Management of high, moderate, and low penetrance ovarian cancer susceptibility mutations: an assessment of current risk reduction practices.

OBJECTIVE: Limited information exists regarding risk reduction strategies for women with moderate and low penetrance ovarian cancer susceptibility mutations. We sought to assess current risk reduction practice patterns for carriers of these mutations through a survey of members of the Society of Gynecologic Oncology. METHODS: Society of Gynecologic Oncology members were emailed a survey consisting of two vignettes: (1) a 35-year-old premenopausal woman; (2) a 55-year-old postmenopausal woman with comorbidities. Each vignette contained sub-scenarios in which the patient had either a BRCA1 (relative risk (RR)=30-60), RAD51C (RR=5.0), or ATM (RR=1.5-2.0) mutation. Respondents were queried about their preferred management approach. Summary statistics were performed to describe results of the survey. We used χ2 testing for statistical analyses, comparing results according to mutation type and demographic information. RESULTS: A total of 193 (15%) of 1284 Society of Gynecologic Oncology members responded. For the premenopausal woman, 99%, 80%, and 40% would perform a risk reducing salpingo-oophorectomy prior to menopause in the setting of a BRCA1, RAD51C, and ATM mutation, respectively. For the postmenopausal woman, 98%, 85%, and 42% would proceed with risk reducing salpingo-oophorectomy in the setting of a BRCA1, RAD51C, and ATM mutation, respectively. Response distribution for carriers of RAD51C and ATM mutations were different from BRCA1 in both vignettes (p<0.001). CONCLUSIONS: Respondents were more likely to perform risk reducing salpingo-oophorectomy, in the setting of a BRCA1, RAD51C, and ATM mutation, earlier and more frequently in the setting of a BRCA1 mutation. However, there was a lack of consensus about management of the moderate and low penetrance mutations, suggesting that more data regarding age specific risks and appropriate risk reduction strategies for these alterations are needed.

Acetylation of TUG protein promotes the accumulation of GLUT4 glucose transporters in an insulin-responsive intracellular compartment.

Insulin causes the exocytic translocation of GLUT4 glucose transporters to stimulate glucose uptake in fat and muscle. Previous results support a model in which TUG traps GLUT4 in intracellular, insulin-responsive vesicles termed GLUT4 storage vesicles (GSVs). Insulin triggers TUG cleavage to release the GSVs; GLUT4 then recycles through endosomes during ongoing insulin exposure. The TUG C terminus binds a GSV anchoring site comprising Golgin-160 and possibly other proteins. Here, we report that the TUG C terminus is acetylated. The TUG C-terminal peptide bound the Golgin-160-associated protein, ACBD3 (acyl-CoA-binding domain-containing 3), and acetylation reduced binding of TUG to ACBD3 but not to Golgin-160. Mutation of the acetylated residues impaired insulin-responsive GLUT4 trafficking in 3T3-L1 adipocytes. ACBD3 overexpression enhanced the translocation of GSV cargos, GLUT4 and insulin-regulated aminopeptidase (IRAP), and ACBD3 was required for intracellular retention of these cargos in unstimulated cells. Sirtuin 2 (SIRT2), a NAD(+)-dependent deacetylase, bound TUG and deacetylated the TUG peptide. SIRT2 overexpression reduced TUG acetylation and redistributed GLUT4 and IRAP to the plasma membrane in 3T3-L1 adipocytes. Mutation of the acetylated residues in TUG abrogated these effects. In mice, SIRT2 deletion increased TUG acetylation and proteolytic processing. During glucose tolerance tests, glucose disposal was enhanced in SIRT2 knock-out mice, compared with wild type controls, without any effect on insulin concentrations. Together, these data support a model in which TUG acetylation modulates its interaction with Golgi matrix proteins and is regulated by SIRT2. Moreover, acetylation of TUG enhances its function to trap GSVs within unstimulated cells and enhances insulin-stimulated glucose uptake.

Endoproteolytic cleavage of TUG protein regulates GLUT4 glucose transporter translocation.

To promote glucose uptake into fat and muscle cells, insulin causes the translocation of GLUT4 glucose transporters from intracellular vesicles to the cell surface. Previous data support a model in which TUG traps GLUT4-containing vesicles and tethers them intracellularly in unstimulated cells and in which insulin mobilizes this pool of vesicles by releasing this tether. Here we show that TUG undergoes site-specific endoproteolytic cleavage, which separates a GLUT4-binding, N-terminal region of TUG from a C-terminal region previously suggested to bind an intracellular anchor. Cleavage is accelerated by insulin stimulation in 3T3-L1 adipocytes and is highly dependent upon adipocyte differentiation. The N-terminal TUG cleavage product has properties of a novel 18-kDa ubiquitin-like modifier, which we call TUGUL. The C-terminal product is observed at the expected size of 42 kDa and also as a 54-kDa form that is released from membranes into the cytosol. In transfected cells, intact TUG links GLUT4 to PIST and also binds Golgin-160 through its C-terminal region. PIST is an effector of TC10α, a GTPase previously shown to transmit an insulin signal required for GLUT4 translocation, and we show using RNAi that TC10α is required for TUG proteolytic processing. Finally, we demonstrate that a cleavage-resistant form of TUG does not support highly insulin-responsive GLUT4 translocation or glucose uptake in 3T3-L1 adipocytes. Together with previous results, these data support a model whereby insulin stimulates TUG cleavage to liberate GLUT4 storage vesicles from the Golgi matrix, which promotes GLUT4 translocation to the cell surface and enhances glucose uptake.