Sudarshan.rajagopal

Life Sci. 2026 Jul 9;402:124576. doi: 10.1016/j.lfs.2026.124576. Online ahead of print.

ABSTRACT

AIMS: Protein kinase C (PKC) is classically viewed as a downstream effector of Gq/11-coupled G protein-coupled receptors (GPCRs), which activate phospholipase C to generate the diacylglycerol and Ca²⁺ signals required for PKC activation. However, several non-Gq/11 GPCRs have also been reported to activate PKC, a finding that has remained mechanistically unresolved. Here, we asked whether this unresolved question is determined not by receptor class itself, but by the signaling bias engaged downstream of receptor activation.

MATERIALS AND METHODS: Biased variants of the Gi/o-coupled dopamine D₂ receptor (D₂R), together with pharmacological perturbation and biochemical analyses, were used to compare G protein-biased and arrestin-biased pathways leading to PKCβII regulation.

KEY FINDINGS: We found that G protein-biased, but not arrestin-biased, signaling selectively promotes PKCβII activation through a spatially organized multistep pathway. In this pathway, released Gβγ facilitates nuclear entry of PKCβII, where Mdm2-mediated ubiquitination appears to support subsequent activating steps and plasma membrane translocation. Upstream, this pathway depends on EGFR transactivation, which links receptor activation to convergent PI3K-PDK1 and PLCγ-DAG signaling. In contrast, arrestin-biased signaling suppresses PKCβII activation by redirecting Mdm2 toward preferential ubiquitination of arrestin3, thereby limiting PKCβII access to this regulatory pathway. Similar signaling logic was observed for the dopamine D₃ receptor and cannabinoid CB₁ receptor.

SIGNIFICANCE: These findings show that PKCβII activation downstream of non-Gq GPCRs is determined by signaling bias rather than by canonical receptor coupling alone, and identify competitive Mdm2-mediated ubiquitination as a mechanism linking biased GPCR signaling to differential PKC output.

PMID:42425403 | DOI:10.1016/j.lfs.2026.124576

EMBO J. 2023 Jun 1;42(11):e112940. doi: 10.15252/embj.2022112940. Epub 2023 Apr 11.

ABSTRACT

The peptide hormone angiotensin II regulates blood pressure mainly through the type 1 angiotensin II receptor AT₁ R and its downstream signaling proteins G_q and β-arrestin. AT₁ R blockers, clinically used as antihypertensive drugs, inhibit both signaling pathways, whereas AT₁ R β-arrestin-biased agonists have shown great potential for the treatment of acute heart failure. Here, we present a cryo-electron microscopy (cryo-EM) structure of the human AT₁ R in complex with a balanced agonist, Sar¹ -AngII, and G_q protein at 2.9 Å resolution. This structure, together with extensive functional assays and computational modeling, reveals the molecular mechanisms for AT₁ R signaling modulation and suggests that a major hydrogen bond network (MHN) inside the receptor serves as a key regulator of AT₁ R signal transduction from the ligand-binding pocket to both G_q and β-arrestin pathways. Specifically, we found that the MHN mutations N111^3.35 A and N294^7.45 A induce biased signaling to G_q and β-arrestin, respectively. These insights should facilitate AT₁ R structure-based drug discovery for the treatment of cardiovascular diseases.

PMID:37038975 | PMC:PMC10233375 | DOI:10.15252/embj.2022112940