Background: During energy starvation, cells utilize intracellular resources for survival; however, the resources used during glucose starvation are unknown. Results: In glucose-starved yeast, vacuolar hydrolysis and endocytosis promote survival whereas autophagy is dispensable. Conclusion: Vacuolar hydrolysis blocks autophagy and provides resources for survival during glucose starvation. Significance: This new survival mechanism could protect cells from starvation in many situations.

A major challenge to breast cancer research is the identification of alterations in the architecture and composition of the breast that are associated with breast cancer progression. The aim of the present investigation was to characterize the mammary adipose phenotype from Brca1 mutant mice in the expectation that this would shed light on the role of the mammary tissue environment in the early stages of breast tumorigenesis. We observed that histological sections of mammary tissue from adult Brca1 mutant mice abnormally display small, multilocular adipocytes that are reminiscent of brown adipose tissue (BAT) as compared to wildtype mice. Using a marker for BAT, the uncoupling protein 1 (UCP1), we demonstrated that these multilocular adipose regions in Brca1 mutant mice stain positive for UCP1. Transcriptionally, UCP1 mRNA levels in the Brca1 mutant mice were elevated greater than 50-fold compared to age-matched mammary glands from wildtype mice. Indeed, BAT has characteristics that are favorable for tumor growth, including high vascularity. Therefore, we also demonstrated that the multilocular brown adipose phenotype in the mammary fat pad of Brca1 mutant mice displayed regions of increased vascularity as evidenced by a significant increase in the protein expression of CD31, a marker for angiogenesis. This Brca1 mutant mouse model should provide a physiologically relevant context to determine whether brown adipose tissue can play a role in breast cancer development.

Background Information. In the yeast Saccharomyces cerevisiae, acute glucose starvation induces rapid endocytosis followed by vacuolar degradation of many plasma membrane proteins. This process is essential for cell viability, but the regulatory mechanisms that control it remain poorly understood. Under normal growth conditions, a major regulatory decision for endocytic cargo occurs at the trans-Golgi network (TGN) where proteins can recycle back to the plasma membrane or can be recognized by TGN-localised clathrin adaptors that direct them towards the vacuole. However, glucose starvation reduces recycling and alters the localization and post-translational modification of TGN-localised clathrin adaptors. This raises the possibility that during glucose starvation endocytosed proteins are routed to the vacuole by a novel mechanism that bypasses the TGN or does not require TGN-localised clathrin adaptors. Results. Here, we investigate the role of TGN-localised clathrin adaptors in the traffic of several amino acid permeases, including Can1, during glucose starvation. We find that Can1 transits through the TGN after endocytosis in both starved and normal conditions. Can1 and other amino acid permeases require TGN-localised clathrin adaptors for maximal delivery to the vacuole. Furthermore, these permeases are actively sorted to the vacuole, because ectopically forced de-ubiquitination at the TGN results in the recycling of the Tat1 permase in starved cells. Finally, we report that the Mup1 permease requires the clathrin adaptor Gga2 for vacuolar delivery. In contrast, the clathrin adaptor protein complex AP-1 plays a minor role, potentially in retaining permeases in the TGN, but it is otherwise dispensable for vacuolar delivery. Conclusions and significance. This work elucidates one membrane trafficking pathway needed for yeast to respond to acute glucose starvation. It also reveals the functions of TGNlocalised clathrin adaptors in this process. Our results indicate that the same machinery is needed for vacuolar protein sorting at the GN in glucose starved cells as is needed in the presence of glucose. In addition, our findings provide further support for the model that the TGN is a transit point for many endocytosed proteins, and that Gga2 and AP-1 function in distinct pathways at the TGN.

Energy is required for all cellular functions and diverse mechanisms allow the cell to overcome acute energy starvation. A new study reveals that starved cells inhibit type V myosins and actin depolymerization, measures that may conserve energy while temporarily retaining cell polarity.

A major challenge to breast cancer research is the identification of alterations in the architecture and composition of the breast that are associated with breast cancer progression. Mammary epithelial cells are surrounded by an environment of supporting cell types, including the extracellular matrix, fibroblasts, and adipose tissue. Recent studies have demonstrated that this surrounding environment is an important regulator of tumor cell fate. The aim of the present investigation was to characterize the mammary adipose phenotype in the mammary gland of the Brca1 mutant mice in the expectation that this would shed light on the role of the mammary tissue environment in the early stages of breast tumorigenesis. We have observed sustained deposition of multilocular lipids in the mammary fat pad of Brca1 mutant mouse from puberty into adulthood that was reminiscent of brown adipose tissue (BAT) as compared to wildtype mice. Using a marker for BAT, the uncoupling protein 1 (UCP1), we demonstrated that these multilocular mammary adipose regions in Brca1 mutant mice stain positive for UCP1. Transcriptionally, UCP1 mRNA in the Brca1 mutant mice was elevated greater than 50-fold over levels seen in the age-matched mammary glands from wildtype mice. To gain insight into the origin of the multilocular adipocyte phenotype in the Brca1 mutant mouse mammary gland, we measured the expression of PRDM16, a regulator of brown fat differentiation. PRDM16 mRNA expression was increased 2-fold in Brca1 mutant mouse mammary gland compared to wildtype mice. Additionally, we show that protein levels of the bone morphogenetic protein 7 (BMP7), a protein known to induce brown adipogenesis in subcutaneous white adipose tissue, is significantly increased in mammary glands from Brca1 mutant mice compared to wildtype mice. These findings suggest that BMP7 could play a role in the sustained brown adipose tissue phenotype observed in adult Brca1 mutant mice. Interestingly, BMP7 has also been implicated in breast cancer pathogenesis and has been shown to induce breast cancer cell migration and invasion. We also demonstrate that the multilocular brown adipose phenotype in the mammary fat pad of Brca1 mutant mice has increased vascularity, a characteristic that is favorable for tumor development. Given that adipose tissue is the major contributor to the volume of the breast, it is critical to determine whether the sustained deposition of multilocular brown adipocytes in the mammary gland can impact breast cancer development. This Brca1 mutant mouse model should provide a physiologically relevant context to further examine the role of the plasticity of adipose tissue in breast cancer development. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3278. doi:1538-7445.AM2012-3278

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