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

A cell regulatory agent, CeReS-18, inhibits mouse 3T6 cell proliferation but not polyomavirus replication

We have purified a cell regulatory sialoglycopeptide, CeReS-18, from intact bovine cerebral cortex cells. This is an 18-kDa molecule that reversibly inhibits cellular DNA synthesis and the proliferation of a wide array of target cells. In the present study, the effect of CeReS-18 on mouse 3T6 host cell proliferation and polyomavirus replication was investigated. The results showed that CeReS-18 was able to inhibit 3T6 cell cycling in a concentration-dependent, calcium-sensitive, and reversible manner. Despite the inhibition of cell proliferation, CeReS-18 did not influence polyomavirus infection of 3T6 cells. Indirect immunofluorescent assays revealed that CeReS-18-treated, and cell cycle-arrested, 3T6 cells remained permissive to polyomavirus replication. Electron microscopy and immunogold labeling showed that new viral particles were assembled inside the nuclei of infected cells in the presence of CeReS-18 and during cell cycle arrest. The cellular requirements for the replication of polyomavirus DNA and the synthesis of viral proteins, as well as for the assembly of viral particles, therefore, remained available in CeReS-18-inhibited 3T6 cells. In addition, although polyomavirus infection can be mitogenic, infection of CeReS-18-treated 3T6 cells did not reverse the cell cycle arrest mediated by this cell cycle inhibitor.

CeReS-18, a cell regulatory sialoglycopeptide, inhibits proliferation and migration of rat vascular smooth muscle cells

CeReS-18, a cell regulatory sialoglycopeptide, has been shown to inhibit proliferation of a wide array of target cells. In the present study, the effect of CeReS-18 on vascular smooth muscle cell (SMC) proliferation was characterized in cultured rat aorta SMCs (A7r5). More extensively, the effect of CeReS-18 on platelet-derived growth factor (PDGF)-induced SMC migration was examined using a modified Boyden's chamber assay. CeReS-18 inhibits both SMC proliferation and migration in a concentration-dependent, calcium-sensitive, and reversible manner. Furthermore, cells preincubated with the inhibitor had an increased sensitivity to CeReS-18-mediated inhibition of SMC migration. Immunoprecipitation and in vitro phosphorylation assays demonstrated that MAP kinase activity was inhibited in the CeReS-18-treated cells and pretreatment with CeReS-18 suppressed the activation of MAP kinase stimulated by PDGF. However, it is not likely that the suppression of the MAP kinase pathway was directly responsible for the ability of CeReS-18 to inhibit migration of the rat aorta smooth muscle cells since a MEK-specific inhibitor, PD98059, did not influence A7r5 cell migration.

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

BACKGROUND

Polypeptide growth factors are positive and negative regulators of prostatic growth and function, and many positive regulators of growth in the prostate have been extensively studied. However, very few inhibitors of prostate cell proliferation have been identified. We have isolated a unique 18-kDa sialoglycopeptide (CeReS-18) which inhibits cell proliferation of three separate lines of human prostate cancer cells, as well as inducing cellular cytotoxicity via an apoptotic pathway unrelated to the Bcl-2 family of proteins.

METHODS

Cell cycle inhibition was analyzed by direct cell counts with a Coulter (Miami, FL) cell counter. Apoptotic cells were analyzed by electron microscopy, annexin V-fluorescein isothiocyanate (FITC) staining, fluorescence microscopy, and propidium iodide uptake measured with a fluorescence-activated cell sorter. Expression of the proteins of the Bcl-2 family was detected by Western blot analysis.

RESULTS

We found that CeReS-18 inhibits cell proliferation of androgen-responsive, LNCaP.FGC human prostate cancer cells, as well as of androgen-nonresponsive DU-145 and PC3 human prostate cancer cells. Furthermore a, fivefold increase over the inhibitory concentration of CeReS-18 elicited a cytotoxic response by all three cell lines. We thus characterized the cytotoxic mechanism as apoptotic in nature, and we measured the expression of several members of the Bcl-2 family in PC3 cells upon treatment with CeReS-18.

CONCLUSIONS

The data indicate that CeReS-18 is a potent inhibitor of cellular progression through the cell cycle by both androgen-responsive and androgen-nonresponsive human prostate cancer cells. In addition, treatment of both types of cells with increased concentrations of CeReS-18 induces cellular cytotoxicity, characterized as apoptosis.

CeReS-18, a novel cell surface sialoglycopeptide, induces cell cycle arrest and apoptosis in a calcium-sensitive manner

Very few growth inhibitors have been identified which can inhibit the proliferation of a broad spectrum of human breast cancer cell lines. CeReS-18, a novel cell surface sialoglycopeptide growth inhibitor, can reversibly inhibit the proliferation of both estrogen receptor positive (MCF-7) and negative (BT-20) human breast cancer cell lines. In addition, at concentrations above those required for the reversible inhibition of cell proliferation, CeReS-18 can also induce cell death in MCF-7 cells. Changes in nuclear and cytoplasmic morphology, characteristic of apoptosis, were detected in MCF-7 cells treated with a cytotoxic concentration of CeReS-18, and internucleosomal DNA cleavage was also observed. The sensitivity of MCF-7 and BT-20 cells to the biological properties of CeReS-18 could be influenced by altering the calcium concentration in the extracellular growth medium, such that when the calcium concentration in the environment was decreased, and increased sensitivity to CeReS-18-induced growth inhibition and cytotoxicity were observed. The addition of the calcium chelating agent EGTA to MCF-7 cells, cultured in a normal calcium environment, could mimic the increased sensitivity to the biological effects of CeReS-18 observed under reduced calcium conditions.