SH3RF2

SH3RF2 Full Name

SH3 domain containing ring finger 2

SH3RF2 Introduction

SH3RF2 (SH3 domain containing ring finger 2), a member of the SH3RF family of scaffold proteins that also includes SH3RF1/POSH and SH3RF3, combines multiple protein-interaction modules with an E3 ubiquitin ligase domain to coordinate signaling complexes in the cell. The SH3RF proteins are best known as scaffolds for the JNK signaling cascade, a stress-responsive pathway that controls apoptosis, inflammation, and cell survival: they simultaneously engage upstream kinases of the mixed-lineage kinase family and downstream components such as MKK7, thereby positioning the JNK module for efficient activation in response to cellular stress. SH3RF2, like its relatives, thereby functions as a signal integrator whose levels and localization determine whether a cell commits to death or mounts a protective response. Beyond its pro-apoptotic signaling role, SH3RF2 has been implicated in cardiac and neuronal biology, and dysregulated expression of the protein has been reported in cancer, where it may influence tumor cell survival and metastasis. The multi-domain organization of SH3RF2, which includes SH3 domains, a RING finger, and zinc-finger motifs, allows it to act as a platform that both scaffolds kinases and directs the ubiquitination of specific targets, a dual functionality that makes it a rich subject for cell signaling research.

Figure 1. The structure of SH3RF2.

Scaffold Domain Organization and Kinase Module Assembly
SH3RF2 belongs to the POSH (plenty of SH3s) family of scaffold proteins, named for their content of several Src-homology 3 (SH3) domains that mediate protein-protein interactions.
In addition to its SH3 repeats, the protein carries a C-terminal RING finger characteristic of E3 ubiquitin ligases and additional cysteine/histidine-rich zinc-binding motifs that contribute to its interactions.
The primary biochemical function of the SH3RF scaffold is the assembly of the JNK signaling module: it binds upstream kinases such as the mixed-lineage kinases and the GTPase Rac, while simultaneously recruiting downstream components including MKK7 and JNK itself.
By holding the sequentially acting kinases in close proximity, the scaffold accelerates signal flow along the cascade and ensures that JNK is activated strongly and rapidly when the cell is exposed to stress.
SH3RF2 can also engage the ubiquitin machinery through its RING finger, and it has been reported to ubiquitinate substrates or partner proteins, coupling scaffolding to the regulated destruction of signaling components.
The SH3RF2 gene is located on human chromosome 5, and the transcript is expressed in multiple tissues, including heart and brain, where scaffold function is particularly important.
Alternative splicing and post-translational modifications provide additional layers of control over the localization and signaling capacity of the protein.

JNK-Dependent Stress Signaling, Cardiac and Neuronal Roles, and Cancer
Through its capacity to activate JNK signaling, SH3RF2 influences whether cells respond to stress by dying, surviving, or adapting, and dysregulation of this balance is relevant to degenerative and malignant disease.
In the heart, scaffold-dependent JNK signaling participates in the response to pressure overload and ischemia, and animal studies have linked SH3RF2 to the regulation of cardiac remodeling and heart failure progression.
In neurons, SH3RF family scaffolds contribute to the signaling events that govern apoptosis during development and in neurodegenerative settings, where excessive JNK activation can drive cell death.
Expression analyses in human cancers have revealed altered SH3RF2 levels in several tumor types, and functional experiments suggest that the protein can modulate tumor cell survival, migration, and metastatic potential in a context-dependent manner.
Because the scaffold organizes a whole kinase cascade, small molecules that disrupt SH3RF2-mediated complex assembly could, in principle, blunt pathological JNK signaling more selectively than inhibitors of JNK itself.
Understanding how SH3RF2 balances its scaffolding and ubiquitin ligase activities, and how these are regulated in different tissues, will be critical for translating these findings into therapeutic strategies.

Alternate Names for SH3RF2

SH3RF2; SH3 domain containing ring finger 2; PPP1R39, protein phosphatase 1, regulatory subunit 39; putative E3 ubiquitin-protein ligase SH3RF2; FLJ23654; heart protein phosphatase 1 binding protein; Hepp1; POSH eliminating RING protein; POSHER; RNF158