The TSC2/mTOR pathway drives endothelial cell transformation induced by the Kaposi's sarcoma-associated herpesvirus G protein-coupled receptor.

The Kaposi's sarcoma-associated herpesvirus (KSHV), the infectious causative agent of Kaposi's sarcoma (KS), encodes a G protein-coupled receptor (vGPCR) implicated in the initiation of KS. Here we demonstrate that Kaposi's sarcomagenesis involves stimulation of tuberin (TSC2) phosphorylation by vGPCR, promoting the activation of mTOR through both direct and paracrine mechanisms. Pharmacologic inhibition of mTOR with rapamycin prevented vGPCR sarcomagenesis, while overactivation of this pathway was sufficient to render endothelial cells oncogenic. Moreover, mice haploinsufficient for TSC2 are predisposed to vascular sarcomas remarkably similar to KS. Collectively, these results implicate mTOR in KS initiation and suggest that the sarcomagenic potential of KSHV may be a direct consequence of the profound sensitivity of endothelial cells to vGPCR dysregulation of the TSC2/mTOR pathway.

Bringing a Structural Competency Framework to the (Simulated) Bedside: The Premature Discharge Objective Structured Clinical Exam.

PROBLEM: Structural competency is increasingly valued as a framework to address health equity within undergraduate medical education. As of academic year 2023-2024, the Liaison Committee on Medical Education (LCME) requires that medical schools have content regarding basic principles of structurally competent health care. Despite encouraging data about the effectiveness of structural competency curricula, most occur within the walls of a classroom and do not enter the authentic or simulated clinical space. APPROACH: From 2022 to 2023, an objective structured clinical exam (OSCE) focused on premature discharge, previously known as discharge against medical advice, was integrated into the required fourth-year Health Policy course at Weill Cornell Medical College, which uses the framework of structural competency. After a simulated clinical encounter, students completed a reflection assignment and participated in group debriefing to reflect on how policy coursework affected their simulated clinical experience. Students completed an evaluation about their OSCE experience, and OSCE checklist performance was analyzed. OUTCOMES: Of 82 students who participated in the curriculum, 68 completed a curricular evaluation, and 62 consented to have their OSCE performance evaluated for research. Mean overall OSCE checklist performance evaluating students' patient-centered communication skills, harm reduction skills, and discharge planning and counseling was 14.3/16 (89.6%; standard deviation 9.8%). Students reported it was valuable to focus on structural factors affecting care within the simulated clinical encounter by using the structural competency framework. NEXT STEPS: To the authors' knowledge, this is the first OSCE for medical students designed to deepen their understanding of structural competency by embedding the experience into an existing course using the framework. Future work should explore how this curriculum affects students' attitudes toward structurally vulnerable patients. With structural competency as an LCME requirement, the use of OSCEs may give educators a means to teach and assess fundamental concepts.

The Kaposi's sarcoma-associated herpesvirus G protein-coupled receptor as a therapeutic target for the treatment of Kaposi's sarcoma.

The Kaposi's sarcoma-associated herpesvirus (KSHV) encodes a G protein-coupled receptor (vGPCR) that has been implicated in the initiation of Kaposi's sarcoma, identifying vGPCR as an attractive target for preventing Kaposi's sarcoma. However, as only a fraction of cells in advanced Kaposi's sarcoma lesions express vGPCR, it is unclear whether this unique viral oncogene contributes to Kaposi's sarcoma progression. We therefore set out to determine whether the few cells that express vGPCR in established tumors represent an appropriate therapeutic target for the treatment of patients with preexisting Kaposi's sarcoma. To this end, we generated endothelial cell lines stably expressing vGPCR or key KSHV latently expressed proteins (vCyclin, vFlip, and LANA1). The endothelial cell line expressing vGPCR was rendered sensitive to treatment with the nucleoside analogue ganciclovir by using a bicistronic construct coexpressing the herpes simplex virus 1 thymidine kinase. S.c. injection into nude mice with mixed-cell populations formed tumors that approximate the ratio of vGPCR-expressing and KSHV latent gene-expressing cells. These mice were then treated with ganciclovir to specifically target only the vGPCR-expressing cells. Surprisingly, despite the expression of KSHV latent genes in the vast majority of tumor cells, specifically targeting only the few vGPCR-expressing cells in established tumors resulted in tumor regression. Moreover, we observed an increase in apoptosis of latent gene-expressing cells after the pharmacologic deletion of the vGPCR-expressing cells. These findings indicate that vGPCR may play a key role in Kaposi's sarcoma progression and provide experimental justification for developing molecular-based therapies specifically targeting vGPCR and its effectors for the treatment of Kaposi's sarcoma patients.

The small GTPase Rac1 links the Kaposi sarcoma-associated herpesvirus vGPCR to cytokine secretion and paracrine neoplasia.

Kaposi sarcoma (KS) is a multifocal angioproliferative neoplasm strictly dependent on angiogenic growth factors and cytokines and invariably associated with infection by the Kaposi sarcoma-associated herpesvirus (KSHV or HHV8). A G protein-coupled receptor encoded by KSHV (vGPCR) is able to initiate KS-like tumors when targeted to the vascular endothelium of mice. Analogous to human KS, vGPCR sarcomagenesis involves the paracrine secretion of angiogenic growth factors and proinflammatory molecules from vGPCR-expressing cells. Here we demonstrate that vGPCR up-regulates expression and secretion of critical KS cytokines by stimulating key transcription factors, including nuclear factor-kappaB (NF-kappaB), activator protein-1 (AP-1), and nuclear factor of activated T cells (NFAT), through the activation of the small G protein Rac1. Inhibition of Rac1 blocked vGPCR-induced transcription and secretion of KS cytokines, including interleukin-6 (IL-6), IL-8, and growth-regulated oncogene alpha (GROalpha), in vitro and reduced vGPCR tumorigenesis in vivo. Moreover, endothelial-specific infection with the constitutively active Rac1QL induced vascular lesions in mice that were remarkably similar to early vGPCR experimental lesions. These results identify Rac1 as a key mediator of vGPCR paracrine neoplasia, suggesting that this small G protein and its downstream effectors may represent suitable therapeutic targets for the treatment of KS.