Metabolism of Heparan Sulfate Proteoglycan in Rat Hepatocyte Cell Line and Its Role for Regulation of Cell Growth

151 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1988.A rat hepatocyte cell line which accumulates free heparan sulfate (HS) chains in the nucleus was labeled with $\sp{35}$SO$\sb4\sp{2-}$ and the rate of appearance of ($\sp{35}$SO$\sb4$) HS in the nucleus was measured. ($\sp{35}$SO$\sb4$) HS began to accumulate in the nucleus 2 h after the addition of $\sp{35}$SO$\sb4\sp{2-}$ and reached a steady state level after 20 h. HS was lost from the nuclei of pre-labeled cells with a t$\sb{1/2}$ of 8 h. At both 37$\sp\circ$C and 16$\sp\circ$C exogenous ($\sp{35}$SO$\sb4$) heparan sulfate proteoglycan (HSPG) was taken up by the cells and converted to free chains and about 10 percent of the internalized HS was transported into nucleus.The core protein of newly secreted HSPG appears in the cell matrix covalently linked to a phosphatidylinositol moiety on plasma membrane which is then cleaved by a plasma membrane phospholipase C. The released HSPG becomes found to a inositol-PO$\sb4$ (IP)-specific receptor and is internalized and a portion of it is processed by a non-lysosomal pathway before delivery to the nucleus. Insulin activates the activity of the plasma membrane phospholipase C.The level of nuclear HS is inversely prop. to the cell doubling time and, when growing cells reach confluence, increases 3-fold as the HS undergoes a change in structure. Culture conditions which lower the nuclear HS lower the rate of cell division in growing cells and cause confluent cells to lose contact inhibition. A cell surface HSPG released by treatment of the cells with IP, which is internalized very efficiently by cells and a portion of the internalized HSPG is processed and delivered to the nuclei, from confluent but not growing cultures causes cessation of cell division in logarithmically growing cells for approximately one cell cycle. In contrast, HSPG from growing cells but not from confluent cells stimulates the rate of cell division in growing cells. The dynamic metabolism of HS in hepatocyte and its correlations with cell growth suggest HS plays some role for the regulation of cell growth.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD