Sigma1 Regulates Lipid Droplet-mediated Redox Homeostasis Required for Prostate Cancer Proliferation

Lipid droplets (LD) are dynamic organelles that serve as hubs of cellular metabolic processes. Emerging evidence shows that LDs also play a critical role in maintaining redox homeostasis and can mitigate lipid oxidative stress. In multiple cancers, including prostate cancer, LD accumulation is associated with cancer aggressiveness, therapy resistance, and poor clinical outcome. Prostate cancer arises as an androgen receptor (AR)-driven disease. Among its myriad roles, AR mediates the biosynthesis of LDs, induces autophagy, and modulates cellular oxidative stress in a tightly regulated cycle that promotes cell proliferation. The factors regulating the interplay of these metabolic processes downstream of AR remain unclear. Here, we show that Sigma1/SIGMAR1, a unique ligand-operated scaffolding protein, regulates LD metabolism in prostate cancer cells. Sigma1 inhibition triggers lipophagy, an LD selective form of autophagy, to prevent accumulation of LDs which normally act to sequester toxic levels of reactive oxygen species (ROS). This disrupts the interplay between LDs, autophagy, buffering of oxidative stress and redox homeostasis, and results in the suppression of cell proliferation in vitro and tumor growth in vivo. Consistent with these experimental results, SIGMAR1 transcripts are strongly associated with lipid metabolism and ROS pathways in prostate tumors. Altogether, these data reveal a novel, pharmacologically responsive role for Sigma1 in regulating the redox homeostasis required by oncogenic metabolic programs that drive prostate cancer proliferation.

SIGNIFICANCE

To proliferate, cancer cells must maintain productive metabolic and oxidative stress (eustress) while mitigating destructive, uncontrolled oxidative stress (distress). LDs are metabolic hubs that enable adaptive responses to promote eustress. Targeting the unique Sigma1 protein can trigger distress by disrupting the LD-mediated homeostasis required for proliferation.

Abstract 284: Sigma1 regulates lipid droplet mediated redox homeostasis required for prostate cancer proliferation

Lipid droplets (LDs) are dynamic organelles that serve as hubs of cellular metabolic processes. Emerging evidence shows that LDs also play a critical role in maintaining redox homeostasis and can mitigate lipid oxidative stress. In multiple cancers, including prostate cancer (PCa), LD accumulation is associated with cancer aggressiveness, therapy resistance, and poor clinical outcome. PCa arises as an androgen receptor (AR) driven disease. Among its myriad roles, AR mediates the biosynthesis of LDs, induces autophagy, and modulates cellular oxidative stress in a tightly regulated cycle that promotes cell proliferation. The factors regulating the interplay of these metabolic processes downstream of AR remain unclear. Here, we show that Sigma1/SIGMAR1, a unique ligand-operated scaffolding protein, regulates LD metabolism in PCa cells. Sigma1 inhibition triggers lipophagy, an LD selective form of autophagy, to prevent accumulation of LDs which normally act to sequester toxic levels of reactive oxygen species (ROS). This disrupts the interplay between LDs, autophagy, buffering of oxidative stress and redox homeostasis, and results in the suppression of cell proliferation in vitro and tumor growth in vivo. Consistent with these experimental results, SIGMAR1 transcripts are strongly associated with lipid metabolism and reactive oxygen species pathways in prostate tumors. Altogether, these data reveal a novel, pharmacologically responsive role for Sigma1 in regulating the redox homeostasis required by oncogenic metabolic programs that drive PCa proliferation.

Citation Format: Halley M. Oyer, Alexandra R. Steck, Charles Longen, Sanjana Venkat, Konuralp Bayrak, Eleanor Munger, Dan Fu, Christina Sanders, Justin Myers, Matthew Schiewer, Nan Chen, Elahe Mostaghel, Felix J. Kim. Sigma1 regulates lipid droplet mediated redox homeostasis required for prostate cancer proliferation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 284.

[Aspects of multimodal pain therapy in old age]

Chronic pain in older adults should be explained and treated on the basis of the biopsychosocial model. With its interdisciplinary and interprofessional approach, multimodal pain therapy is the method of choice. In old age freedom from pain is usually not the primary goal. It is more important to restore the quality of life of those affected and to maintain independence and autonomy with a versatile treatment offer. This article explains the basics of multimodal pain therapy and its special features in old age.

Treatment of severely mutilated incisors: a challenge to the pedodontist

Dental caries is the single most common chronic childhood disease. In early childhood caries, there is early carious involvement and gross destruction of the maxillary anterior teeth. This leads to difficulty in speech, decreased masticatory efficiency, development of abnormal tongue habits and subsequent malocclusion and psychological problems if esthetics are compromised. The restoration of severely decayed primary incisors is often a difficult procedure that presents a special challenge to pediatric dentists. This case report documents the restoration of severely mutilated lateral incisors in a patient with early childhood caries.

Radioadaptive response in human lymphocytes in vitro

Exposure to low doses of radiation and/or chemicals can prime an organism to withstand the stress of a subsequent exposure to higher doses of the same agent. In the case of radiation, this phenomenon has been called radioadaptive response. Cytogenetic studies have been undertaken in human lymphocytes to investigate adaptive response (AR) to ionizing radiation, in particular to seek the role of variables such as priming dose, cell cycle stage, and age and gender of the donor. We demonstrated that pre-exposure of lymphocytes in whole blood cultures to very low doses in the range of about 1 cGy (priming or adaptive dose [AD]) reduced the frequency of micronuclei in binucleated cells induced by 100 cGy--that is, produced an AR in these cells in vitro. However, pre-exposure of cells to 10.0 cGy did not reduce the chromosomal damage (micronuclei) induced by the challenging dose (CD) of 100 cGy under the same protocol, thus exhibiting an inverse dose-response relationship. There was marked variability in the AR among the individuals investigated in the study. The extent of AR also depended on the stage of cell cycle exposed to the CD of radiation. Maximum AR was observed when CD of 100 cGy was given 4 hours after AD, 30 hours following the mitogenic stimulation of lymphocytes. The least AR was observed when CD was given 48 hours after stimulation. Interestingly, AR was also found to be dependent on the age of the donor, a decrease in AR being observed with an increasing age. No significant difference in AR was observed between male and female donors. To understand the molecular events underlying AR, protein synthesis patterns were studied in human lymphocytes subjected to mitogen, heat, or radiation stress. Heat shock (45 degrees C, for 15 min) induced 7 proteins with molecular weights ranging from 40 to 80 kDa, while treatment with phytohemagglutinin (40 microg/mL) showed induction of 2 proteins of molecular weights 38 and 48 kDa, respectively. However, exposure of human lymphocyte cultures to gamma radiation did not significantly induce synthesis of any protein, up to 800 cGy dose. Lack of induction of proteins by gamma radiation in human lymphocytes contrasts with the previous reports showing X-ray radiation-enhanced gene expression in melanoma cells and/or human tumor fibroblasts.

Radio-adaptive response in human lymphocytes in vitro

An attempt has been made to investigate the adaptive response to ionizing radiation in the human lymphocytes in vitro using cytochalasin-B blocked micronucleated binucleate cells (mn-BNCs) as a cytogenetic end point. Whole blood samples drawn from healthy donors, of either sex were irradiated in vitro at a dose of 1 cGy (adaptive or conditioning dose) Cobalt-60 gamma radiation (dose rate 1.12 cGy/min) at about 26 hr after mitogenic stimulation. After 31 hr of their initiation, groups of cultures were subsequently exposed to a challenging dose of 100 cGy gamma radiation (dose rate 82 cGy/min.). Eight males in the age group ranging from 25 to 55 years and eight females (age group 25 to 29 years), have been analysed during this study. Analysis of data revealed 40.6% reduction in the frequency of mn-BNCs among the males with a range from 25.7% to 54.7%. In case of females, also the per cent reduction varied from 26.3% to 49.0%, with a mean value of 33.7%. Pooling the data from males and females gave an overall reduction of 37.1% in the frequency of radiation induced mn-BNCs due to pre-exposure to 1 cGy radiation.