Lysophosphatidic Acid Receptor 4 Research Articles

Abstract 2979: Pancreatic cancer cells upregulate LPAR4 in response to isolation stress to create a fibronectin-rich extracellular matrix niche and promote tumor initiation

Abstract Tumor initiation is an inefficient process in which tumor cells must develop cell-autonomous mechanisms to survive harsh microenvironments, establish colonies, and thereby overcome “isolation stress.” We report that pancreatic cancer cells transiently upregulate lysophosphatidic acid receptor 4 (LPAR4), a G-protein coupled receptor, in response to microenvironmental stress or chemotherapy, which promotes stress tolerance, drug resistance, and tumor initiation. Even without exogenous LPA, LPAR4 drives the expression of a subset of extracellular matrix (ECM) genes via an AKT/CREB axis, including fibronectin and versican, which are established drivers of cancer stemness. The upregulation of fibronectin is indispensable for LPAR4-induced tumor initiation in vivo and anchorage-independent growth in vitro. Furthermore, the ligation of this fibronectin-containing ECM created by LPAR4-positive cells via integrins α5β1 or αvβ3 can transfer cancer stemness and stress tolerance to LPAR4-negative cells by activating Yes-associated protein 1 (YAP). Our findings reveal that in response to isolation stress, pancreatic tumor cells that upregulate LPAR4 can autonomously generate a fibronectin-enriched ECM niche and thereby initiate tumor formation. Citation Format: Chengsheng Wu, Taha Rakhshandehroo, Hiromi I. Wettersten, Alejandro Campos, Tami Von Schalscha, Shashi Jain, Ziqi Yu, Jiali Tan, Evangeline Mose, Betzaira G. Childers, Andrew M. Lowy, Sara M. Weis, David A. Cheresh. Pancreatic cancer cells upregulate LPAR4 in response to isolation stress to create a fibronectin-rich extracellular matrix niche and promote tumor initiation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2979.

Upregulation of fibronectin and its integrin receptors - an adaptation to isolation stress that facilitates tumor initiation.

Tumor initiation at either primary or metastatic sites is an inefficient process in which tumor cells must fulfill a series of conditions. One critical condition involves the ability of individual tumor-initiating cells to overcome 'isolation stress', enabling them to survive within harsh isolating microenvironments that can feature nutrient stress, hypoxia, oxidative stress and the absence of a proper extracellular matrix (ECM). In response to isolation stress, tumor cells can exploit various adaptive strategies to develop stress tolerance and gain stemness features. In this Opinion, we discuss how strategies such as the induction of certain cell surface receptors and deposition of ECM proteins enable tumor cells to endure isolation stress, thereby gaining tumor-initiating potential. As examples, we highlight recent findings from our group demonstrating how exposure of tumor cells to isolation stress upregulates the G-protein-coupled receptor lysophosphatidic acid receptor 4 (LPAR4), its downstream target fibronectin and two fibronectin-binding integrins, α5β1 and αvβ3. These responses create a fibronectin-rich niche for tumor cells, ultimately driving stress tolerance, cancer stemness and tumor initiation. We suggest that approaches to prevent cancer cells from adapting to stress by suppressing LPAR4 induction, blocking its downstream signaling or disrupting fibronectin-integrin interactions hold promise as potential strategies for cancer treatment.

SOX17-mediated LPAR4 expression plays a pivotal role in cardiac development and regeneration after myocardial infarction

Lysophosphatidic acid receptor 4 (LPAR4) exhibits transient expression at the cardiac progenitor stage during pluripotent stem cell (PSC)-derived cardiac differentiation. Using RNA sequencing, promoter analyses, and a loss-of-function study in human PSCs, we discovered that SRY-box transcription factor 17 (SOX17) is an essential upstream factor of LPAR4 during cardiac differentiation. We conducted mouse embryo analyses to further verify our human PSC in vitro findings and confirmed the transient and sequential expression of SOX17 and LPAR4 during in vivo cardiac development. In an adult bone marrow transplantation model using LPAR4 promoter-driven GFP cells, we observed two LPAR4+ cell types in the heart following myocardial infarction (MI). Cardiac differentiation potential was shown in heart-resident LPAR4+ cells, which are SOX17+, but not bone marrow-derived infiltrated LPAR4+ cells. Furthermore, we tested various strategies to enhance cardiac repair through the regulation of downstream signals of LPAR4. During the early stages following MI, the downstream inhibition of LPAR4 by a p38 mitogen-activated protein kinase (p38 MAPK) blocker improved cardiac function and reduced fibrotic scarring compared to that observed following LPAR4 stimulation. These findings improve our understanding of heart development and suggest novel therapeutic strategies that enhance repair and regeneration after injury by modulating LPAR4 signaling.

Pancreatic cancer cells upregulate LPAR4 in response to isolation stress to promote an ECM-enriched niche and support tumour initiation.

Defining drivers of tumour initiation can provide opportunities to control cancer progression. Here we report that lysophosphatidic acid receptor 4 (LPAR4) becomes transiently upregulated on pancreatic cancer cells exposed to environmental stress or chemotherapy where it promotes stress tolerance, drug resistance, self-renewal and tumour initiation. Pancreatic cancer cells gain LPAR4 expression in response to stress by downregulating a tumour suppressor, miR-139-5p. Even in the absence of exogenous lysophosphatidic acid, LPAR4-expressing tumour cells display an enrichment of extracellular matrix genes that are established drivers of cancer stemness. Mechanistically, upregulation of fibronectin via an LPAR4/AKT/CREB axis is indispensable for LPAR4-induced tumour initiation and stress tolerance. Moreover, ligation of this fibronectin-containing matrix via integrins α5β1 or αVβ3 can transfer stress tolerance to LPAR4-negative cells. Therefore, stress- or drug-induced LPAR4 enhances cell-autonomous production of a fibronectin-rich extracellular matrix, allowing cells to survive 'isolation stress' and compensate for the absence of stromal-derived factors by creating their own tumour-initiating niche.

Elucidating the binding mechanism of LPA species and analogs in an LPA4 receptor homology model

Lysophosphatidic acid receptor 4 (LPA4) has emerged as a potential therapeutic target for the treatment of a variety of diseases, including cancer and obesity-induced diabetes, but its structure remains to be revealed. In the present work, a homology model of LPA4 was built for studying the binding mechanism of LPA species and analogs. Then five selected LPA species and analogs with structural variations in their phosphate groups, substitutions on the glycerol backbone, and fatty acyl chains were docked into the LPA4 model, followed by molecular dynamics simulations and energy analyses. The computational results revealed that the aliphatic residues located at the vertical cleft of LPA4 may form a hydrophobic environment for the fatty acyl moiety of LPA species and their analogs. Meanwhile, the positively charged residues in the central cavity of LPA4 may form ionic interactions with the negatively charged hydrophilic head group of LPA species and their analogs. In addition, it was noted that a different binding mode of the hydrophilic head group in each species with the central cavity of the LPA4 might lead to a special rearrangement of the fatty acyl moiety. Taken together, these results may facilitate understanding of the activation mechanism of LPA4 and help design selective ligands to modulate its function for therapeutic purposes.

Lysophosphatidic Acid Receptor 4 Is Transiently Expressed during Cardiac Differentiation and Critical for Repair of the Damaged Heart

Efficient differentiation of pluripotent stem cells (PSCs) into cardiac cells is essential for the development of new therapeutic modalities to repair damaged heart tissue. We identified a novel cell surface marker, the G protein-coupled receptor lysophosphatidic acid receptor 4 (LPAR4), specific to cardiac progenitor cells (CPCs) and determined its functional significance and therapeutic potential. During in vitro differentiation of mouse and human PSCs toward cardiac lineage, LPAR4 expression peaked after 3−7 days of differentiation in cardiac progenitors and then declined. In vivo, LPAR4 was specifically expressed in the early stage of embryonal heart development, and as development progressed, LPAR4 expression decreased and was non-specifically distributed. We identified the effective agonist octadecenyl phosphate and a p38 MAPK blocker as the downstream signal blocker. Sequential stimulation and inhibition of LPAR4 using these agents enhanced the in vitro efficiency of cardiac differentiation from mouse and human PSCs. Importantly, in vivo, this sequential stimulation and inhibition of LPAR4 reduced the infarct size and rescued heart dysfunction in mice. In conclusion, LPAR4 is a novel CPC marker transiently expressed only in heart during embryo development. Modulation of LPAR4-positive cells may be a promising strategy for repairing myocardium after myocardial infarction.

Abstract 264: Upstream and Downstream Regulators of Lysophosphatidic Acid Receptor 4 are Critical for Cardiac Differentiation and Repair

The therapeutic application of cell therapy to repair the damaged heart requires a comprehensive understanding of the process of cardiac differentiation of stem cells. We discovered a cardiac-specific marker, lysophosphatidic acid receptor 4 (LPAR4), which is G protein-coupled receptor (GPCR) and demonstrated its functional significance during cardiac differentiation. We screened GPCR expressing on mouse cardiac progenitor cells at differentiation day 3 compared to mouse undifferentiated pluripotent stem cells (PSCs). Among candidates, we identified LPAR4. We have found that in both mouse and human PSCs, LPAR4 has a transient expression pattern during cardiac differentiation. During in vitro differentiation of mouse and human PSCs toward cardiomyocytes, LPAR4 expression peaked for 3-5 days and then and declined immediately. Treatment with ODP (LPAR4 specific agonist) followed by p38MAPK blocker (SB203580) in the cardiac differentiation protocol significantly increased cardiac differentiation efficiency. Then we performed RNA sequencing to find transcription factors that regulate LPAR4. We screened 2-fold up-regulated transcription factors that related to cardiac differentiation during human iPSCs toward cardiomyocytes. The expression of LPAR4 is regulated by SOX17 expression, demonstrating that SOX17 is an upstream regulator of LPAR4. During cardiac differentiation, when knocking down SOX17 by siRNA, the expression of LPAR4 decreased as the expression of SOX17 mRNA decreased, resulting in no progression of cardiac differentiation. Besides, cardiac differentiation did not progress when SOX17 was overexpressed. SOX17 plays a role early in cardiac differentiation and that the expression should be reduced. However, it is assumed that sox17 lentivirus was gene-integrated and continued expression without decreasing expression. SOX17 overexpression needs further study. In conclusion, we demonstrated that LPAR4 is a novel cardiac progenitor cell marker and modulation of the upstream and downstream regulators shown functional significance during cardiac differentiation. Furthermore, our findings provide new insight into cell-free cardiac repair by the modulation of LPAR4 positive cells in the heart. Funding Source: This study was supported by "Strategic Center of Cell and Bio Therapy for Heart, Diabetes & Cancer" (HI17C2085) through the Korea Health Industry Development Institute, funded by the Ministry of Health & Welfare, Republic of Korea.

Lysophosphatidic acid receptor 4 regulates osteogenic and adipogenic differentiation of progenitor cells via inactivation of RhoA/ROCK1/β-catenin signaling.

Recent evidence revealed that lysophosphatidic acid receptor 4 (LPAR4) plays a role in osteogenesis and bone remodeling in mice. However, the molecular mechanism by which LPAR4 controls osteogenic and adipogenic differentiation of mesenchymal progenitor cells remains pending. In the current study, our data showed that Lpar4 was expressed in bone and adipose tissue and the expression increased during osteoblast and adipocyte differentiation. Lpar4 overexpression in stromal ST2 and preosteoblastic MC3T3-E1 cells inhibited osteogenic differentiation. By contrast, Lpar4 overexpression in ST2 and mesenchymal C3H10T1/2 cells enhanced adipogenic differentiation. Conversely, depletion of endogenous Lpar4 in the progenitor cells induced osteogenic differentiation and inhibited adipogenic differentiation. Furthermore, enhanced osteoblast differentiation and alleviated fat accumulation were observed in marrow of mice after in vivo transfection of Lpar4 siRNA. Mechanism investigations revealed that LPAR4 inhibited the activation of ras homolog family member A (RhoA)/Rho-associated kinases 1 (ROCK1) and canonical Wnt signal pathways. ROCK1 was shown to be able to activate Wnt/β-catenin pathway. We further demonstrated that the overexpression of ROCK1 stimulated osteogenic differentiation and restrained adipogenic differentiation from stromal progenitor cells. Moreover, overexpression of ROCK1 attenuated the inhibition of osteogenic differentiation by LPAR4. The current study has provided evidences demonstrating that RhoA/ROCK1 activates β-catenin signaling to promote osteogenic differentiation and conversely restrain adipogenic differentiation. The inactivation of RhoA/ROCK1/β-catenin signaling is involved in LPAR4 regulation of the directional differentiation of marrow stromal progenitor cells.

P3479Sequential stimulation and inhibition of lysophosphatidic acid receptor 4 are critical for cardiac differentiation and repair

Abstract Background The clinical application of cell therapy to repair the damaged heart needs to understand the precise differentiation process of stem cells and the characteristics of cardiac progenitor cells. Purpose We examined the cardiac-specific markers that expressed on the cell surface and determined their functional significance during cardiac differentiation. Methods and results We screened cell-surface expressing proteins on cardiac progenitor cells at differentiation day 3 compared to undifferentiated pluripotent stem cells (PSCs). Among candidates, we identified lysophosphatidic acid receptor 4 (LPAR4) that is a G protein-coupled receptor. During in vitro differentiation of mouse PSCs toward cardiac cells, LPAR4 expression peaked for 3–5 days and then and declined immediately. Also in vivo, LPAR4 was specifically expressed in the early stage of heart development in embryos and disappeared completely in adults, suggesting that stimulatory signal of LPAR4 at an early stage should be shut off for further progression of differentiation. We next have identified the LPAR4 downstream signaling molecule, p38MAPK, by comparing PSCs and LPAR4 knockdown PSCs. In both mouse and human PSCs, ODP (LPAR4 specific agonist) followed by p38MAPK blocker (SB203580) treatment significantly increased cardiac differentiation efficiency. Furthermore, we investigated whether LPAR4 is the maker for adult cardiac progenitor cells. We found that LPAR4-positive cells were rarely present in normal adult mouse hearts, but LPAR4-positive cells were increased when the heart was damaged. LPAR4-positive cells from adult hearts differentiated into cardiomyocytes. After myocardial infarction (MI), the sequential stimulation and inhibition of LPAR4 with ODP and p38MAPK blocker resulted in the reduction of infarct size and improvement of left ventricular dysfunction. Conclusion We demonstrated that LPAR4 is a cardiac progenitor-specific marker and its functional significance during cardiac differentiation and regeneration. Our findings provide a new insight in cell-free cardiac repair by the modulation of progenitor-specific downstream signaling. Acknowledgement/Funding Grants from “Strategic Center of Cell and Bio Therapy” (grant number: HI17C2085) and “Korea Research-Driven Hospital” (HI14C1277)

LPA4-Mediated Vascular Network Formation Increases the Efficacy of Anti-PD-1 Therapy against Brain Tumors.

: The structure and function of tumor blood vessels profoundly affects the tumor microenvironment. Signals mediated through the lysophosphatidic acid receptor 4 (LPA4) promote vascular network formation to restore normal vascular barrier function in subcutaneous tumors and thus improve drug delivery. However, the characteristics of the vasculature vary by organ and tumor types, and how drug delivery and leukocyte trafficking are affected by modification of vascular function by LPA in different cancers is unclear. Here, we show that LPA4 activation promotes the formation of fine vascular structures in brain tumors. RhoA/ROCK signaling contributed to LPA-induced endothelial cell-cell adhesion, and RhoA/ROCK activity following LPA4 stimulation regulated expression of VCAM-1. This resulted in increased lymphocyte infiltration into the tumor. LPA improved delivery of exogenous IgG into brain tumors and enhanced the anticancer effect of anti-programmed cell death-1 antibody therapy. These results indicate the effects of LPA on vascular structure and function apply not only to chemotherapy but also to immunotherapy. SIGNIFICANCE: These findings demonstrate that lysophosphatidic acid, a lipid mediator, promotes development of a fine capillary network in brain tumors by inducing tightening of endothelial cell-to-cell adhesion, facilitating improved drug delivery, and lymphocyte penetration.

The Hypoxic Tumor Microenvironment Promotes Invadopodia Formation and Metastasis through LPA1 Receptor and EGFR Cooperation.

Hypoxia, a common feature of solid tumors, has been critically involved in cell invasion and metastasis, but the underlying mechanisms remain poorly understood. Previously, it has been observed that the lysophosphatidic acid receptor 4 (LPA4) signaling axis mediates production of the degradative subcellular structures invadopodia, which are known to be required for metastasis. Here, it is demonstrated that LPA1 (LPAR1) is a common and major receptor used for hypoxia-induced invadopodia production in various cancer cell lines. The widespread use of LPA1 was not due to increased LPA1 expression but rather relied on Src-mediated cross-talk with EGFR. LPA1-mediated phosphorylation of Y845-EGFR under hypoxia led to PI3K/Akt activation, an event that increases the ability of cells to produce invadopodia. Moreover, phospho-Y845-EGFR was upregulated in hypoxic zones of tumors and a combination of EGFR and LPA1 inhibition synergistically suppressed metastasis in vivo Implications: This study uncovers an LPA1-EGFR signaling axis that is used for cell invasion in hypoxia and suggests a potential target to impede cancer metastasis. Mol Cancer Res; 16(10); 1601-13. ©2018 AACR.

The LPA-LPA4 axis is required for establishment of bipolar morphology and radial migration of newborn cortical neurons.

Newborn neurons in the developing neocortex undergo radial migration, a process that is coupled with their precise passage from multipolar to bipolar shape. The cell-extrinsic signals that govern this transition are, however, poorly understood. Here, we find that lysophosphatidic acid (LPA) signaling contributes to the establishment of a bipolar shape in mouse migratory neurons through LPA receptor 4 (LPA4). LPA4 is robustly expressed in migratory neurons. LPA4-depleted neurons show impaired multipolar-to-bipolar transition and become arrested in their migration. Further, LPA4-mediated LPA signaling promotes formation of the pia-directed process in primary neurons overlaid on neocortical slices. In addition, LPA4 depletion is coupled with altered actin organization as well as with destabilization of the F-actin-binding protein filamin A (FlnA). Finally, overexpression of FlnA rescues the morphology and migration defects of LPA4-depleted neurons. Thus, the LPA-LPA4 axis regulates bipolar morphogenesis and radial migration of newborn cortical neurons via remodeling of the actin cytoskeleton.

Abstract 382: Mice with Endothelial-Targeted Inactivation of PPAP2B (Lipid Phosphate Phosphatase 3) Display Enhanced Vascular Inflammation and Permeability

Meta-analysis of data from a series of genome-wide association studies (GWAS) revealed a striking association between the PPAP2B loci and coronary artery disease. The PPAP2B gene encodes for the lipid phosphate phosphatase 3 (LPP3) integral membrane enzyme, that dephosphorylates lysophosphatidic acid (LPA), sphingosine 1-phosphate (S1P) and related bioactive lipids. While emerging evidence suggests a role for both LPA and S1P in experimental models of atherosclerosis, essentially nothing is understood about the pathophysiologic role of LPP3, largely due to the fact that genetic inactivation results embryonic lethality. We report that constitutive inactivation of LPP3 in vascular endothelial cells accomplished by breeding mice with floxed Ppap2b to mice expressing Cre recombinase under control of the Tie1 promoter results in embryonic lethality, indicating that dysregulation of LPP3-dependent vascular endothelial cell function likely underlies the developmental phenotype observed in Ppap2b -null embryos. Using an estrogen inducible Cre transgene under control of the Tie1 promoter, we have inactivated Ppap2b expression in endothelial cells in adult mice and confirmed the lack of vascular endothelial LPP3 by immunologic and biochemical approaches. The absence of vascular endothelial LPP3 results in a 2.2±0.5 fold increase in basal vascular permeability, as assessed by Evans blue dye extravasation in lung tissue. The permeability difference is exaggerated following an inflammatory challenge (LPS; 2 mg/kg), and LPS-induced expression of plasma inflammatory markers IL6 and KC were 3.3±0.5 and 1.9±0.6 fold higher in mice lacking endothelial LPP3. LPS-enhanced permeability in the absence of LPP3 was attenuated by administration of an LPA receptor antagonist. Mice lacking LPA receptors 1 and 2 (LPA1, LPA2) or LPA receptor 4 (LPA4) were protected from LPS-mediated permeability. These results demonstrate a fundamental role for LPP3, possibility via modulation of local LPA levels and signaling through LPA1, LPA2, and LPA4 receptors, in maintaining the integrity of the vascular endothelium.