Edited by John M. DenuThe hormone prolactin (PRL) contributes to breast cancer pathogenesis through various signaling pathways, one of the most notable being the JAK2/signal transducer and activator of transcription 5 (STAT5) pathway. PRL-induced activation of the transcription factor STAT5 results in the up-regulation of numerous genes implicated in breast cancer pathogenesis. However, the molecular mechanisms that enable STAT5 to access the promoters of these genes are not well understood. Here, we show that PRL signaling induces chromatin decompaction at promoter DNA, corresponding with STAT5 binding. The chromatin-modifying protein high mobility group nucleosomal binding domain 2 (HMGN2) specifically promotes STAT5 accessibility at promoter DNA by facilitating the dissociation of the linker histone H1 in response to PRL. Knockdown of H1 rescues the decrease in PRL-induced transcription following HMGN2 knockdown, and it does so by allowing increased STAT5 recruitment. Moreover, H1 and STAT5 are shown to function antagonistically in regulating PRL-induced transcription as well as breast cancer cell biology. While reduced STAT5 activation results in decreased PRL-induced transcription and cell proliferation, knockdown of H1 rescues both of these effects. Taken together, we elucidate a novel mechanism whereby the linker histone H1 prevents STAT5 binding at promoter DNA, and the PRL-induced dissociation of H1 mediated by HMGN2 is necessary to allow full STAT5 recruitment and promote the biological effects of PRL signaling.In the mammary gland, signals from the polypeptide hormone prolactin (PRL) are essential for normal development (1-4), and these physiological effects are mediated through the homologous transcription factors signal transducer and activator of transcription 5a and 5b (referred to as STAT5) (5). PRL signals by binding to the PRL receptor (PRLR), 2 a transmembrane receptor of the cytokine receptor superfamily. Binding of PRL to the PRLR results in the activation of STAT5 via phosphorylation by the tyrosine kinase Janus kinase 2 (JAK2) (6 -8). Phosphorylated STAT5 dimerizes, and the active STAT5 dimers translocate to the nucleus. In the nucleus, STAT5 recognizes and binds to consensus elements in the DNA, which induces the expression of STAT5 target genes (9).PRL-induced STAT5 activation results in the up-regulation of many pro-proliferative genes (10 -12). Although essential for proper mammary gland development, aberrant PRL signaling and STAT5 activation also contribute to breast cancer pathogenesis. Transgenic mice that overexpress PRL in the mammary epithelium develop mammary tumors, which can be either estrogen receptor-positive or -negative (13). In epidemiologic studies, women with elevated serum PRL are at an increased risk of developing breast cancer (14 -17). PRL also enhances the proliferation, motility, and survival of breast cancer cells (18 -20). Similarly, overexpression of STAT5 in the mammary gland of transgenic mice results in mammary tumor development (21), whereas hemizygous los...

Intraosseous hemangiomas are rare bony neoplasms that infrequently develop in the calvarium or facial bones. Due to their highly vascular nature, biopsy or resection of these tumors can present a surgical challenge, with reports of significant blood loss during tumor resection. Traditional surgical resection of intraosseous hemangiomas often includes the use of high speed oscillating or sagittal saws. Ultrasonic aspirators, which spare adjacent soft-tissue structures and minimize blood loss, have been successfully used in resection of firm soft tissue masses of the orbit; however, this technology has not been demonstrated in the treatment of a vascular tumor in the orbit. The authors present the case of a 37-year-old woman who presented with an intraosseous hemangioma at the left inferior orbital rim and maxilla; the mass was successfully resected with the aid of a Sonopet Ultrasonic Aspirator bone knife. The knife allowed for simultaneous emulsification and cautery of the bone encasing the mass with low risk to sensitive surrounding tissue.

Background Neuroblastomas are the most common extracranial solid malignancy in children with variable manifestations and complications depending on the presence of paraneoplastic syndromes. Materials and Methods We performed a single institution retrospective cohort study of all patients less than 18 years old diagnosed with neuroblastoma or ganglioneuroblastoma between January 2002 and July 2022. Patients were identified through the pathology and cancer registry and cross-referenced with pediatric records. Patient demographics, clinical presentation, treatment, and outcomes were collected. A univariate descriptive analysis of the collected data was conducted. Results In our study period, 130 children were diagnosed with neuroblastoma, and 15 were diagnosed with ganglioneuroblastoma. There were 12 children with a paraneoplastic syndrome identified, 8 with NBL and 4 with ganglioneuroblastoma (GNBL). The average age at diagnosis was 22 months. All but 1 underwent resection prior to treatment of paraneoplastic syndrome, and 4 children required neoadjuvant therapy. Neurological complications were the most common with 10 children (83%). The average time from symptom onset to diagnosis was 0.7 months. Eight children had complete resolution of their symptoms after treatment and resection, 2 children recently started treatment within a year, 1 had partial resolution, and 1 died during treatment. The presence of tumor-infiltrating lymphocytes occurred in 4 children with neurologic paraneoplastic syndromes. Six children had neuropil rich tumors. Conclusion The histological profile of paraneoplastic syndromes of neuroblastoma and ganglioneuroblastoma and their treatment across a single institution can be highly variable. The presence of tumor-infiltrating lymphocytes and neuropil may have an impact on paraneoplastic pathology.

Stat5 is a transcription factor utilized by several cytokine/hormone receptor signaling pathways that promotes transcription of genes associated with proliferation, differentiation, and survival of cancer cells. However, there are currently no clinically approved therapies that target Stat5, despite ample evidence that it contributes to breast cancer pathogenesis. Previous research in our lab has shown that the high mobility group nucleosome binding domain 2 (HGMN2) protein serves as a Stat5 co-activator. The activity of HMGN2 has been previously shown to be regulated by acetylation. Here, we show that deacetylation of HMGN2 on lysine residue K2 by histone deacetylase 6 (HDAC6) promotes Stat5-mediated transcription and breast cancer growth. Conversely, in vitro HDAC6 inhibition by pharmacologic and knockdown approaches enhanced HMGN2 acetylation with a concomitant reduction of in vitro Stat5-mediated signaling and global gene expression, and breast cancer growth. These data, combined with global in silico ChIP-Seq analysis, indicate that HDAC6 serves as a regulator of the pioneer function of HMGN2 for Stat5 transcriptional function. In vitro and in vivo treatment of traditional and patient-derived xenograft models with HDAC6 inhibitors resulted in a highly significant reduction of tumor growth. Translationally, it was also found that high levels of acetylated K2 were present in normal human breast tissue, which was lost in primary breast cancers and lymph node metastases. This suggests that blockade of HMGN2 deacetylation as described above is a novel treatment for breast cancer, given that existing HDAC6 inhibitors have a favorable toxicity profile in phase I trials of other tumor types. Altogether, these results reveal a novel mechanism through which HDAC6 regulates the transcription of Stat5 target genes and demonstrates the utility of HDAC6 inhibition as a potential breast cancer therapeutic. Citation Format: Justin M. Craig, Suzanne M. Schauwecker, Charles V. Clevenger. HDAC6 as a therapeutic target in human breast cancer [abstract]. In: Proceedings of the AACR Special Conference: Advances in Breast Cancer Research; 2017 Oct 7-10; Hollywood, CA. Philadelphia (PA): AACR; Mol Cancer Res 2018;16(8_Suppl):Abstract nr B11.