EMSY inhibits homologous recombination repair and the interferon response, promoting lung cancer immune evasion.

Non-small cell lung cancers (NSCLCs) harboring KEAP1 mutations are often resistant to immunotherapy. Here, we show that KEAP1 targets EMSY for ubiquitin-mediated degradation to regulate homologous recombination repair (HRR) and anti-tumor immunity. Loss of KEAP1 in NSCLC induces stabilization of EMSY, producing a BRCAness phenotype, i.e., HRR defects and sensitivity to PARP inhibitors. Defective HRR contributes to a high tumor mutational burden that, in turn, is expected to prompt an innate immune response. Notably, EMSY accumulation suppresses the type I interferon response and impairs innate immune signaling, fostering cancer immune evasion. Activation of the type I interferon response in the tumor microenvironment using a STING agonist results in the engagement of innate and adaptive immune signaling and impairs the growth of KEAP1-mutant tumors. Our results suggest that targeting PARP and STING pathways, individually or in combination, represents a therapeutic strategy in NSCLC patients harboring alterations in KEAP1.

The F-Box Domain-Dependent Activity of EMI1 Regulates PARPi Sensitivity in Triple-Negative Breast Cancers.

The BRCA1-BRCA2-RAD51 axis is essential for homologous recombination repair (HRR) and is frequently disrupted in breast cancers. PARP inhibitors (PARPis) are used clinically to treat BRCA-mutated breast tumors. Using a genetic screen, we identified EMI1 as a modulator of PARPi sensitivity in triple-negative breast cancer (TNBC) cells. This function requires the F-box domain of EMI1, through which EMI1 assembles a canonical SCF ubiquitin ligase complex that constitutively targets RAD51 for degradation. In response to genotoxic stress, CHK1-mediated phosphorylation of RAD51 counteracts EMI1-dependent degradation by enhancing RAD51's affinity for BRCA2, leading to RAD51 accumulation. Inhibition of RAD51 degradation restores HRR in BRCA1-depleted cells. Human breast cancer samples display an inverse correlation between EMI1 and RAD51 protein levels. A subset of BRCA1-deficient TNBC cells develop resistance to PARPi by downregulating EMI1 and restoring RAD51-dependent HRR. Notably, reconstitution of EMI1 expression reestablishes PARPi sensitivity both in cellular systems and in an orthotopic mouse model.

Cytoskeletal association of ATP citrate lyase controls the mechanodynamics of macropinocytosis.

Macropinocytosis is an actin-dependent mode of nonselective endocytosis that mediates the uptake of extracellular fluid-phase cargoes. It is now well recognized that tumor cells exploit macropinocytosis to internalize macromolecules that can be catabolized and used to support cell growth and proliferation under nutrient-limiting conditions. Therefore, the identification of molecular mechanisms that control macropinocytosis is fundamental to the understanding of the metabolic adaptive landscape of tumor cells. Here, we report that the acetyl-CoA-producing enzyme, ATP citrate lyase (ACLY), is a key regulator of macropinocytosis and describes a heretofore-unappreciated association of ACLY with the actin cytoskeleton. The cytoskeletal tethering of ACLY is required for the spatially defined acetylation of heterodimeric actin capping protein, which we identify as an essential mediator of the actin remodeling events that drive membrane ruffling and macropinocytosis. Furthermore, we identify a requirement for mitochondrial-derived citrate, an ACLY substrate, for macropinocytosis, and show that mitochondria traffic to cell periphery regions juxtaposed to plasma membrane ruffles. Collectively, these findings establish a mode of metabolite compartmentalization that supports the spatiotemporal modulation of membrane-cytoskeletal interactions required for macropinocytosis by coupling regional acetyl-CoA availability with dynamic protein acetylation.

Metabolic reprogramming of tumor-associated macrophages by collagen turnover promotes fibrosis in pancreatic cancer.

A hallmark of pancreatic tumors is their highly desmoplastic stroma composed of fibroblasts, immune cells, and a dense network of collagen fibers. Tumor-associated macrophages are one of the most abundant immune cell populations in the pancreatic tumor stroma. Their protumorigenic function has been attributed predominantly to their capacity to promote immune evasion and metastasis. Tumor-assoc iated macrophages are also well known for their role in the remodeling of the stroma via collagen production and degradation, with the latter being mediated by mannose receptor (MRC1)-dependent endocytosis of collagen. Here we show that MRC1-mediated collagen internalization and subsequent lysosomal degradation by macrophages harboring a tumor-associated phenotype are accompanied by the accumulation of collagen-derived intracellular free amino acids and increased arginine biosynthesis. The resulting increase in intracellular arginine levels leads to the up-regulation of inducible nitric oxide synthase and the production of reactive nitrogen species. Furthermore, reactive nitrogen species derived from internalized and degraded collagen promotes a profibrotic phenotype in pancreatic stellate cells resulting in enhanced intratumoral collagen deposition. Overall, our findings identify a role for extracellular matrix remodeling in the functional modulation of tumor-associated macrophages via metabolic rewiring.

Loss of caspase-2 augments lymphomagenesis and enhances genomic instability in Atm-deficient mice.

Caspase-2, the most evolutionarily conserved member of the caspase family, has been shown to be involved in apoptosis induced by various stimuli. Our recent work indicates that caspase-2 has putative functions in tumor suppression and protection against cellular stress. As such, the loss of caspase-2 enhances lymphomagenesis in Eµ-Myc transgenic mice, and caspase-2 KO (Casp2(-/-)) mice show characteristics of premature aging. However, the extent and specificity of caspase-2 function in tumor suppression is currently unclear. To further investigate this, ataxia telangiectasia mutated KO (Atm(-/-)) mice, which develop spontaneous thymic lymphomas, were used to generate Atm(-/-)Casp2(-/-) mice. Initial characterization revealed that caspase-2 deficiency enhanced growth retardation and caused synthetic perinatal lethality in Atm(-/-) mice. A comparison of tumor susceptibility demonstrated that Atm(-/-)Casp2(-/-) mice developed tumors with a dramatically increased incidence compared with Atm(-/-) mice. Atm(-/-)Casp2(-/-) tumor cells displayed an increased proliferative capacity and extensive aneuploidy that coincided with elevated oxidative damage. Furthermore, splenic and thymic T cells derived from premalignant Atm(-/-)Casp2(-/-) mice also showed increased levels of aneuploidy. These observations suggest that the tumor suppressor activity of caspase-2 is linked to its function in the maintenance of genomic stability and suppression of oxidative damage. Given that ATM and caspase-2 are important components of the DNA damage and antioxidant defense systems, which are essential for the maintenance of genomic stability, these proteins may synergistically function in tumor suppression by regulating these processes.

A Multivalent Peptoid Conjugate Modulates Androgen Receptor Transcriptional Activity to Inhibit Therapy-resistant Prostate Cancer.

Prostate cancers adapt to androgen receptor (AR) pathway inhibitors and progress to castration resistance due to ongoing AR expression and function. To counter this, we developed a new approach to modulate the AR and inhibit castration-resistant prostate cancer (CRPC) using multivalent peptoid conjugates (MPC) that contain multiple copies of the AR-targeting ligand ethisterone attached to a peptidomimetic scaffold. Here, we investigated the antitumor effects of compound MPC309, a trivalent display of ethisterone conjugated to a peptoid oligomer backbone that binds to the AR with nanomolar affinity. MPC309 exhibited potent antiproliferative effects on various enzalutamide-resistant prostate cancer models, including those with AR splice variants, ligand-binding mutations, and noncanonical AR gene expression programs, as well as mouse prostate organoids harboring defined genetic alterations that mimic lethal human prostate cancer subtypes. MPC309 is taken up by cells through macropinocytosis, an endocytic process more prevalent in cancer cells than in normal ones, thus providing an opportunity to target tumors selectively. MPC309 triggers a distinct AR transcriptome compared with DHT and enzalutamide, a clinically used antiandrogen. Specifically, MPC309 enhances the expression of differentiation genes while reducing the expression of genes needed for cell division and metabolism. Mechanistically, MPC309 increases AR chromatin occupancy and alters AR interactions with coregulatory proteins in a pattern distinct from DHT. In xenograft studies, MPC309 produced significantly greater tumor suppression than enzalutamide. Altogether, MPC309 represents a promising new AR modulator that can combat resistant disease by promoting an AR antiproliferative gene expression program.

Exploiting cancer's drinking problem: regulation and therapeutic potential of macropinocytosis.

Macropinocytosis, an evolutionarily conserved endocytic mechanism that mediates non-specific fluid-phase uptake, is potently upregulated by various oncogenic pathways. It is now well appreciated that high macropinocytic activity is a hallmark of many human tumors, which use this adaptation to scavenge extracellular nutrients for fueling cell growth. In the context of the nutrient-scarce tumor microenvironment, this process provides tumor cells with metabolic flexibility. However, dependence on this scavenging mechanism also illuminates a potential metabolic vulnerability. As such, there is a great deal of interest in understanding the molecular underpinnings of macropinocytosis. In this review, we will discuss the most recent advances in characterizing macropinocytosis: the pathways that regulate it, its contribution to the metabolic fitness of cancer cells, and its therapeutic potential.