Quantity Control of the ErbB3 Receptor Tyrosine Kinase at the Endoplasmic Reticulum

Abstract

The ErbB3 receptor tyrosine kinase contributes to a variety of developmental processes, and its overexpression and aberrant activation promote tumor progression and therapeutic resistance. Accumulating evidence suggests that tumor overexpression may be mediated by the loss of posttranscriptional negative regulatory mechanisms, such as protein degradation, that normally keep receptor levels in check. Our previous studies indicate that the RING finger E3 ubiquitin ligase Nrdp1, a protein lost in breast and other tumor types, suppresses ErbB3 levels by mediating ligand-independent receptor ubiquitination and degradation. Here we demonstrate that Nrdp1 preferentially associates with the nascent form of ErbB3 to accelerate its degradation, and we show that the two proteins colocalize at the endoplasmic reticulum (ER). Blocking the exit of ErbB3 from the ER does not affect the ability of Nrdp1 to mediate receptor ubiquitination or degradation, while functional disruption of the conserved ER-associated degradation (ERAD) pathway ATPase VCP/p97 leads to the Nrdp1-dependent accumulation of ubiquitinated ErbB3 but blocks receptor degradation. Further evidence indicates that the ErbB3 targeted by Nrdp1 for degradation is properly folded and fully functional. Collectively, these observations point to a novel mechanism of receptor tyrosine kinase quantity control wherein steadystate levels of signaling-competent receptor are dictated by an ER-localized degradation pathway.

Oligomerization of the Nrdp1 E3 Ubiquitin Ligase Is Necessary for Efficient Autoubiquitination but Not ErbB3 Ubiquitination

“…5B). As we have previously observed (21), the presence of Nrdp1 markedly augments the amount of ubiquitin associated with ErbB3, whereas the 32 variant and the ligase-deficient CSHQ double point mutant do not significantly affect ErbB3 ubiquitination. Quantification of the degree of ErbB3 ubiquitination indicates that Nrdp1⌬cc induced similar levels of ErbB3 ubiquitination as does wild type Nrdp1 (not shown).…”

Reciprocal cross-regulation between RNF41 and USP8 controls cytokine receptor sorting and processing

“…Finally, RNF41 and USP8 activity are also affected by their subcellular localization. Both endoplasmic reticulum (ER)-and endosome-localized RNF41 are implicated in ErbB3 degradation (Cao et al, 2007;Fry et al, 2011), while growth factor stimulation and DUB inactivation enhance recruitment of USP8 to early endosomes (Mizuno et al, 2005;Row et al, 2006). In addition to this, we show that RNF41 expression causes a drastic intracellular redistribution of USP8 in HeLa cells.…”

Effects of Membrane Trafficking on Signaling by Receptor Tyrosine Kinases

“…First, ER-based ubiquitination and degradation mechanisms can regulate the levels of nascent RTKs eventually targeted to the plasma membrane, as recently shown for ErbB3 levels controlled by the E3 ubiquitin ligase Nrdp1 at the ER (Fry et al 2011). Second, ER-localized protein tyrosine phosphatase PTP1B plays multiple roles in inactivating ligand-bound RTKs after internalization and in modulating their endocytic trafficking (Stuible and Tremblay 2010;Sangwan et al 2011).…”