Stearic acid (stearate) is an 18-carbon saturated fatty acid that has been shown to inhibit invasion and proliferation and induce apoptosis in various human cell types. The specificity of stearate-induced apoptosis for cancerous versus noncancerous breast cells has not been examined, and the mechanism underlying stearate-induced apoptosis is unknown. Morphological analysis, cell viability, and caspase-3 activity assays demonstrated that stearate activated apoptosis preferentially in cancerous breast cells in a time- and dose-dependent manner. Inhibition of de novo diacylgycerol synthesis or protein kinase C (PKC) blocked stearate-induced caspase-3 activity, indicating the involvement of a novel or classical PKC isozyme. To our knowledge this is the first study showing that stearate induces apoptosis preferentially in breast cancer cells and implicates protein kinase C in the signaling cascade. These results raise the possibility of dietary stearate having a beneficial role in the prevention or treatment of breast cancer.
