UVB-induced calmodulin increase in pig epidermis: Analysis of the effect of the calmodulin antagonist, W-13

Calmodulin (CaM) is a multifunctional calcium-binding protein that has been implicated in the control of cell proliferation. In order to determine the role of CaM in keratinocyte proliferation, we investigated the effect of the CaM antagonist, W-13 on thymidine incorporation into pig epidermis. W-13 significantly inhibited thymidine incorporation into pig epidermis, while W-12, a closely related compound with much less anti-CaM activity, had little effect. The effect of W-13 was detected after as little as 2 h of incubation. Using a short-term (2-h) incubation system, the effects of other chemicals affecting various transmembrane signalling systems of keratinocytes were also investigated. None of these chemicals (epinephrine, histamine, forskolin, HA-1004, bradykinin, mezerein, phorbol 12-myristate, 13-acetate, H-7, staurosporin) inhibited thymidine incorporation. The effect of W-13 was reversible; its removal from the incubation medium resulted in the reinitiation of thymidine incorporation. Pig epidermis responded to 2.5 MED UVB irradiation showing an initial (24-48 h after irradiation) decrease and a subsequent (96-120 h after irradiation) increase in thymidine incorporation. The CaM content was not significantly altered during the initial hypoproliferative phase, but was significantly increased during the 72-120 h after UVB irradiation sometimes slightly preceding but mostly coinciding with the increase in thymidine incorporation. The inhibitory effect of W-13 on keratinocyte proliferation was observed at time 0, and at 72 h and 168 h following the UVB irradiation but not at 24-48 h or 96-144 h, i.e. during the hypo- and hyperproliferative phases, respectively. Methotrexate, which inhibits de novo nucleic acid synthesis significantly augmented thymidine incorporation into the UVB-induced hyperproliferative epidermis, but the addition of W-13 together with methotrexate caused no inhibitory effect on thymidine incorporation into UVB-induced hyperproliferative epidermis. © 1995 Springer-Verlag.