Membrane biogenesis during B cell differentiation: most endoplasmic reticulum proteins are expressed coordinately.

Abstract

Abstract. The induction of high-rate protein secretion entails increased biogenesis of secretory apparatus organelles. We examined the biogenesis of the secretory apparatus in the B cell line CH12 because it can be induced in vitro to secrete immunoglobulin (Ig). Upon stimulation with lipopolysaccharide (LPS), CH12 cells increased secretion of IgM 12-fold. This induced secretion was accompanied by preferential expansion of the ER and the Golgi complex. Three parameters of the rough ER changed: its area and volume increased 3.3-and 3.7-fold, respectively, and the density of membrane-bound ribosomes increased 3.5-fold. Similarly, the area of the Golgi stack increased 3.3-fold, and its volume increased 4.1-fold. These changes provide sufficient biosynthetic capacity to account for the increased secretory activity of CH12. Despite the large increase in IgM synthesis, and because of the expansion of the ER, the concentration of IgM within the ER changed less than twofold during the differentiation process.During the amplification of the rough ER, the expression of resident proteins changed according to one of two patterns. The majority (75%) of rough microsomal (RM) proteins increased in proportion to the increase in rough ER size. Included in this group were both lumenal proteins such as Ig binding protein (BiP), and membrane proteins such as ribophorins I and II. In addition, the expression of a minority (,'~9%) of RM polypeptides increased preferentially, such that their abundance within the RM of secreting CH12 cells was increased. Thus, the expansion of ER during CH12 differentiation involves preferential increases in the abundance of a few resident proteins, superimposed upon proportional increases in most ER proteins.

Thyroglobulin Transport along the Secretory Pathway

“…Further, compared with CHO-P cells, there was no appreciable change in the total amount of rough ER in CHO-G cells, based on the levels of ribophorin II and calnexin (Fig. 2C), which are among the membrane proteins that appear to reflect the cellular quantity of rough ER (41,42). Moreover, increased expression of GRP94 did not alter the concentrations of any of the other ER lumenal resident proteins that were examined, calreticulin, PDI, ERp72, and ER60 (Fig.…”

Stress signaling from the lumen of the endoplasmic reticulum: coordination of gene transcriptional and translational controls

“…The coordinated synthesis of ER membrane and constituent proteins responds to environmental and physiological stimuli, as well as the differentiation state of the (Wiest et al 1990). The smooth ER in hepatocytes expands as the enzymes that oxidize and detoxify drugs (such as cytochrome P450, which oxidizes phenobarbitol) are induced to meet their demand.…”

Analysis in vivo of GRP78-BiP/substrate interactions and their role in induction of the GRP78-BiP gene.

“…These perturbations include inhibition of glycosylation (Chang et al, 1987;Kozutsumi et al, 1988;Watowich and Morimoto, 1988), disruption of intracellular calcium stores (Drummond et al, 1987), increased expression of soluble proteins (Domer et al, 1989;Wiest et al, 1990), and direct expression of proteins that cannot fold normally (Kozutsumi et al, 1988;Watowich et al, 1991). In addition to the expression of malfolded HN causing an induction of GRP78-BiP transcription, we have observed that in SV5-infected cells the flux of synthesis of folding-competent HN molecules stimulates GRP78-BiP transcription (Watowich et al, 1991).…”

“…The polypeptides identified by these groups were later shown to be identical, thus linking its glucose-regulated expression with a biochemical property (Munro and Pelham, 1986). Other cellular perturbations that result in an induction of GRP78-BiP synthesis include inhibition of N-linked glycosylation and modification Watowich and Morimoto, 1988), disruption of intracellular calcium stores (Drummond et al, 1987), infection by enveloped viruses (Peluso et al, 1978;Stoeckle et al, 1988), the expression in the ER of mutant polypeptides deficient in folding (Kozutsumi et al, 1988), and the increased expression of secretory proteins (Dorner et al, 1989;Wiest et al, 1990). These treatments affect processes in the ER where GRP78-BiP is localized, which suggests the existence of a feedback loop to regulate the expression of the gene.…”