Plasticity in the cell division processes of obligate intracellular bacteria.

Most bacteria divide through a highly conserved process called binary fission, in which there is symmetric growth of daughter cells and the synthesis of peptidoglycan at the mid-cell to enable cytokinesis. During this process, the parental cell replicates its chromosomal DNA and segregates replicated chromosomes into the daughter cells. The mechanisms that regulate binary fission have been extensively studied in several model organisms, including Eschericia coli, Bacillus subtilis, and Caulobacter crescentus. These analyses have revealed that a multi-protein complex called the divisome forms at the mid-cell to enable peptidoglycan synthesis and septation during division. In addition, rod-shaped bacteria form a multi-protein complex called the elongasome that drives sidewall peptidoglycan synthesis necessary for the maintenance of rod shape and the lengthening of the cell prior to division. In adapting to their intracellular niche, the obligate intracellular bacteria discussed here have eliminated one to several of the divisome gene products essential for binary fission in E. coli. In addition, genes that encode components of the elongasome, which were mostly lost as rod-shaped bacteria evolved into coccoid organisms, have been retained during the reductive evolutionary process that some coccoid obligate intracellular bacteria have undergone. Although the precise molecular mechanisms that regulate the division of obligate intracellular bacteria remain undefined, the studies summarized here indicate that obligate intracellular bacteria exhibit remarkable plasticity in their cell division processes.

The Unique N-Terminal Domain of Chlamydial Bactofilin Mediates Its Membrane Localization and Ring-Forming Properties.

Chlamydia trachomatis is an obligate intracellular bacterial pathogen. In evolving to the intracellular niche, Chlamydia has reduced its genome size compared to other bacteria and, as a consequence, has a number of unique features. For example, Chlamydia engages the actin-like protein MreB, rather than the tubulin-like protein FtsZ, to direct peptidoglycan (PG) synthesis exclusively at the septum of cells undergoing polarized cell division. Interestingly, Chlamydia possesses another cytoskeletal element-a bactofilin ortholog, BacA. Recently, we reported BacA is a cell size-determining protein that forms dynamic membrane-associated ring structures in Chlamydia that have not been observed in other bacteria with bactofilins. Chlamydial BacA possesses a unique N-terminal domain, and we hypothesized this domain imparts the membrane-binding and ring-forming properties of BacA. We show that different truncations of the N terminus result in distinct phenotypes: removal of the first 50 amino acids (ΔN50) results in large ring structures at the membrane whereas removal of the first 81 amino acids (ΔN81) results in an inability to form filaments and rings and a loss of membrane association. Overexpression of the ΔN50 isoform altered cell size, similar to loss of BacA, suggesting that the dynamic properties of BacA are essential for the regulation of cell size. We further show that the region from amino acid 51 to 81 imparts membrane association as appending it to green fluorescent protein (GFP) resulted in the relocalization of GFP from the cytosol to the membrane. Overall, our findings suggest two important functions for the unique N-terminal domain of BacA and help explain its role as a cell size determinant. IMPORTANCE Bacteria use a variety of filament-forming cytoskeletal proteins to regulate and control various aspects of their physiology. For example, the tubulin-like FtsZ recruits division proteins to the septum whereas the actin-like MreB recruits peptidoglycan (PG) synthases to generate the cell wall in rod-shaped bacteria. Recently, a third class of cytoskeletal protein has been identified in bacteria-bactofilins. These proteins have been primarily linked to spatially localized PG synthesis. Interestingly, Chlamydia, an obligate intracellular bacterium, does not have PG in its cell wall and yet possesses a bactofilin ortholog. In this study, we characterize a unique N-terminal domain of chlamydial bactofilin and show that this domain controls two important functions that affect cell size: its ring-forming and membrane-associating properties.

How Safe Is Cancer Care?

Cancer Morbidity, Mortality, and Improvement Rounds is a series of articles intended to explore the unique safety risks experienced by oncology patients through the lens of quality improvement, systems and human factors engineering, and cognitive psychology. For purposes of clarity, each case focuses on a single theme, although, as is true for all medical incidents, there are almost always multiple, overlapping, contributing factors. The quality improvement paradigm used here, which focuses on root cause analyses and opportunities to improve care delivery systems, was previously outlined in this journal.

Localized cardiolipin synthesis is required for the assembly of MreB during the polarized cell division of Chlamydia trachomatis.

Pathogenic Chlamydia species are coccoid bacteria that use the rod-shape determining protein MreB to direct septal peptidoglycan synthesis during their polarized cell division process. How the site of polarized budding is determined in this bacterium, where contextual features like membrane curvature are seemingly identical, is unclear. We hypothesized that the accumulation of the phospholipid, cardiolipin (CL), in specific regions of the cell membrane induces localized membrane changes that trigger the recruitment of MreB to the site where the bud will arise. To test this, we ectopically expressed cardiolipin synthase (Cls) and observed a polar distribution for this enzyme in Chlamydia trachomatis. In early division intermediates, Cls was restricted to the bud site where MreB is localized and peptidoglycan synthesis is initiated. The localization profile of 6xHis tagged Cls (Cls_6xH) throughout division mimicked the distribution of lipids that stain with NAO, a dye that labels CL. Treatment of Chlamydia with 3',6-dinonylneamine (diNN), an antibiotic targeting CL-containing membrane domains, resulted in redistribution of Cls_6xH and NAO-staining phospholipids. In addition, 6xHis tagged MreB localization was altered by diNN treatment, suggesting an upstream regulatory role for CL-containing membranes in directing the assembly of MreB. This hypothesis is consistent with the observation that the clustered localization of Cls_6xH is not dependent upon MreB function or peptidoglycan synthesis. Furthermore, expression of a CL-binding protein at the inner membrane of C. trachomatis dramatically inhibited bacterial growth supporting the importance of CL in the division process. Our findings implicate a critical role for localized CL synthesis in driving MreB assembly at the bud site during the polarized cell division of Chlamydia.

Oncology Medical Home: ASCO and COA Standards.

PURPOSE: To provide Standards on the basis of evidence and expert consensus for a pilot of the Oncology Medical Home (OMH) certification program. The OMH model is a system of care delivery that features coordinated, efficient, accessible, and evidence-based care and includes a process for measurement of outcomes to facilitate continuous quality improvement. The OMH pilot is intended to inform further refinement of Standards for OMH model implementation. METHODS: An Expert Panel was formed, and a systematic review of the literature on the topics of OMH, clinical pathways, and survivorship care plans was performed using PubMed and Google Scholar. Using this evidence base and an informal consensus process, the Expert Panel developed a set of OMH Standards. Public comments were solicited and considered in preparation of the final manuscript. RESULTS: Three comparative peer-reviewed studies of OMH met the inclusion criteria. In addition, the results from 16 studies of clinical pathways and one systematic review of survivorship care plans informed the evidence review. Limitations of the evidence base included the small number of studies of OMH and lack of longer-term outcomes data. More data were available to inform the specific Standards for pathways and survivorship care; however, outcomes were mixed for the latter intervention. The Expert Panel concluded that in the future, practices should be encouraged to publish the results of OMH interventions in peer-reviewed journals to improve the evidence base. STANDARDS: Standards are provided for OMH in the areas of patient engagement, availability and access to care, evidence-based medicine, equitable and comprehensive team-based care, quality improvement, goals of care, palliative and end-of-life care discussions, and chemotherapy safety. Additional information, including a Standards implementation manual, is available at www.asco.org/standards.

A Dynamic, Ring-Forming Bactofilin Critical for Maintaining Cell Size in the Obligate Intracellular Bacterium Chlamydia trachomatis.

Bactofilins are polymer-forming cytoskeletal proteins that are widely conserved in bacteria. Members of this protein family have diverse functional roles such as orienting subcellular molecular processes, establishing cell polarity, and aiding in cell shape maintenance. Using sequence alignment to the conserved bactofilin domain, we identified a bactofilin ortholog, BacACT, in the obligate intracellular pathogen Chlamydia trachomatis. Chlamydia species are obligate intracellular bacteria that undergo a developmental cycle alternating between infectious nondividing elementary bodies (EBs) and noninfectious dividing reticulate bodies (RBs). As Chlamydia divides by a polarized division process, we hypothesized that BacACT may function to establish polarity in these unique bacteria. Utilizing a combination of fusion constructs and high-resolution fluorescence microscopy, we determined that BacACT forms dynamic, membrane-associated filament- and ring-like structures in Chlamydia's replicative RB form. Contrary to our hypothesis, these structures are distinct from the microbe's cell division machinery and do not colocalize with septal peptidoglycan or MreB, the major organizer of the bacterium's division complex. Bacterial two-hybrid assays demonstrated BacACT interacts homotypically but does not directly interact with proteins involved in cell division or peptidoglycan biosynthesis. To investigate the function of BacACT in chlamydial development, we constructed a conditional knockdown strain using a newly developed CRISPR interference system. We observed that reducing bacACT expression significantly increased chlamydial cell size. Normal RB morphology was restored when an additional copy of bacACT was expressed in trans during knockdown. These data reveal a novel function for chlamydial bactofilin in maintaining cell size in this obligate intracellular bacterium.

Prior Frequent Emergency Department Use as a Predictor of Emergency Department Visits After a New Cancer Diagnosis.

PURPOSE: To determine whether emergency department (ED) visit history prior to cancer diagnosis is associated with ED visit volume after cancer diagnosis. METHODS: This was a retrospective cohort study of adults (≥ 18 years) with an incident cancer diagnosis (excluding nonmelanoma skin cancers or leukemia) at an academic medical center between 2008 and 2018 and a safety-net hospital between 2012 and 2016. Our primary outcome was the number of ED visits in the first 6 months after cancer diagnosis, modeled using a multivariable negative binomial regression accounting for ED visit history in the 6-12 months preceding cancer diagnosis, electronic health record proxy social determinants of health, and clinical cancer-related characteristics. RESULTS: Among 35,090 patients with cancer (49% female and 50% non-White), 57% had ≥ 1 ED visit in the 6 months immediately following cancer diagnosis and 20% had ≥ 1 ED visit in the 6-12 months prior to cancer diagnosis. The strongest predictor of postdiagnosis ED visits was frequent (≥ 4) prediagnosis ED visits (adjusted incidence rate ratio [aIRR]: 3.68; 95% CI, 3.36 to 4.02). Other covariates associated with greater postdiagnosis ED use included having 1-3 prediagnosis ED visits (aIRR: 1.32; 95% CI, 1.28 to 1.36), Hispanic (aIRR: 1.12; 95% CI, 1.07 to 1.17) and Black (aIRR: 1.21; 95% CI, 1.17 to 1.25) race, homelessness (aIRR: 1.95; 95% CI, 1.73 to 2.20), advanced-stage cancer (aIRR: 1.30; 95% CI, 1.26 to 1.35), and treatment regimens including chemotherapy (aIRR: 1.44; 95% CI, 1.40 to 1.48). CONCLUSION: The strongest independent predictor for ED use after a new cancer diagnosis was frequent ED visits before cancer diagnosis. Efforts to reduce potentially avoidable ED visits among patients with cancer should consider educational initiatives that target heavy prior ED users and offer them alternative ways to seek urgent medical care.

Reimbursement Matters: Overcoming Barriers to Clinical Trial Accrual.

BACKGROUND: Accrual to cancer clinical trials is suboptimal. Few data exist regarding whether financial reimbursement might increase accruals. OBJECTIVE: The objective of this study was to assess perceptions about reimbursement to overcome barriers to trial accrual. RESEARCH DESIGN: This was a cross-sectional survey. SUBJECTS: Oncologists identified from the American Medical Association Physician Masterfile. MEASURES: We report descriptive statistics, associations of physician characteristics with perceptions of reimbursement, domains, and subthemes of free-text comments. RESULTS: Respondents (n=1030) were mostly medical oncologists (59.4%), ages 35-54 (67%), and male (75%). Overall, 30% reported discussing trials with >25% of patients. Barriers perceived were administrative/regulatory, physician/staff time, and eligibility criteria. National Cancer Institute cooperative group participants and practice owners were more likely to endorse higher reimbursement. Respondents indicated targeted reimbursement would help improve infrastructure, but also noted potential ethical problems with reimbursement for discussion (40.7%) and accrual (85.9%). Free-text comments addressed reimbursement sources, recipients, and concerns about the real and apparent conflict of interest. CONCLUSIONS: Though concerns about a potential conflict of interest remain paramount and must be addressed in any new system of reimbursement, oncologists believe reimbursement to enhance infrastructure could help overcome barriers to trial accrual.

Penicillin-binding proteins regulate multiple steps in the polarized cell division process of Chlamydia.

Chlamydia trachomatis serovar L2 and Chlamydia muridarum, which do not express FtsZ, undergo polarized cell division. During division, peptidoglycan assembles at the pole of dividing Chlamydia trachomatis cells where daughter cell formation occurs, and peptidoglycan regulates at least two distinct steps in the polarized division of Chlamydia trachomatis and Chlamydia muridarum. Cells treated with inhibitors that prevent peptidoglycan synthesis or peptidoglycan crosslinking by penicillin-binding protein 2 (PBP2) are unable to initiate polarized division, while cells treated with inhibitors that prevent peptidoglycan crosslinking by penicillin-binding protein 3 (PBP3/FtsI) initiate polarized division, but the process arrests at an early stage of daughter cell growth. Consistent with their distinct roles in polarized division, peptidoglycan organization is different in cells treated with PBP2 and PBP3-specific inhibitors. Our analyses indicate that the sequential action of PBP2 and PBP3 drives changes in peptidoglycan organization that are essential for the polarized division of these obligate intracellular bacteria. Furthermore, the roles we have characterized for PBP2 and PBP3 in regulating specific steps in chlamydial cell division have not been described in other bacteria.

Division without Binary Fission: Cell Division in the FtsZ-Less Chlamydia.

Chlamydia is an obligate intracellular bacterial pathogen that has significantly reduced its genome size in adapting to its intracellular niche. Among the genes that Chlamydia has eliminated is ftsZ, encoding the central organizer of cell division that directs cell wall synthesis in the division septum. These Gram-negative pathogens have cell envelopes that lack peptidoglycan (PG), yet they use PG for cell division purposes. Recent research into chlamydial PG synthesis, components of the chlamydial divisome, and the mechanism of chlamydial division have significantly advanced our understanding of these processes in a unique and important pathogen. For example, it has been definitively confirmed that chlamydiae synthesize a canonical PG structure during cell division. Various studies have suggested and provided evidence that Chlamydia uses MreB to substitute for FtsZ in organizing and coordinating the divisome during division, components of which have been identified and characterized. Finally, as opposed to using an FtsZ-dependent binary fission process, Chlamydia employs an MreB-dependent polarized budding process to divide. A brief historical context for these key advances is presented along with a discussion of the current state of knowledge of chlamydial cell division.

A randomized trial of mail and email recruitment strategies for a physician survey on clinical trial accrual.

BACKGROUND: Patient participation in cancer clinical trials is suboptimal. A challenge to capturing physicians' insights about trials has been low response to surveys. We conducted a study using varying combinations of mail and email to recruit a nationally representative sample of medical, surgical, and radiation oncologists to complete a survey on trial accrual. METHODS: We randomly assigned eligible physicians identified from the American Medical Association MasterFile (n = 13,251) to mail- or email-based recruitment strategies. Mail-based recruitment included a survey packet with: (1) cover letter describing the survey and inviting participation; (2) paper copy of the survey and postage-paid return envelope; and (3) a web link for completing the survey online. Email-based recruitment included an e-mail describing the survey and inviting participation, along with the web link to the survey, and a reminder postcard 2 weeks later. RESULTS: Response was higher for mail-based (11.8, 95% CI 11.0-12.6%) vs. email-based (4.5, 95% CI 4.0-5.0%) recruitment. In email-based recruitment, only one-quarter of recipients opened the email, and even fewer clicked on the link to complete the survey. Most physicians in mail-based recruitment responded after the first invitation (362 of 770 responders, 47.0%). A higher proportion of responders vs. non-responders were young (ages 25-44 years), men, and radiation or surgical (vs. medical) oncologists. CONCLUSIONS: Most physicians assigned to mail-based recruitment actually completed the survey online via the link provided in the cover letter, and those in email-based recruitment did not respond until they received a reminder postcard by mail. Providing the option to return a paper survey or complete it online may have further increased participation in the mail-based group, and future studies should examine how combinations of delivery mode and return options affect physicians' response to surveys.

Critical Role for the Extended N Terminus of Chlamydial MreB in Directing Its Membrane Association and Potential Interaction with Divisome Proteins.

Chlamydiae lack the conserved central coordinator protein of cell division FtsZ, a tubulin-like homolog. Current evidence indicates that Chlamydia uses the actin-like homolog, MreB, to substitute for the role of FtsZ in a polarized division mechanism. Interestingly, we observed MreB as a ring at the septum in dividing cells of Chlamydia We hypothesize that MreB, to substitute for FtsZ in Chlamydia, must possess unique properties compared to canonical MreB orthologs. Sequence differences between chlamydial MreB and orthologs in other bacteria revealed that chlamydial MreB possesses an extended N-terminal region, harboring predicted amphipathicity, as well as the conserved amphipathic helix found in other bacterial MreBs. The conserved amphipathic helix-directed green fluorescent protein (GFP) to label the membrane uniformly in Escherichia coli but the extended N-terminal region did not. However, the extended N-terminal region together with the conserved amphipathic region directed GFP to restrict the membrane label to the cell poles. In Chlamydia, the extended N-terminal region was sufficient to direct GFP to the membrane, and this localization was independent of an association with endogenous MreB. Importantly, mutating the extended N-terminal region to reduce its amphipathicity resulted in the accumulation of GFP in the cytosol of the chlamydiae and not in the membrane. The N-terminal domain of MreB was not required for homotypic interactions but was necessary for interactions with cell division components RodZ and FtsK. Our data provide mechanistic support for chlamydial MreB to serve as a substitute for FtsZ by forming a ringlike structure at the site of polarized division.IMPORTANCEChlamydia trachomatis is an obligate intracellular pathogen, causing sexually transmitted diseases and trachoma. The study of chlamydial physiology is important for developing novel therapeutic strategies for these diseases. Chlamydiae divide by a unique MreB-dependent polarized cell division process. In this study, we investigated unique properties of chlamydial MreB and observed that chlamydial species harbor an extended N-terminal region possessing amphipathicity. MreB formed a ring at the septum, like FtsZ in Escherichia coli, and its localization was dependent upon the amphipathic nature of its extended N terminus. Furthermore, this region is crucial for the interaction of MreB with cell division proteins. Given these results, chlamydial MreB likely functions at the septum as a scaffold for divisome proteins to regulate cell division in this organism.

Patient and provider perspectives on delivery of oral cancer therapies.

OBJECTIVE: The introduction of oral cancer therapies presents new challenges to delivery of quality cancer care. Little is known about how patients and providers address and overcome these challenges. We conducted a qualitative study exploring the range of patient and provider perspectives on oral cancer therapies. METHODS: We conducted semi-structured interviews with patients and providers at a tertiary referral center and county safety-net hospital in Dallas, TX. Interviews probed perspectives on differences between parenteral chemotherapy and oral therapies, adherence, communication, and cost/insurance. Interview transcripts were analyzed thematically using a deductively-driven coding scheme corresponding to the interview guide. RESULTS: We conducted 22 patient (13 at tertiary referral center, 9 at safety-net hospital) and 10 provider (7 oncologists, 2 nurses, 1 pharmacist) interviews. Key themes from interviews included: (1) differences in parenteral chemotherapy vs. oral therapy; (2) adherence and dosing; and (3) experiences related to cost and communication. CONCLUSIONS: Nearly all providers described challenges engaging with and educating patients about oral cancer therapies. Despite our initial hypothesis, safety-net patients encountered few barriers accessing oral therapies compared to patients receiving care in the tertiary referral center. PRACTICE IMPLICATIONS: Our findings will guide future interventions to monitor and support cancer patients receiving oral therapies.

Care coordination for complex cancer survivors in an integrated safety-net system: a study protocol.

BACKGROUND: The growing numbers of cancer survivors challenge delivery of high-quality survivorship care by healthcare systems. Innovative ways to improve care coordination for patients with cancer and multiple chronic conditions ("complex cancer survivors") are needed to achieve better care outcomes, improve patient experience of care, and lower cost. Our study, Project CONNECT, will adapt and implement three evidence-based care coordination strategies, shown to be effective for primary care conditions, among complex cancer survivors. Specifically, the purpose of this study is to: 1) Implement a system-level EHR-driven intervention for 500 complex cancer survivors at Parkland; 2) Test effectiveness of the strategies on system- and patient-level outcomes measured before and after implementation; and 3) Elucidate system and patient factors that facilitate or hinder implementation and result in differences in experiences of care coordination between complex patients with and without cancer. METHODS: Project CONNECT is a quasi-experimental implementation study among 500 breast and colorectal cancer survivors with at least one of the following chronic conditions: diabetes, hypertension, chronic lung disease, chronic kidney disease, or heart disease. We will implement three evidence-based care coordination strategies in a large, county integrated safety-net health system: 1) an EHR-driven registry to facilitate patient transitions between primary and oncology care; 2) co-locating a nurse practitioner trained in care coordination within a complex care team; 3) and enhancing teamwork through coaching. Segmented regression analysis will evaluate change in system-level (i.e. composite care quality score) and patient-level outcomes (i.e. self-reported care coordination). To evaluate implementation, we will merge quantitative findings with structured observations and physician and patient interviews. DISCUSSION: This study will result in an evaluation toolkit identifying key model elements, barriers, and facilitators that can be used to guide care coordination interventions in other safety-net settings. Because Parkland is a vanguard of safety-net healthcare nationally, findings will be widely applicable as other safety-nets move toward increased integration, enhanced EHR capability, and experience with growing patient diversity. Our proposal recognizes the complexity of interventions and scaffolds evidence-based strategies together to meet the needs of complex patients, systems of care, and service integration. TRIAL REGISTRATION: ClinicalTrials.gov, NCT02943265 . Registered 24 October 2016.

Impact on Oncology Practices of Including Drug Costs in Bundled Payments.

INTRODUCTION: This analysis evaluates the impact of bundling drug costs into a hypothetic bundled payment. METHODS: An economic model was created for patient vignettes from: advanced-stage III colon cancer and metastatic non-small-cell lung cancer. First quarter 2016 Medicare reimbursement rates were used to calculate the average fee-for-service (FFS) reimbursement for these vignettes. The probabilistic risk faced by practices was captured by the type of patients seen in practices and randomly assigned in a Monte Carlo simulation on the basis of the given distribution of patient types within each cancer. Simulations were replicated 1,000 times. The impact of bundled payments that include drug costs for various practice sizes and cancer types was quantified as the probability of incurring a loss at four magnitudes: any loss, > 10%, > 20%, or > 30%. A loss was defined as receiving revenue from the bundle that was less than what the practice would have received under FFS; the probability of loss was calculated on the basis of the number of times a practice reported a loss among the 1,000 simulations. RESULTS: Practices that treat a substantial proportion of patients with complex disease compared with the average patient in the bundle would have revenue well below that expected from FFS. Practices that treat a disproportionate share of patients with less complex disease, as compared with the average patient in the bundle, would have revenue well above the revenue under FFS. Overall, bundled payments put practices at greater risk than FFS because their patient case mix could greatly skew financial performance. CONCLUSION: Including drug costs in a bundle is subject to the uncontrollable probabilistic risk of patient case mixes.

CRISPR/Cas9 targeting of GPRC6A suppresses prostate cancer tumorigenesis in a human xenograft model.

BACKGROUND: GPRC6A is implicated in the pathogenesis of prostate cancer, but its role remains uncertain because of a purported tolerant gene variant created by substitution of a K..Y polymorphism in the 3rd intracellular loop (IL) that evolved in the majority of humans and replaces the ancestral RKLP present in 40% of humans of African descent and all other species. METHODS: We determined whether the K..Y polymorphism is present in human-derived prostate cancer cell lines by sequencing the region of the 3rd IL and assessed the cellular localization of a "humanized" mouse GPRC6A containing the K..Y sequence by immunofluorescence. We assessed functions of GPRC6A in PC-3 cells expressing endogenous GPRC6A and in GPRC6A-deficient PC-3 cells created using CRISPR/Cas9 technology. The effect of GPRC6A on basal and ligand stimulated cell proliferation and migration was evaluated in vitro in wild-type and PC-3-deficient cell lines. The effect of editing GPRC6A on prostate cancer growth and progression in vivo was assessed in a Xenograft mouse model implanted with wild-type and PC-3 deficient cells and treated with the GPRC6A ligand osteocalcin. RESULTS: We found that all of the human prostate cancer cell lines tested endogenously express the "K..Y" polymorphism in the 3rd IL. Comparison of mouse wild-type GPRC6A with a "humanized" mouse GPRC6A construct created by replacing the "RKLP" with the "K..Y" sequence, found that both receptors were predominantly expressed on the cell surface. The transfected "humanized" GPRC6A receptor, however, preferentially activated mTOR compared to ERK signaling in HEK-293 cells. In contrast, in PC-3 cells expressing the endogenous GPRC6A with the "K..Y" polymorphism, the ligand osteocalcin stimulated ERK, AKT and mTOR phosphorylation, promoted cell proliferation and migration, and upregulated genes regulating testosterone biosynthesis. Targeting GPRC6A in PC-3 cells by CRISPR/Cas9 significantly blocked these responses in vitro. In addition, GPRC6A deficient PC-3 xenografts exhibited significantly less growth and were resistant to osteocalcin-induced prostate cancer progression compared to control PC-3 cells expressing GPRC6A. CONCLUSIONS: Human GPRC6A is a functional osteocalcin and testosterone sensing receptor that promotes prostate cancer progression. GPRC6A may contribute to racial disparities in prostate cancer, and is a potential therapeutic target to develop antagonists to treat prostate cancer.