ROLE OF CALCIUM IN GROWTH-INHIBITION INDUCED BY A NOVEL CELL-SURFACE SIALOGLYCOPEPTIDE

Our laboratory has purified an 18 kDa cell surface sialoglycopeptide g rowth inhibitor (CeReS-18) from intact bovine cerebral cortex cells. E vidence presented here demonstrates that sensitivity to CeReS-18-induc ed growth inhibition in BALB-c 3T3 cells is influenced by calcium, suc h that a decrease in the calcium concentration in the growth medium re sults in an increase in sensitivity to CeReS-18. Calcium did not alter CeReS-18 binding to its cell surface receptor and CeReS-18 does not b ind calcium directly. Addition of calcium, but not magnesium, to CeReS -18-inhibited 3T3 cells results in reentry into the cell cycle. A grea ter than 3-hour exposure to increased calcium is required for escape f rom CeReS-18-induced growth inhibition. The calcium ionophore ionomyci n could partially mimic the effect of increasing extracellular calcium , but thapsigargin was ineffective in inducing escape from growth inhi bition. Increasing extracellular calcium 10-fold resulted in an approx imately 7-fold increase in total cell-associated Ca-45(+2), while free intracellular calcium only increased approximately 30%. However, addi tion of CeReS-18 did not affect total cell-associated calcium or the i ncrease in total cell-associated calcium observed with an increase in extracellular calcium. Serum addition induced mobilization of intracel lular calcium and influx across the plasma membrane in 3T3 cells, and pretreatment of 3T3 cells with CeReS-18 appeared to inhibit these calc ium mobilization events. These results suggest that a calcium-sensitiv e step exists in the recovery from CeReS-18-induced growth inhibition. CeReS-18 may inhibit cell proliferation through a novel mechanism inv olving altering the intracellular calcium mobilization/regulation nece ssary for cell cycle progression. (C) 1995 Wiley-Liss, Inc.