Role of calcium in growth inhibition induced by a novel cell surface sialoglycopeptide

Abstract

Our laboratory has purified an 18 kDa cell surface sialoglycopeptide growth inhibitor (CeReS-18) from intact bovine cerebral cortex cells. Evidence presented here demonstrates that sensitivity to CeReS-18-induced growth inhibition in BALB-c 3T3 cells is influenced by calcium, such that a decrease in the calcium concentration in the growth medium results 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 bind calcium directly. Addition of calcium, but not magnesium, to CeReS-18-inhibited 3T3 cells results in reentry into the cell cycle. A greater than 3-hour exposure to increased calcium is required for escape from CeReS-18-induced growth inhibition. The calcium ionophore ionomycin could partially mimic the effect of increasing extracellular calcium, but thapsigargin was ineffective in inducing escape from growth inhibition. Increasing extracellular calcium 10-fold resulted in an approximately 7-fold increase in total cell-associated 45Ca+2, while free intracellular calcium only increased approximately 30%. However, addition of CeReS-18 did not affect total cell-associated calcium or the increase in total cell-associated calcium observed with an increase in extracellular calcium. Serum addition induced mobilization of intracellular calcium and influx across the plasma membrane in 3T3 cells, and pretreatment of 3T3 cells with CeReS-18 appeared to inhibit these calcium mobilization events. These results suggest that a calcium-sensitive step exists in the recovery from CeReS-18-induced growth inhibition. CeReS-18 may inhibit cell proliferation through a novel mechanism involving altering the intracellular calcium mobilization/regulation necessary for cell cycle progression.

CeReS-18 inhibits growth and induces apoptosis in human prostatic cancer cells

“…1A,C), when medium calcium concentrations are compared, it becomes evident that the difference in sensitivities of these cell lines to CeReS-18 is simply a function of the level of Ca +2 concentration in the medium. This is consistent with previous reports that cells become more sensitive to the effect of CeReS-18 when treated in an environment with a decreased Ca +2 concentration [5,14]. Although PC3 and LNCaP.FGC appear to be similarly influenced by CeReS-18, the DU-145 cultures were significantly more refractory to the effect of CeReS-18.…”

“…Cell growth was monitored at intervals, either by direct cell counts as in the case of DU-145 and PC3 cultures, or by measurement of total cellular protein content, as in the case of LNCaP.FGC cultures. Since CeReS-18 inhibits cells in a calcium-dependent manner [13,14], the concentration of CeReS-18 utilized in these experiments varied from cell line to cell line, depending on the specific medium calcium concentration for each culture (refer to Materials and Methods for specific medium calcium concentrations). The optimal inhibitory concentration of CeReS-18 for DU-145 cells was 8 × 10 −7 M, while the required concentration for inhibiting LNCaP.FGC cells was 2 × 10 −7 M. Only 6.6 × 10 −8 M CeReS-18 was sufficient to inhibit PC3 cells (Fig.…”