RGS17 Human

What is RGS17 and what is its basic molecular structure?

RGS17 is a protein encoded by the RGS17 gene located on chromosome 6q in humans. It belongs to the regulator of G-protein signaling family and contains several key structural elements:

• A conserved 120 amino acid RGS domain that is characteristic of the RGS family

• A cysteine-rich region that plays important roles in protein function

• Two zinc-binding motifs in the N-terminus that coordinate zinc binding to four cysteine residues in a tetrahedral conformation

• Two SUMO (small ubiquitin-like modifiers)-interacting motifs and one sumoylation consensus site

RGS17 is also known by alternative names including RGS-17, RGSZ2, and hRGS17 .

How does RGS17 regulate G-protein signaling pathways?

RGS17 functions as a negative regulator of G protein-coupled receptor (GPCR) signaling through the following mechanisms:

• It attenuates signaling by binding to activated, GTP-bound G alpha subunits

• Acts as a GTPase activating protein (GAP), accelerating the conversion of GTP to GDP

• This hydrolysis facilitates the binding of G alpha subunits to G beta/gamma subunit heterodimers

• The resulting inactive G-protein heterotrimers terminate the signal transduction

RGS17 exhibits preferential binding to GNAZ and GNAI2 subunits, accelerating their GTPase activity and influencing their signaling actions. It can modulate Gα i/o and Gα q signaling pathways, but has no activity against Gα s pathways .

What is the tissue distribution of RGS17 expression?

RGS17 expression was initially reported in rat atrial myocytes in 2001, with expression detected in 85-90% of tested atrial myocytes. In humans, RGS17 shows a more widespread distribution:

• Highly expressed in certain regions of the brain

• Detected in lung tissue (with upregulation in lung cancer)

• Present in prostate tissue (with elevated expression in prostate cancer)

• Found in colorectal tissues (with increased expression in colorectal carcinoma)

Interestingly, early studies by Larminie et al. suggested RGS17 was expressed almost exclusively in the brain, but recent research has demonstrated expression in multiple tissue types, particularly in cancer contexts .

How does RGS17 participate in opioid receptor signaling?

RGS17 plays a critical role in the regulation of opioid receptor signaling through several mechanisms:

• Along with RGS4, RGS9, and RGS14, RGS17 terminates signaling by mu opioid receptors

• It contributes to the development of tolerance to opioid analgesic drugs

• RGS17 negatively regulates mu-opioid receptor-mediated activation of G-proteins

• Post-translational modifications of RGS17 act as scaffolds for its function in μ-opioid receptor signaling

• Unlike direct RGS17 interaction with some GPCRs, its interaction with the μ-opioid receptor requires the histidine triad nucleotide-binding protein 1 for recruitment

This role in opioid signaling has significant implications for pain management and addiction research, as it may offer targets for reducing tolerance development .

What is the role of RGS17 in calcium and zinc regulation?

RGS17 exhibits important regulatory functions in cellular metal ion homeostasis:

• RGS17 cocrystallizes with Ca²⁺ bound to conserved positions on its predicted Gα-binding surface

• It has greater than 55-fold higher affinity for Ca²⁺ than for Mg²⁺

• Ca²⁺ promotes interactions between RGS17 and activated Gα and decreases the Km for GTP hydrolysis

• RGS17 functions in the release of zinc, with exposure of its cysteine-rich domain to nitric oxide donors resulting in zinc release

• It is essential for regulation of intracellular zinc stores, as demonstrated by RGS17 knockdown mice exhibiting reduced levels of endogenous zinc release

• Zinc supports the translocation of downstream signaling proteins to the GPCR environment

These interactions with calcium and zinc suggest RGS17 may function as a redox transducer regulated by GPCRs .

How does the cAMP-PKA-CREB pathway interact with RGS17?

RGS17 has been demonstrated to interact with the cyclic AMP-PKA-CREB pathway, particularly in cancer contexts:

• RGS17 is overexpressed in lung and prostate cancers, where it induces cAMP production

• It promotes CREB phosphorylation and CREB-responsive gene expression

• This pathway activation contributes to tumor cell proliferation

• The interaction between RGS17 and the cAMP-PKA-CREB pathway appears to be a key mechanism by which RGS17 exerts its proto-oncogenic effects

Understanding this interaction is crucial for developing targeted therapeutic approaches in cancers with RGS17 overexpression .

What techniques are effective for studying RGS17 protein structure?

The crystal structure of RGS17 has been determined at 1.5 Å resolution, representing the most complete and highest-resolution structure of an RZ subfamily member. Researchers investigating RGS17 structure should consider:

• X-ray crystallography to determine high-resolution structures

• Nuclear Magnetic Resonance (NMR) chemical shift perturbations to confirm binding sites in solution

• Protein structure modeling based on homology with other RGS family members

• Site-directed mutagenesis to test the functional significance of specific residues

• Molecular dynamics simulations to predict protein-protein interactions

These approaches can reveal important insights about RGS17's functional domains and interaction surfaces .

What are effective approaches for modulating RGS17 expression in experimental systems?

Several methods have been successfully employed to alter RGS17 expression for functional studies:

• siRNA-mediated knockdown: Specific siRNAs targeting RGS17 have been used to decrease expression in cultured colorectal carcinoma cells, resulting in decreased cell proliferation rates

• Expression plasmid overexpression: Transfection with RGS17 expression plasmids has been shown to increase proliferation rates in cultured cells

• In vivo knockdown: Depletion of RGS17 in mouse models of colorectal carcinoma has significantly inhibited tumor growth

• CRISPR-Cas9 genome editing: Can be used for complete knockout of RGS17 in cell lines

• Inducible expression systems: Allow for temporal control of RGS17 expression

When designing knockdown experiments, researchers should consider testing multiple siRNA sequences to confirm specificity and rule out off-target effects .

What assays are recommended for measuring RGS17 GAP activity?

Several biochemical and cellular assays can be employed to measure RGS17's GTPase activating protein (GAP) activity:

• Single turnover assays: Can detect GAP activity of recombinant sumoylated RGS17 toward Gα subunits

• GTP hydrolysis assays: To determine the Km for GTP hydrolysis in the presence of RGS17

• Binding affinity measurements: To assess RGS17 binding to both GTP-bound Gα and transition state Gα subunits

• GDP release assays: Sumoylation of RGS17 has been shown to delay GDP release, which can be measured

• Fluorescence-based G protein activation assays: To monitor RGS17 effects on G protein cycling in real time

When conducting these experiments, it's important to consider the effects of calcium, as Ca²⁺ has been shown to promote interactions between RGS17 and activated Gα and decrease the Km for GTP hydrolysis .

What evidence supports RGS17 as a potential oncogene in lung cancer?

Multiple lines of evidence indicate RGS17's role in lung cancer development and progression:

• RGS17 is a putative lung cancer susceptibility gene located within the lung cancer associated locus on chromosome 6q

• It is overexpressed in lung cancer tissues compared to normal lung tissue

• RGS17 induces cAMP production, CREB phosphorylation, and CREB responsive gene expression in lung cancer cells

• Expression of RGS17 is required for maintaining proliferation in lung tumor cell lines

• Targeting RGS17 may represent a promising therapeutic approach for lung cancer

These findings suggest RGS17 functions as an oncogenic driver in lung cancer through specific signaling mechanisms involving the cAMP-PKA-CREB pathway .

How is RGS17 involved in colorectal carcinoma progression?

Studies have demonstrated that RGS17 plays significant roles in colorectal carcinoma:

• RGS17 is upregulated in clinical colorectal carcinoma tissues compared to normal tissues

• It is also overexpressed in cultured colorectal carcinoma cells

• Knockdown of RGS17 by specific siRNA decreases cell proliferation rates

• Overexpression of RGS17 with expression plasmids increases proliferation rates

• In mouse models, depletion of RGS17 significantly inhibits colorectal tumor growth in vivo

• Transwell assays show that RGS17 promotes the ability of colorectal carcinoma cells to migrate and invade

These findings suggest that RGS17 functions as a proto-oncogene in colorectal carcinoma and may serve as a potential therapeutic target .

What are the molecular mechanisms by which RGS17 promotes cancer progression?

RGS17 promotes cancer progression through several molecular mechanisms:

• Activation of the cAMP-PKA-CREB pathway: RGS17 induces cAMP production, CREB phosphorylation, and CREB-responsive gene expression

• Cell proliferation: Expression of RGS17 is required for maintenance of proliferation in lung tumor cell lines

• Migration and invasion: RGS17 promotes the ability of colorectal carcinoma cells to migrate and invade

• Potential gene regulation: Sumoylation of RGS17 may allow it to function in the suppression of tumor-suppressing genes

• Interaction with miRNAs: In non-small cell lung cancer, the circ_0006220/miR-203-3p/RGS17 axis may participate in cancer progression

Understanding these mechanisms provides potential avenues for therapeutic intervention in cancers with RGS17 overexpression .

How do post-translational modifications affect RGS17 function?

RGS17 undergoes several post-translational modifications that significantly impact its function:

• Sumoylation: RGS17 contains two SUMO-interacting motifs and one sumoylation consensus site

• Effects of sumoylation:

  • Sumoylation does not affect RGS17 binding to Gα i

  • Recombinant sumoylated RGS17 has little or no GAP activity to Gα i in single turnover assays

  • Sumoylation does not affect RGS17's affinity for the transition state of Gα subunits

  • Sumoylation delays the release of GDP

  • Sumoylation is a key factor in RGS17 localization to the plasma membrane

These modifications create additional layers of regulation for RGS17 function and may provide opportunities for specific therapeutic targeting .

What is the significance of calcium binding to RGS17?

Calcium binding to RGS17 has several important functional implications:

• RGS17 cocrystallizes with Ca²⁺ bound to conserved positions on the predicted Gα-binding surface

• NMR chemical shift perturbations confirm that Ca²⁺ binds in solution to the same site

• RGS17 has greater than 55-fold higher affinity for Ca²⁺ than for Mg²⁺

• Ca²⁺ promotes interactions between RGS17 and activated Gα

• Ca²⁺ decreases the Km for GTP hydrolysis, potentially by altering the binding mechanism between RGS17 and G proteins

• This suggests that Ca²⁺ positively regulates RGS17's GAP activity

These findings suggest a general mechanism by which increased Ca²⁺ concentration promotes the GAP activity of the RZ subfamily, leading to RZ-mediated inhibition of Ca²⁺ signaling—a potentially important negative feedback mechanism .

What are the emerging therapeutic approaches targeting RGS17?

As RGS17 emerges as a potential therapeutic target, several approaches are being explored:

• High-throughput screening for RGS17 inhibitors: This powerful tool has led to the discovery of several RGS inhibitors

• siRNA-based approaches: Knockdown of RGS17 has shown promise in reducing tumor growth in animal models

• Targeting post-translational modifications: Modulating RGS17 sumoylation could provide a specific approach to alter its function

• Disrupting protein-protein interactions: Compounds that interfere with RGS17 binding to G proteins could modulate its activity

• Exploiting the circ_0006220/miR-203-3p/RGS17 axis: This pathway has been implicated in non-small cell lung cancer progression

The development of specific RGS17 inhibitors appears promising as screening technologies advance, potentially leading to novel targeted therapeutics for cancers with RGS17 overexpression .

What are the current limitations in RGS17 research methodologies?

Several methodological challenges currently limit RGS17 research:

• Specificity of inhibitors: With approximately 30 members in the RGS family, developing highly specific inhibitors for RGS17 remains challenging

• Tissue-specific functions: RGS17 may have different functions in different tissues, requiring context-specific research approaches

• Redundancy among RGS proteins: Other RGS family members may compensate for RGS17 function in knockout models

• Translating in vitro findings: Moving from biochemical assays to in vivo models presents challenges in maintaining specificity

• Limited understanding of interaction partners: The full spectrum of RGS17 binding partners remains to be elucidated

Addressing these limitations will require continued development of more specific tools and comprehensive approaches to study RGS17 function in diverse contexts .

How might RGS17 function in non-cancer pathological conditions?

While RGS17's role in cancer has been a primary focus, its potential functions in other pathological conditions warrant investigation:

• Opioid tolerance and addiction: Given RGS17's role in opioid receptor signaling, it may be involved in the development of tolerance and addiction

• Neurological disorders: As RGS17 is expressed in the brain, it may play roles in various neurological conditions

• Cardiovascular diseases: RGS17 expression in atrial myocytes suggests potential roles in cardiac function and pathology

• Inflammatory conditions: G protein signaling is crucial in immune cell function, suggesting RGS17 may modulate inflammatory responses

• Metabolic disorders: G protein-coupled receptors regulate numerous metabolic processes, indicating potential RGS17 involvement

Expanding research into these areas could reveal new therapeutic applications for RGS17 modulation beyond cancer treatment .

What novel experimental systems might advance RGS17 research?

Several emerging experimental approaches could significantly advance RGS17 research:

• Organoid models: Patient-derived organoids could better recapitulate the complexity of RGS17 function in human tissues

• Single-cell analysis: Examining RGS17 expression and function at the single-cell level could reveal cell type-specific roles

• CRISPR-based screening: Genome-wide CRISPR screens could identify novel interactors and regulators of RGS17

• Proteomics approaches: Mass spectrometry-based interactome analysis could comprehensively map RGS17 binding partners

• In vivo imaging: Development of tools to visualize RGS17 activity in living organisms could provide dynamic insights into its function