Endoplasmic reticulum retention and degradation of T cell antigen receptor β chain

Abstract

The T cell antigen receptor-CD3 (TCR/CD3) complex is assembled in the endoplasmic reticulum (ER) of T cells after synthesis of individual chains, and is transported to the cell surface for immune recognition and regulation. Partially assembled or unassembled TCR chains are retained and rapidly degraded in the ER. These processes are strictly regulated in the ER at post-translational level for the maintenance of cellular homeostasis. In order to identify the region responsible for the ER retention and rapid degradation of the TCR chain, number of mutants were engineered and their fates, after synthesis in the ER of the HeLa cells, were investigated. Extensive mutagenic analysis of TCR chain, including changing the charged amino acid residues and two tyrosine residues of the transmembrane region into hydrophobic amino acid residues, did not alter the ER retention and rapid degradation. Soluble TCR chain and cytoplasmic tail truncation mutant were also rapidly degraded in the ER. However, N-glycosylation rate of soluble TCR chain in the ER was significantly increased possibily due to the increased exposure of the N-glycosylation site. These results suggest that the ER retention of TCR chain is mediated through its extracellular and transmembrane-cytoplasmic regions and that the rapid ER degradation can be caused by an exposure of unassembled subregion of TCR chain, either extracellular domain or hydrophobic transmembrane region to the hydrophilic environment (lumen of the ER) rather than by presence of a specific degradation signal.

Idiotypic T cells specific for Morbillivirus nucleocapsid protein process and present their TCR to cognate anti-idiotypic CD8+ T cells

“…We demonstrate in mouse T cells that newly synthesized TCR beta chain proteins are formed as DRiPs and this extends the earlier reported formation of DRiPs and their degradation in other cell types [2,3,27]. In HeLa cells transfected with cDNA of TCR␤ chain, more than 80% of newly synthesized TCR beta chain was retained in ER and rapidly degraded in ER [40]. HeLa cells do not express CD3 molecules.…”

Serine Residues in the Cytosolic Tail of the T-cell Antigen Receptor α-Chain Mediate Ubiquitination and Endoplasmic Reticulum-associated Degradation of the Unassembled Protein

“…Thus, serinedependent ubiquitination is likely a conserved mechanism for ERAD of unassembled TCR␣ among mammals. The ␤-subunit of the TCR (TCR␤) is also degraded when it cannot assemble with other TCR subunits (27,40). TCR␤ from different mammalian species has a cytosolic tail of 5-7 amino acid residues that contains 2-3 lysine residues (supplemental Fig.…”

The Large Hsp70 Grp170 Binds to Unfolded Protein Substrates in Vivo with a Regulation Distinct from Conventional Hsp70s

“…Many ER proteins are glycosylated on asparagine residues within Asn-X-Ser/Thr sequons (1,3). It has been reported that the T cell receptor ␤-chain (TCR␤) populates two isoforms that vary in their degree of glycosylation and which are readily distinguished by SDS-PAGE (28,36). Although the majority of TCR␤ is glycosylated at two sites co-translationally, a species can be detected that is only glycosylated on a single site 35 S]cysteine/methionine for 1 h and chased for 1 h to allow maturation of the chaperones before lysing either in the presence of ATP or apyrase.…”