INDUCTION OF DOLICHYL-SACCHARIDE INTERMEDIATE BIOSYNTHESIS CORRESPONDS TO INCREASED LONG-CHAIN CIS-ISOPRENYLTRANSFERASE ACTIVITY DURING THEMITOGENIC RESPONSE IN MOUSE B-CELLS

There are large increases in the rates of Glc(3)-Man(9)GlcNAc(2)-P-P-D ol (Oligo-P-P-Dol) biosynthesis and protein N-glycosylation during the proliferative response of murine B lymphocytes (B cells) to bacterial lipopolysaccharide (LPS). To learn more about the regulation of dolic hyl-saccharide biosynthesis, the possible relationships between develo pmental changes in specific steps in dolichyl phosphate (Dol-P) and N- acetyl-glucosaminylpyrophosphoryldolichol (GlcNAc-P-P-Dol) biosynthesi s and the induction of Oligo-P-P-Dol biosynthesis were investigated. T hese studies describe an impressive induction of long chain cis-isopre nyltransferase (cis-IPTase) activity, an enzyme system required for th e chain elongation stage in de novo Dol-P synthesis, which corresponde d to the striking increase in the rate of Oligo-P-P-Dol biosynthesis i n LPS-activated B cells. The cellular level and specific activity of c is-IPTase increase 15-fold in LPS-treated cells with relatively unalte red affinity for isopentenyl pyrophosphate. The rates of Dol-P and Oli go-P-P-Dol synthesis increased substantially when cis-IPTase activity was induced, suggesting a regulatory relationship between the level of cis-IPTase activity and lipid intermediate synthesis. Distinctly diff erent developmental patterns were observed for cis-IPTase and HMG-CoA reductase activity, and when sterol biosynthesis was drastically inhib ited by lovastatin, the rate of synthesis of Dol-P was slightly higher in the presence of the drug. Modest elevations in the cellular levels of dolichol kinase, Dol-P phosphatase, and UDP-GlcNAc:Dol-P N-acetylg lucosaminylphosphoryltransferase (L-G1PT) activities were also observe d, but these changes were relatively small compared with the increases in cis-IPTase activity and the rates of Dol-P, GlcNAc-P-P-Dol, and Ol igo-P-P-Dol synthesis. The expression of the L-G1PT gene is an early e vent in the developmental program for Oligo-P-P-Dol synthesis, but Glc NAc-P-P-Dol formation is apparently not rate-limiting. In summary, lar ge increases in cis-IPTase activity and the rate of Dol-P biosynthesis appear to play a key regulatory role in the induction of Oligo-P-P-Do l biosynthesis during the proliferative response of B cells to LPS, an d the biosynthetic pathways for Dol-P and cholesterol are regulated in dependently in dividing B cells.