Retinoids increase transglutaminase activity and inhibit ornithine decarboxylase activity in Chinese hamster ovary cells and in melanoma cells stimulated to differentiate.

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Abstract
Transglutaminase (TGase) and ornithine decarboxylase (ODCase) activities were measured after the addition of retinoid analogs to Chinese hamster ovary (CHO) cells released from quiescence and Cloudman S91 (CCL 53.1) mouse melanoma cells stimulated to differentiate with MSH. In both cell culture lines, a biphasic increase in TGase activity and a single peak of ODCase activity was detected within 7 h after release or stimulation. Retinoid analogs altered the expression of the initial TGase peak in both CHO and melanoma cells. Retinol increased the activity of TGase 1 h after release in CHO cells, and the activity remained elevated until the 4th h. A broad peak of TGase activity also occurred after the addition of .alpha.-difluoromethylornithine, an irreversible inhibitor of ODCase, and after addition of .alpha.-difluoromethylornithine plus retinol. In mouse melanoma cells, retinoic acid plus MSH markedly enhanced the activity of the initial TGase peak compared to MSH alone. Retinoic acid alone also increased TGase activity biphasically in these cells without the addition of MSH. Retinoid effects that increase TGase activity may alter the ODCase expression in proliferation and differentiation.