Expression of intracisternal A-type particles is increased when a B-cell lymphoma differentiates into an immunoglobulin-secreting cell

Abstract

The murine B-cell lymphoma CH12, like many other murine cells, expresses intracisternal A-type particles (TAPs). When CH12 cells are treated with lipopolysaccharide, the cells differentiate and secrete immunoglobulin M. The expression of IAP genes was also increased, in parallel with the increased expression of immunoglobulin genes. The amount of IAP mRNA increased within 48 h of lipopolysaccharide treatment and reached a level fivefold higher than that in unactivated CH12 cells. The two major IAP transcripts (7.2 and 5.4 kilobases) were induced to similar extents. The increased level of mRNA was reflected in higher levels of the major IAP structural protein p70, whose abundance increased 3.6-fold. The number of IAP particles per cell also increased upon activation of CH12, from 67 in nonsecreting CH12 to 290 in secreting cells. All of the IAPs were confined to the cisternae of the endoplasmic reticulum (ER), regardless of the differentiation state of the cell. Accompanying the induction of p70 was the induction of the related IAP polypeptide p102. A third viral polypeptide, p120, was also made in CH12; its abundance was almost unchanged. Localization of the IAP proteins on ultrathin frozen sections showed that most were assembled into particles in the ER. However, there were small pools of unassembled proteins both in the ER and on the plasma membrane. p70 and p120 could be detected, by iodination, on the surfaces of both secreting and nonsecreting CH12 cells. Unlike p70 and p120, p102 did not seem to be membrane associated. Taken together, these observations show that IAP expression is regulated developmentally in B lymphocytes. Also, these observations point to possible interactions between IAP genes and other cellular genes.

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

“…Within RM, its abundance was increased fivefold. This magnitude of change is larger than that observed for the resident ER retroviral protein p73 (52) and for the Ig chains.…”

“…Labeling of CHI2 cells with [3SS]methionine (>600 Ci/mmol, Amersham Corp., Arlington Heights, IL) was done as described previously (52), at 100 p, Ci/ml. Cell lysis, immunoprecipitation, and digestion with endoglycosidase H (endo H) were performed as described (3).…”

“…Equal quantities of protein from non-secreting and secreting CHI2 cells were analyzed on 9-15% polyacrylamide gradient SDS gels (3) and the proteins were visualized by silver staining. Gels intended for immunoblotting were transferred to nitrocellulose (0.45 /xm pore size, Vanguard International, Neptune, NJ), blocked, and probed as described (52). The antibodies were used at the following dilutions: (a) anti-ribophorins I and II, 1:100; (b) anti-BiP, hybridoma culture supernatant, and (c) anti-glycosylation site binding protein, 1 ~g/ml (15; a kind gift of Dr. W, Lennarz).…”

Stage-specific expression of intracisternal A-particle sequences in murine myelomonocytic leukemia cell lines and normal myelomonocytic differentiation

“…This report, the first systematic survey of IAP expression in both normal and leukemic cells of the myelomonocytic lineage, has demonstrated stage-specific expression of IAP sequences. Previous studies in different systems (1,38,49,53) have certain disadvantages with respect to the present study. Preimplantation embryos (38,53) FIG.…”

“…In preimplantation embryos, both IAPs and the mRNA have been shown to accumulate up to the blastocyst stage and then decrease (38,53). IAP mRNA levels decreased in a Friend murine erythroleukemia cell line induced to differentiate with dimethyl sulfoxide (1), and IAP mRNA level increased in the CH12 B-cell lymphoma when the cells were induced to differentiate from the resting state to the immunoglobulin-secreting phase by bacterial lipopolysaccharide (49). However, in vitro clonal variation in the numbers of IAPs have also been reported (15,20,37), and these have been considered to be random events since the alterations did not correlate with particular differentiation markers (37).…”