The formation of cellular aggregates (foci) in CV-1 cells following infection with Yaba tumor poxvirus is dependent upon cell passage level, temperature of incubation, and calcium concentration in the medium. Resistance of older cells can be reversed by maintaining calcium at 0.1 mm or by adding cortisone acetate (1 μg/ml), hydrocortisone, or estradiol-17β to the cultures. In susceptible cells, foci formation was inhibited slightly by methyltestosterone and inhibited completely by dexamethasone, aldosterone, and progesterone. Activities and patterns of enzymes associated with cytoplasmic membranes (alkaline phosphatase, mononucleotidase, and Na+-K+-adenosine triphosphatase) and lysosomes (β-glucuronidase and acid phosphatase) of the younger susceptible and the older resistant CV-1 cells differed. These differences apparently occurred in concert with phenotypic changes in the membranes that reduced the mobility of older resistant cells. In susceptible cultures, uninfected cells migrated to the infected cell and participated in foci formation. Reduction of the calcium content to 0.1 mm apparently removed some of the constraints on mobility of the resistant cells. Although the hormones may have had a similar effect, the changes in enzyme patterns indicated basic alterations in protein synthesis. The development of resistance to foci formation occurred between the 45th and 50th passage level. Hormonal reversal of this resistance resulted in enzyme profiles that reflected the pattern of young susceptible cells.

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This work was supported in part by Grant CA-11613-04 from the USPHS and Grant 3192-A1 from the Ohio Division of the American Cancer Society.

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