV+HNCs and CCs differed in their patterns of gene expression yet shared many changes compared to HPV-HNCs. Some of these shared changes were predicted, but many others were not. Notably, HPV+HNCs and CCs were found to be upregulated in their expression of a distinct and larger subset of cell cycle genes than observed in HPV-HNC. Moreover, HPV+ cancers over-expressed testis-specific genes that are normally expressed only in meiotic cells. Many, though not all, of the hallmark differences between HPV+HNC and HPV-HNC were a direct consequence of HPV and in particular the viral E6 and E7 oncogenes. This included a novel association of HPV oncogenes with testes specific gene expression. These findings in primary human tumors provide novel biomarkers for early detection of HPV+ and HPV- cancers, and emphasize the potential value of targeting E6 and E7 function, alone or combined with radiation and/or traditional chemotherapy, in the treatment of HPV+ cancers. Experiment Overall Design: All tissue samples were fresh frozen in liquid nitrogen and collected with patientsâ?? consent under approval of the Institutional Review Boards from all participating institutions. Each tissue sample was cryosectioned, and selected sections stained with hematoxylin/eosin, and reviewed to determine tumor content, pathological status, and freedom from necrosis and freezing artifacts. Epithelial cells from all normal samples and tumor cells from HNC or CC samples with less than 80% tumor were laser capture microdissected from adjacent sections using a PixCell II LCM system. For guidance, an adjacent section was briefly stained with hematoxylin to visualize tissue structure. Total RNA was extracted from sectioned and/or microdissected samples as follows: 1 ml of TRIzol (Invitrogen, Carlsbad, CA) was added to each tissue sample, homogenized by passing through a 20 gauge needle, and added to 0.2 ml chloroform. After centrifugation at 20,000 xg for 20 min at 4oC, RNA in the aqueous phase was precipitated with an equal volume of isopropanol for 30 min at 4oC, pelleted, and washed twice with cold 70% ethanol. Double strand (ds) cDNA was synthesized from this RNA using a SuperScript ds cDNA synthesis kit (Invitrogen) and T7 promoter-linked oligo (dT)24. Complementary RNA (cRNA) was synthesized from T7 promoter-linked ds cDNA using a MEGAscript high transcription kit (Ambion, Austin, TX). To obtain a sufficient cRNA for 2 microarray hybridizations, this amplification process was repeated. Second round cRNA was biotin labeled using a BioArray High Yield RNA Transcript Labeling Kit (Enzo Life Sciences, Farmingdale, NY) and stored at -80oC until hybridized. cRNA quality and quantity was determined by gel electrophoresis and UV spectrophotometry. Whole human gene expression was profiled using Affymetrix Human Genome U133 Plus 2.0 arrays.

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Endogenous APOBEC3B overexpression characterizes HPV-positive and HPV-negative oral epithelial dysplasias and head and neck cancers.

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