Divergent regulation of α-arrestin ARRDC3 function by ubiquitination

The α-arrestin ARRDC3 is a recently discovered tumor suppressor in invasive breast cancer that functions as a multifaceted adaptor protein to control protein trafficking and cellular signaling. However, the molecular mechanisms that control ARRDC3 function are unknown. Other arrestins are known to be regulated by posttranslational modifications, suggesting that ARRDC3 may be subject to similar regulatory mechanisms. Here we report that ubiquitination is a key regulator of ARRDC3 function and is mediated primarily by two proline-rich PPXY motifs in the ARRDC3 C-tail domain. Ubiquitination and the PPXY motifs are essential for ARRDC3 function in regulating GPCR trafficking and signaling. Additionally, ubiquitination and the PPXY motifs mediate ARRDC3 protein degradation, dictate ARRDC3 subcellular localization, and are required for interaction with the NEDD4-family E3 ubiquitin ligase WWP2. These studies demonstrate a role for ubiquitination in regulating ARRDC3 function and reveal a mechanism by which ARRDC3 divergent functions are controlled.

Prolonged fasting times reap greater geroprotective effects when combined with caloric restriction in adult female mice

Emerging new evidence highlights the importance of prolonged daily fasting periods for the health and survival benefits of calorie restriction (CR) and time-restricted feeding (TRF) in male mice; however, little is known about the impact of these feeding regimens in females. We placed 14-month-old female mice on five different dietary regimens, either CR or TRF with different feeding windows, and determined the effects of these regimens on physiological responses, progression of neoplasms and inflammatory diseases, serum metabolite levels, and lifespan. Compared with TRF feeding, CR elicited a robust systemic response, as it relates to energetics and healthspan metrics, a unique serum metabolomics signature in overnight fasted animals, and was associated with an increase in lifespan. These results indicate that daytime (rest-phase) feeding with prolonged fasting periods initiated late in life confer greater benefits when combined with imposed lower energy intake.

Replenishment of myeloid-derived suppressor cells (MDSCs) overrides CR-mediated protection against tumor growth in a murine model of triple-negative breast cancer

Caloric restriction (CR) is the leading non-pharmacological intervention to delay induced and spontaneous tumors in pre-clinical models. These effects of CR are largely attributed to canonical inhibition of pro-growth pathways. However, our recent data suggest that CR impairs primary tumor growth and cancer progression in the murine 4T1 model of triple negative breast cancer (TNBC), at least in part, through reduced frequency of the myeloid-derived suppressor cells (MDSC). In the present study, we sought to determine whether injection of excess MDSCs could block regression in 4T1 tumor growth and metastatic spread in BALB/cJ female mice undergoing daily CR. Our findings show that MDSC injection impeded CR-mediated protection against tumor growth without increasing lung metastatic burden. Overall, these results reveal that CR can slow cancer progression by affecting immune suppressive cells.Impact statement: Inoculation of MDSCs from donor mice effectively impedes the ability of calorie restriction to protect against primary tumor growth without impacting lung metastatic burden in recipient animals.

Uncovering the Molecular Underpinnings of Oxidative Stress-Induced Senescence

The aging process is sexually dimorphic, with males having higher occurrence rates of cancer and facing a greater risk of mortality. Sexual dimorphism in the response to cellular damage may account for distinct phenotypic changes with age as they relate to the accumulation of cellular damage leading to cancer. Cellular senescence triggers permanent cell cycle arrest in order to protect against malignant growth. However, organismal senescence increases with age and is associated with the release of pro-inflammatory signals (cytokines, chemokines, and proteases) known as the ‘senescence-associated-secretory-phenotype’ (SASP) that, if unchecked, accelerates tissue damage and creates a microenvironment ripe for cancer development. In this study, we hypothesized that sexual disparities in mortality and cancer prevalence stems from differences in the rate of accumulation of senescent cells in mice. Male and female C57BL/6J mice were fed ad libitum or subjected to 30% calorie restriction, a nutritional intervention known to delay the onset of various cancers and prevent senescent cell accumulation. Primary skin fibroblasts were collected longitudinally to allow measurement of cell proliferation, wound healing and the release of SASP factors. The results indicate that when compared to males, fibroblasts of CR-fed females showed significant improvements in cell growth rate, wound healing and SASP markers vs. AL controls. Work is underway to determine how sex influences cellular protective pathways. Thus, like other cell processes, cellular senescence is unequal between males and females and CR delays the emergence of the senescence phenotype.

4:10 Cycles of Very Low Calories Protect Against Tumor Xenografts, but Not Metastases in the Absence of Chemotherapy

Cancer is a leading cause of mortality, with its incidence only expected to rise with an increasingly aging population. Dietary interventions, primarily caloric restriction (CR), lower cellular energy metabolism and have long been utilized to slow the aging process and protect against age-related diseases, including cancer. However, due to the stringency of CR, dietary alternatives that offer the same beneficial outcomes in cancer prevention and longevity have become increasingly attractive. Periodic cycles (4 days twice a month) of low caloric intake followed by a standard ad libitum (AL) diet was previously shown to promote health-span in mice and humans and protect against primary tumorigenesis and enhanced the effects of chemotherapy. The aim of our study was to compare the tumorigenic potential of 4T1 cells, a murine model of stage IV breast cancer, in young and aged female BALB/c mice fed either periodic cycles of low caloric diets versus chronic 20% CR. Compared to AL controls, we found a significant delay in primary tumor growth in mice regardless of diet composition by the 4:10 cycles of very low caloric intake. However, unlike in CR, CR-alternative diets were not protective against lung metastases in the absence of chemotherapy. Our study sheds light into the underlying differences of calorie-based interventions in the absence of chemotherapy.

Metabolic Flexibility: Interplay of Diet Composition and Intermittent Fasting on Healthspan (P08-053-19)

Objectives

4:10 periodic fasting schedule is proposed to improve biomarkers of healthspan through metabolic flexibility in mice on both standard and high fat diets.

Methods

Our study adopted the 4:10 fasting schedule using the fasting-mimicking diet (FMD) as our model. FMD is a plant-based, low-protein, and low-sugar diet regime implemented for four days every two-week cycle. Its regenerative effect is observed in the refeeding phase following starvation, allowing for the breakdown of cells via increased autophagy. In comparison to stricter fasting regimes such as intermittent fasting, chronic caloric restriction, and periodic fasting, FMD is well-tolerated in the clinical setting. 74 12-month old C57BL/6 mice were randomized into two diet groups: standard diet or high-fat diet. For 4 days out of every fourteen days, the mice were severely caloric restricted and refed with ad-libitum of either standard or high fat diets for the remaining 10 days, matching the controls who were fixed on the ad-libitum diet. The 4:10 fasting schedule was repeated 11 times before the mice were sacrificed. To measure metabolic flexibility, metabolic cages, ELISA, and glucose meters were used.

Results

Body weight and composition, metabolic flexibility, and insulin sensitivity indicate differences between fasting on diet composition. Not only did those on the fasting high-fat diet (FHFD) remain overweight, identical to their HFD controls, insulin sensitivity was also attenuated in FHFD groups. Fasting standard diet (FSD) had a reduction of 5% in body weight and 15% in body fat. Carbohydrate and lipid metabolism differences indicated by the respiratory exchange ratio as well as motor function performance differences further support the positive impact of fasting on SD groups, not HFD groups. Characteristic of positive healthspan biomarkers, reduced leptin and improved insulin sensitivity was observed with FSD, not FHFD.

Conclusions

We found that while the FMD schedule improved healthspan as indicated by biomarkers of healthy aging for mice on the standard diet, it could not counteract the negative health effects of the obesogenic diet. These results demonstrate the importance of not only time of feeding but also diet composition in respect to healthspan.

Funding Sources

National Institute on Aging (NIA) – National Institutes of Health (NIH).

RECK isoforms have opposing effects on cell migration

Cell migration is a highly conserved process involving cytoskeletal reorganization and restructuring of the surrounding extracellular matrix. Although there are many studies describing mechanisms underlying cell motility, little has been reported about the contribution of alternative isoform use toward cell migration. Here, we investigated whether alternative isoform use can affect cell migration focusing on reversion-inducing-cysteine-rich protein with Kazal motifs (RECK), an established inhibitor of cell migration. We found that a shorter isoform of RECK is more highly expressed in proliferating fibroblasts, in TGF-β-treated fibroblasts, and in tumors compared with differentiated tissue. Knockdown of this short RECK isoform reduces fibroblast migration through Matrigel. Thus, this short isoform of RECK generated by a combination of alternative splicing and alternative polyadenylation plays an opposing role to the canonical RECK isoform, as knockdown of canonical RECK results in faster cell migration through Matrigel. We show that the short RECK protein competes with matrix metalloprotease 9 (MMP9) for binding to the Kazal motifs of canonical RECK, thus liberating MMP9 from an inactivating interaction with canonical RECK. Our studies provide a new paradigm and a detailed mechanism for how alternative isoform use can regulate cell migration by producing two proteins with opposing effects from the same genetic locus.