TRF2 (TERF2) binds to telomeric repeats and is critical for telomere integrity. Evidence suggests that it also localizes to non-telomeric DNA damage sites. However, this recruitment appears to be precarious and functionally controversial. We find that TRF2 recruitment to damage sites occurs by a two-step mechanism: the initial rapid recruitment (phase I), and stable and prolonged association with damage sites (phase II). Phase I is poly(ADP-ribose) polymerase (PARP)-dependent and requires the N-terminal basic domain. The phase II recruitment requires the C-terminal MYB/SANT domain and the iDDR region in the hinge domain, which is mediated by the MRE11 complex and is stimulated by TERT. PARP-dependent recruitment of intrinsically disordered proteins contributes to transient displacement of TRF2 that separates two phases. TRF2 binds to I-PpoI-induced DNA double-strand break sites, which is enhanced by the presence of complex damage and is dependent on PARP and the MRE11 complex. TRF2 depletion affects non-sister chromatid homologous recombination repair, but not homologous recombination between sister chromatids or non-homologous end-joining pathways. Our results demonstrate a unique recruitment mechanism and function of TRF2 at non-telomeric DNA damage sites.

Considerable controversy exists within the field of dermatopathology in differentiating keratoacanthoma (KA) from squamous-cell carcinoma (SCC). KAs are rapidly growing, benign squamous tumors that are typically well differentiated. This controversy stems from the diverging perspectives on the management, classification, and diagnosis of each entity. Many believe that KAs are benign neoplasms in which intervention may be unnecessary since they are self-limiting and resolve on their own. On the other hand, SCC needs to be treated, as it carries significant morbidity and mortality risks. Early diagnosis and treatment are vital to prevent serious consequences of SCC. Nevertheless, KAs may resemble SCC grossly and microscopically. Various ancillary tests, including immunohistochemical (IHC) staining, have been proposed to differentiate between these entities, though mixed patterns of expression can limit the diagnostic utility of these techniques. Research into this topic is ongoing, with newer genetic and molecular findings illuminating the previously difficult-to-understand aspects of KA and increasing our understanding of this entity. In this review, KA and SCC will be compared along the lines of histological features, genetic, immune, and molecular markers, differential diagnosis, and management to clarify the similarities, differences, and misconceptions about both entities.

Ganglioneuromas (GNs) are rare, benign tumors composed of ganglion cells, nerve fibers, and glial cells. Three types of colonic GN lesions exist: polypoid GNs, ganglioneuromatous polyposis, and diffuse ganglioneuromatosis. Less than 100 cases of GN are documented in the literature. A 10-year retrospective search of the pathology database at our institution identified eight cases of colonic GNs. All cases were incidental. Seven of the eight cases presented with colonoscopy findings of small sessile polyps (ranging between 0.1 and 0.7 cm) treated with polypectomy, whereas one case showed a 4 cm partially circumferential and partially obstructing mass in the ascending colon, treated with right hemicolectomy. Almost two-thirds of the cases (5/8) demonstrated associated diverticulosis. All cases were positive for S100 protein and Synaptophysin via immunohistochemistry (IHC). No syndromic association was identified in any of the cases. We also conducted a comprehensive review using PubMed to identify cases of colonic GN reported in the literature. In total, 173 studies were retrieved, among which 36 articles met our inclusion criteria (35 patients and 3 cases on animals). We conclude that while most GNs are incidental and solitary small sessile lesions, many can be diffuse and associated with syndromes. In these cases, the tumor can result in bowel obstruction simulating adenocarcinoma.