RPS6KB2, encoding ribosomal protein S6 kinase B2 (also known as p90RSK or RSK2), is a serine/threonine protein kinase that functions as a critical link between mitogen-activated protein kinase (MAPK) signaling cascades and translational control. This 90 kDa protein represents one of the most abundant and widely expressed kinases in mammalian cells, with particularly high expression in the central nervous system. RPS6KB2 serves as a key effector downstream of extracellular signal-regulated kinases (ERK1/2), translating extracellular signals into intracellular responses that regulate protein synthesis, cell survival, and neuronal differentiation.
RPS6KB2, encoding ribosomal protein S6 kinase B2 (also known as p90RSK or RSK2), is a serine/threonine protein kinase that functions as a critical link between mitogen-activated protein kinase (MAPK) signaling cascades and translational control. This 90 kDa protein represents one of the most abundant and widely expressed kinases in mammalian cells, with particularly high expression in the central nervous system. RPS6KB2 serves as a key effector downstream of extracellular signal-regulated kinases (ERK1/2), translating extracellular signals into intracellular responses that regulate protein synthesis, cell survival, and neuronal differentiation.
Function/Biology
RPS6KB2 functions as a dual-specificity kinase containing two kinase domains: an N-terminal kinase domain (NTKD) and a C-terminal kinase domain (CTKD). The NTKD phosphorylates substrates including ribosomal protein S6 and elongation factor 2 kinase, directly influencing protein translation rates. The CTKD acts as an autophosphorylation domain that regulates the kinase's activation state.
Upon activation by ERK1/2 phosphorylation, RPS6KB2 rapidly translocates to the ribosome and phosphorylates the 40S ribosomal subunit protein S6, promoting translation of mRNAs containing 5' terminal oligopyrimidine tracts—a class enriched in genes encoding translation machinery and growth-promoting factors. Beyond translational control, RPS6KB2 phosphorylates and activates CREB (cAMP response element binding protein), facilitating transcriptional responses to growth factors and neurotrophic signals. The kinase also interacts with and phosphorylates BAD (Bcl2-associated agonist of death), promoting cell survival pathways.
Neurodegeneration" style="color:#4fc3f7;margin:1.5rem 0 0.6rem;font-size:1.15rem;font-weight:700;border-bottom:2px solid rgba(79,195,247,0.3);padding-bottom:0.3rem">Role in Neurodegeneration
RPS6KB2 dysfunction has emerged as a significant factor in multiple neurodegenerative contexts. Mutations in RPS6KB2 cause Coffin-Lowry syndrome (CLS), a rare X-linked intellectual disability and developmental disorder characterized by progressive neurological decline, facial dysmorphism, and skeletal abnormalities. This syndrome demonstrates direct pathological consequences of impaired kinase function in neuronal development and maintenance.
In Alzheimer's disease and other amyloid-related pathologies, altered RPS6KB2 signaling contributes to pathological translation patterns and reduced neuronal resilience. Dysregulation of RPS6KB2-mediated translation can lead to accumulation of aberrant proteins and impaired synthesis of neuroprotective factors. The kinase's role in ribosomal biogenesis and protein quality control positions it as a potential contributor to the translational dysfunction observed in various neurodegenerative diseases.
Molecular Mechanisms
RPS6KB2 activation requires dual phosphorylation events. ERK1/2-mediated phosphorylation at threonine 573 within the activation loop is the primary activation mechanism, while autophosphorylation at serine 380 provides stabilization. Activated RPS6KB2 exists in a feedback loop with MAPK signaling through phosphorylation of upstream regulators including SOS1 and ERK itself, allowing both amplification and negative regulation of ERK/MAPK cascades.
The kinase directly interfaces with the mTORC1 pathway through substrate interactions with S6K1, collectively regulating the phosphorylation status of ribosomal protein S6 and 4E-BP1. This positioning makes RPS6KB2 an integrator of growth factor, nutrient, and stress signals crucial for maintaining protein synthesis homeostasis in neurons.
Clinical/Research Significance
RPS6KB2 represents a therapeutic target in cancers where MAPK pathway hyperactivation drives progression. In neurodegeneration research, understanding RPS6KB2 dysfunction provides