Identification of Multiple Forms of 180-kDa Ribosome Receptor in Human Cells

Abstract

Herein, we describe the analysis and mapping of cDNA clones encoding variant forms of the human homolog of the canine 180-kDa ribosome receptor (p180). One form, similar to the chicken ES/130 homolog, possesses a large uninterrupted C-terminal region composed predominantly of heptad repeats predicted to form an alpha-helical double-stranded coiled-coil rod. Other forms contain in addition a 10-amino acid consensus motif, NQGKKAEGAQ, repeated up to 54 times in tandem close to the N-terminus. Such repeats in canine p180 represent a ribosome-binding domain. The cDNA hybridized to a major 6-kb transcript in all tissues examined, where very high expression was observed in tissues that carry out a high level of secretion such as pancreas, liver, and placenta. The ES130/p180 gene was mapped to chromosome 20p12, and a potential pseudogene appears to reside on chromosome 7. In summary, the data suggest that p180 exists in humans in different forms because of complete removal of tandem repeats, or partial intraexonic splicing, creating different repeat lengths with potentially novel ribosome-binding characteristics.

Multifunctional Roles for the Protein Translocation Machinery in RNA Anchoring to the Endoplasmic Reticulum

“…In total, these data support a function for the Sec61 complex, subunits of the oligosaccharyltransferase complex, and, to a lesser degree, the transloconassociated protein complex in the direct anchoring of mRNAs to the ER. The identification of p180 in the RM, but not HeLaderived fractions, is consistent with prior reports that p180 is highly expressed in terminally differentiated "professional" secretory cells but only very weakly in HeLa cells, where it did not meet statistical criteria for selection in the mRNA interactome or as a candidate RNA-binding protein (60,76). Thus, we are unable to identify a role for p180 in the direct anchoring of endomembrane protein-encoding mRNAs to the HeLa ER, although a related function in terminally differentiated secretory cells remains plausible.…”

“…SR␣ and reticulon 4a, the high molecular weight isoform of reticulons 4b and 4c, were recently identified as members of the HeLa mRNA interactome (60) and thus might contribute to mRNA-ER interactions in the BrS, but not BrR, fractions. The ribosome receptor p180 (RRBP1) was detected as two isoforms: 1) a 180-kDa form (p180) with reported ribosome receptor and microtubule binding activity (25,75) and, more recently, described as a candidate general ER-poly(A) mRNA-binding protein (14) and 2) a 130-kDa form (ES130), which lacks the ribosome-binding decapeptide repeat motif but retains the coiled-coil microtubule binding domain (76). The two isoforms encode a common transmembrane domain, yet their Brij35 solubilization profiles were strikingly different, with ES130 partitioning to the BrS ER and p180 to the BrR ER.…”

Coordinate Regulation of Phospholipid Biosynthesis and Secretory Pathway Gene Expression in XBP-1(S)-induced Endoplasmic Reticulum Biogenesis

“…Such functions might be performed by the Rrbp1-encoded p180 protein that was originally characterized as a ribosome receptor and shown to elicit proliferation of rough ER upon enforced expression in yeast (52,53). Notably, Rrbp1 transcripts are highly expressed in secretory tissues (54) and up-regulated in our XBP-1(S)-transduced cells (Table 1).…”

IN02, A Positive Regulator of Lipid Biosynthesis, Is Essential for the Formation of Inducible Membranes in Yeast

“…The canine ribosome receptor is an integral membrane protein of the endoplasmic reticulum (ER) consisting of three distinct regions based on its amino acid sequence (Wanker et al, 1995). Briefly, full-length p180 (FL) consists of an amino terminal membrane-anchoring domain, a basic region consisting of 54 tandem decapeptide repeats involved in ribosome binding and a C-terminal predicted coiled-coil domain of unknown function (Langley et al, 1998). Expression of FL results in the proliferation of rough membranes evenly spaced throughout the cytoplasm.…”