Involvement of protein kinase C in mouse mammary gland development

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Abstract
The relationship between kinase C activity and mammary gland differentiation was investigated by following kinase activity throughout the mouse reproductive cycle and by pharmacologically perturbing the kinase, while monitoring biochemical differentiation. Protein kinase C activity declined during pregnancy and remained low throughout lactation, suggesting an inverse relationship with milk protein expression. This negative association was further supported by the use of quercetin (50–100 μmol/l) and gossypol (50 μmol/l), which are both protein kinase C inhibitors. These compounds doubled α-lactalbumin levels in mammary explants cultured with hormones. However, a phorbol ester, known to activate protein kinase C, had no effect on α-lactalbumin production, although it did stimulate this milk protein 2·5-fold in the presence of the calcium ionophore, A23187. In the absence of raised calcium levels, protein kinase C activity therefore appeared to be inversely correlated with biochemical differentiation; but, in the presence of increased calcium concentrations, both calcium and the kinase acted synergistically to augment hormone-induced α-lactalbumin expression. J. Endocr. (1986) 109, 29–34

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