Related Experiment Video
Updated: Aug 6, 2026
07:41
A Kinetic Fluorescence-based Ca2+ Mobilization Assay to Identify G Protein-coupled Receptor Agonists, Antagonists, and Allosteric Modulators
Published on: February 20, 2018
Mitogenic signaling by lysophosphatidic acid (LPA) involves Galpha12
V Radhika1, Ji Hee Ha, Muralidharan Jayaraman
1Fels Institute for Cancer Research and Molecular Biology, Temple University School Medicine, Philadelphia, PA 19140, USA.
Oncogene
|April 28, 2005
Summary
Lysophosphatidic acid (LPA) activates Galpha12 in NIH3T3 cells, driving proliferation and oncogenic transformation. This study reveals LPA-receptor signaling as a key pathway in serum-dependent neoplastic cell growth.
Area of Science:
- Molecular Biology
- Cell Biology
- Oncology
Background:
- Lysophosphatidic acid (LPA) is a serum-derived ligand that activates G protein-coupled receptors (GPCRs), including those coupled to G(i), G(q), and G12/13.
- Overexpression of Galpha12 (Galpha12WT) induces serum-dependent oncogenic transformation in NIH3T3 cells.
- LPA's potent growth-stimulating activity suggests a role in serum-mediated neoplastic transformation.
Purpose of the Study:
- To investigate the hypothesis that serum-dependent neoplastic transformation of Galpha12WT-NIH3T3 cells is mediated by LPA-receptor (LPAR) stimulation.
- To elucidate the signaling pathway linking LPAR, Galpha12, and downstream effectors in cell proliferation.
Main Methods:
- Guanine nucleotide exchange assay and GST-TPR binding assay to assess Galpha12 activation by LPA.
- Assays for JNK activation, DNA synthesis, and cell proliferation in response to LPA.
- Treatment with suramin, a receptor-uncoupling agent, to evaluate the role of cell surface LPAR signaling.
Main Results:
- LPA treatment (2 μM) activated Galpha12 in Galpha12WT-NIH3T3 cells.
- LPA stimulated JNK activation, DNA synthesis, and proliferation, substituting for serum.
- LPA-mediated proliferation involved Galpha12, not Galpha13, and was inhibited by suramin, indicating LPAR-Galpha12 signal coupling.
Conclusions:
- LPA signaling through LPARs and Galpha12 is a critical mediator of serum-dependent neoplastic transformation in NIH3T3 cells.
- Understanding the LPAR-Galpha12 signaling axis provides insights into oncogenic pathways.
- This mechanistic understanding may identify novel therapeutic targets for cancer treatment.
Related Concept Videos
01:19Interactions Between Signaling Pathways
Signaling cascades usually lack linearity. Multiple pathways interact and regulate one another, allowing cells to integrate and respond to diverse environmental stimuli.
Convergence and divergence, and cross-talk between signaling pathways
Two distinct signaling pathways can converge on a single functional unit, which may either be a single protein or a complex of proteins. The response is either functionally distinct or synergistic between the two pathways but different from the response...
Convergence and divergence, and cross-talk between signaling pathways
Two distinct signaling pathways can converge on a single functional unit, which may either be a single protein or a complex of proteins. The response is either functionally distinct or synergistic between the two pathways but different from the response...
01:15Amplifying Signals via Second Messengers
Many receptor binding ligands are hydrophilic; they do not cross the cell membrane but bind to cell-surface receptors. Thus, their message must be relayed by second messengers present in the cell cytoplasm. There are several second messenger pathways, each with its own way of relaying information. For example, the G protein-coupled receptors can activate both phosphoinositol and cyclic AMP (cAMP) second messenger pathways. The phosphoinositol pathway is active when the receptor induces...
01:22Amplifying Signals via Enzymatic Cascade
When a ligand binds to a cell-surface receptor, the receptor's intracellular domain changes shape, which may either activate its enzyme function or allow its binding to other molecules. The initial signal is amplified by most signal transduction pathways. This means that a single ligand molecule can activate multiple molecules of a downstream target. Proteins that relay a signal are most commonly phosphorylated at one or more sites, activating or inactivating the protein. Kinases catalyze the...
01:07MAPK Signaling Cascades
Mitogen-activated protein kinase, or MAPK pathway, activates three sequential kinases to regulate cellular responses such as proliferation, differentiation, survival, and apoptosis. The canonical MAPK pathway starts with a mitogen or growth factor binding to an RTK. The activated RTKs stimulate Ras, which recruits Raf or MAP3 Kinase (MAPKKK), the first kinase of the MAPK signaling cascade. Raf further phosphorylates and activates MEK or MAP2 Kinases (MAPKK), which in turn phosphorylates MAP...
01:22Activation and Inactivation of G Proteins
Heterotrimeric G proteins are guanine nucleotide-binding proteins. As the name suggests, heterotrimeric G proteins are composed of three subunits: alpha, beta, and gamma. They remain GDP-bound or GTP-bound inside the cells and switch between inactive/active states. The Gα subunit possesses the nucleotide-binding pocket that binds guanine nucleotides and switches between GDP or GTP-bound states. In contrast, the Gꞵ and Gγ subunits are always bound together with high affinity and are together...
01:11IP3/DAG Signaling Pathway
Membrane lipids such as phosphatidylinositol (PI) are precursors for several membrane-bound and soluble second messengers. Specific kinases phosphorylate PI and produce phosphorylated inositol phospholipids. One such inositol phospholipids are the phosphatidylinositol-4,5 bisphosphate [PI(4,5)P2], present in the inner half of the lipid bilayer. Upon ligand binding, GPCR stimulates Gq proteins to turn on phospholipase Cꞵ. Activated phospholipase Cꞵ cleaves PI(4,5)P2 and produces two-second...