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  • Title: Loss of mouse epidermal protein kinase C isozyme activities following treatment with phorbol ester and non-phorbol ester tumor promoters.
    Author: Wang XJ, Warren BS, Rupp T, Beltrán LM, DiGiovanni J.
    Journal: Carcinogenesis; 1994 Dec; 15(12):2795-803. PubMed ID: 8001237.
    Abstract:
    The present study has examined changes in activities and levels of four protein kinase C (PKC) isozymes (PKC alpha, PKC beta, PKC gamma and PKC delta) detectable in mouse epidermal preparations following both single and multiple treatments with 12-O-tetradecanoylphorbol-13-acetate (TPA). In addition, PKC epsilon and PKC eta protein levels were monitored by immunoblotting following TPA application. Finally, PKC isozyme activity profiles were also examined in epidermal preparations from mice treated with single applications of two non-phorbol ester tumor promoters: chrysarobin (CHRY) and okadaic acid (OA). Fifteen minutes following topical treatment with a tumor promoting dose of TPA (3.4 nmol), the activities of PKC beta and PKC gamma decreased in the epidermal cytosol to 30% and 50% of control values, respectively, while these activities were increased in the epidermal particulate fraction by approximately 50%. PKC delta activity, found predominantly in the particulate fraction of control epidermis, was greatly diminished in both subcellular fractions at 15 min while PKC alpha activity was translocated approximately 20% from cytosol to particulate fraction. Significant reductions in all four detectable PKC isozyme activities in both particulate and cytosol fractions were observed 48 h after a single treatment with TPA, although particulate PKC alpha activity appeared to be less affected at this point in time compared to the other PKC isozymes. Immunoblotting analyses of PKC isozyme protein levels after TPA treatment followed the changes in activity for cytosolic PKC alpha, PKC beta and PKC gamma. However, particulate PKC delta and PKC epsilon protein levels remained relatively unchanged while particulate PKC eta protein levels were significantly down-regulated after a single TPA treatment. Multiple topical treatments (twice-weekly for 2 weeks) with TPA produced a pattern of loss followed by only partial recovery of total PKC activity. Furthermore, all four PKC isozyme activities examined by hydroxylapatite (HA) chromatography were significantly reduced, including PKC alpha, after four applications of TPA. Cytosolic PKC alpha, PKC beta and PKC gamma protein levels as determined by immunoblotting again followed the activity profiles; particulate PKC eta protein levels were significantly reduced, whereas particulate PKC delta and PKC epsilon levels again appeared relatively unchanged. Fifteen minutes after topical application of 220 nmol CHRY, an approximately 25% decrease in particulate associated with PKC alpha activity was observed while particulate activities associated with PKC beta, PKC gamma and PKC delta were unaffected by CHRY at this time point.(ABSTRACT TRUNCATED AT 400 WORDS)
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