Integrating transcriptomic sequencing with conventional cytogenetics, we identified WWTR1 (WW domain–containing transcription regulator 1) (3q25) and CAMTA1 (calmodulin-binding transcription activator 1) (1p36) as the two genes involved in the t(1;3)(p36;q25) chromosomal translocation that is characteristic of epithelioid hemangioendothelioma (EHE), a vascular sarcoma. This WWTR1/CAMTA1 gene fusion is under the transcriptional control of the WWTR1 promoter and encodes a putative chimeric transcription factor that joins the amino terminus of WWTR1, a protein that is highly expressed in endothelial cells, in-frame to the carboxyl terminus of CAMTA1, a protein that is normally expressed only in brain. Thus, CAMTA1 expression is activated inappropriately through a promoter-switch mechanism. The gene fusion is present in virtually all EHEs tested but is absent from all other vascular neoplasms, demonstrating it to be a disease-defining genetic alteration. A sensitive and specific break-apart fluorescence in situ hybridization assay was also developed to detect the translocation and will assist in the evaluation of this diagnostically challenging neoplasm. The chimeric WWTR1/CAMTA1 transcription factor may represent a therapeutic target for EHE and offers the opportunity to shed light on the functions of two poorly characterized proteins.

Although gastrointestinal stromal tumors (GISTs) harboring activating KIT or platelet-derived growth factor receptor A ( PDGFRA ) mutations respond to treatment with targeted KIT/PDGFRA inhibitors such as imatinib mesylate, these treatments are rarely curative. Most often, a sizeable tumor cell subpopulation survives and remains quiescent for years, eventually resulting in acquired resistance and treatment failure. Here, we report that imatinib induces autophagy as a survival pathway in quiescent GIST cells. Inhibiting autophagy, using RNAi-mediated silencing of autophagy regulators (ATGs) or antimalarial lysosomotrophic agents, promotes the death of GIST cells both in vitro and in vivo. Thus, combining imatinib with autophagy inhibition represents a potentially valuable strategy to promote GIST cytotoxicity and to diminish both cellular quiescence and acquired resistance in GIST patients.

Introduction: Estrogen and insulin-like growth factor-1 (IGF-1) play important roles in mammary gland development and breast cancer. SirT1 is a highly conserved protein deacetylase that can regulate the insulin/IGF-1 signaling in lower organisms, as well as a growing number of transcription factors, including NF-κB, in mammalian cells. Whether SirT1 regulates the IGF-1 signaling for mammary gland development and function, however, is not clear. In the present study, this role of SirT1 was examined by studying SirT1-deficient mice. Methods: SirT1-deficient (SirT1^ko/ko) mice were generated by crossing a new strain of mice harboring a conditional targeted mutation in the SirT1 gene (SirT1^co/co) with CMV-Cre transgenic mice. Whole mount and histology analyses, immunofluorescence staining, immunohistochemistry, and western blotting were used to characterize mammary gland development in virgin and pregnant mice. The effect of exogenous estrogen was also examined by subcutaneous implantation of a slow-releasing pellet in the subscapular region. Results: Both male and female SirT1^ko/ko mice can be fertile despite the growth retardation phenotype. Virgin SirT1^ko/ko mice displayed impeded ductal morphogenesis, whereas pregnant SirT1^ko/ko mice manifested lactation failure due to an underdeveloped lobuloalveolar network. Estrogen implantation was sufficient to rescue ductal morphogenesis. Exogenous estrogen reversed the increased basal level of IGF-1 binding protein-1 expression in SirT1^ko/ko mammary tissues, but not that of IκBα expression, suggesting that increased levels of estrogen enhanced the production of local IGF-1 and rescued ductal morphogenesis. Additionally, TNFα treatment enhanced the level of the newly synthesized IκBα in SirT1^ko/ko cells. SirT1 deficiency therefore affects the cellular response to multiple extrinsic signals. Conclusion: SirT1 modulates the IGF-1 signaling critical for both growth regulation and mammary gland development in mice. SirT1 deficiency deregulates the expression of IGF-1 binding protein-1 and attenuates the effect of IGF-1 signals, including estrogen-stimulated local IGF-1 signaling for the onset of ductal morphogenesis. These findings suggest that the enzymatic activity of SirT1 may influence both normal growth and malignant growth of mammary epithelial cells.